?Introduction to Cited Articles

This paper is another contribution to the study of the structure-property relationship in cemented carbides by the research team, following their previous works:

1. Regulation of interfacial phase stability in cemented carbides (Acta Mater. 2018, 149, 164?178,https://doi.org/10.1016/j.actamat.2018.02.018)

2.New methods and principles for enhancing the distribution of characteristic grain boundaries in cemented carbides(Acta Mater. 2019, 175, 171?181, https://doi.org/10.1016/j.actamat.2019.06.015)

3.Accurate analysis of residual thermal stress (RTS) in cemented carbides and its mechanism affecting material mechanical behavior (Acta Mater. 2021, 221, 117428, https://doi.org/10.1016/j.actamat.2021.117428)

Article link: https://doi.org/10.1016/j.actamat.2024.119649

About the Research

Research Background of WC grain morphology

For cemented carbides, a typical composite material, the influence of WC grain morphology on the mechanical behavior of the material, especially representative mechanical properties such as strength and toughness, remains unclear. Furthermore, cemented carbides prepared by powder metallurgy inevitably contain high-magnitude and complexly distributed residual thermal stress (RTS), and its accurate quantitative description is a common challenge in the field of cermet composites. Moreover, when working tools manufactured from cemented carbides are in use, the interaction between as-prepared RTS and external loads inevitably affects the material’s mechanical behavior and service performance. Therefore, studying the coupling effect of WC grain morphology and as-prepared RTS on the stress-strain response during material loading is of great significance for comprehensively understanding the mechanical behavior, failure mechanism, and performance enhancement approaches of cemented carbides in practical applications.

Research Methods

In this study, a method for constructing finite element models of real microstructures and phase distributions in cermet composites was proposed. Combining finite element simulation with quantitative analyses such as transmission electron microscopy (TEM) observation and X-ray diffraction (XRD) experiments, the influence of WC grain morphology on RTS characteristics and the mechanical behavior and properties of materials under external loads was analyzed. This provides important scientific evidence for optimizing microstructural stress-strain distribution through regulating grain morphology to achieve strengthening and toughening of cermet composites.

Fig. 1 Microstructural characteristics and finite element models of WC-10wt.%Co cemented carbides with different WC grain morphologies: (a) SEM image of E-WC-Co; (b) SEM image of P-WC-Co; (c) Schematic diagram of equivalent elliptical area method; (d) Probability distribution of WC grain geometric shape factors

Through the design of preparation methods and regulation of process parameters, WC-10wt.%Co cemented carbides with equiaxed and plate-like WC grain structures were successfully prepared, respectively. Based on EBSD experiments, a method for constructing finite element models was developed to reproduce the real microstructure, morphological and mechanical characteristics of cemented carbides, which can reflect the local stress field, strain field and properties of actual materials.

Research Findings

The researchers found that the compressive RTS level is higher in the WC region near the acute dihedral angle of WC/Co. In contrast, the RTS in WC near the WC/Co phase boundary away from the vertex of the acute dihedral angle mainly exhibits tensile stress. Furthermore, a higher geometric shape factor leads to more narrow WC connections in the cemented carbides with plate-like WC grain structures, where the WC regions have highly concentrated compressive RTS.

Fig. 2 RTS distribution in WC-10wt.%Co cemented carbides with different WC grain morphologies: (a) Transverse RTS distribution nephogram of WC grains in E-WC-Co; (b) Axial RTS distribution nephogram of WC grains in E-WC-Co; (c) Transverse RTS distribution nephogram of WC grains in P-WC-Co; (d) Axial RTS distribution nephogram of WC grains in P-WC-Co; (e) Transverse RTS distribution nephogram of Co phase in E-WC-Co;

(e) Transverse RTS distribution nephogram of Co phase in E-WC-Co; (f) Axial RTS distribution nephogram of Co phase in E-WC-Co; (g) Transverse RTS distribution nephogram of Co phase in P-WC-Co; (h) Axial RTS distribution nephogram of Co phase in P-WC-Co

It was found that the average RTS of WC grains presents an asymmetric dumbbell-shaped distribution with respect to the WC geometric shape factor. When the WC grain geometric shape factor is between 3 and 5, the average RTS distribution range of WC grains is narrow, and the average RTS of WC grains is in a compressive stress state. In addition, both finite element simulation and X-ray diffraction experimental results show that the WC grain morphology has little effect on the phase-averaged RTS of cemented carbides.

Fig. 3 The variation law of the average residual thermal stress (RTS) of WC grains with the WC geometric shape factor.

Fig. 4 Experimental determination of RTS in WC phase of cemented carbides with different WC grain morphologies: E-WC-Co

The compressive and tensile properties of cemented carbides exhibit significant asymmetry. The presence of RTS improves the compressive strength of both E-WC-Co and P-WC-Co. Compared with E-WC-Co, P-WC-Co has a relatively lower compressive yield strength but shows larger strain after yielding without obvious hardening. The presence of RTS reduces the tensile yield strength of E-WC-Co, while having little effect on the tensile strength of P-WC-Co.

Fig. 5 Strain responses of WC-10wt.%Co cemented carbides with different WC grain morphologies and initial stress states during compression and tension: (a) Compressive stress-strain curve of E-WC-Co; (b) Compressive stress-strain curve of P-WC-Co.

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Conclusions

The study shows that the compressive deformation of cemented carbides can be divided into three stages: the elastic stage, the elastoplastic stage, and the plastic stage.

1.In the initial elastic stage of loading, the hard ceramic phase WC and the ductile metal phase Co undergo independent elastic deformation.

2.In the elastoplastic stage, plastic deformation occurs preferentially in the metal phase Co, while the ceramic phase WC remains in an elastic deformation state.

3.In the plastic stage, due to the much larger plastic strain in the metal phase Co than in the ceramic phase WC, strain gradients and strain localization are likely to occur in the Co region near the WC/Co phase boundary. These strain gradients and localization increase with the applied load, leading to an increase in dislocation density and strain hardening.

This article focuses on introducing suitable powder raw materials for ultrafine-grained cemented carbides. Our next two weeklies will delve into the topics of grain growth inhibitors and sintering processes.

Quality Requirements for Powder Grains

The primary prerequisite for preparing ultrafine-grained or nanocrystalline cemented carbides is the production of ultrafine/nano WC powder or WC-Co composite powder, which has become a current research focus. According to relevant literature, ultrafine/nano powder raw materials must meet stringent criteria, including uniform average grain size with a narrow distribution, high purity, and reasonable carbon and oxygen content. Additionally, factors such as particle morphology, crystallographic perfection, and subgrain size directly influence the performance of ultrafine-grained cemented carbides.

Achievements in Powder Production

In 1989, Rutgers University in the United States took the lead in successfully developing nanostructured cemented carbides. Subsequently, Nanodyne Company developed nanostructured WC-Co cemented carbide composite powder with a particle size of 40 nm based on this foundation. Renowned companies in Japan, Switzerland, Germany, and other countries have also successively developed nanostructured cemented carbides. Among them, Switzerland’s Sandvik Company’s T002 ultrafine-grained cemented carbide has the finest grains, reaching 200 nm. Domestically, Zigong 746 Factory and Zhuzhou 601 Factory have both developed their own nanostructured cemented carbides, with grain sizes less than 500 nm, hardness of 93 HRA, and strength of 4000 MPa.

Technological Development in Ultrafine-Grained Cemented Carbide Powder Production

In summary, the preparation technologies for ultrafine/nano-grained cemented carbide powders at home and abroad mainly include the following aspects:

(1) Oxide Reduction-Carbonization Technology

This method involves granulating a mixture of WO and carbon black, followed by low-temperature carbonization reduction under N?and H?atmospheres to produce ultrafine WC with a grain size of 0.5 μm. This technology was jointly developed by Tokyo Tungsten and Sumitomo Electric in Japan. Its characteristics include rapid and continuous production of ultrafine and uniform WC powder, with the finest WC powder achieving a BET grain size of 0.11-0.13 nm. However, its drawback is that during the carbonization reduction process, H? reacts chemically with carbon black, making it difficult to control the carbon content in the product. The U.S. company EMO introduced the Rapid Carbonthermal Reduction (RCR) technology from Dow Chemical, operating at temperatures of 1500-2000°C. This technology is characterized by low cost and mass production capabilities, yielding WC powders with grain sizes of 0.2 μm, 0.4 μm, and 0.8 μm.

Domestically, significant progress has also been made in this technology. Wuhan University of Technology has improved the oxide reduction-carbonization process by employing vacuum or inert gas atmospheres, thereby avoiding the adverse effects of H? on the reduction products and successfully producing ultrafine WC-Co composite powders with grain sizes ranging from 0.1 to 0.3 μm.

Advantages:

Enables rapid and continuous production, with the finest grain size reaching 0.11-0.13 μm (BET method).

Low cost and suitable for large-scale production (e.g., EMO’s mass production of 0.2-0.8 μm WC powders).

Disadvantages:

H? reaction with carbon black makes carbon content control challenging.

Although vacuum/inert gas atmospheres mitigate this issue, they increase process complexity.

(2) Low-Temperature Reduction-Carbonization Technology

This method involves reducing blue or purple tungsten oxide with hydrogen gas at low temperatures to produce tungsten powder, which is subsequently carbonized into ultrafine WC powder. This technique is widely adopted in China, with notable users including Xiamen Golden Egret Special Alloy Co., Ltd., Zhuzhou Cemented Carbide Group, and Zigong Cemented Carbide Plant.

Advantages:

Simple process and extensive domestic application (e.g., Xiamen Golden Egret, Zhuzhou Cemented Carbide Group).

Low equipment requirements.

Disadvantages:

Insufficient precision in carbon content control, necessitating inhibitor optimization.

Potential limitations in grain size distribution uniformity.

(3) Thermochemical Synthesis Technology (Spray Drying)

Thermochemical synthesis, or spray drying, comprises three main steps: (a) preparing cobalt solutions from ammonium metatungstate and cobalt chloride or ethylenediamine tungstate, followed by homogeneous mixing; (b) spray-drying the mixture to obtain ultrafine and uniform cobalt-cobalt salt composite powders; and (c) reducing and carbonizing the powders in a fluidized bed reactor to produce nano WC-Co composite powders. Characteristics: The nano WC-Co composite powders retain the morphology of the precursors, with grain sizes controllable by adjusting reaction temperature, holding time, and carbonization gas activation. They exhibit high specific surface area and enable alloy densification at relatively low temperatures. Disadvantages: The process is complex, and carbon content control is inaccurate, though controllability can be improved by effectively blending carbonization atmospheres as carbon sources.

Advantages:

Controllable grain size (via temperature, time, and carbonization atmosphere adjustments).

High specific surface area and excellent low-temperature densification performance.

Disadvantages:

Complex process and challenging carbon content control.

Requires carbonization atmosphere regulation for stability.

(4) In-Situ Carburization Technology

In-situ carburization involves directly reducing precursors to single-phase nano WC-Co composite powders using hydrogen gas without external carbon sources (e.g., CO/CO?). This is achieved by dissolving tungstic acid and cobalt salt in a polyacrylonitrile solution, followed by low-temperature drying and reduction in a 90% Ar-10% H? mixed gas atmosphere at 800-900°C, yielding WC-Co powders with grain sizes of 50-80 nm. This method was first reported by Y.T. Zhou of the University of Texas in 1994. Key Innovation: Replacing CO/CO? mixtures with polyacrylonitrile as the in-situ carbon source, enabling direct hydrogen reduction of precursors to single-phase nano WC-Co composites. Process parameters such as reduction temperature, atmosphere, and trace cobalt acetate catalyst additives significantly influence the final nano composite powder quality. Disadvantages: Insufficient reduction due to shortened diffusion times results in residual undecomposed polymers or free carbon, adversely affecting product performance.

Advantages:

Highly innovative, achieving grain sizes of 50-80 nm.

Simplifies the process by eliminating traditional carbon sources (e.g., CO/CO?).

Disadvantages:

Incomplete reduction leads to residual polymer or free carbon, impacting performance.

High sensitivity to temperature, atmosphere, and catalysts (e.g., cobalt acetate).

(5) Plasma Technology

Plasma technology utilizes a plasma-generated heat source maintained at 4000-5000°C to decompose, react, and synthesize raw materials (W, WC, or WO?) and carbon sources (CH?), yielding products with grain sizes as fine as 5-20 nm. The primary heat sources include direct current (DC) plasma, high-frequency plasma, or a combination of both. Disadvantages: Plasma sustainability is poor, making it difficult to ensure complete evaporation and reaction of the raw materials.

Advantages:

Produces extremely fine grain sizes (5-20 nm), suitable for ultra-high-end applications.

Rapid reaction rates.

Disadvantages:

Poor plasma stability leads to incomplete raw material evaporation and reactions.

High equipment costs and energy consumption.

(6) Sol-Gel Technology

The sol-gel process involves the hydrolysis and polycondensation of hydrolyzable metal compounds in a solvent, followed by gelation, drying, and reduction to produce nanostructured powders. This low-temperature process relies on hydrolysis and polymerization reactions, resulting in high-purity powders with narrow grain size distributions, high chemical activity, and homogeneous multi-component mixtures. For instance, scientists like Srikanth Rahunathan have utilized sol-gel technology to develop nano W-Co, W-Mo, and W-Cu composite powders. Characteristics: The sol-gel method offers precise chemical controllability, simple operation, and low cost for producing nanostructured composite powders with uniform structures. Disadvantages: The process is complex and challenging to scale for mass production.

Advantages:

High purity, narrow grain size distribution, and controllable chemical activity.

Suitable for multi-component composite powders (e.g., W-Co, W-Mo).

Disadvantages:

Complex preparation process and difficulty in large-scale production.

Higher costs and longer production cycles.

(7) Mechanical Cemente Carbide Alloying Technology

Mechanical alloying involves blending elemental powders in specific ratios and milling them under inert gas protection in a high-energy ball mill. Mechanical energy from milling induces repeated deformation, cold welding, and fracturing of the powders, resulting in a dispersion of ultrafine particles and solid-state alloying. Advantages: The process is technically simple, requires minimal equipment, and is easy to operate. Disadvantages: Alloying may introduce impurities, and internal stresses/agglomeration within the powders due to compressive/shear forces can negatively impact compressibility and sintering behavior.

Advantages:

Simple technology, inexpensive equipment, and ease of operation.

Disadvantages:

Risk of impurity introduction during alloying.

Significant internal stresses and severe agglomeration in powders, affecting compaction and sintering properties.

Domestically, the Institute of Physics, Chinese Academy of Sciences, successfully produced nano WC powder with a grain size of 7.2 nm using mechanical alloying in 1944. Similarly, Professor Wu Xijun of Zhejiang University synthesized nano single-phase W?C powder with an average grain size of 6.0 nm using the same method.

Advantages:

Simple equipment and easy operation.

Capable of producing extremely fine grain sizes (e.g., 7.2 nm WC powder).

Disadvantages:

High risk of impurity introduction.

Significant internal stress in powders and severe agglomeration, adversely affecting compaction and sintering properties.

Summary

For the production of ultrafine-grained cemented carbide powders:

1.Oxide reduction-carbonization and low-temperature reduction-carbonization technologies are suitable for large-scale production due to their low cost and mature processes. Plasma and sol-gel technologies can produce nano-scale powders but require addressing stability and cost challenges.

2.In-situ carburization introduces polymer-based carbon sources as an innovative approach to carbon content control, though optimization of reduction completeness is needed.

3.Institutions such as Wuhan University of Technology and the Institute of Physics, Chinese Academy of Sciences, have achieved notable advancements in improving conventional processes (e.g., vacuum carbonization, mechanical alloying). However, high-end powders (e.g., sub-50 nm grades) still rely on imports.

Cemented carbides are widely used in demanding engineering applications where corrosion resistance is crucial for long-term performance. While extensive research has focused on conventional hard alloys, the corrosion behavior of materials with controlled matrix granule-to-network structure ratios remains poorly understood. This structural parameter significantly influences both mechanical properties and chemical stability, yet systematic studies comparing different configurations are notably absent from the literature.

Fig.1?FSEM morphology of matrix and granular cemented carbide

Comparative Investigation of Corrosion Mechanisms in Hard Alloys with Engineered Matrix Granule-to-Network Architectures

This study systematically examines how controlled variations in the granule-to-network ratio (20:80 to 80:20) influence the electrochemical degradation behavior of WC-Co cemented carbides. Using a combination of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and advanced microstructural characterization, we establish quantitative correlations between three-dimensional phase connectivity and key corrosion parameters, including charge transfer resistance, corrosion current density (i_corr), and passive film stability. The research particularly focuses on elucidating how network continuity versus granular isolation affects: (1) anodic dissolution kinetics of the cobalt binder phase, (2) galvanic coupling effects between WC grains and metallic binder, and (3) penetration pathways for corrosive species in marine-grade NaCl environments. Our findings provide a microstructure design roadmap for developing next-generation hard alloys with optimized corrosion-wear synergy for extreme service conditions in offshore, mining, and chemical processing applications.

Corrosion Resistance: A Critical Factor in Cemented Carbide Applications

Cemented carbides are widely used in engineering practice, and their corrosion resistance has always been a critical factor affecting engineering reliability. In industrial applications, cemented carbides are susceptible to oxidation, chemical corrosion, and erosion. After exposure to corrosion, the alloy exhibits various degradation phenomena during service, leading to a sharp deterioration in surface properties and wear resistance, thereby shortening the operational lifespan of engineering components. Therefore, enhancing both physical properties and corrosion resistance is crucial for materials intended for complex working environments.

Fig.2?Mechanical properties of cellular cemented carbides with?different matrix granule ratios

(a)XW5；(b) XW6；(c) XW7；(d) XW8

Fig.3 SEM morphology of cellular cemented carbides with different matrix granule ratios

Grain Size Effects on Electrochemical Corrosion Behavior

ZHANG L et al. investigated the electrochemical corrosion behavior of WC-10Co cemented carbides with different WC grain sizes. Their results demonstrated a strong linear correlation between charge transfer resistance, corrosion current density, and WC grain in the solution. Similarly, KELLNER F J J et al. studied the corrosion behavior of cemented carbides with varying grain sizes using electrochemical methods. Their experimental findings revealed that smaller grain sizes enhance corrosion resistance, and the corrosion behavior is significantly influenced by the dissolved W and C content in the Co binder phase.

Fig.4 Potential polarization curve of cellular cemented carbides with different matrix granule ratios

Research Gap: Network-Structured Alloys in Corrosive Environments

While the corrosion behavior of conventional cemented carbides has been extensively studied, there is limited comprehensive research on network-structured alloys in corrosive environments. In this study, YG10-grade alloy was selected as the matrix material, and YG8-grade alloy as the granular material to fabricate network-structured alloys. The research focuses on examining the influence of matrix-to-granule volume ratio on the microstructure and corrosion performance of the network-structured alloy.

Fig.5 Nyquist curve of cellular cemented carbides with different matrix granule ratios

Fig.6 Bode curve of cellular cemented carbides with different matrix granule ratios

Fig.7 Equivalent circuit diagram used to fit EIS

(a)XW5；(b) XW6；(c) XW7；(d) XW

Fig.8 Corrosion topography of cellular cemented carbides with different matrix granule ratios

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Conclusion

This study investigated the effects of the matrix-to-granule ratio on the microstructure and corrosion resistance of network-structured alloys in a 3.5% NaCl solution. The key findings are as follows:

1.Mechanical Properties

As the granule proportion increased, the Vickers hardness of the alloy first increased and then decreased, while the flexural strength gradually improved.

The optimal comprehensive mechanical properties were achieved at a matrix-to-granule ratio of 30:70.

2.Polarization Curve Analysis

Both the corrosion potential and corrosion current density initially decreased and then increased with higher granule proportions.

Increasing the granule ratio reduced both the corrosion tendency and corrosion rate of the network-structured alloy.

3.Electrochemical Impedance Spectroscopy (EIS) Results

A higher granule proportion enhanced the electrochemical impedance of the alloy.

At a matrix-to-granule ratio of 30:70, the fitted charge transfer resistance (R_t = 1,860 Ω·cm2) and constant phase element exponent (n = 0.8878) reached their maximum values, indicating minimal surface corrosion and the fewest corrosion pits.

Understanding Tungsten Carbide’s Machinability

Tungsten carbide’s extreme hardness (1,300–1,900 HV) means traditional cutting tools like carbide or high-speed steel (HSS) quickly wear out or fail. Additionally, its brittleness makes it prone to chipping under mechanical stress, while its low thermal conductivity causes heat to concentrate at the cutting zone, accelerating tool degradation.

The material’s machinability also depends on its cobalt content. High-cobalt grades (10–20% Co) are tougher but slightly softer, making them more suitable for grinding and EDM. Low-cobalt grades (3–6% Co) are harder and more wear-resistant but require even more precise machining techniques to avoid cracking.

Optimal Machining Methods

Grinding: The Go-To Method for Precision Finishing

Grinding remains the most effective way to machine tungsten carbide, especially for achieving tight tolerances and fine surface finishes. Diamond grinding wheels are the preferred choice due to their superior hardness and wear resistance. For rough grinding, cubic boron nitride (CBN) wheels can be used, but they are less efficient than diamond for finishing operations.

Key parameters for successful grinding include:

Wheel speed: 15–25 m/s

Feed rate: 0.005–0.02 mm per pass

Coolant: Essential to prevent thermal cracking and extend wheel life

Electrical Discharge Machining (EDM): Ideal for Complex Geometries

When grinding isn’t feasible—such as when machining intricate internal features or deep cavities—EDM is the next best option. This non-contact process uses electrical sparks to erode the material, making it ideal for hard, conductive materials like tungsten carbide.

Wire EDM is particularly effective for cutting complex profiles, while sinker EDM is better suited for creating molds and dies. To optimize results:

Use graphite or copper electrodes for better wear resistance.

Maintain a well-filtered dielectric fluid to prevent arcing.

Apply high flushing pressure to remove debris and improve cutting speed.

Laser Machining: Precision Micro-Cutting and Drilling

For ultra-fine features, laser machining offers a high-precision alternative. Fiber lasers (1μm wavelength) are the most efficient, capable of cutting thin tungsten carbide sheets with minimal heat distortion. Picosecond lasers provide even finer control, reducing the heat-affected zone (HAZ) for critical applications.

However, laser cutting is slow for thicker sections (>5 mm) and may require multiple passes. Using an inert assist gas (such as nitrogen or argon) helps prevent oxidation and improves edge quality.

Conventional Machining: Limited but Possible in Certain Cases

While traditional milling or turning is generally impractical for sintered tungsten carbide, it can be used for green-state (unsintered) carbide before final heat treatment. Polycrystalline diamond (PCD) tools are the only viable option for such operations, but even then, cutting parameters must be carefully controlled:

Speed: 30–50 m/min

Feed: 0.02–0.1 mm/rev

Depth of cut: <0.5 mm to avoid excessive tool wear

Tool Selection and Process Optimization

Choosing the right tooling is critical for successful tungsten carbide machining. Diamond-coated tools outperform carbide in grinding and milling, while EDM requires high-quality electrodes to maintain precision. When using lasers, pulse duration and assist gas selection significantly influence cut quality.

To minimize common issues like cracking, tool wear, and poor surface finish:

For grinding: Use fine-grit diamond wheels (600+ grit) for mirror-like finishes and dress wheels frequently to maintain sharpness.

For EDM: Optimize spark frequency and dielectric flushing to prevent uneven erosion.

For laser cutting: Use pulsed mode to reduce heat buildup and improve edge quality.

Conclusion: Best Practices for Machining Tungsten Carbide

Successfully machining tungsten carbide requires a combination of the right techniques, tooling, and process parameters. Grinding and EDM are the most reliable methods, while laser cutting excels in precision applications. Conventional machining is only viable for pre-sintered carbide and must be approached with caution.

By following these guidelines—prioritizing coolant use, optimizing feed rates, and selecting appropriate tool materials—manufacturers can achieve high-quality results while extending tool life. For those working with tungsten carbide regularly, investing in advanced grinding or EDM equipment will yield the best long-term efficiency and cost savings.

For custom tungsten carbide components, consulting with a specialist can help determine the most effective machining strategy for your specific needs.

This study examines picosecond laser processing of carbide product across different energy densities, analyzing effects on surface roughness, composition and material removal to identify distinct interaction mechanisms.

Mechanism of Laser Processing

Laser processing may sound like futuristic sci-fi tech, but it works by focusing a laser beam to deliver energy to the workpiece, locally heating the material to melt, vaporize, or remove it—all without physical contact. Unlike traditional grinding, this method eliminates tool wear and deformation while boosting efficiency and precision. Most importantly, laser processing isn’t limited by material hardness or toughness, making it ideal for even the most challenging alloys.

Laser processing isn’t limited to just one approach. Based on pulse duration, it can be categorized into:

1.Nanosecond lasers – Like a broadsword:Longer pulses (wider heat-affected zone)?and suitable for less precision-critical applications

2.Picosecond & femtosecond lasers – Like precision engraving tools:Ultra-short pulses (minimal heat-affected zone),enable high-precision, low-damage processing, and femtosecond lasers (pulses in quadrillionths of a second) remove/modify material instantaneously with zero peripheral impact.

While femtosecond lasers offer extreme precision, their equipment costs too much. Picosecond lasers strike the ideal balance, including simplified design,stable performance,lower operating costs,and sufficient efficiency for most applications.Those points make picosecond lasers the preferred choice for processing of carbide product in industrial settings.

Experimental equipment and plan

The experiment used YG8 carbide product with sample dimensions of 50mm×50mm×2mm. Laser processing was conducted on a self-developed five-axis picosecond laser milling machine. The laser parameters were:

Wavelength: 1064nm

Pulse width: 10ps

Repetition rate: 2000kHz

Spot diameter: 30μm

Four energy density (ED) levels were tested:

0.45J/mm2, 1.05J/mm2, 1.65J/mm2, and 2.25J/mm2

A 10% scan overlap ratio was selected based on appropriate beam traversal speed ranges and experimental requirements, with single-pass processing (one laser scan per surface).

The energy density calculation formula is:

where:

P = Laser power (W)

D = Focused laser beam diameter (mm)

V? = Laser transverse scanning speed (mm/s)

Energy density variation was achieved by adjusting laser power. As shown in Figure 1, the laser followed path a for transverse motion and path b for cross-feed motion. Post-processing, samples were ultrasonically cleaned in anhydrous ethanol for 15 minutes and dried.

The three-dimensional contour morphology of the sample surface after laser processing was observed by using the product measuring instrument (Bruker Alicona Infinite Focus SL), and the surface roughness and processing depth were detected. The obtained results were all the average values of the five measurement results.

(a) Experimental apparatus

(b) Processing procedure

Figure 1 Ultrafast laser processing of carbide product

Experimental Results and Discussion

Surface microstructure of carbide product

When processing the surface of materials with ultrafast lasers, the energy flow density of the laser needs to reach above the ablation threshold of the material to cause ablation to the material. The surface morphologies processed by laser under different energy densities are shown in Figure 2.

(a) The energy flow density is 0.45J/mm 2

(b) The energy flow density is 1.05J/mm 2

(c) The energy flow density is 1.65J/mm 2

(d)The energy flow density is 2.25J/mm 2

Figure 2 Surface morphology of laser processing with different energy flow densities

At low energy density (0.45J/mm2), the laser-processed surface shows varied ablation morphologies due to the Gaussian beam profile. Only the central high-energy zone exceeds the ablation threshold, forming sparse LIPSS structures (Fig.2a3), while peripheral areas retain base material features (Fig.2a1). Partial Co binder removal between WC particles creates micron-scale protrusions via thermal diffusion.

Above 1.05J/mm2, stable LIPSS structures form, with periodicity determined by laser wavelength and material dielectric properties. These result from laser-induced phase transitions and resolidification. Energy variations along cross-feed directions create morphological differences.

With increasing energy density:

1.05J/mm2 produces periodic LIPSS with nano-protrusions (Fig.2b1) from phase explosion

1.65J/mm2 shows reduced protrusions and added nanoparticles (Fig.2c1)

2.25J/mm2 exhibits complete protrusion replacement by dense nanoparticles (Fig.2d1)

Surface Roughness of Machined Surfaces

Surface defects in laser processing are closely related to material defects and process parameters. Understanding their formation mechanisms enables better process optimization for smooth, defect-free surfaces. When laser-material interaction is thermally dominant at low energy densities (0.45J/mm2), a shallow surface melting mechanism occurs, achieving laser polishing.

As shown in Figs. 3a-b, laser-processed WC-Co surfaces (0.45J/mm2) become smoother compared to original ground surfaces with visible scratches. This improvement results from melted convex peaks flowing into adjacent valleys under capillary forces. Fig. 3f demonstrates that laser processing at 0.45J/mm2 reduces surface roughness by ~15% versus the original ground surface (Ra=0.187μm).

（a）The original grinding surface of the carbide product / (b) The energy flow density is 0.45J/mm2 /(c) The energy flow density is 1.05J/mm2

(d) The energy flow density is 1.65J/mm 2./(e) The energy flow density is 2.05J/mm 2. /(f) The influence of the energy flow density on the roughness of the machined surface

Figure 3 Three-dimensional contour morphologies of laser machined surfaces with different energy flow densities

At high energy densities (>1.05J/mm2), surface roughness increases significantly due to uniform ablation reaching WC-Co’s threshold. The molten surface develops ordered wavy microstructures (Fig.3e) from Gaussian energy distribution and thermal accumulation, causing uneven material removal. Higher energy densities intensify these laser traces, further increasing roughness.

Surface Elemental Changes

WC-Co composites show differential behavior:

Co binder (melting point: 1495°C) becomes unstable above 1250-1300°C

At 0.45J/mm2, EDS analysis (Fig.4) reveals preferential Co removal, with:

1.Laser-processed Co < Ground surface Co < YG8 nominal Co

2.Grinding fluid leaches Co initially

3.Low-energy laser selectively ablates Co while incompletely removing WC

(a)C?element

(b)W?element

(c) Element O

(d)Co element

Figure 4 shows the variation of elemental composition on the surface processed by laser with different energy flow densities

With increasing laser energy intensity, distinct transformations occur in the LIPSS morphology on the surface of carbide product. The uniform LIPSS distribution indicates that the ablation threshold of the WC-Co composite has been reached, resulting in stable and continuous material removal. As shown in Fig.5, the material removal depth increases progressively with higher energy density.

The laser ablation reveals compositional gradients in WC-Co along the depth direction, originating from liquid-phase sintering during manufacturing. When initial carbon content varies, cobalt migrates toward carbon during sintering, creating a cobalt gradient. EDS analysis (Fig.6a) confirms this cobalt concentration gradient from the surface to the subsurface. As laser ablation removes the cobalt-depleted surface layer and reaches cobalt-rich deeper regions, the processed surface at high energy densities shows higher overall cobalt content compared to the original ground surface.

Figure 5 The influence of energy flow density on the depth of material removal

At high energy densities, the Co binder content continuously increases, likely due to Co phase eruption and diffusion during laser processing. The thermal properties of WC particles and Co binder differ significantly: Co has lower melting (1490°C) and boiling (2927°C) points than WC (2870°C and 6000°C respectively).

Laser irradiation involves rapid heating and cooling. In the near-infrared region, WC’s absorption coefficient (~0.8) is higher than Co’s (~0.55). When irradiated, WC absorbs energy more efficiently and transfers it to surrounding Co. This heat causes structural changes in WC particle arrangements, driving molten Co to flow internally.

Due to Co’s higher thermal expansion coefficient (1.6×10??/K vs. WC’s 5.2×10??/K), the molten Co binder expands and diffuses toward the WC-Co surface. The high-temperature laser processing further promotes Co precipitation, increasing surface Co concentration.

WC-Co material removal

The influence of different energy densities varies significantly on laser processing mechanisms, surface morphology, and elemental composition changes. At low energy density (0.45J/mm2), the laser-WC-Co interaction mechanism is shown in Fig.6c, where the laser-material interaction follows a laser polishing mechanism that optimizes defects from the original ground surface. The surface morphology shows selective removal of the Co binder phase and incomplete ablation of WC forming non-uniform LIPSS structures, while the elemental composition mainly exhibits reduced Co content.

(a)Distribution of Co elements \? (b) Original grinding cross-section of WC-Co

(c) Low energy flow density WC-Co laser processing section \ (d) High energy flow density WC-Co laser processing section

Figure 6 Removal process of WC-Co material

At high energy density (1.05J/mm2), the laser-WC-Co interaction mechanism is shown in Fig.6d. The processed surface exhibits complete LIPSS structures microscopically and periodic wavy patterns macroscopically, indicating uniform melting effects with stable depth-wise material removal. Increased energy density intensifies laser traces, raising surface roughness. Elemental analysis shows higher Co content on laser-processed surfaces than original surfaces.

This occurs because depth-wise material removal reveals WC-Co’s inherent composition gradient from liquid-phase sintering. As Co-depleted surface layers are removed, underlying Co-rich regions interact with laser-induced high temperatures, causing Co precipitation that further increases surface Co content.

Both surface morphology and Co content changes significantly impact WC-Co products. Surface morphology directly affects roughness critical for quality, while Co content variations alter mechanical properties and wear resistance. Controlling laser energy density enables tailoring surface characteristics and Co distribution in WC-Co products.

?

Conclusion

This study analyzes laser processing of WC-Co carbide product and discusses the relationship between laser energy density and material removal based on laser-matter interaction theory, reaching the following conclusions.

(1) Laser parameters significantly affect surface roughness. As energy density increases, material removal depth rises while surface roughness first decreases then increases.

(2) At low energy density (0.45J/mm2), the laser-material interaction mainly follows a polishing mechanism. The surface morphology shows selective Co binder removal and incomplete WC ablation forming non-uniform LIPSS structures, with reduced Co content.

(3) At high energy density (1.05-2.25J/mm2), the mechanism involves stable depth-wise material removal. The surface displays complete LIPSS structures microscopically and periodic wavy patterns macroscopically, with overall higher Co content than the original surface.

Ceramic Materials for Smartphone Casings

Among all ceramic materials, zirconia (ZrO?) ceramics have emerged as a next-generation smartphone body material following plastics, metals, and glass. Beyond demonstrating high strength, hardness, and chemical stability (resisting acids/alkalis and corrosion), zirconia ceramics additionally provide:
? Superior abrasion and scratch resistance
? Zero signal interference
? Excellent thermal dissipation
? Premium aesthetic quality

Figure 1 illustrates a zirconia ceramic smartphone back panel.

Ceramic feels similar to glass but is much harder (second only to sapphire on the Mohs scale), making ceramic phones more scratch-resistant and durable – an ideal back cover material. Currently mainly used for phone back panels and fingerprint sensor covers. When first applied to phone frames, the new and unperfected process resulted in only 35% yield, leading to low production capacity and high prices. After machining optimization, the yield can be increased to over 80%.

Analysis of the Processing Technology of Ceramic Phone Case Parts

Part drawing and clamping method

The ceramic phone case parts are shown in Figure 2, and the processing and clamping methods of the parts are shown in Figure

The main problems in the production machining

The machining quality stability of components is poor, with frequent defects (see Fig.4). Main issues include significant dimensional deviations and surface flaws such as flow lines, tool marks, scratches, circular tool patterns, uneven textures, and machining vibrations. The defect distribution is shown in Fig.7.

a)Streamlined texture

b) Vibration marks

c) Knife connection marks

d) Brushing

e) Knife ring pattern

f) Light and shade patterns

Figure 5 Processing defects

Figure 6 Defect Distribution

Based on actual part processing performance and machining analysis, the following conclusions are drawn:

1.Ceramic is a new material with machining techniques still in exploration, lacking mature reference processes.

2.Its machining characteristics demand higher requirements for equipment, tools, and fixtures.

3.Poor surface quality with defects like dimensional inaccuracies, overcut marks, uneven textures, tool rings, and vibrations.

4.Initial yield rate is extremely low (~35%).

5.Unpredictable grinding tool lifespan due to ceramic firing process, compromising dimensional accuracy.

Key solutions focus on eliminating defects, stabilizing accuracy, improving yield, and reducing rework through comprehensive optimization of equipment, processes, fixtures, and cutting tools.

Influencing factors of machining quality and the process for solving problems

During part machining, numerous factors affect processing quality, including machine tool mechanical accuracy, CNC system parameter matching, program quality, tool selection, and measuring equipment precision. Issues in any of these areas can lead to unstable part quality. The influencing factors are shown in Fig.7.

The machining of solving the problem is shown in Figure 8. Analyze the processing problems one by one according to the flowchart and seek solutions.

Figure 8 The process of solving the problem

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The influence of cutting tools on processing

It was found that the cutting tools were severely worn during production. The hardness grade of zirconia ceramics is 9.0. The only material that can be processed is diamond grinding wheels. Different from traditional processing techniques, the wear rate of diamond grinding wheels is relatively fast. The wear of the grinding head is shown in Figure 9.

Tool manufacturing machining

There are currently two grinding head manufacturing processes: sintering and electroplating. The sintering process creates chemical bonds between the matrix metal and diamond particles with high encapsulation, making diamonds less likely to detach, thus offering better wear resistance and longer lifespan. The electroplating process mechanically encapsulates diamond particles with weaker retention than sintering, resulting in inferior wear resistance and lifespan but sharper edges. Additionally, sintering is unsuitable for certain slender and pointed products as it may deform the substrate. The high sintering temperature can also degrade diamond performance. The electroplating process is currently used.

Vibration marks and tool marks analysis

After machining one part using the program, measurements of grinding heads T4 and T5 showed inconsistent wear between the two tools, with a 0.01mm error difference. The tool measurements are shown in Fig.10.

a)Grinding head dimensions before processing

b) Dimensions of the grinding head after processing

Figure 10 Measurement of the cutting tool

Analysis of the machining program revealed that when two tools simultaneously act on the same machining surface with inconsistent wear amounts, the finishing grinding head cannot fully reach the target surface at machining protrusions, resulting in tool mark phenomena on the machined surface.

As shown in Figure 11, the machining paths of grinding heads T4 and T5 differ significantly, leading to substantial variations in their wear amounts. According to process requirements, both tools machining the sidewall must act on the same wall simultaneously. When wear amounts are inconsistent, tool marks will appear on the sidewall (see Figure 12).

a) Grinding head tool path No. T4

b) T5 grinding head tool path

Figure 11 Program trajectory

a)Phenomenon of knife marks on the side wall

b) Local magnification

Figure 12 Phenomenon of knife marks(3) Measures to Solve Sidewall Vibration Marks and Tool Marks

Replace the grinding head manufacturing machining with sintering technology to improve wear resistance. Modify the machining program by using CAM software to position the sidewall program as close as possible to the median tolerance zone, ensuring first-piece success rate. After initial machining, add an in-machine tool measurement procedure to promptly compensate for tool wear and ensure product consistency. A comparison of part surfaces before and after process optimization is shown in Figure 13.

a)Before optimization

b) After optimization

Figure 13 Comparison of the parts’ surfaces before and after process optimization

The influence of programs on processing

The requirements in machining can generally be summarized as high efficiency, high quality, and high precision. These three factors are often difficult to achieve simultaneously and require trade-offs. In actual machining, due to the special application of ceramic phone cases, the smoothness of machined surfaces and dimensional accuracy are particularly critical. On this basis, production efficiency should be improved as much as possible, with program optimization being key to enhancing production quality. According to on-site conditions, machining programs need to be optimized, with the optimization machining shown in Figure 14.

Figure 14 Program optimization process

?Impact of program precision on machining

As shown in Figure 15, the left-side graphic shows simulation results from a CAM-generated program with 4-decimal precision (4 digits after decimal point), demonstrating smoother workpiece surfaces. The right-side graphic, simulated with 3-decimal precision, clearly exhibits streaking patterns on the workpiece surface.

Figure 15 Comparison of program accuracy

?Influence of program tolerance on machined surfaces

The NC machining program generated by CAM post-processing directly affects surface quality. Different program tolerances produce distinct machining effects on the surface. A comparison of program tolerances is shown in Figure 16.

a)The CAM tolerance is 8μm

b) The CAM tolerance is 1μm

Figure 16 Comparison of program tolerances

In summary, when generating programs with CAM software, appropriate machining strategies, point stepover, and feed rates should be selected to optimize the point distribution in NC programs. Good point distribution can improve surface quality and reduce machining time. Conversely, poor distribution will degrade surface quality.

Main measures to address flow line issues

The flow line phenomenon is shown in Figure 17. The tool path point distribution in ceramic mold machining directly relates to the sidewall flow line phenomenon.

Figure 17 Streamline phenomenon

Optimize the tool path by setting the CAM software point spacing to 0.2mm and program tolerance to 0.006mm. The premium surface optimization function can replace the fine surface optimization function for cutting. The premium surface optimization function will re-optimize unsatisfactory points and tool paths in the program. After optimization, flow line textures completely disappear. A comparison of machining effects before and after program optimization is shown in Figure 19.

a) Point distribution before program optimization

b) Point distribution after program optimization

c) Pre-machined surface for point position optimization

d) The machined surface after point position optimization

Figure 18 Comparison of machining effects before and after program optimization

Tool mark pattern analysis

Tool marks are common machining issues that may appear as regular/irregular rings, gradient rings, single rings or corner rings during linear feed or at corners, resembling Audi’s logo.

These marks occur at tool direction changes with varying spacing. As marks fade with distance, vibrations are identified at reversal points. During reversal, X/Y axis screws accelerate/decelerate, where acceleration settings cause slight overshoot and vibration, creating entry/corner marks.

Solutions for tool marks

Adjust acceleration parameters to reduce overshoot/vibration. Add “Top surface” command to smooth bad points, reduce impact and eliminate contour errors. Optimize toolpaths with more arcs for smoother turns. Post-optimization comparison (Fig.19) shows near elimination of tool marks.

a)Optimize the rake path

b) Optimize the rear cutting path

c) Machining surfaces before program optimization

d) The processed surface after program optimization

Figure 19 Comparison of processing effects before and after tool path optimization

The influence of mechanical and system parameters on processing

Influence of mechanical and backlash on machining

The impact of backlash on machining is shown in Figure 20. When machining molds using the same program under identical working conditions, backlash compensation and static friction compensation significantly affect the machined surface.

a)The reverse clearance is large before adjustment

b) The backlash before adjustment is small

Figure 20 The influence of backlash on processing

Impact of speed inconsistency on machining

Cutting tests were conducted to study the effect of system parameters. Different maximum axis jerk values (system parameter MD32431) were tested using the same program while monitoring toolpath speed via system Trace function. Analysis of monitoring data using AMWT software produced the red/yellow/blue curves in Figure 21, where colors indicate speed variations (red=fastest, blue=slowest). Results demonstrate system parameters directly affect machining speed variations.

Figure 21 The influence of system parameters on processing speed

The impact of speed optimization on machining is shown in Figure 22. When the toolpath speed is inconsistent, the tool’s varying speed on the machined surface creates uneven textures, known as “streaking phenomenon.” This can be optimized by adjusting system parameters and program tolerances.

a)Velocity variation before optimization

b) Speed variation after optimization

c) Speed optimization of the pre-machined surface

d) The processed surface after speed optimization

Figure 22 The influence of speed optimization on processing before and after

Disable static friction compensation. Precisely measure backlash values (MD32450) using dial indicators or laser interferometers, focusing on the Z-axis. If excessive backlash exists (linear guides should be ≤0.005mm), perform mechanical adjustments like screw pre-tensioning and bearing alignment. If adjustment isn’t possible, set the value to half the actual backlash or disable backlash compensation for test cuts. Optimize path speed and program tolerance while enabling the “Jerktime” system function. Implementing these optimizations effectively eliminates streaking, as shown in the before/after comparison in Figure 23.

a)The machined surface before parameter optimization

b) The processed surface after parameter optimization

Figure 23 Comparison of processing effects before and after the wire drawing phenomenon is eliminated

Summary

Through comprehensive optimization of machining equipment, processes, and tools, the processing defects of ceramic materials were overcome. The yield rate of phone casings increased from the original 35% to over 80%, meeting mass production standards and reducing costs. The product has now successfully entered the market.

Ceramic phone casings offer a smooth texture, high hardness, scratch and drop resistance, and zero signal interference. As production techniques mature, ceramic casings are expected to gain widespread consumer preference.

Fig. 1 Relationship between WC-Co hardness and WC grain size and Co content

WC-Co is traditionally made via injection molding, extrusion, or powder metallurgy, but these methods face limitations in geometry, efficiency, and cost. Additive manufacturing (AM) enables complex designs (e.g., internal cooling channels) with lower time/cost. Key AM methods for WC-Co include SLM and BJAM, though challenges like cracks, porosity, and dimensional accuracy persist. Post-processing (e.g., HIP, machining) is often needed, adding cost.

Fig2. SEBM WC-13Co samples

In this review, the current status of additive manufacturing of WC-Co hardmetals is reviewed. The advantages and disadvantages of different AM processes used for producing WC-Co parts, including selective laser melting, binder jet additive manufacturing, selective electron beam melting, 3D gel-printing, and fused-filament fabrication are discussed. The studies on microstructures, defects, and mechanical properties of WC-Co parts manufactured by different AM processes are reviewed. Finally, the remaining issues and suggestions on future research on additive manufacturing of WC-Co hardmetals are put forward.

Additive manufacturing processes used for WC-Co hardmetals

Additive manufacturing processes used for fabrication of WC-Co hardmetals include the following: (1) selective laser melting (SLM, also called laser powder bed fusion, L-PBF), (2) selective electron beam melting (SEBM, also called electron beam powder bed fusion, E-PBF), (3) binder jet additive manufacturing (BJAM), (4) 3D gel-printing (3DGP), and (5) fused filament fabrication (FFF).

SLM and SEBM

SLM is currently the most promising AM technology for metal materials, which selectively melts powder layer by layer with a laser beam (as illustrated in Fig. 2) to form dense parts with good mechanical properties comparable to casting or forging . Subsequently, post-processing is sometimes essential for SLM due to the need to reduce defects and eliminate residual stress .

Fig. 3 Schematic diagram of SLM process

SEBM is similar to SLM, but also different in some aspects. For metal AM, SLM is more widely used than SEBM mainly due to lower equipment cost. SEBM can only be used for conductive materials since electric conductivity is required . The most important difference is the heat sources. The heat source of the SEBM is an electron beam, which can be controlled by a magnetic field and causes the scanning speed to be much higher than the SLM .

Cost/accessibility: SLM has lower equipment costs and only requires argon (vs. SEBM’s vacuum)

Materials: SEBM limited to conductive materials

Process: SEBM’s pre-sintering reduces support structures, offering greater geometric freedom

Temperature: SEBM operates at higher temperatures

BJAM

Binder Jet Additive Manufacturing (BJAM) is a powder-based process where layers are selectively bound by liquid binder to form a “green part” (Fig. 3), later sintered (>1400°C for WC-Co) for strength. Unlike melting-based methods, BJAM enables complex geometries but typically yields porous parts, sometimes requiring metal infiltration (e.g., Co into WC skeleton). However, precise Co content control remains challenging due to the infiltration process.

Fig. 4 Schematic diagram of BJAM process

Compared to SLM, BJAM is more cost-effective but involves three steps, with unavoidable sintering shrinkage requiring design-stage compensation that limits dimensional precision. SLM’s rapid cooling creates uneven microstructures with high residual stress, often leading to porosity and micro-cracks. For powder-based AM (including SLM/BJAM), powder flowability is critical – requiring spherical, defect-free 10-50μm particles, with spray-dried pre-alloyed WC-Co powder preferred for non-infiltrated BJAM/SLM, while pure WC powder suits infiltrated BJAM . Moisture control is essential to prevent high-temperature porosity.

3D gel-printing

3D gel-printing (3DGP) merges gel casting and FDM, where powder is mixed into a slurry with organic solvents, then extruded through a nozzle (Fig. 4) alongside initiator/catalyst via compressed air. The deposited slurry polymerizes into a green part, later debonded and sintered. Unlike powder-bed methods, 3DGP eliminates fluidity requirements and material waste since no powder spreading is needed.

Fig. 5 Schematic diagram of 3D gel-printing (3DGP), (1) screw extruder, (2) nozzle, and (3) green body

Fused filament fabrication of hardmetal

Fused Filament Fabrication (FFF) is an AM technique akin to 3DGP but uses powder-based filaments instead of slurry. The process involves mixing powder with binders, extruding into filaments via capillary rheometer, then depositing through a nozzle to build green parts (Fig. 5). Post-printing, a unique two-step debonding (solvent immersion followed by thermal treatment) precedes final sintering.

Fig. 6 Schematic diagram of fused filament fabrication (FFF)

Summary

In this paper, the current status of additive manufacturing of WC-Co hardmetals is reviewed. The advantages and disadvantages of different AM processes used for producing WC-Co parts, including selective laser melting (SLM), selective electron beam melting (SEBM), binder jet additive manufacturing (BJAM), 3D gel-printing (3DGP), and fused filament fabrication (FFF) are discussed. The studies on microstructures, defects, and mechanical properties of WC-Co parts manufactured by different AM processes are reviewed.

Fig7. Shrinkage of the BJAM printed WC-12Co part after sintering

Summary

In conclusion, the above five additive manufacturing processes can be divided into two types: selective melting process and shaping-debonding-sintering (SDS) process. Selective melting processes include SLM and SEBM, which make parts by melting powder with a heat source. This type of process is very simple and enables one-step molding. But sometimes post-processing is needed to eliminate stress and defects. The SDS process includes BJAM, 3DGP, and FFF.

The SDS type processes are characterized by forming a green part with organic compounds as binder and then sintering. Compared with the selective melting process, the SDS process is more complicated. Because SLM, SEBM, and BJAM all contain a powder spreading step, all three processes require the powder to have good flowability. While 3DGP and FFF prepare powders as slurry and filament for printing, there is no need for powder flowability. The application of SEBM is limited by its very high equipment cost. SLM suffers from uneven microstructure, carbon loss, and evaporation of Co.

Tungsten carbides represent the primary sector of the tungsten products industry. This article analyzes the current practices of major global Tungsten carbide companies (Sandvik, Kennametal, Iscar, Mitsubishi Materials, and Ceratizit) in terms of raw materials, markets, recycling capabilities, and responses to tariff policies, drawing insights to propose strategic recommendations for China’s tungsten products industry.

Analysis of Major Global Tungsten carbide and Tungsten Product Companies

Dependence on Chinese Raw Materials

China accounts for ~85% of global tungsten ore production (International Tungsten Industry Association, 2024), serving as a critical raw material source for the Tungsten carbide industry.

Kennametal and Sandvik exhibit high dependence on Chinese tungsten raw materials (40% and 35%, respectively), making them significantly vulnerable to tariff measures. Both are accelerating efforts to diversify their supply chains.

Ceratizit has lower dependence (20%) and adopts a more flexible procurement strategy.

Global trends suggest that China’s share in raw material supply may decline by an average of 10%-15% by 2026. However, complete substitution remains difficult in the short term, underscoring the strategic value of China’s tungsten resources.

Dependence on the Chinese Market

China constitutes ~30% of the global cutting tools market (China Machine Tool & Tool Builders’ Association, 2024), with annual growth of 15% driven by aerospace and new energy demand.

Sandvik and Mitsubishi Materials rely heavily on the Chinese market (15%-20%), but their localized production in China helps mitigate tariff impacts.

Kennametal and Ceratizit have lower dependence (10% and 8%, respectively), enabling easier shifts to Southeast Asian and European markets.

China’s market size is RMB 60 billion. If tariff issues persist long-term without significant improvement, foreign companies may accelerate local production, threatening domestic market share.

Chart1.Localized Production Facilities of Major Enterprises in China

Tungsten Scrap Recycling Capacity and Recovery Rate

Globally, tungsten scrap recycling accounts for 30% of total supply (ITIA, 2024).

Chart2.Recycling Capacities of Major Enterprises

Opportunities and Challenges for China’s Tungsten Products Industry

Analysis of global companies reveals both opportunities and challenges for China’s tungsten products industry, forming the fundamental development logic for our country’s tungsten product supply chain strategy.

Breakthrough Technological Bottlenecks to Capture High-End Markets

The high-end cutting tool market offers a profit margin of 30%, far exceeding the 10% margin in the low-end segment. Compared to foreign technologies like Sandvik’s CoroPlus?, China’s technological gap remains significant. Therefore, accelerating innovation is imperative. The government should provide higher R&D tax incentives (e.g., 30%) to encourage capable enterprises to increase R&D investment (e.g., 5% of revenue). Efforts should focus on developing nano-grade tungsten powder, high-performance coated tools, AI-optimized processing technologies, and high-end customization.

Collaborations between companies like China Tungsten & Hightech (Zhuzhou Cemented Carbide) and Xiamen Tungsten (Xiamen Golden Egret) with institutions such as Tsinghua University, Central South University, and Xiamen University can advance low-cobalt alloy development to reduce production costs. Enterprises should adopt Iscar’s modular tool approach, introducing replaceable toolhead systems to lower customer replacement costs.

China should aim to increase its high-end cutting tool market share from 20% to 35% by 2028–2030, generating annual revenue growth of approximately RMB 200–250 billion. This expansion would cater to demands in aerospace (e.g., C919, C929, fifth- and sixth-generation aircraft, drones), low-altitude economy, and new energy (battery and automotive tools/molds).

Optimize Global Layout to Mitigate Trade Barriers

Current tariff tensions may compress export volumes and profit margins. Following the examples of Kennametal (Mexico factory) and Iscar (India expansion), overseas expansion is critical. China should encourage Xiamen Tungsten and Zhuzhou Cemented Carbide to establish factories in Vietnam and India to capture more overseas capacity and markets, producing low-cost tools (estimated 15% price reduction). Additionally, securing tungsten ore agreements with Brazil, Central Asia, and Mongolia could lock in 10% of global raw material supply and primary smelting capacity. Exploring assembly plants in Mexico under USMCA’s low tariffs would facilitate entry into the North American market (25% of global tool demand).

The government should introduce overseas M&A incentives (e.g., 50% investment subsidies) and resource development support (e.g., low-interest loans) to help acquire tungsten mines in Australia/Canada or European toolmakers (e.g., small coating technology firms). Synergies with domestic supply chains, such as CATL’s European plants, should be leveraged.

This strategy capitalizes on low-cost regions (Vietnam’s 20–50% cheaper labor) and high-growth markets (Southeast Asia’s 10% annual growth), boosting export profits and raising Southeast Asia’s market share from 15% to 20%+. It also facilitates local resource development and recycling of tungsten scrap.

Promote Tungsten Scrap Recycling to Build a Green Supply Chain

China’s tungsten recycling rate is alarmingly low, wasting 5,000 tons annually and incurring 30% higher costs. Learning from Ceratizit (45% recycling rate) and Sandvik (40%), China must act under the Solid Waste Law (2020) and Restricted Waste Import List (2020), which currently limit tungsten scrap imports. Domestic scrap collection rates are only 20%, hindering circular economy goals. Recommendations:

Ease Scrap Import Restrictions: Revise policies to allow imports with strict environmental monitoring.

Expand Domestic Recycling: Build recycling hubs in Hunan (Zhuzhou), Jiangxi (Ganzhou), Xiamen (Longyan), and Hebei, adopting zinc/chemical methods to achieve a 30% recycling rate by 2028.

Adopt 3D Printing: Reduce tool costs through additive manufacturing.

Increase R&D Investment

Establish a National Tungsten Recycling Laboratory with Central South University to develop electrochemical methods (target: 50% recycling rate). Encourage enterprises to allocate more revenue to R&D.

Introduce Tax Incentives

Reduce corporate income tax for recyclers, subsidize green equipment, and build a scrap collection network covering 80% of tool manufacturers. Align with carbon neutrality goals (2060).

Foster Industry Collaboration

Partner with COMAC (aviation) and CRRC (rail) to develop customized tools (e.g., composite materials for aerospace, rail processing), targeting 50% market share by 2027–2030. Expand mid-to-high-end capacity while serving SMEs and overseas low-end markets.

Advance Smart Manufacturing

Promote industrial IoT, big data centers, and AI-driven design (e.g., high-entropy tungsten alloys) to leverage China’s institutional and resource advantages.

Strengthen Global Cooperation

Collaborate with Japan/Korea on semiconductor-grade tools to dominate Asia’s high-end market.

Host international trade fairs and lead ITIA to shape global standards.

Establish an Industry Fund

Create funds (e.g., Jiangxi/Hunan governments + SSE) to balance supply-demand, fulfill national reserves, and counter foreign capital control.

Conclusion

Global leaders like Sandvik and Ceratizit thrive on diversified supply chains, localized production, and high recycling rates—exposing China’s gaps in technology, recycling, and global strategy. By prioritizing tech breakthroughs, recycling optimization, and overseas expansion—while fostering partnerships with aviation/rail sectors—China can secure its position as a tungsten resource, production, and recycling powerhouse. Liberalizing scrap imports and upgrading recycling tech will solidify this leadership, ensuring long-term dominance in the global tungsten industry.

Fracture Process

The fracture and separation of materials during metal cutting constitute a complex dynamic process involving multiple physical mechanisms. Research indicates that this process primarily consists of three key stages:

Plastic deformation occurs first. Crack initiation and propagation follow. Finally, material separation is achieved.

Based on extensive experimental data and theoretical analysis, this phenomenon can be systematically explained as follows:

Fracture Types and Mechanisms

According to material response and processing conditions, fracture can be divided into the following categories:

Shear fracture

Dominant type, where shear bands form at the tool-workpiece contact surface, and material separates along slip planes. For example, pure shear fracture is common in highly plastic materials (such as low-carbon steel), with fracture surfaces appearing wedge-shaped; microvoid coalescence fracture achieves separation through microvoid nucleation and aggregation.

Tensile fracture

At the tool’s leading edge or chip’s free surface, material forms tear ridges due to tensile stress, mostly occurring in brittle materials or under high cutting speed conditions.

Cleavage fracture

Under low temperature or impact loading, cracks rapidly propagate along specific crystal planes (cleavage planes), producing flat and shiny fracture surfaces, commonly seen in body-centered cubic metals (such as ferritic steel).

Basic Stages of Fracture

The fracture in metal cutting can be divided into three stages:

Crack initiation: When the tool contacts the workpiece, localized stress concentration leads to the formation of microcracks inside or on the surface of the material. For example, in the first deformation zone (chip formation zone) during cutting, the material undergoes slip deformation due to shear stress, thereby initiating cracks.

Crack propagation

As the tool advances, the crack extends along specific paths. The propagation direction is influenced by stress state and material properties, potentially manifesting as shear fracture (along the direction of maximum shear stress) or tensile fracture (along the direction of maximum normal stress).

Final separation

The crack penetrates through the material to form chips, and the resulting fracture surface may exhibit either ductile (fibrous) or brittle (crystalline) characteristics.

Dynamic Fracture in Cutting Process

Stage Division

Taking the cutting card theory illustrated in the following diagram as an example, the cutting process is divided into four stages: initial contact, crack initiation, material uplift, and cyclic phase. The crack initiation stage represents the critical point for fracture formation, while the cyclic phase involves periodic crack nucleation, resulting in saw-tooth shaped chips.

Deformation Zone Effects

Primary Deformation Zone (A-H region): Material undergoes intense shear deformation, forming initial cracks.

Secondary Deformation Zone (G-E region): Friction between chip and tool causes additional plastic deformation, potentially accompanied by localized fracture.

Tertiary Deformation Zone (E-D region): Workpiece surface material fractures due to tool flank face compression, forming the machined surface.

Key Influencing Factors

Tool Parameters: The tool’s rake angle, clearance angle, and major cutting edge angle affect stress distribution. For example, increasing the major cutting edge angle reduces cutting forces but may alter crack propagation paths.

Cutting Speed

Low speed → Ductile fracture; High speed → Brittle fracture (thermal softening effect reduces material strength).

Feed Rate

Large feed increases cutting thickness, promoting fracture (as utilized in chip breaker design).

Tool Rake Angle

Negative rake angle increases compressive stress, suppressing fracture; Positive rake angle intensifies tensile stress.

Edge Roundness Radius

Dull cutting edges enhance extrusion, easily inducing microcracks in brittle materials.

Clearance Setting

In shearing operations, the clearance between upper and lower blades (typically 5-10% of material thickness) controls crack meeting position. Improper clearance leads to increased burrs or rough fracture surfaces.

Material Properties

High ductility materials (e.g., aluminum) tend toward ductile fracture, forming fibrous fracture surfaces; Brittle materials (e.g., cast iron) readily exhibit cleavage or intergranular fracture.

Machining Conditions

High-speed cutting may induce adiabatic shear bands, causing periodic cracks and saw-toothed chips; Low temperature or alternating loads promote brittle fracture.

Material Characteristics

Performance in Actual Metal Cuttings

Chip morphology: Continuous cutting produces ribbon-like chips, while periodic fracture leads to saw-toothed chips.

Surface quality: Incomplete fracture generates burrs, whose height is positively correlated with clearance and material ductility. For example, excessive clearance significantly increases burr height.

Energy consumption: The fracture process requires overcoming material shear strength and plastic deformation energy; optimizing tool angles can reduce energy consumption.

Typical Case Analysis

Case 1: Crumbling Control in Cast Iron Cylinder Metal Cutting

Problem: Edge chipping occurs when cutting gray cast iron, and surface roughness exceeds standards.

Solution:

Switch to CBN tools (high hardness reduces compressive stress);

Use small feed rate (f = 0.1 mm/rev) and negative rake angle (?5°).

Case 2: Adiabatic Shear Fracture in Titanium Alloy Aerospace Components

Problem: Localized melting and adhesion of chips to the tool during cutting.

Solution:

High-pressure coolant to suppress temperature rise;

Optimize cutting speed to vc = 50 m/min.

Summary

Fracture in metal cutting results from the combined effects of mechanical response and metal cutting parameters. By controlling tool design (e.g., rake angle, clearance), optimizing cutting parameters (e.g., speed, feed rate), and considering material properties (e.g., ductility, fracture toughness), efficient and low-damage material separation can be achieved. Understanding fracture mechanisms is crucial for improving metal cutting quality, reducing burrs, and extending tool life.

When applied correctly, surface treatments can improve both the physical properties and functionality of machined parts. Since different types of CNC machining surface finishes involve distinct procedures and outcomes, understanding the fundamentals of these treatments is essential to determine the best option that meets the requirements of your intended application.

Why Do Machined Parts Require Surface Finishing?

CNC machining processes (including milling and turning) often leave visible cutting marks, which can compromise the surface quality of machined parts. Although CNC machining delivers precision components, these parts frequently require surface finishing for various reasons.

Why Surface Finishing Is Crucial for CNC-Machined Metal Parts:

Enhancing Appearance

Surface treatments such as sanding, polishing, electroplating, or painting help conceal sharp edges and machining marks left during CNC processing. As a result, these finishes enhance the visual appeal of CNC-machined parts.

Improving Corrosion Resistance

Most CNC-machined materials are susceptible to corrosive substances. To protect the surface of machined components and extend their service life, product designers often employ surface treatments like anodizing, polishing, and passivation.

Ensuring Hygiene & Cleanliness

Manufacturers apply various surface finishes to CNC-machined parts to ensure they are easy to clean and maintain. This is particularly critical in applications where hygiene is paramount, such as food processing equipment and medical devices.

Optimizing Fucctional Performance

Different CNC surface treatments are used to enhance material properties (e.g., conductivity), reduce friction, and add other desirable characteristics—improving overall functional performance.

Customization Options

By selecting the appropriate surface finish for your machined parts, you can customize them to meet specific preferences and requirements. A variety of finishes can be achieved to deliver desired surface properties, textures, or colors.

Common Types of Surface Finishes

Different surface treatments are suitable for various CNC machining materials, each with distinct surface roughness values. However, it is crucial to select the surface finish that best ensures optimal performance, functionality, durability, and visual appeal of the machined parts.

Below are the commonly used surface finishes for metal CNC-machined parts:

Polishing

Polishing is a classic mechanical finishing process that uses chemical agents or abrasives to create a highly glossy, mirror-like surface on metal parts. This finishing technique enhances the physical properties of machined metal components, improves corrosion resistance, ensures better cleanliness, and reduces friction.

Polishing is particularly suitable for metals such as aluminum, stainless steel, and brass. It is widely adopted by product designers and manufacturers in the food processing, medical, and luxury goods industries due to its functional and aesthetic benefits.

Although polishing can produce a smooth, reflective surface that enhances visual appeal, the process can be time-consuming and labor-intensive. This is especially true for machined parts requiring extremely high finishes or those with complex geometries.

Electroplating

Electroplating is a finishing process that involves depositing a layer of metal coating onto machined parts to increase their thickness. Applying this surface treatment to CNC-machined components protects them from corrosion, impact, high temperatures, and rust, ensuring long-term durability. This process is most suitable for metals such as chromium, cadmium, tin, copper, nickel, and gold. Electroplating enhances adhesion between the substrate and its external coating while also enabling machined parts to acquire magnetic or conductive properties depending on the plated metal.

Unlike other CNC surface treatments, electroplating is not environmentally friendly due to its generation of hazardous waste. Improper handling can lead to significant pollution. Additionally, electroplating is time-consuming and relatively expensive, requiring specialized equipment, metals, and chemicals—especially when multiple layers are needed on metal components.

Passivation

Passivation protects ferrous materials like steel and stainless steel from corrosion and rust, improving appearance, performance, and cleanliness. This chemical treatment involves immersing machined metal parts in acidic solutions such as nitric or citric acid to remove surface iron, resulting in a smooth, polished finish.

Since passivation is not a coating, it does not require masking or add thickness to the machined part. The acid bath eliminates traces of iron and rust from the surface, forming a protective layer composed of chromium or nickel. While nitric acid is the traditional choice for passivation, citric acid baths have gained widespread acceptance due to their shorter processing times.

Passivated parts exhibit excellent rust resistance, making them ideal for outdoor applications. Moreover, passivation is widely used across industries—from aerospace (requiring high-quality steel and tight tolerances) to medical sectors (where sterilization and longevity are critical).

However, passivation may extend production lead times because machined metal parts must undergo pretreatment, such as cleaning to remove debris, grease, or other contaminants. While immersion is the most common passivation technique (offering faster cycles and better consistency), acid spraying serves as a viable alternative.

Anodizing

Anodizing creates a protective oxide layer on the surface of machined metal parts. This coating shields the metal from corrosion and wear while being compatible with various colors. It is non-conductive and highly durable (Type III). Anodizing is ideal for forming corrosion-resistant coatings on aluminum and titanium components.

To anodize a CNC-machined metal part, it is immersed in a diluted sulfuric acid solution, and an electrical current is applied between the part (anode) and a cathode. This triggers an electrochemical reaction, converting the exposed surface into hard titanium or aluminum oxide. However, critical features like threaded holes—which must remain conductive—should be masked before anodizing.

Anodized parts can be dyed in colors such as gold, red, black, or blue before sealing. The coating’s thickness and density can be adjusted by varying the anodizing time, consistency, and duration. There are three primary anodizing variants, each with distinct processes, coating thicknesses, and properties:

Type I (Chromic Acid Anodizing)

Produces the thinnest layer, preserving part dimensions.

Results in a grayish finish that cannot be dyed.

Type II (Boric-Sulfuric Acid Anodizing)

A safer option with better paint adhesion, allowing for color customization.

Known as “decorative” or standard anodizing, with coatings up to 25 μm thick.

Type III (Hardcoat Sulfuric Acid Anodizing)

The most common type, especially for aluminum and titanium alloys.

Provides the clearest surface, enabling the widest color compatibility.

Coating thickness ranges from 0.001 to 0.004 inches (25–100 μm).

Combined with PTFE/Teflon, it forms a dry lubricated surface.

Alodine

Alodine or chem film is the brand name for chromate conversion coating. This chemical surface treatment requires immersing machined components in a proprietary chemical solution primarily composed of chromium. When selecting Alodine treatment for metal CNC machined parts, please ensure the process complies with the MIL-DTL-5541F standard. This standard specifies the technical requirements for chemical conversion coatings on aluminum and aluminum alloys in U.S. military specifications.

The Alodine protective coating effectively inhibits corrosion. More importantly, it can be used in conjunction with decorative surface treatments as it significantly improves the adhesion of paints and adhesives. Unlike other surface treatments that reduce the thermal and electrical conductivity of aluminum parts, Alodine actually enhances the electrical conductivity of aluminum components. This surface treatment method is relatively low-cost, but its coating is more prone to scratches and surface damage.

Coating

Powder coating is an electrostatic process that applies dry powder to form a thin, uniform protective layer on the surface of CNC-machined parts. This technique is compatible with all metals and enhances the strength, corrosion resistance, and wear resistance of the components.

Unlike anodized metal parts, powder-coated metal parts exhibit superior impact resistance and are available in a wide range of colors. The process can be combined with sandblasting to produce machined parts with smooth, uniform surfaces and exceptional corrosion resistance. The powders used can be either thermosetting or thermoplastic polymers.

Although similar to painting, powder coating involves applying dry powder to the metal part surface and curing it in an oven. For optimal corrosion protection, machined parts may first require a primer treatment, such as chromate conversion or phosphating. The parts are then coated with dry powder using an electrostatic spray gun and cured in an oven at 200°C (392°F). Multiple layers can be applied to achieve the desired coating thickness, typically ranging from 18 μm to 72 μm.

Electroplating

Electroplating is a finishing process that deposits a metallic coating onto machined metal parts to increase their thickness. This surface treatment enhances CNC-machined components by protecting them against corrosion, impact, high temperatures, and rust, significantly extending their service life. The process is most suitable for metals such as chromium, cadmium, tin, copper, nickel, and gold. Electroplating improves adhesion between the substrate and external coatings while also enabling customized properties—magnetic or conductive—depending on the plated metal.

Unlike other CNC surface treatments, electroplating is not environmentally friendly due to its generation of hazardous waste. Improper disposal can lead to severe pollution. Additionally, the process is time-consuming and relatively costly, requiring specialized equipment, metals, and chemicals—especially for multi-layer plating.

Passivation

Passivation protects ferrous materials (e.g., steel, stainless steel) from corrosion and rust, improving appearance, performance, and cleanliness. This chemical treatment involves immersing machined parts in acidic solutions (nitric or citric acid) to remove surface iron, resulting in a smooth, polished finish.

As passivation is not a coating, it requires no masking and adds no thickness to the part. The acid bath eliminates iron and rust residues, forming a protective chromium/nickel oxide layer. While nitric acid is the traditional choice, citric acid baths are now widely adopted for their shorter cycle times.

Passivated parts excel in rust resistance, making them ideal for outdoor applications. The process is critical across industries—from aerospace (demanding high-grade steel and tight tolerances) to medical (requiring sterilization-compatible surfaces).

However, passivation may extend lead times due to mandatory pre-treatment (e.g., cleaning to remove debris or oils). Immersion remains the most common method for its consistency, though acid spraying offers an efficient alternative for complex geometries.

Electroless Nickel Plating

The electroless nickel plating process involves forming a nickel alloy protective layer on CNC machined parts to enhance their corrosion resistance. It uses a nickel bath and chemical reducing agents (such as sodium hypophosphite) to deposit a nickel alloy coating (typically nickel-phosphorus) on metal components. This process uniformly applies the nickel alloy coating to complex parts with features like holes and grooves.

There are several types of electroless nickel plating, each with different phosphorus contents. These include low-phosphorus, medium-phosphorus, and high-phosphorus nickel.

Parts treated with nickel plating typically exhibit excellent hardness and wear resistance. Additionally, they can be made harder through heat treatment. The electroless nickel plating process is suitable for various metals, including stainless steel, aluminum, and steel.

Despite its significant advantages, this method has certain limitations, including:

Subsequent reduction in plating rate

Accumulation of contaminants in the nickel bath

Increasing phosphorus content

Furthermore, electroless nickel plating is less suitable for rough, uneven, or poorly machined surfaces.

Conclusion

Metal CNC machined parts can undergo any surface treatment to ensure they meet your project requirements. In this article, we have discussed the most common surface treatments for metal CNC parts, each with its unique advantages and disadvantages. We hope this helps you understand how these surface treatments work and their outcomes, enabling you to determine the most suitable surface treatment for your specific application.