WC Phase Research Articles

Consolidation and mechanical properties of WC-Al2O3 composite prepared via high energy ball milling and spark plasma sintering

The rapid sintering of WC-Al2O3 ceramic composite containing 15 wt% Al2O3 was investigated with focus on mechanical properties and consolidation using Spark Plasma Sintering (SPS). The initial WC-15 wt% Al2O3 powders were milled for 1, 4, and 10 h followed by sintering via SPS at 1550 °C. The morphology, structure and mechanical properties of the powders and sintered sample were carefully investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD), laser particle size and Vickers hardness techniques, respectively. The results showed morphological modification of the WC and Al2O3 phases, accompanied by fragmentation and refinement of the composite particles. As milling time increased, the mean particle size decreased from 2.46 to 1.63 μm. Furthermore, a decrease in crystallite sizes was accompanied by an increase in micro-strain. Changes in the lattice parameters of both phases were observed. The process has the advantage of increase densification (98.84–99.65%) and decrease porosity of samples. The formation of the W2C phase was identified by XRD and the quantitative analysis showed that the percentage of W2C ranged from 1.81 to 12.47%. The ceramic composite showed a maximum Vickers hardness of 19 GPa.

Deposition of nano-crystalline tungsten carbide powders from gaseous WO2(OH)2

Lower WC grain sizes in the nanometer range have positive effects on the properties of hardmetals (e.g., hardness), but the established production processes of WC are limited to grain sizes of about 150 nm. To produce WC powder with grain sizes in the lower nanometer range, an alternative WC production process based on the chemical vapor transport (CVT) reaction of WO3 and H2O forming gaseous WO2(OH)2 at about 1100 °C, followed by a carburation reaction with H2/CH4-gas mixtures was investigated. The influences of different process parameters such as furnace temperature, humidity and gas flows were investigated to improve the process. With the right set of parameters the produced powder consisted mainly of agglomerated WC grains with a size of about 5 nm. Beside the common hexagonal WC phase, the cubic WC1−x phase was stabilized due to the small crystallite sizes. In addition, a thin layer of amorphous carbon was present on the powder surface due to the catalytic methane decomposition on the WC surface. The amount of oxidic and metallic residues in the product powder was minimized with the parameter optimization and the powder yield was increased up to about 50%. With further optimization of the process parameters and usage of improved flow breakers, the purity and yield of the product powder can be further improved. Since an application in the hardmetal section is not realistic at the moment, applications in the catalysis sector could be considered due to the small grain size and good catalytic activity of the cubic WC1−x phase.

Experimental and numerical investigations of micro-meso damage evolution for a WC/Co-type tool material

Commercial Co/WC/diamond composites with 90vol.% Co also belong to hard metals and, as a kind of tool materials, are very useful. Their deformation behavior can be both ductile and quasi-brittle, determined by the diamond portion and local morphology. Another characteristic is that submicron-sized WC particles, possessing non-negligible strengthening influence due to the size effect, cannot be fully present in a representative microstructure. This work emphasizes the local damage evolutions’ dependence on microstructural features. Rice&Tracey damage and cohesive zone model describe the ductile and quasi-brittle damage behavior. The mechanism-based strain gradient plasticity takes the size effect of submicron-sized WC particles into consideration. Both real and artificial microstructures are used. Besides homogeneous boundary conditions (BCs), the periodic BCs are also applied in a 2D damage simulation. This work proves that FE models with two phases, the homogenized Co-WC matrix and diamond particles, can correctly predict damage evolution. FE results show that the WC phase has a higher mean stress value than the diamond phase, which is proved by the nano-indentation test. From FE simulation results, local hot spots appear in the matrix closed to sharp diamond corners/edges and crossing regions of shear bands. The experimental and numerical results are compared on micro and macro scales. For the local strain distribution and the damage development, numerical predictions match the reality well, even in morphological details. Furthermore, since the published data about WC-Co type tool materials with Co>50vol.% are rare, the obtained knowledge in this work also contributes to the data collection.

Morphological features and phase composition of W-containing coatings formed on diamond via its interaction with WO3

In the present work, W-containing coatings were deposited on the surface of diamond microcrystals. The coatings formed as diamond reacted with a WO3 powder in the die of a hot press at elevated temperatures. The morphology and phase composition of the coatings were studied as functions of the treatment temperature and treatment time. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. After treatment of the mixture at 850 °C for 15 min, WO2 and W18O49 were found on the diamond surface. After treatment at 950 °C (15 min), tungsten was the dominant phase of the coating. Treatment at 1150 °C (15 min) led to the formation of the WC and W2C phases; no metallic tungsten was present in the coating obtained at this temperature. The reaction sequence describing the coating formation process was proposed. During the coating formation, the deposition selectivity with regard to the diamond facet was observed. The {100} facets of diamond were preferentially coated. The coating developed through the formation and coalescence of islands, which were of square shape on the {100} facets and of triangular shape on the {111} facets of diamond.

Characterisation of Spheroidised tungsten carbide metco 32c powder using radio frequency plasma

Metco 32C is a coarse grey powder, which mostly consists of tungsten carbide and cobalt; with small traces of nickel, chromium, boron, iron silicon and carbon. Metco 32C powder has the role of supporting oxidation and corrosion resistance at high temperatures as well as increasing the hardness of the coated materials. The spheroidal morphology of Metco 32C improves flowability during layer application methods such thermal spraying. There has been a growing interest in the development / improvement of methods producing powders of cast tungsten carbide and other high-melting-point materials of uniform composition, characterised by a high sphericity of the particles and having higher physical-mechanical properties. Spherical particles are generally preferred in the additive manufacturing process as they pack together for uniform powder bed density, better flowability in machinery, eliminate internal cavities and fractures resulting in a better quality of final product. Similarly, thermal spraying processes also require dense, spherical particles to ensure consistency and reproducibility of the feeding mechanism as well as interaction between the feedstock and thermal spraying heat source. The process of transforming irregularly shaped powder particles into spherical shapes is known as the spheroidisation process and this can be achieved by plasma spheroidisation. It was found that the spheroidisation ratio of the powder increased as the plasma plate power increased. A decrease in density was observed as plasma power increased. The spheroidised powders have a smaller particle size distribution (PSD) than the feed powders (un-spheroidised). The XRD results showed that as the plasma plate power increased the WC phase composition decreased, subsequently the phase composition of W2C increased.

Residual stress evolution enhanced martensite phase transition and texture development in cryogenic-tempered WC-Co ultra-coarse grained cemented carbide

The aim of this study is to clarify the effect of residual stress on the microstructure, martensite phase transition of Co binder phase, texture development of WC hard phase and mechanical properties enhancement in cryogenic-tempered WC-6wt.%Co ultra-coarse grained cemented carbides. Sin2(ψ)-2θ method was used to analyze the residual stress, and EBSD was used to reveal the phase transition of Co phase and texture of WC phase. The results showed that the density, grain size and carbon balance of cemented carbide revealed little difference after cryogenic-tempering treatment. The mean compressive residual stress of WC phase increased by 60.84% after cryogenic treatment, while tempering treatment resulted in a significant relaxation of the residual stress by 101.97% and even transformed the compressive residual stress to tensile stress. EBSD analysis showed that the mean ratio of hcp-to-fcc Co increased from 1.75% to 4.22% and 11.61%. It is difficult to distinguish the effect of residual stress increase and the temperature decrease on the martensite transition during the cooling process. However, the occurrence of martensite phase transition during tempering is not temperature-dependent but highly related to the residual stress evolution. After cryogenic-tempering treatment, {0001}<11 2‾ 0> preferred orientation of WC phase was concentrated, which was related to the basal plane slip and grain deflection of WC grains during the evolution of residual stress. Due to the martensite phase transition strengthening of Co and the preferred orientation of WC, the mean Vickers hardness increased from 1068.4 HV30 to 1149.4 HV30. The mean transverse rupture strength firstly decreased from 2747.5 MPa to 2515.3 MPa, and then increased to 2705.0 MPa, which was related to the increase and relief of residual stress during the post treatment. Furthermore, mean fracture toughness showed a slight increase from 22.5 MPa m1/2 to 23.4 MPa m1/2. The simultaneous increase of fracture toughness with hardness can be attributed to the residual stress evolution and martensite phase transition.

Mechanical properties of casting titanium alloy matrix composites reinforced by WC and TiB2 ceramic particulates

Casting Titanium alloys with Wc and TiB2 additives have their mechanical characteristics examined in this work. The mechanical properties of aged titanium alloys are very impressive. UTS reach 406 MPa and YS of 253 MPa and an El of 7.4 percent. Pinned primary Wc and TiB2 phases reduced fineness by more than half, while enhancing assorted nucleation on Wc and TiB2 initial phases boosted nucleation and growth resistance. Following the heat treatment, foundational designed with the intent emerged from the substrate. There are no more stages in the shell. Those alloys containing Wc, on the other hand, have cores composed of Wc and TiB2. From 0.1 wt% to 0.2 wt% of Wc and TiB2 content, core radius rises, but shell width does not appear to change, and particle density does not appear to be altered. In time, composite particles became coarser, but their core dimensions stayed nearly same. As predicted, the exponent (n-1) is less than the expected value of 0.33, Perhaps this is because of the low temperature, which prevents a developed a semi state from emerging. The kinetics are consistent with the KV model's predictions.

Study of the temperature dependence of a carbidized layer formation on the tungsten surface under plasma irradiation

The paper considers a method of tungsten surface carbidization using a beam-plasma discharge (BPD), which was implemented in a plasma-beam installation (PBI). The advantage of this method is to create conditions for chemical reactions and physical processes as close as possible to those possible in thermonuclear installations. The BPD makes it possible to generate plasma using different working gases. Methane was used as a plasma-forming gas. The working gas pressure in a chamber was (1,3–1,4)·10–1 Pa. The temperature dependence of the carbidized layer formation on the tungsten surface under plasma irradiation was determined in the temperature range of 700 °C–1700 °C. The formation of tungsten carbides in surface layers was confirmed by SEM and x-ray diffraction analysis. It was found that interaction between tungsten and methane in a wide temperature range can proceed with simultaneous or sequential formation of the carbide phases W2C and WC.

Facet-dependent interfacial segregation behavior of V-doped WC-Co cemented carbides

Understanding the interfacial segregation behavior in V-doped WC-Co hard metals is necessary to demystify the effect of dopant on microstructural evolution and mechanical properties. Herein, aberration-corrected scanning transmission electron microscopy was utilized to investigate the atomic level segregation mechanism at WC-Co phase boundaries and WC grain boundaries in V-doped WC-Co composites systematically. A key finding is that the segregation behavior largely depends on the orientation of low-index planes, particularly the basal and prismatic facets that prevail in WC-Co. V solute atoms show a relatively weak segregation at the WC prismatic plane-terminated interfaces, occurring largely within a monolayer with ∼10 at% V at the outermost surface. In contrast, segregation at the basal facets of WC grains distributes within a bilayer with a higher concentration of ∼25 at%. Additionally, this study shows that the facet-dependent interfacial segregation behavior is universal for both phase boundaries and grain boundaries, which often have at least one basal or prismatic WC facet. Our study presents a general solute segregation mechanism at an atomic level and demonstrates that the terminal planes of interfaces determine the atomic structure and segregation profile, while the interfacial orientation has little influence.

Модификация поверхности карбидовольфрамового композиционного материала методами электронно-ионно-плазменного воздействия

The surface of a porous tungsten carbide pseudoalloy of the WC-WCoNiFe system has been modified by a pulsed electron beam and the method of combined electron-ion-plasma, which includes vacuum arc deposition of a film from VT1-0 titanium alloy (1 μm) and subsequent pulsed electron-beam processing of the"coating/substrate" system. Optimal modes of pulsed electron-beam processing were found depending on the energy density in the pulse (40-65 J/cm2) and the pulse duration (150-200 µs). It is shown that electron-beam surface treatment of a material of this class under optimal conditions of electron-beam processing makes it possible to increase the microhardness of the surface layer by 15% relative to the initial material. Using the methods of X-ray phase analysis, it was revealed that the increase in microhardness is due to the formation of the W2C phase in the surface layer and a decrease in the amount of the binder (WCoNiFe). It is concluded that the combined electron-ion-plasma treatment of a porous tungsten carbide pseudoalloy of the WC-WCoNiFe system makes it possible to form a modified layer with a minimum number of pores and cracks on the surface.

Additive Manufacturing feasibility of WC-17Co cermet parts by Laser Powder Bed Fusion

Cermets are composite materials consisting of a ceramic reinforcement and a metal matrix. Laser Powder Bed Fusion (L-PBF) is an Additive Manufacturing (AM) technology. The present paper deals with the feasibility study of AM of cermet parts by L-PBF using WC-17Co powder. The results showed that parametric optimization of the L-PBF process allowed the production of solid WC-17Co part. Structural analysis revealed the presence of significant porosity (1.41%) and small-scale cracks in the as-built samples. Post-processing by HIP (Hot Isostatic Pressure) significantly improved the structure of manufactured parts. The porosity became very low (0.01%) and XRD phase analysis revealed the absence of the fragile W2C phase. Abrasive wear and hardness tests showed that performances of additively manufactured parts were comparable to a reference part produced by powder sintering. The study successfully demonstrated the possibility of manufacturing wear-resistant cermet parts by L-PBF.

Femtosecond laser processing of cemented carbide for selective removal of cobalt

Diamond coating of tungsten carbide-cobalt (WC-Co) cemented carbide tools using chemical vapour deposition (CVD) requires removal of the cobalt (Co) binder phase from the WC-Co surface in order to improve the coating adhesion. Laser ablation is shown to be a promising technique for the selective phase removal of Co, which is based on the difference in melting and boiling temperatures between the different phases. However, laser ablation with conventional nanosecond (ns) laser pulses typically induces surface remelting, incomplete Co removal, and metallurgical changes in the WC phase due to the large heat-affected zone (HAZ) involved. Ultrashort pulsed lasers have emerged as an alternative due to minimized HAZ and thermal stresses, enabling cold ablation. This paper reports on the effect of femtosecond (fs) laser ablation on the selective removal of Co from polished WC-Co surfaces. The influence of several process variables including laser pulse energy, number of pulses, and scanning speed on the surface morphology of the fs-laser ablated surfaces was investigated. Two different WC-Co grades with 6% and 10% wt Co binder and different WC grain sizes were examined in this study. A pulsed ytterbium fiber laser (250 fs, 1030 nm) was used for the laser ablation of different morphologies such as spots, lines, and square regions. Field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) analysis were used to characterize the microstructure and chemical composition of the processed surfaces. The experimental results indicated that fs laser processing at optimized processing parameters could achieve successful removal of the Co phase selectively from the WC-Co surface with minimized morphological changes or thermal effects on the WC grains.

Analysis of Microstructure and Performance of Laser Cladding WC-Fe316L Alloy on the Surface of 27SiMn Steel

In order to solve the problem that the hydraulic support column is affected by the sulfur and chlorine water vapor in the mine, the inner wall will inevitably have different forms of defects, such as surface wear and surface corrosion. The pure Fe316L cladding layer and the WC-Fe316L composite cladding layer with the hard phase WC mass fractions of 10%, 20%, and 30% were prepared on the 27SiMn steel substrate for hydraulic support column by homogenizing broadband laser head. The phase composition, microstructure, microhardness and wear resistance of four cladding samples were studied. The results show that the pure Fe316L cladding layer forms a good metallurgical bond with the substrat, the surface of the cladding layer has no crack defects, and the shape is good. The average microhardness of the pure Fe316L cladding layer is increased by 1.4 times compared with the 27SiMn steel base, and it is increased to 331.2HV0.5. At the same time, the wear rate of the pure Fe316L cladding layer is reduced by 30.8% compared with that of the matrix. The mass fraction of WC particles is 10 %, 20%, and 30% of the WC-Fe316L cladding layer’s microhardness is 1.6, 1.7 and 2.0 times higher than that of the 27SiMn steel matrix to 369.9HV0.5, 408.6HV0.5 and 481.6HV0.5, and each WC The wear rate of Fe316L composite cladding layer was reduced by 45.8%, 66.0% and 82.3% compared with the matri composite cladding layer. The addition of WC particles helps to strengthen the solid solution strengthening and fine-grain strengthening of the composite cladding layer, and the unmelted WC particles also strengthen the dispersion strengthening effect of the composite cladding layer.

Influence of Fe Dilution and W Dissolution on Abrasive Wear Resistance of NiCrBSi–WC Composite Hardfacing Deposited by Plasma Transferred arc Hardfacing

The control of Fe dilution and carbide dissolution plays a vital role on the performance of metal matrix composite hardfacings. In this paper, the NiCrBSi–WC composite hardfacing is deposited on 304 austenitic stainless steel by plasma transferred arc hardfacing at 120[Formula: see text]A (specimen 1) and 140[Formula: see text]A (specimen 2) transferred arc current values to obtain different levels of Fe dilution and W dissolution for comparative investigations. The Fe dilution examined by scanning electron microscopy for specimen 1 was 24.54% and for specimen 2 was 33.09%. The microstructural investigations revealed higher W dissolution for specimen 2 due to higher heat input which led to significant reduction in the amount of WC and W2C hard phases. The slurry abrasive wear test performed as per ASTM G105 showed two times reduction in abrasive wear resistance of specimen 2 as compared to specimen 1. The significant reduction in the performance of specimen 2 is mainly due to higher Fe dilution and higher W dissolution caused due to higher heat input. Hence, selection of appropriate process parameters is vital to control Fe dilution and carbide dissolution in order to achieve superior performance of composite hardfacings.

Microstructure Investigation of WC-Based Coatings Prepared by HVOF onto AZ31 Substrate

In this paper, three commercial cermet powders, WC-Co-Cr, WC-Co and WC-Cr3C2-Ni, were sprayed by the High Velocity Oxy Fuel (HVOF) method onto magnesium alloy AZ31 substrate. The coatings were investigated in terms of their microstructure, phase analysis and residual stress. The manufactured coatings were analyzed extensively using optical microscopy (OM), X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM). Based on microstructure studies, it was noted that the coatings show satisfactory homogeneity. XRD analysis shows that in WC-Co, WC-Co-Cr and WC-Cr3C2-Ni coatings, main peaks are related to WC. Weaker peaks such as W2C, Co0.9W0.1, Co and W for WC-Co and W2C, Cr3C2 and Cr7C3 for WC-Cr3C2-Ni also occur. In all cermet coatings, linear stress showed compressive nature. In WC-Co and WC-Cr3C2-Ni, residual stress had a similar value, while in WC-Co-Cr, linear stress was lower. It was also proved that spraying onto magnesium substrate causes shear stress in the WC phase, most likely due to the low elastic modulus of magnesium alloy substrate.

EFFECT OF HEAT TREATMENT ON THE MICROSTRUCTURE AND PERFORMANCE OF HIGH-VELOCITY AIR-FUEL SPRAYED WC-10Co4Cr COATINGS

In this study a high-velocity air-fuel (HVAF) flame-sprayed WC-10Co4Cr coating was heat-treated at (240; 300; 400) °C for 2 h in an air atmosphere. The effect of the heat treatment on the hardness, fracture toughness, wear resistance, corrosion resistance, phase composition and microstructure behaviour of the coatings was investigated. It could be concluded from the X-ray diffraction (XRD) pattern that the phase of the coatings was mainly composed of tungsten carbide, an amorphous phase, a small amount of W2C and trace metal tungsten. However, the heat-treated coating had a small increase in W2C compared to the original coating, although the amount of amorphous phase did not decrease significantly. The results indicated that as the heat-treatment temperature increased, the hardness of the coating first increased and then decreased, while the fracture toughness increased. The polarization test confirmed that the heat-treated coating had higher corrosion resistance than the original coating. In addition, the results of the reciprocating friction and wear test indicated that small amounts of W2C strengthening phases were formed in the WC-10Co4Cr coating after heat treatment at 400 °C. This process did not eliminate many of the tougher Co and WC phases. Therefore, this coating had the best wear resistance among all the comparative coatings.

Insights into microstructural evolution and dissolution characteristics of reinforced particles in tungsten carbide‑nickel composite coatings prepared by laser hot-wire deposition

Tungsten carbide‑nickel (WC-Ni) composite coatings were firstly prepared on martensite stainless steel 2Cr13 by laser hot-wire deposition. The microstructural evolution and the dissolution characteristics of ceramic particles in the coatings had been systematically investigated. The results showed that the tungsten carbides' dissolution and microstructures in the coatings were close related to the dilution degree of the base metal. Apart form large retained particles, the coating with a lower dilution ratio (8.4%) was composed of Ni, Ni/Ni3B eutectics, and in-situ W2C particles. The W2C phase was preferentially dissolved while the WC was retained in W2C/WC eutectoid-structured particles, which exhibited the typical thermal damage patterns including the dissolution-diffusion and partially/completely fragmentation-dissolution-diffusion. The amount of M6C carbides was increased with the increment of dilution ratio (from 9.5% to 24%), and the ceramic particles suffered from more severe heat damage which mainly exhibited the characteristics of dissolution-diffusion-precipitation. Not only was the W2C phase was dissolved, the WC phase was also decomposed and reacted into M6C carbides. Due to the reinforcement of retained particles and the precipitated carbides, these coatings showed higher hardness and wear resistance which was about 1.9– 2.3 and 12.1– 26.9 times that of 2Cr13 substrate.

Effect of TaC addition on microstructure and microhardness of additively manufactured tungsten

In this study, 5 wt% tantalum carbide (TaC) was added as a secondary component into tungsten (W) samples fabricated by laser powder bed fusion (LPBF) technique. The microstructures were investigated by SEM, EBSD, TEM, XRD and nano-indentation. With the addition of TaC, the density of cracks is significantly reduced compared to the pure W. Cellular structures, consisting of W(Ta) solid solution as base and intercellular tungsten carbides (W2C), were observed at different location with various morphologies. Hexagonal and orthorhombic W2C phases were confirmed. The intercellular W2C were suggested to be formed by in-situ reaction in a divorced eutectic approach during LPBF process. This study provides an effective way to strengthen and refine the W microstructure by a synergistic effect of grain refinement, solid-solution, eutectic and oxygen consumption, thus providing further argument for the novel strengthening method to reduce LPBF W cracks.

Selective synthesis of tungsten carbide phases W2C and WC as hydrogenation catalysts

Tungsten carbides are possible low-cost replacements for noble metal catalysts, but the role of different carbide stoichiometries (W2C, WC) and their polymorphs for catalytic behavior is poorly understood. We develop a “dynamic, isothermal” carburization of WO3 in a mixture of CH4 and H2 to control phase composition and catalytic properties. A design-of-experiments approach reveals that the key parameters are synthesis temperature (670 to 775 °C) and addition of silica as stabilizer (0 or 70 mol%). X-ray diffraction shows that the composition can be adjusted from 14 to 99 wt% W2C, complemented by WC and a small fraction of W metal. Crystalline domain sizes for W2C are smaller than those of WC (≥10 nm), affording thermodynamic stabilization of W2C in agreement with computational predictions (Shrestha et al., Chem. Mater. 2021, 33, 4606–4620). The amount of CO adsorbed scales with W2C content, and so does the performance in butyraldehyde or toluene hydrogenation.

Changes in surface integrity of cemented tungsten carbide with shot peening treatment

This study investigates the changes in the surface integrity of WC-Co cemented carbide, after traditional and dual shot peening treatments, using physical characterization methods in conjunction with finite element simulations. Cast steel balls were used in traditional shot peening, while dual shot peening involved the additional use of ceramic shots. Tensile residual stress was found to coexist with compressive residual stresses within both the WC and Co phases, resulting in the fluctuation of stress amplitude in the surface layer. Steep stress gradients were mainly located in regions near the phase interface, especially around the WC/Co interface. In comparison with traditional shot peening, dual shot peening not only improved the uniformity of residual stress at both the macroscopic and microscopic levels but also refined the microstructure and returned the hardness dispersion to the original value by facilitating the simultaneous and coordinated evolution of the WC and Co phases during further deformation. However, the surface roughness increased significantly after traditional and dual shot peening treatments due to accumulated elastic-plastic deformation. This is likely to deteriorate the surface integrity and thus should be avoided if possible, without compromising the other beneficial effects caused by shot peening.