Dissolution Of WC Research Articles

Dissolution behaviour of WC particles and evolution of precipitated phases in the plasma transfer arc Ni-based composite coating reinforced by 30 wt% WC particles

Ni-WC composite coating was prepared on Q235 steel substrate by plasma transfer arc (PTA) with welding current ranging from 70 A to 85 A. The results show that the dissolution behaviour of WC particles and the elemental diffusion at the interface promoted by the increased welding current promote the formation and evolution of precipitates, including M7(B, C)3 and M6C. The increased current reduced the volume fraction of WC particles in the coating, but increased that of the precipitates. At welding currents of 75 A and 80 A, dendritic-like M7(B, C)3 presented a regular distribution at the bottom of the coating. At a welding current of 80 A, M6C phase began to form at the bottom of the coating. When the welding current reached 85 A, the dendritic structure was broken, and the M6C phase aggregated and grew. The Ni-WC coating had visible delamination. WC particles at the upper part of the coating dissolved more severely compared to those at the middle and bottom of the coating. Ni3Si compound was formed at the upper and middle of the coating, and it had a crystal orientation relationship of [011]Ni3Si∥[011]γ-Ni, (11-1)Ni3Si∥(11-1)γ-Ni, (−200)Ni3Si∥(-200)γ-Ni, (-11-1)Ni3Si 1.3° from (-11-1)γ-Ni with γ-Ni. The average hardness of the coating decreased slightly due to the dissolution of WC, but the hardness at the interface increased, showing an improved bonding of the interface. The newly formed high hardness precipitates can share the load coming from the friction paired ball, thus reducing CoF and wear loss of the coating.

Effects of TaCx on the microstructure and properties of WC composites

WC-5vol%TaCx (where x = 0.5, 0.7, 0.8 and 0.9) binderless cemented carbides with different carbon vacancy contents were prepared by spark plasma sintering (SPS) at a lower sintering temperature of 1800 °C. The phase evolution, microstructure and mechanical properties of these materials were investigated. The results show that the presence of WC, W2C and (Ta1-x, Wx)Cn phases in the sintered body. The formation of (Ta1-x, Wx)Cn solid solution is attributed to the dissolution of WC into TaCx, and the existence of vacancies promotes the atomic diffusion. (Ta1-x, Wx)Cn solid solution was uniformly distributed around the WC matrix, which inhibited the WC grain growth. In terms of fracture mode, the WC-5vol%TaCx composites exhibit a combination of intergranular and transgranular fracture, with crack deflection and bridging contributing to enhanced fracture toughness. Compared to other WC-TaCx composites with varying carbon vacancy content, the WC-5vol%TaC0.8 composite possesses the smallest average particle size and highest intrinsic hardness. Additionally, a semi-coherent interface is formed between (Ta1-x, Wx)Cn and WC, leading to improved mechanical properties such as highest hardness (24.4 GPa) and fracture toughness (8.5 MPa·m1/2). The WC-5vol%TaC0.8 composite, however, exhibits the lowest oxidation onset temperature attributed to its relatively smaller grain size. The introduction of carbon vacancies serves to facilitate atom diffusion and lower the densification temperature, while also functioning as a toughening agent.

Electrochemical separation of tungsten from scrap cemented carbide WC in FLiNaK melt

Molten salt electrolysis is an innovative technology applied to recover tungsten from the scrap of cemented carbide, which enables the realization of energy saving and consumption reduction goals. Currently, numerous studies have focused on the molten salt electrolysis of chlorine salt systems, but still face challenges including low electrolysis efficiency and salt volatilization. Here, we propose to employ the FLiNaK molten salt system for recovering tungsten from the scrap cemented carbide and analyze the feasibility of the dissolution of WC occurring at the anode from the perspective of thermodynamics and electrochemical polarization curves. Moreover, the influence of electrolysis temperature on the dissolution of the anode is also investigated and the productions are identified as nano-flake tungsten powder by characterizing the cathode product using XRD, SEM, EDS, and XPS. A two-step reduction mechanism of W ions was analyzed by electrochemical means such as CV, SWV, etc., and the ionic groups stabilized by W6+ and W4+, and F− in the molten salts were deduced to be WF33+ and WF3+ by DFT simulation calculations. This work provides new guidance for the application of molten salt electrolysis in the recovery of tungsten from scrap cemented carbide.

Additive manufacturing and spark plasma sintering as effective routes for manufacturing of AISI 316L austenitic stainless steel - WC composites

Metal matrix composites (MMCs) are lightweight, high-performance materials with continuous expansion in industrial applications. In this study, Laser Powder Bed Fusion (LPBF), Binder Jetting (BJ), and Spark Plasma Sintering (SPS), were used to produce AISI 316L austenitic stainless steel (SS316L)-WC composite with different compositions and powder preparations. In the present study, the products manufactured with these different technologies and material compositions were compared in terms of final density, microstructure, and mechanical property. Results show a significant difference in the microstructure of the parts produced by these different manufacturing techniques with microstructural analysis showing that samples processed by LPBF exhibit the finest grain size, while the BJ processed samples exhibit the coarsest grain size. Furthermore, analysis of the micrographs and the XRD patterns obtained for all processing routes suggest that there was some level of WC dissolution followed by inter atomic diffusion occurring between the WC inclusions and the SS316L matrix, involving dissolved W and C atoms from the inclusions and Cr and Fe atoms from the steel matrix, with the final structure and microhardness of the composite system depending on the kinetics of the manufacturing process.

The microstructure and mechanical properties of Ce2O3 reinforced WC-Cu-10Ni-5Mn-3Sn-1.5TiC cemented carbides fabricated via pressureless melt infiltration

Microstructure and mechanical properties of WC-Cu-10Ni-5Mn-3Sn-1.5TiC cemented carbides fabricated by pressureless melt infiltration at 1200 °C for 90 min with different Ce2O3 contents (0 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, and 1.0 wt%) were investigated. Ce2O3 accelerated the decomposition and dissolution of WC. The melt infiltration reaction products of high carbon solid solution, such as W, Ni2W4C, and (Ti,W)C1-X are precipitated in binder alloys. High carbon solid solution gradually decreased or even disappeared, and W, Ni2W4C, and (Ti,W)C1-X seemed to grow with the increase of Ce2O3 contents. Considering the influence of decomposition and dissolution of WC and the formation of new phases, the size of WC particles decreased while the surface morphology of WC slowly changed from round and blunt to sharp-angle shaped, and the contiguity value of WC particles first decreased and then increased. The changes in microstructural properties of cemented carbides as a function of Ce2O3 inevitably led to the change in mechanical properties. The sample with 0.4 wt% Ce2O3 additions had the highest hardness (94.8 HRA). The highest values of impact toughness and TRS in 0.6 wt% Ce2O3 cemented carbides were 7.15 J cm−2 and 1977.8 MPa, respectively.

Wear phenomena in different cemented carbides during rotary-percussive drilling in reinforced concrete

Rotary-percussive drilling through steel reinforced concrete not only subjects cemented tungsten carbide drill bits to intensive abrasive wear but additionally induces significant microstructural changes in the near-surface regions. These include micro-, meso- and macroscopic cracking; comminution of the WC; delamination of WC-binder interfaces; binder depletion and pore formation; partial WC dissolution and rearrangement; surface decarburization; and the creation of secondary phases within the binder.In this study, the wear phenomena in cemented carbide drill bits with different WC grain sizes (fine to extra coarse), binder contents (6–12 wt%) and binder types (Co, CoNi and Ni) have been documented, analysed and quantified. Noticeable differences between the various grades are evident.A wide range of experimental variables have been investigated covering the large proportion of real-world cases encountered in the application of these drill bits on the construction site. This paper presents a broad overview highlighting how material choice influences wear.

Laser powder bed fusion of cemented carbides by developing a new type of Co coated WC composite powder

The study addresses the issue of the absence of high-quality WC-Co composite powder for laser powder bed fusion and assessing the printability of the new powder in terms of densification, microstructure and mechanical properties. The fluidized bed chemical vapor deposition (FBCVD) combined with electroless plating process was adopted to make core-shell structured WC-Co composite powder. The excellent uniformity of Co and good powder flowability were achieved by tuning the size and distribution of Co catalyst during FBCVD and regulating their relationship to the subsequent electroless plating behavior. The newly developed composite powder exhibited excellent printability. The densification mechanism was largely dependent on the laser energy density. The liquid formed by the melting of Co was responsible for the densification at low laser energy density, while the Co-W-C ternary liquid resulted from the dissolution of WC into Co melt dominated the densification at high laser energy density. Microstructurally, the morphology and size of WC grains were insignificantly changed because of its non-participation with liquid formation at low laser energy density. The rectangular/triangular WC grain morphology similar to the traditional sintered was formed at high laser energy density because of the precipitation of WC from the Co-W-C ternary liquid. Affected by the different liquid formation processes, increasing laser energy density increased the relative density, promoted the W 2 C phase formation and decreased WC grain size, which remarkably improved the hardness and tribological properties of the printed cemented carbide.

Impact of Ce2O3 on microstructure and properties of matrix-body for PDC drill bits synthesized via pressureless melt infiltration

The materials of matrix-body polycrystalline diamond composite (PDC) bits were fabricated through pressureless melt infiltration method at 1200 °C for 1 h within vacuum furnace using molten CuNi metallic binder, Ni and WC powders (including cast WC, spherical WC, and fine WC). Various weight ratios of Ce2O3/(WC + Ni + CuNi) ranging from 0 to 0.01 were added to matrix-body materials. The influence of Ce2O3 on the microstructure, phase formation, phase transformations, and related mechanical properties of matrix-body materials was thoroughly investigated. The results show that experimental temperature led to the decomposition of WC and partial dissolution of W and C in CuNi binder alloys. In matrix-body materials with no Ce2O3 addition, only new W2C phase was formed. With further increase in Ce2O3/(WC + Ni + CuNi) ratios, spherical WC was dispersed into smaller WC particles. Meanwhile, new phases (namely Ni2W4C, C, and W2C) were found. The material exhibited an optimal hardness (HRA = 93.7) and transverse rupture strength (1846.8 MPa) when Ce2O3/(WC + Ni + CuNi) ratio was 0.006. However, impact toughness was slightly decreased, while the highest value of 6.45 J cm−2 was measured for the sample with Ce2O3/(WC + Ni + CuNi) ratio of 0.01.

A comparative study of tungsten carbide and carbon nanotubes reinforced Inconel 625 composite coatings fabricated by laser cladding

Laser cladding with wire presents clear advantages in economic efficiency and cleanliness over the powder-based system. To find the best coating performance, the Inconel 625 composite coating, and two typical metal matrix composite (MMC) coatings reinforced respectively by tungsten carbide (WC) and carbon nanotubes (CNTs) were fabricated by an off-axis wire cladding system. The differences of morphology, microstructure and mechanical properties among the three samples were investigated. The results showed that the morphology of clad coatings with reinforcement powder generally presented desirable geometric characteristics. The clad coating with WC powder, in particular, presented better wettability compared with the other samples. The main secondary compound of WC dissolution was W2C, which was mainly distributed at grain boundaries. The mechanical properties of powder reinforced MMC coatings were significantly improved. Compared with the Inconel 625 specimen in coating area, the yield strength of the two MMC coatings was improved by 36.3% and 23.4% respectively. In addition, the average microhardness of WC/Inconel 625 coating showed an obvious increase to 589 HV.

Wetting behaviors and interfacial characteristics of molten AlxCoCrCuFeNi high-entropy alloys on a WC substrate

The wettability of molten AlxCoCrCuFeNi (x is from 0 to 1.5, mol.%) high-entropy alloys (HEA) on a WC substrate was measured using a modified sessile drop method at 1823 K in an argon atmosphere. The wetting behaviors and interfacial characteristics between HEAs and WC were studied. Good wettability with final equilibrium contact angles of 0.5°−4.6° is obtained, and addition of Al deteriorates the wettability of the HEAs. The wetting of AlxCoCrCuFeNi/WC system can be roughly divided into an initially sharp spreading stage and a subsequent steady-state phase. In the first stage, the adsorption of Cr atoms at the solid-liquid interface primarily contributes to the wetting, and the contact angle drastically reduces. However, both the wetting behavior and interfacial microstructure are determined by the Al content of the HEA in the next stage. For x ≤ 0.5, the wetting is mainly driven by the dissolution of WC, although a few reaction products of (W, Cr)2C are observed. Moreover, an obvious dissolution pit appears at the surface of the substrate. When the Al content of x ≥ 1, the interfacial reaction is dominant in competition with the dissolution of WC, and massive reaction products precipitate at the HEA/WC interface, which leads to the formation of a continuous reaction layer.

Evaluation of tool wear mechanisms and tool performance in machining single-phase tungsten

Tungsten is commonly used in cemented carbide tooling solutions and as an alloying element in superalloys and steels. In pure form, as a single-phase tungsten, it is used in nuclear and research facilities. Tungsten is known for its poor machinability resulting in excessive tool wear, which puts high requirements on the selected tooling solution. Also, single-phase tungsten is a highly brittle material, thus often leading to surface damage when machining. In this study, eleven different tool materials: ceramics, coated and uncoated cemented carbide, cermet, PcBN and PCD have been tested in longitudinal turning of high purity tungsten (W > 99.9%) in order to identify suitable tool candidates. Seven cutting tool solutions consistently suffered from excessive tool wear or breakage after a few seconds of engagement time. Only two tool materials, PCD and PVD (TiAlN – TiSiN) coated cemented carbide provided sufficient performance. Analysis of their wear mechanisms with scanning and transmission electron microscopy revealed abrasion, oxidation and cracking of WC grains and diffusional dissolution of WC and Co in case of carbide tools. For PCD tools the main identified mechanisms are abrasion and diffusional dissolution. Cracking, formation of build-up edges, presence of workpiece porosity and W adhesion on the machined surface was found to be responsible for poor surface quality and sub-surface damage. Surface roughness for the PCD ranged within Ra = 1.3–1.7 μm and for the PVD coated carbide tool Ra = 1.0–1.5 μm.

Microstructures and wear-resistance of WC-reinforced high entropy alloy composite coatings by plasma cladding: effect of WC morphology

ABSTRACT WC-reinforced FeCoCrNi high entropy alloy (HEA) composite coatings with different WC morphology of spherical and irregular shape, were prepared by plasma cladding. The effects of WC morphology on carbide evolution, WC dissolution, and the wear resistance of the coatings were investigated. The results indicated that the evolution of the massive and fish-bone M6C carbides were significantly influenced by the WC morphology, due to the different curvature radius of WC particles. The dissolution mechanism of spherical WC was diffusion, which of irregular WC was decarburization and oxidation. Although irregular WC particles were broken due to the WC→W2C transformation, the wear resistance of the coating with irregular WC was relatively stable, only slightly lower than that of spherical WC, because the developed fish-bone carbide in HEA matrix resisted the three-body abrasive wear of broken WC and W2C fragments.

Effect of annealing temperature on the microstructure evolution, mechanical and wear behavior of NiCr–WC–Co HVOF-sprayed coatings

Abstract

Densification behavior and mechanical properties of hot-pressed TiC–WC ceramics

The purpose of this paper was to investigate the influence of WC as a sintering aid on the sinterability and mechanical characteristics of TiC. For this purpose, two specimens, namely TiC-5 vol% WC and monolithic TiC, were manufactured using the hot-pressing route at 2000 °C for 2 h under 50 MPa. The addition of WC uplifted the sintering behavior of TiC. The XRD and microscopical evaluations revealed the precipitation of graphitized carbon in the TiC matrix. The results also manifested the complete dissolution of WC in the matrix, forming the (Ti,W)C solid solution. The addition of WC improved the Vickers hardness and flexural strength of TiC by ~12% and ~20%, respectively. Grain size, remaining porosity, and composition of the matrix were identified as the essential factors in boosting the mechanical properties of the TiC-WC specimen compared to the monolithic TiC.

Characteristics of WC reinforced Ni-based alloy coatings prepared by PTA + PMI method

The WCP/Ni60A coating and the Ni@WCP/Ni60A coating were clad on the surface of Q235 steel by plasma transferred arc welding (PTA) and plasma melt injection (PMI) method. The microstructure, hardness and wear resistance of the clad coatings were investigated respectively. The results showed that, the PTA + PMI method can effectively avoid the burning and sinking of WC particles. Both the coatings had relatively uniform microstructure, which were mainly composed of γ-Ni, Cr23C6, CrB, WC, W2C, and Cr7C3-typed compounds. The average hardness of the matrix for the WCP/Ni60A and Ni@WCP/Ni60A coatings were 1006.27 ± 40.25 HV and 905.77 ± 36.23 HV respectively. The wear mechanism of both coatings was mild adhesion wear, in contrast with the severe adhesion wear of substrate. Moreover, attributed to slighter dissolution of WC, the Ni@WCP/Ni60A coating possessed better wear resistance, whose wear mass loss was only 1/30 that of the Q235 substrate.

Near-surface phenomena occurring in cemented carbides with different binders during rotary-percussive drilling of reinforced concrete: FE simulation and microstructural investigations

Rotary-percussive drilling through steel rebar in reinforced concrete subjects drill bits to intensive thermomechanical loading and wear. Significant microstructural changes occur in near-surface regions. These include, but are not limited to, micro- and mesoscopic cracking; fracture at WC-binder interfaces; WC comminution; partial WC dissolution and rearrangement; surface decarburization; binder depletion and pore formation; and the creation of secondary phases within the binder [1–4].Cemented carbide drill bits with three different binders (Co, CoNi and Ni) were drilled in steel reinforced concrete. After sectioning the drill bits, numerous analysis methods were employed to identify the type and composition of phases present; to characterize microstructural changes and wear phenomena; and to locally measure the properties of the modified surface microstructure. Noticeable differences between the binder types are evident.A variety of finite element (FE) simulation methods were used to describe the thermo-mechanical loading spectrum acting on the drill bits. Transient (dynamic) impact loading and quasi-static indentation simulations calculated the stresses and temperatures generated in the application. The magnitude, orientation vectors and spatial distribution of the simulated stress and temperature fields were correlated with the experimental findings regarding crack initiation sites and regions experiencing thermo-mechanically induced surface microstructural and compositional modification. This paper presents some of these findings from extensive experimental and simulation studies.

Microstructure and Properties of NiFeCrBSi/WC Composite Coatings Fabricated by Vacuum Cladding

Abstract—In this study, WC-reinforced Ni-based alloy composite coatings were fabricated on the surface of ASTM 1045 steel by vacuum cladding. The microstructure, hardness, and wear resistance of coatings with different tungsten carbide (WC) content and dissolution mechanisms for WC at different cladding temperatures were studied. The bonding phase was mainly composed of austenite (Ni2.9Cr0.7Fe0.36, FeNi), and the reinforced phases consisted of WC, carbides (Cr7C3, (Cr,Fe)7C3), borides, and silicides. The dissolution of WC became severe with increasing cladding temperature, and the reaction products mainly included rounded block-shaped WC particles, lath-shaped rich tungsten carbide, and fine granular carbides. The Ni-based coating with 30% WC sintering at 1225°C performed better wear resistance, six times greater than that of matrix steel.

THE FEATURES OF DETONATION SPRAYING TECHNOLOGY FOR TUNGSTEN CARBIDE BASED COATINGS

The authors studied the effect of key parameters of detonation spraying process on tungsten carbidebased coatings and their mechanical properties, microstructure, and phase composition. Two main tasks are solved when developing the technology for spraying the carbide-containing materials. The relationship is established between the phase composition of tungsten-based coatings and their strength, hardness, and substrate adhesion. It was established that the WC dissolution in the metal phase promotes the increase of substrate adhesion as well as strength and hardness of coating material. A procedure of spraying coatings in the reduction mode is proposed: i.e., using working gas mixtures with excess acetylene. It prevents the decarbonization of WC carbides under the action of detonation products and environment. The phase composition heterogeneity (both along with the layer thickness and along the spraying spot diameter) is established. This depends on a complex of factors that determine the intensity of heat removal from the area of layer formation. For optimizing the structure and the mechanical characteristics of the coating, we need to control decarbonization of carbide component (WC) and formation of Ni (W) solid solution at different stages of spraying. Even a minor departure from carbon content leads to either appearance of graphite or formation of the fragile phase (Co3W3C), thus strongly reducing the mechanical properties.

Ultrafine WC-0.5Co-xTaC cemented carbides prepared by spark plasma sintering

Ultrafine (below 500 nm) tungsten carbide (WC) - 0.5 wt% cobalt (Co) cemented carbides were prepared by spark plasma sintering (SPS), containing varied tantalum carbide (TaC) contents, at 1500 °C under 50 MPa. The sintering behavior and microstructure of these materials were investigated. It was found that adding TaC could get a rapid shrinkage period during sintering and make a finer microstructure with a more narrowing range of the grain-size distribution. Adding inadequate or excessive amount of TaC, however, not only lower the sinterability but also get a result against the finer microstructure. Moreover, the (Ta,W)C solid-solution phase (formed by the part dissolution of WC in TaC grains) was mainly gathered at the WC grain boundary, and Co film was found. Benefiting from the ultrafine and homogeneous microstructure, these materials maintained excellent hardness and improved fracture toughness.

PROCESSING OF TECHNOGENIC WASTES OF PSEUDOALLOYS WC–CO

The possibility of chemical and electrochemical dissolution of secondary raw materials on the basis of tungsten carbides electrolytes from solutions of acids HNO3, HCl, H2SO4 has been considered. The influence of nature and concentration of electrolyte on the process of anodic dissolution of the alloy WC–Co has been studied. It has been established that the final product of the dissolution of the WC–Co alloy in acid solutions is the higher tungsten oxide WO3. The reduction of the electrochemical process efficiency in the series HNO3 + HF > HCl > H2SO4 has been shown. In order to obtain tungsten carbide or tungsten powder, during the electrochemical treatment of the WC–Co alloy, the introduction of an admixture-reductant in a solution of sulfate acid has been proposed for the preparation of tungsten powder. On the basis of the conducted studies, a working electrolyte has been selected which allows to obtain the target product WC or W. Bibl. 10, Fig. 6.