WC Layer Research Articles

Self-assembling WC interfacial layer on diamond grains via gas-phase transport mechanism during sintering of metal matrix composite

Diamond wire saws are widely used in machining of high strength reinforced concrete and steel structures. In such operation conditions, the tools wear down rather quickly, which has significant technical and economic implications. Currently, there are three main ways to improve a quality of diamond cutting tools: increasing (1) strength of a binder (metal matrix), (2) diamond grain grade and (3) adhesion strength between diamond and a binder. In this work, an effective approach involving simultaneous improvement of (1) and (3) during diamond composite material sintering is reported. The mechanism of spontaneous formation of WC layer on a diamond surface during sintering with metal matrix composite in the presence of WC nanopowder as a reinforcing additive is studied. The layer is formed via gas-phase transport mechanism leading to chemisorption of volatile tungsten oxide WO3 onto a diamond surface followed by WO3 reduction and carbide formation. The simultaneous enhancement of mechanical properties of the binder and formation of protective WC interfacial layer on diamonds provide a synergistic effect, which results in increased productivity and cutting speed of diamond tools.

Fe–W–C thermodynamics and in situ preparation of tungsten carbide-reinforced iron-based surface composites by solid-phase diffusion

Tungsten carbide (WC)-reinforced Fe-based surface composites were prepared by in situ solid-phase diffusion at 1423K for 4, 6, and 8h. The thermodynamics, phase composition, microstructure, microhardness, and wear-resistance of the Fe–W–C ternary system of the samples were examined by X-ray diffraction, scanning electron microscopy, Vickers hardness test, and wear test, respectively. Thermodynamic calculations showed that the thermodynamically favored products of the Fe–W–C system were W2C, WC, and Fe3C. W also exhibited a stronger carbide-forming tendency than Fe. The Gibbs free-energies of W2C and WC, which were stable carbides, significantly decreased with increased temperature. The main phases of the composite were WC, γ-Fe, Fe3C, graphite, and η-carbide (M6C) with fishbone-like morphology. The longitudinal section of the composite could be easily divided into three reaction zones, namely, WC layer, “no graphite area,” and M6C-reinforced area. WC particles in the WC layer were irregularly shaped with 0.3–12μm particle size, with volume fraction of up to >80%. The average microhardness value of the dense ceramic layer was 2152HV0.1. The maximum relative wear-resistance, which was 230.4 times higher than that of gray cast iron, was obtained at 20N. The high wear-resistance of the composite was due to the in situ formation of dense and hard WC particulates that acted as a reinforcement phase.

Preparation of ultra-fine grain Ni–Al–WC coating with interlocking bonding on austenitic stainless steel by laser clad and friction stir processing

The ultra-fine structured Ni–Al–WC layer with interlocking bonding was fabricated on austenitic stainless steel by combination of laser clad and friction stir processing (FSP). Laser was initially applied to Ni–Al elemental powder preplaced on the austenitic stainless steel substrate to produce a coating for further processing. The as-received coating was subjected to FSP treatment, processed by a rotary tool rod made of WC–Co alloy, to obtain sample for inspection. Microstructure, phase constitutions, hardness and wear property were investigated by methods of scanning electronic microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) microanalysis, and X-ray diffraction (XRD), hardness test alongside with dry sliding wear test. The results show that the severe deformation effect exerted on the specimen resulted in an ultra-fine grain layer of about 100 μm in thickness and grain size of 1–2 μm. Synergy between introduction of WC particles to the deformation layer and deformation strengthening contributes greatly to the increase in hardness and friction resistance. An interlocking bonding between the coating and matrix which significantly improves bonding strength was formed due to the severe deformation effect.

The influence of microstructure on mechanical property of polytypic TiC/WC nanomultilayers

TiC/WC nanomultilayers were prepared by multi-target magnetron sputtering device. The dependence of microstructure evolution and mechanical properties has been investigated. The results showed that “mutual growth effect” and “superhardness effect” were observed in the multilayers. The polytypic WC monolayer exhibited with both triclinic α-WC and cubic β-WC structure for the carbon loss in the sputtering process. When alternately deposited with TiC layers, TiC/WC nanomultilayer would grow coherently with each other when WC layer thickness was less than 1 nm. The multilayer exhibited with cubic structure, and it would achieve 41.5 GPa when WC layer was 0.5 nm. Further increasing WC layer thickness, the hardness would drop down quickly accompanied with the disruption of coherent growth structure, and the multilayers gradually turned to exhibit polytypic structure.

Electrochemical slurry jet micro-machining of tungsten carbide with a sodium chloride solution

Electrochemical slurry jet micro-machining (ESJM) is a new non-conventional process that couples abrasive slurry jet machining (ASJM) and electrochemical jet machining (ECJM) concurrently. A micro-jet of abrasive particles and electrolytic solution is made to impinge on the target while applying a DC potential between the jet nozzle and the workpiece. ESJM can be used to remove material that is difficult to machine through a combination of erosion, corrosion and synergistic effects. This study focuses on ESJM of tungsten carbide (WC) using a pH-neutral NaCl electrolyte rather than an alkaline solution which is more commonly used in the electrochemical processing of WC. For the studied process parameters, it was shown that the erosion due to ASJM alone was not able to erode the WC, and that the corrosion under ECJM was slow and produced unacceptably wide channels. The combined ESJM process however, was found to involve erosion of the developed oxide layer and subsequent exposure of un-corroded WC, leading to a much higher machining current density, corrosion rate, and machining localization than using ECJM alone. It was also found that the total abrasive kinetic energy, working voltage and solution concentration strongly affected the machining current density, material removal rate and aspect ratio (depth to width ratio). The results indicate that ESJM has a high potential to machine difficult-to-cut metals efficiently and economically.

Substrate heating and post-annealing effect on tungsten/tungsten carbide bilayers grown by non-reactive DC magnetron sputtering

Abstract Tungsten–tungsten carbide (W/WC) bilayers were produced by non-reactive DC magnetron sputtering at various substrate temperatures between room temperature and 300 °C. The coatings were characterized in terms of morphology, structure and chemical composition using several techniques such as X-ray diffraction (XRD), Raman Spectroscopy, Auger Electron Spectroscopy (AES), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Scanning Probe Microscopy (SPM) in the Atomic Force Microscopy (AFM) mode. Bragg peaks corresponding to the (110) diffraction plane of the W phase and (111), (200), (220) and (311) peaks corresponding to the cubic WC phase were identified. From the XRD analysis, a strong influence of the substrate temperature on the grain size and crystallographic texture was observed; nevertheless, a poor influence on the lattice parameter and microstrain was detected. Furthermore, different vibrational modes of the W3C structure and characteristic peaks corresponding to O3W3O bonds were observed. Depth profile analysis was also carried out using AES, which revealed the presence of C, W, O and Fe. Initially, carbon and tungsten were observed in the WC layers. After the films were totally etched, Fe from the substrate was detected. However, the morphology was not significantly affected by temperature. An important result was the improvement in the coatings' adherence when an interlayer of W was inserted. In this work, the bilayers' behavior during annealing was also studied. The films were observed to oxidize at approximately 600 °C.

Growth of Crystalline Tungsten Carbides Using 1,1,3,3-Tetramethyl-1,3-disilacyclobutane on a Heated Tungsten Filament

A method of forming crystalline tungsten carbides was reported by exposing the heated tungsten filament to 1,1,3,3-tetramethyl-1,3-disilacyclobutane (TMDSCB) in a hot-wire chemical vapor deposition process. Methyl radicals produced from the decomposition of TMDSCB on the filament serve as the carbon source. The formation of tungsten carbides was investigated by X-ray diffraction, cross-sectional scanning electron microscopy, and in-situ filament resistance measurements. A pure W2C phase was formed at a high temperature of 2400 °C after 1–2 h exposure time with a growth rate of 4.4 μm min–1. The growth of the W2C layer is found to be a diffusion-controlled process. Our study at longer deposition time of 3–4 h shows that once the metal filament is fully carburized to form W2C, the carbon-rich WC phase starts to form on the outside layer upon further exposure to TMDSCB. A WC layer with no contamination from the W2C phase was found to be formed at 2400 °C and 4 h deposition time.

Performance of Wire-Sawing of Glass Assisted by Electro-Chemical Discharge

This paper deals with a combination machining method of slicing with electro-chemical discharge machining (ECDM). Glass and fine ceramics are hard to machine, and cracks are generated on their surface during cutting and grinding because of their brittleness and hardness. ECDM has been studied for machining such insulating materials. The authors have proposed a deposition method of WC layer by electrical discharge machining (EDM) with a compressed WC-Co powder as an electrode. The improvement of removal rate is expected by combining wire-sawing with ECDM. A silica glass rod was cut with a saw wire with the WC layer. The removal rate of the combination machining is larger than that of individual use of ECDM or wire sawing. The groove width by wire sawing was smaller than the others. Cracks were seldom observed on the bottom and side walls of the groove. Providing the fresh working fluid also assisted to decrease the cracks. The synergy of wire-sawing with ECDM was obtained.

Effect of carbon on hydrogen behaviour in tungsten: first-principle calculations

Using the first-principle method, we investigated the effect of tungsten carbide (WC) surface layers on hydrogen retention in W. The results showed that C is not capable of capturing H atoms efficiently because of Coulomb repulsion between negatively charged C and H atoms in tungsten. Meanwhile, the repulsive force enhances the migration barrier for H to travel through WC layers. The high barrier, therefore, prevents the implanted H from escaping the W matrix. With H implanted continually, more and more H atoms are accumulated in the bulk and diffuse far from the WC layer, which contributes to blister formation in W.

Study on the Microstructures and Wear Resistance of ZG30Cr Steel Surface Layer

In this paper ,the WC and high-Cr Cast Iron layer were obtained on the surface of ZG30Cr steel by casting-penetrating process, the organization and wear properties of penetrating layer were studied.The results show that the layer is dense, without pores, slag and other defects, the penetrating layer and substrate are metallurgical bonding. When 30 %WC and 70 % Cr-Fe with 100～120 mesh are added to permeability agent ,the penetrating layer has the best wear resistance, is 6.8 times the matrix materials. Keywords: The layer structure; Particle size; Wear resistance

Study on the Microstructures and Wear Resistance of ZG30 Steel Surface Layer

The WC and high-Cr cast iron layer were obtained on the surface of ZG30 steel by infiltration casting process, so the surface alloying of ZG30 steel was realized. The microstructures and phase structures of penetrating layer were studied by SEM, TEM, XRD, the hardness of the test material was measured by the hardness tester, and the wear resistance was tested by wear test machine. The mechanism of alloyed layer forming was analyzed. The effects of WC contents on the wear resistance of alloyed layer were studied. The results show that the layer is dense, without pores, slag and other defects, the thickness of the alloyed layer is about 6-7mm, and the penetrating layer and matrix are metallurgical bonding. The maximum hardness of the alloyed layer surface is 820Hv. When the content of WC is 15%, the penetrating layer has the highest wear resistance which is 18.8 times as high as the matrix.

Investigation of Thermal Sprayed Stainless Steel/WC-12wt%Co Nanocomposite Coatings

The thermal spray coatings of stainless steel with nano-sized particles as reinforcement have been studied. Stainless steel powder mixed with 0, 2.5, 5 and 10 wt% WC-12wt%Co nano-sized powder was flame sprayed. The presence of WC-12wt%Co nano-particles in mixed powders as feedstock was confirmed. The microstructure of the coatings has been investigated using a wide range of characterization techniques: optical microscopy with image analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) to understand the microstructure evolution. Chemical composition and microstructure of the coatings showed that the coatings contained stainless steel, WC, Co, and oxide layers. The addition of WC-12wt%Co increased cross-sectional hardness, reduced porosity and friction coefficient. The improved wear properties demonstrate a high potential for industrial applications of stainless steel/WC-12wt%Co coatings.

Adhesion and wear resistance of CVD diamond coatings on laser treated WC–Co substrates

Abstract A novel method using a high power diode laser to selectively remove cobalt binder from the outermost layer of Co-cemented tungsten carbide (WC–Co 5.8 wt.%) is hereby discussed. A continuous 940-nm wavelength diode laser source at power of 600–1500 W and scanning speed of 1 mm/s was used to perform the thermal treatments. Hot Filament-Chemical Vapour Deposition (HF-CVD) was then used to deposit PolyCrystalline Diamond (PCD) coatings. Increasing the laser fluence, Co-binder was progressively and selectively evaporated from the WC–Co substrate. The selective removal of the Co-binder from the outermost layer of WC–Co induces a significant corrugation of the substrate, very promising to deposit on it high quality diamond with improved adhesion. Indeed, too much high laser fluence must be avoided, as it would tend to induce the resintering or the local melting of the tungsten carbide grains.

Study on the Wear Resistance of Cast-Oozing Different Content of WC

In this paper, the WC and high-Cr Cast Iron layer were obtained on the surface of ZG30Cr steel by casting-penetrating process, the organization and wear properties of penetrating layer were studied. The results show that the layer is dense, without pores, slag and other defects, the penetrating layer and substrate are metallurgical bonding. When 20 %WC and 80 % Cr-Fe with are added to permeability agent, the penetrating layer has the best wear resistance, is 11.3 times the matrix materials.

Surface Integrity of C-40 Steel Processed with WC-Cu Powder Metallurgy Green Compact Tools in EDM

Electric discharge machining (EDM) is an electrothermal process where recast layer on the machined surface and heat-affected (HAZ) zone just below the machined surface are common phenomena. Thus, the assessment of surface integrity in EDM is a very important task. In this study, an attempt was made to modify the surface integrity of C-40 steel in EDM. WC-Cu powder metallurgy (P/M) green compact tools were used so that the tool material could be transferred to the work surface and thereby the surface characteristics could be altered. WC was used as tool material because of its ability to produce a hard layer over the work surface. A detailed experimental study was performed. The effect of various process parameters on the surface characteristics were presented with the support of analyses such as material transfer rate (MTR), tool wear rate (TWR), surface roughness, optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray (EDX), x-ray diffraction (XRD), microhardness testing, etc. It was established that the surface integrity of the workpiece changes with the desired deposition of a hard composite layer of WC and copper over the work surface.

High temperature fretting wear behavior of WC–25Co coatings prepared by D-gun spraying on Ti–Al–Zr titanium alloy

Detonation gun (D-gun) spraying is one of the most promising spraying techniques for producing wear-resistance coatings. A thick layer (about 0.3 mm thickness) of WC–25Co with high hardness was covered on Ti–Al–Zr titanium alloy by D-gun spraying and the fretting wear behavior of WC–25Co coatings was studied experimentally on a high precision hydraulic fretting wear test rig. An experimental layout was designed to perform fretting wear tests at elevated temperatures from room temperature (25 °C) to 400 °C in ambient air. In the tests, a sphere (Si 3N 4 ceramic ball) was designed to rub against a plane (Ti–Al–Zr titanium alloy with or without WC–25Co coatings). It was found that the fretting running regimes of WC–25Co coatings were obviously different from those of Ti–Al–Zr titanium alloy. The mixed fretting regime disappeared in WC–25Co coatings, and the boundaries in the running condition fretting map (RCFM) showed hardly any change as temperature increased. The worn scars were examined using a laser confocal scanning microscope (LCSM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that the coefficients of friction (COF) of WC–25Co coatings at elevated temperatures were nearly constant in the partial slip regime and very low in the steady state. The fretting damage of the coatings was very slight. In the slip regime, the WC–25Co coatings exhibited a good wear resistance, and the wear volume of the coatings obviously decreased with increasing tested temperature. The fretting wear mechanisms of WC–25Co coatings were delamination, abrasive wear and oxidation wear at elevated temperature. The oxide debris layer formed at higher temperature was denser and thicker on top of WC–25Co coatings, thus providing more surface protection against fretting wear, which played an important role in the low fretting wear of the coatings.

Microstructures and mechanical properties of metallic NiCrBSi and composite NiCrBSi–WC layers manufactured via hybrid plasma/laser process

Thermal spraying is already used in industry to protect mechanical parts against wear and/or corrosion, but results are not always satisfactory due to porosity and microstructures. In this study, atmospheric plasma spraying (APS) and in situ laser irradiation by diode laser processes were combined to modify structural characteristics of metallic NiCrBSi and composite NiCrBSi–WC coatings. The microstructure evolution was studied with the chemical composition analysis by XRD and SEM coupled with EDS techniques. Instrumented nanoindentation tests were also conducted employing a Berkovich indenter. Moreover, the effect of the influence of the volume fraction of the reinforcing WC particles on the formation and mechanical performances of the layer was also investigated. Results show that in situ laser remelting induces the growth of a dendritic structure which strongly decreases the porosity of as-sprayed coatings, without solidification cracking (one of the major defects that can occur during the solidification of metallic or composite alloys) and improves the mechanical properties of the layer. Indeed, the layer properties such as hardness, elastic modulus, shear strength and wear rate are dependent on the percentage of WC particles in the mixture.

Proposal for Abrasive Layer Fabrication on Thin Wire by Electrical Discharge Machining

This paper deals with a method of fabricating an abrasive layer on a thin wire by means of electrical discharge machining (EDM). An electrodeposited wire saw is useful for slicing a silicon ingot. However, strong acids are used in the production process and the depositing speed is slow. To overcome these problems, a fabrication process for an abrasive layer on a thin wire by EDM is proposed. The layer deposited by EDM with a green compact electrode is porous under certain electrical conditions so that the layer is composed of abrasive grit, pores and bond. A mixture of WC, Co, and the abrasive was compressed to make the green compact electrode. Two green compact electrodes were placed facing each other and were reciprocally fed during the process. The WC layer was deposited in 1s on an area in a preliminary experiment. The feed rate of 0.12-mm piano wire was set to 50mm/min. Al2O3abrasive powders with a size of 35-50µm were able to be contained in the WC layer on the wire. The deposit containing the abrasive firmly adhered. Because the deposited WC layer was very hard, tight gripping of the grit can be also expected. A copper block was cut with a raw piano wire, with wires with or without the abrasive deposited by EDM, and with electrodeposited or resinoid wire saws available on the market to compare their cutting performance. The initial tension was set to 5N and the cutting load was changed from 5.5 to 9.0N. The average feed speed of the wire was set to 8m/min. After 2000 reciprocating motions, the amounts machined with the deposited wire were larger than those with the wire saw available on the market. The deposited wire endured the same cutting load as the electrodeposited wire saw.

Nanostructured WC–Co particles produced by carbonization of spark eroded powder: Synthesis and characterization

Particles of homogeneous elementary composition are formed by spark erosion of a WC–Co hard alloy in a special assembly. The average particle diameter is 4.0 μm, and the specific surface area is 3.33 m2/g. The powder was carbonized for 4 h in CO gas. The particles produced by carbonization consist of a WC frame, with cobalt situated in WC interlayers. The thickness of WC layers in most of the particles ranges from 10 to 200 nm. The microhardness of these particles (HV = 23.7 ± 4.2 GPa) exceeds the microhardness of the initial standard hard alloy (HV = 15.47 ± 1.71 GPa).

Correlation between deuterium retention and microstructure change for tungsten under triple ion implantation

Triple ion (C+, D2+ and He+) implantation onto a tungsten substrate was performed to investigate the hydrogen isotope and microstructure behavior under fusion conditions. The results are compared to the ones from dual ion (C+ and D2+) implanted tungsten. It was found that the TDS spectrum for the triple ion implanted sample is quite different from that for the dual ion implanted sample and the deuterium retention decreased when He+ was added to the incident beam indicating that the helium prevented deuterium trapping. TEM images show that dislocations and dislocation loops were introduced in tungsten in both the dual and triple ion irradiation experiments and helium bubbles were formed on the triple ion implanted tungsten. After heating up to 1173 K, not only the dislocations and dislocation loops but also helium bubbles remained on the triple ion implanted sample, but the dislocations and dislocation loops were moved and/or annihilated on the dual ion implanted sample. The formation of a WC layer was inhibited in the triple ion implanted sample.