WC 10Co Research Articles

Comparative analysis of tribological behavior of plasma- and high-velocity oxygen fuel-sprayed WC-10Co-4Cr coatings

PurposeThe purpose of this study is to prepare WC-10Co-4Cr coatings using two processes of plasma spraying and high-velocity oxygen fuel (HVOF) spraying. The decarburization behaviors of the different processes are analyzed individually. The microstructural characteristics of the as-sprayed coatings are presented and the wear mechanisms of the different WC–10Co–4Cr coatings are discussed in detail.Design/methodology/approachThe WC–10Co–4Cr coatings were formed on the surface of Q235 steel by plasma and HVOF spraying.FindingsPlasma spraying causes more decarburizing decomposition of the WC phase than HVOF spraying. In the plasma spraying process, η(Cr25Co25W8C2) phase appears and the C content decreases from the top surface of the coating to the substrate.Practical implicationsIn this study, two WC–10Co–4Cr coatings on Q235 steel prepared by plasma and HVOF spraying were compared with respect to the sliding wear behavior.Originality/valueThe wear mechanisms of the plasma- and HVOF-sprayed coatings were abrasive and oxidation, respectively.

Fine platelet-like grained WC–Co cemented carbides: Preparation, characterization, properties and application in PVD coating substrates

Strengthening of the adhesion strength and its stability of PVD coated cemented carbides has always been the focus of attention. Commercial ultrafine WC–12Co composite powder by spray conversion processing was used as the raw material. WC–12Co–0.05La2O3, WC–12Co–0.9Cr3C2–0.05La2O3, WC–12Co–0.5Cr3C2–0.4VC–0.05La2O3 and WC–12Co–0.9Cr3C2–0.4VC–0.05La2O3 alloys were prepared by a conventional long-time ball-milling. The results show that fine platelet-like grained WC–12Co–0.9Cr3C2–0.4VC–0.05La2O3 alloy is characterized with a homogenous microstructure, the best property combination of high strength, high hardness and high toughness and the highest WC (0001) texture coefficient. By using fine platelet-like grained WC–Co cemented carbides as the substrates, larger than 100N adhesion strength expressed by critical load LC2 for AlCrN, AlTiN and (AlCrSiWN+AlCrN) PVD coatings is achieved. The related strengthening mechanisms are discussed.

CHANGE IN STRENGTH, HARDNESS AND CRACKING RESISTANCE IN TRANSITION FROM MEDIUM-GRAINED TO ULTRAFINE HARD ALLOY

The paper studies the microstructure and mechanical characteristics of samples of medium-grained (WC–8Co), submicron (WC– 8Co–1Cr3C2) and ultrafine (WC–8Co–0,4VC–0,4Cr3C2) hard alloys produced by liquid-phase sintering of powders of appropriate dispersity. The paper shows that a decrease in the average grain diameter from 1,65 to 0,37 μm leads to an increase in hardness of resulting alloys from 1356 to 1941 HV. At the same time, the cracking resistance decreases from 19,0 to 8,5 MPa·√ —m and strength decreases from 2080 MPa to 1210 MPa. Comparison with the literature data showed that alloys considered in this paper are highly competitive in hardness and crack resistance with analogues produced by sintering under pressure, hot pressing, electric spark and induction sintering. At the same time, the bending strength of alloys produced by liquid phase sintering was 1,5–2,5 times lower than for alloys produced by pressure sintering or pressing, due to the presence of pores with a maximum diameter estimated at 40 μm. The paper analyses obtained results and the literature data against the theoretical regularities. It is shown that in general, dependences of hardness, cracking resistance and strength on the average grain diameter of produced alloys and their analogues correspond to conventional regularities based on the Hall–Petch and Orovan–Griffiths laws, despite the existence of theoretical prerequisites for deviating from them.

A comparative study on wear and corrosion behaviour of HVOF- and HVAF-sprayed WC–10Co–4Cr coatings

In this work, WC–10Co–4Cr coatings were separately deposited on 300M steel by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) spraying processes. Microstructure, porosity, micro-hardness, bonding strength, wear and corrosion resistance of the coatings after different processing were investigated and compared. The result shows that dense and homogeneous microstructure existed in both two WC–10Co–4Cr coatings. Owing to lower temperature flames and higher particle velocity in the HVAF process, the HVAF-sprayed WC–10Co–4Cr coating exhibited less decarburisation, lower porosity (0.74%), higher micro-hardness (1162 HV0.3) and bonding strength (74.68 MPa) than HVOF-sprayed WC–10Co–4Cr coating. In addition, wear and corrosion resistance of these two coatings were evaluated by sliding wear test and electrochemical corrosion test. The HVAF-sprayed WC–10Co–4Cr coating also exhibited excellent wear resistance and superior corrosion property than HVOF-sprayed WC–10Co–4Cr coating.

Effect of grinding parameters on the wear resistance and residual stress of HVOF-deposited WC–10Co–4Cr coating

Abstract Application of WC–10Co–4Cr coating deposited by High Velocity Oxygen Fuel (HVOF) has been widely developed for its high wear and corrosion resistance. The finishing of the coated surface by grinding process is essential because of the high surface roughness of carbide coatings. The present study investigated the effect of grinding parameters including cutting speed, feedrate, and depth of cut on the wear resistance and the residual stress of WC–10Co–4Cr coating by HVOF. The wear properties of coating were evaluated using a pin on disk apparatus. The residual stress of coating was measured by the X-ray diffraction (XRD) technique using sin2ψ method. In addition, the effect of diffraction peak positioning method on the accuracy of residual stress of WC–10Co–4Cr coating was determined in the XRD technique. The results showed that the wear resistance and the compressive residual stress of the WC–10Co–4Cr coating increase after grinding process. The higher value of compressive residual stress, which is caused by the increase of the depth of cut and feedrate and the decrease of the cutting speed, improves the wear resistance of the coating.

Tribological behaviour of HVOF sprayed WC-12Co, WC-10Co-4Cr and Cr3C2−25NiCr coatings

In the present work erosive and abrasive wear behaviour of HVOF deposited WC-12Co, WC–10Co–4Cr and Cr3C2−25NiCr coatings was investigated. The maximum wear rate was exhibited by Cr3C2−25NiCr coating under both solid particle erosion and abrasion. The coatings exhibited composite erosion response. The erosion response was rationalized on the basis of velocity exponents, erosion mechanisms and mechanical properties. Erosion damage parameter and severity of contact can be useful indicator of transition in failure modes. The wear mechanisms were influenced by microstructure of the coatings and the test conditions, involving fracture and pull out of carbides, removal of splats and subsurface cracking. The lowest coefficient of friction exhibited by Cr3C2−25NiCr coating was attributed to formation of tribo oxide film.

Properties of WC–8Co hardmetals with plate-like WC grains prepared by plasma-assisted milling

WC–8Co hardmetals with different proportions of prismatic WC grains and plate-like WC grains were directly produced through sintering the W–C–8Co elemental powder mixture which was fabricated by dielectric barrier discharge plasma (DBDP)-assisted milling. The morphology of prepared WC–8Co hardmetals, geometry and the preferential orientation of plate-like WC were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The results demonstrate that the microstructure and mechanical properties of the sintered hardmetals are related to the morphology of W grain which is dependent on DBDP-milling time. The DBDP for 1 h (DBDP-1 h)-milled W–C–Co powder contains granular W particles that tend to form prismatic WC grains, while the DBDP for 3 h (DBDP-3 h)-milled powder contains lamellar W particles that generate plate-like WC grains. By adjusting the weight ratio of DBDP-1 h powder and DBDP-3 h powder in W–C–8Co mixture, the proportion of plate-like WC in the hardmetals can be controlled, and relatively high transverse rupture strength (TRS) is obtained as the proportion of plate-like WC grain in the hardmetals is about 35 % in present experimental condition. The DBDP-1 h-milled W–C–8Co powder (Sample A) contains granular W particles that tend to form prismatic WC grains, while the DBDP-3 h-milled powder (Sample B) contains lamellar W particles that generate plate-like WC grains. When the weight ratio of Samples A to B powder is 1:1, Sample A1B1 has relatively high transverse rupture strength (TRS) along both Sections V and P, with proportion of plate-like WC grain of ~35 %.

Influence of WC carbide particle size on the microstructure and abrasive wear behavior of WC–10Co–4Cr coatings for aircraft landing gear

WC–Co–Cr thermal spray coatings are possible replacements for hard chrome plating on aircraft landing gear because of their superior wear resistance and environmentally friendly properties. In this study, four HVOF spray WC–10Co–4Cr coatings were deposited. During deposition, WC (tungsten carbide) particles were mixed into the coating. These included two types of single particle size distributions and two types of bimodal particle size distributions. The microstructure and abrasive wear behavior of these coatings were studied. The relationship among WC particle distributions, the deposit microstructure, and the three-body abrasive wear rates by rounded quartz grains was determined. The coating that only contained single particle size distribution of 1.2μm-sized WC particles exhibited the best abrasive wear resistance.

Laser surface remelting of WC–12Co coating: finite element simulations and experimental analyses

A three-dimensional finite element model taking into account interfacial topography, porosity of plasma sprayed coatings, temperature dependent thermophysical parameters and phase change has been developed to simulate multipass laser remelting process. Temperature evolution, temperature gradient, melting pool shape and dimensions are simulated. The laser remelting experiments are carried out on the plasma sprayed WC–12Co coatings. The simulated results are in good agreement with the experimental measurements. After laser remelting, a denser and more homogenous coating is obtained. The microhardness of the coating is significantly enhanced owing to the dispersion strengthening, the fine grain strengthening and the solution strengthening, which is increased by three times compared with that of the plasma sprayed coatings.

Tool life and wear mechanism of WC–5TiC–0.5VC–8Co cemented carbides inserts when machining HT250 gray cast iron

Cutter development has drawn a lot of attention for cast iron machining in recent years. In this study, a special cemented carbide of WC–5TiC–0.5VC–8Co (WTVC8) was used for a comprehensive HT250 gray cast iron machining test. Compared with the baseline plain WC–8Co(WC8) carbides, WTVC8 shows significantly higher tool life under the same cutting conditions due to significantly higher hardness and red hardness. The worn flank face observation shows that adhesion wear and oxidation are the main wear mechanisms and there is no apparent chipping/breakage and abrasion wear for both WTVC8 and WC8. Based on Taylor's equation, the accurate tool life models for both WTVC8 and WC8 have been constructed, which shows clearly that cutting speed has the most significant effect on tool life, followed by depth of cut and feed rate. The tool life models can serve as a quantified guidance for cutting performance optimization.

Erosion behaviour of WC–10Co–4Cr coating on 23-8-N nitronic steel by HVOF thermal spraying

WC–10Co–4Cr coating was deposited by high-velocity oxy-fuel (HVOF) process on cast and solution treated (1220°C/150min) 23-8-N nitronic steel substrates. Solution treated substrate has shown higher toughness, ductility and impact energy with a marginal reduction in hardness as compared to cast substrate. This influence the coating deposition efficiency and erosion behaviour. Erosion resistance of coatings was evaluated by air jet erosion tester on two different impact angles (30° and 90°). Phases, microstructure and eroded surface of the coating were characterised by X-ray diffraction (XRD) analysis and field-emission scanning electron microscopy (FESEM) respectively. It is observed that coating on solution treated substrate was superior to cast substrate. The reason being that coating has dense and well-bonded structure with low porosity, less decarburization and inter-splat oxidation. Higher erosion resistance of coated solution treated 23-8-N nitronic steel was attributed to combination of high fracture toughness and hardness of coating including optimum mechanical properties of the substrate. FESEM analysis reveals that erosion response of WC–10Co–4Cr coating also dependent on the relative size of the impact crater with respect to the WC grain size. Coating is removed by combined mode of ductile and brittle erosion.

Electrochemical corrosion behaviors of straight WC–Co alloys: Exclusive variation in grain sizes and aggressive media

The electrochemical corrosion behaviors of straight WC–10Co cemented carbides with grain sizes of 1.2, 2.6, 6.1 and 8.2μm, were comparatively investigated in the solutions of NaOH (pH=13), Na2SO4 (pH=7) and H2SO4 (pH=1) respectively. To insure a sole variable of WC grain sizes, specific magnetic saturation values of the alloys are adjusted to be identical. The results show a good linear dependence for Rct (charge transfer resistance) and Icorr (corrosion current density) against the grain sizes. A high sensitivity of the grain sizes to both Rct and Icorr are identified in NaOH and H2SO4. In the solutions of NaOH and Na2SO4, the alloys with smaller WC grain sizes exhibit better corrosion resistances, while the alloys with larger WC grain sizes exhibit better corrosion resistances in H2SO4. Additionally, in terms of the corrosiveness, NaOH is the weakest and H2SO4 is the most aggressive for all the alloys. The corrosion mechanisms were discussed in light of the SEM surface observation, X-ray photoelectron spectroscope analysis and the electrical equivalent circuits for electrochemical impedance spectroscopy.

Structure-property correlations in nanostructured WC–12Co microwave clad

Nanostructured materials are known for enhanced properties as compared to their conventional counterparts. In the present work, microwave cladding technique was explored for depositing nanostructured WC–12Co clads on stainless steel substrates. Phase analysis of the WC–12Co microwave clads revealed the presence of Co6W6C, Co7W6, Co3W9C4, W2C and WC phases. The microstructure of the WC–12Co clads confirmed uniform distribution of nano-carbides in the form of clusters enclosed in the carbide network. Mechanical characterisation of the nanostructured clads was carried in terms of microhardness assessment and flexural strength measurement. The microwave induced clads exhibited excellent metallurgical bonding with the substrate and were free from interfacial cracks. The average microhardness of the developed clads was found in the order of 1760±128HV. The flexural strength of the developed clads was observed to be 671±28MPa. The nanostructured clads exhibited good adhesion with the substrate without getting peeled-off under a load of 3.75kN and a displacement of 3.72mm.

Effects of Ni addition and cyclic sintering on microstructure and mechanical properties of coarse grained WC–10Co cemented carbides

Coarse grained WC–10(Co, Ni) cemented carbides with different Ni contents were fabricated by sintering-HIP and cyclic sintering at 1450°C. The effects of Ni addition and cyclic sintering on the microstructures, magnetic behavior and mechanical properties of coarse grained WC–10(Co, Ni) cemented carbides have been investigated using scanning electron microscope (SEM), magnetic performances tests and mechanical properties tests, respectively. The results showed that the mean grain size of hardmetals increases from 3.8μm to 5.78μm, and the shape factor Pwc decreases from 0.72 to 0.54, with the Ni content increases from 0 to 6wt.%. Moreover, the W solubility reaches the highest value of 10.33wt.% when the Ni content is 2wt.%. The hardness and transverse rupture strength of WC–8Co–2Ni are 1105HV30 and 2778MPa, respectively. The cyclic sintering is conducive to increase the WC grain size of WC–10(Co, Ni) and improves the transverse rupture strength of WC–10Co without compromising the hardness of alloys.

Synergistic effect of ultrasonic cavitation erosion and corrosion of WC–CoCr and FeCrSiBMn coatings prepared by HVOF spraying

The high-velocity oxygen-fuel (HVOF) spraying process was used to fabricate conventional WC–10Co–4Cr coatings and FeCrSiBMn amorphous/nanocrystalline coatings. The synergistic effect of cavitation erosion and corrosion of both coatings was investigated. The results showed that the WC–10Co–4Cr coating had better cavitation erosion–corrosion resistance than the FeCrSiBMn coating in 3.5wt.% NaCl solution. After eroded for 30h, the volume loss rate of the WC–10Co–4Cr coating was about 2/5 that of the FeCrSiBMn coating. In the total cumulative volume loss rate under cavitation erosion–corrosion condition, the pure cavitation erosion played a key role for both coatings, and the total contribution of pure corrosion and erosion-induced corrosion of the WC–10Co–4Cr coating was larger than that of the FeCrSiBMn coating. Mechanical effect was the main factor for cavitation erosion–corrosion behavior of both coatings.

Characteristics and removal mechanism in laser cutting of cBN–WC–10Co composites

Laser cutting of a cBN–WC–10Co composite material was carried out using a pulsed Nd: YAG laser. The cutting characteristics, as well as the changes in microstructure and mechanical property, were investigated. It was found that cracks were induced by laser machining on the sub-surface and the evidence of phase transformation from cBN to hBN was observed on the cut surface. Cutting parameters had significant effect on the cut surface. A higher laser power produced a smoother cut surface, but a larger heat-affected zone, in comparison to the lower laser power used. No radical cracks were found on the cross-section at the laser power of 100W. The surface roughness and the heat-affected zone depth decreased with the increased cutting speed and the gas pressure. The material removal involved in the laser cutting of cBN–WC–Co composite was attributed to the melting or evaporation of cBN and WC–Co. The dropping of cBN particles from the cut surface was also found during the cutting at the laser power of 30W for the loss of the supporting from the WC–Co matrix.

Abrasive and erosive wear behaviour of nanometric WC–12Co microwave clads

The present work examines the abrasive and the erosive wear performance of WC–12Co microwave clads. Cladding of micrometric and nanometric WC–12Co powders was carried out on austenitic stainless steel substrate using microwave hybrid heating technique. The micrometric clads exhibited the presence of skeleton structured carbides uniformly distributed in the metallic matrix. On the other hand, presence of clusters of nanocarbides was observed in the nanometric WC–12Co clads. The average microhardness of the nanometric (1564±53HV) was approximately 1.37 times higher than the micrometric clad (1138±90HV). A dry sand rubber wheel apparatus using silica sand as the abradant was used to evaluate the three body abrasive wear performance of the clads at various loads (30, 60 and 90N). The erosive wear performance of the clads was evaluated at various impact angles (30°, 60° and 90°) using solid particle erosion using alumina as the erodent. Lower binder mean free path, higher microhardness and enhanced carbide volume fraction lead to the higher abrasive and erosive wear resistance of the nanometric WC–12Co clads.

Comparison between WC–10Co–4Cr and Cr3C2–25NiCr coatings sprayed on H13 steel by HVOF

WC–10Co–4Cr and Cr3C2–25NiCr coatings were deposited on H13 steel by high velocity oxy fuel (HVOF) spraying. To enhance the thermal stability of the WC–10Co–4Cr coating, NiCr powders were sprayed between the surface coating and substrate. The microstructures of the surface and cross section, thermal shock and wear resistance of these two coatings were investigated in detail. The carbon diffusion in the two coatings was explained from the view of the thermodynamic. And the adhesive strength of Cr3C2–25NiCr coating (64.40 MPa) is almost the same as that of WC–10Co–4Cr coating (61.69 MPa). The friction tests show that the Cr3C2–25NiCr coating has higher friction coefficient than the WC–10Co–4Cr coating at both 500 and 600 °C. The wear resistance of the Cr3C2–25NiCr coating is better than that of the WC–10Co–4Cr coating.

Effect of the Cubic Phase Distribution on Ultrafine WC–10Co–0.5Cr–xTa Cemented Carbide

The (Ta, W)C cubic phase distribution plays a key role in the microstructure and mechanical properties of ultrafine WC–Co–Cr3C2–TaC cemented carbides. By integration of thermodynamic calculations and key experiments, the influence of the cubic phase distribution in ultrafine WC–10Co–0.5Cr–xTa cemented carbides was systematically investigated. A series of ultrafine grained cemented carbides were designed and fabricated through ball‐milling and vacuum sintering at 1410°C for 1 h. The microstructure was investigated using scanning electron microscopy (SEM). The electron backscattered diffraction (EBSD) was used to measure the orientation and size of cubic phase segregation. The results indicate that the cubic phase in the microstructure distributes more heterogeneously in the range of 0.2 to 0.7 wt% Ta addition, but finally the isolated cubic phase is homogeneously distributed with a Ta content from 0.7 to 1 wt%. Combining the thermodynamic calculation with the experiment, the mechanism for the microstructure evolution has been revealed. The mechanical properties of alloys substantially depend on the cubic phase distribution in the microstructure. A synergetic correlation between the transverse rupture strength (TRS) and Rockwell hardness was observed. The homogeneity of cubic phase can be designed and controlled effectively via the present approach.

Properties of the pulsed electric current sintered Ni–Mn–Ga–Co–WC composites

Two double dispersion composites were prepared by pulsed electric current sintering (PECS) from two powders on Ni–Mn–Ga–Co/WC–Co system. Composite 1 consists of 90 vol% WC–12Co and 10 vol% of non-modulated Ni–Mn–Ga–Co martensite and Composite 2 of 18 vol% of WC–12Co and 82 vol% of 10 M Ni–Mn–Ga–Co martensite. Damping capabilities of both composites were studied with DMA and cavitation erosion resistance tests. Both composites show promise as candidates as damping element materials when high hardness and wear resistance is required but Composite 2 had a higher damping capability. The high damping ability of composites are proposed to be derived from the combined effect of energy dissipation by twin boundary movement in the Ni–Mn–Ga matrix combined with the high hardness and wear resistance arising from the tungsten carbides.