Increasing WC Content Research Articles

Investigation for the Fracture Process of WC<sub>p</sub>/Cu Functionally Graded Materials under Three-Point-Bending

In this paper, the fracture process of WCp/Cu functionally graded materials(FGMs) was investigated. The used materials were fabricated by powder metallurgy using tungsten carbide(WC) particles and copper(Cu) matrix, and had functionally graded layers. In order to investigate the fracture process of the FGM, three-point-bending tests of rectangular specimens were carried out. From the results, it can be seen that the bending performance of FGM structures with increasing WC content from head layer to the bottom layer excels that of FGM structures with decreasing WC content in three-point-bending tests.

Effect of thermal fatigue on the wear resistance of graphite cast iron with bionic units processed by laser cladding WC

Thermal fatigue and wear exist simultaneously during the service life of brake discs. Previous researchers only studied thermal fatigue resistance or abrasion resistance of compact graphite cast iron (CGI), rather than combining them together. In this paper, wear resistance after thermal fatigue of CGI was investigated basing on the principle of bionics, which was close to actual service condition of the brake discs. In the meanwhile, the effect of thermal fatigue on wear resistance was also discussed. Non-smooth bionic units were fabricated by laser cladding WC powder with different proportions (50wt.%, 60wt.%, 70wt.%). Microstructure and microhardness of the units were investigated, and wear mass losses of the samples were also compared. The results indicate that thermal fatigue has a negative effect on the wear resistance. After the same thermal fatigue cycles times, the wear resistance of laser cladding WC samples is superior to that of laser remelting ones and their wear resistance enhances with the increase of WC content.

Effect of SiC content, additives and process parameters on densification and structure–property relations of pressureless sintered ZrB2–SiC composites

The effect of SiC content, additives, and process parameters on densification and structure–property relations of pressureless sintered ZrB2–(10–40vol%) SiC particulate composites have been studied. The ZrB2–SiC composite powders mixed by ball-milling with 1.2wt% C (added as phenolic resin) and 3wt% B4C have been uniaxially cold-compacted and sintered in argon environment at 1950–2050°C for 2h, or at 2000°C for durations between 1/2 and 3h. The amount of densification is found to increase with sintering duration, and by prior holding at 1250 and 1600°C for reduction of oxide impurities (ZrO2, B2O3 and SiO2) on powder particle surfaces by the aforementioned additives. Presence of SiC with average size smaller than that of ZrB2 appears to aid in densification by enhancing green density, increasing WC content by erosion of milling media, and inhibiting matrix grain growth. Both SiC and WC appear to aid in reduction of oxide impurities. Furthermore, the impurities enriched in W, Fe and Co obtained from milling media are found to be segregated at ZrB2 grain boundaries, and appear to assist in densification by forming liquid phase, which completely wets the ZrB2 grains. Hardness increases with SiC content or with sintering duration till 1h, but decreases for periods ≥2h due to grain growth. The experimentally measured elastic moduli approaches corresponding theoretically predicted values with increasing SiC content due to reduction in porosity.

Effect of WC content on the microstructures and corrosion behavior of Ti(C, N)-based cermets

The influence of WC content on the microstructure and corrosion behavior of Ti(C, N)-based cermets in 2mol/L nitric acid solution was studied in this paper. There exists typical core/rim structure in the cermets. The cores appear black or white, and the rim is divided into white inner rim and grey outer rim. The undissolved Ti(C, N) particles normally appear as black cores, while the white core, inner rim and outer rim are (Ti, W, Mo) (C, N) solid solution formed at different sintering stages. The inner rim and white core appear brighter atomic contrast than the outer rim and black core, which is attributed to their higher W and Mo content. The thickness of the inner rim increases with WC addition, but the grain size of core/rim phase becomes finer. Meanwhile, the amount of white cores increases and that of black cores decreases. WC is more easily oxidized and dissolved in the nitric acid solution, compared with Ti(C, N). Therefore, the degradation of inner rim phase and the white core becomes more considerable with the increase of WC content. Consequently, the corrosion rate of cermets increases and the corrosion resistance of Ti(C, N)-based cermets is deteriorated with the increase of WC content.

Microstructure and Sliding Wear Resistance of Laser Cladded WC/Ni Composite Coatings with Different Contents of WC Particle

The aim of this article was to address the effect of WC content on the microstructure, microhardness, and sliding wear resistance of laser cladded WC/Ni composite coatings. The content of WC particle in the feed powder varied in the range of 0-80 wt.%. Experimental results showed that the laser cladded coatings exhibited homogeneous microstructure without pores or cracks. By comparing with the 45# steel substrate, the microhardness of WC/Ni composite coatings was relatively high. The microhardness of coating increased with increasing the content of WC particles. The wear resistance of WC/Ni composite coatings was strongly dependent on the content of WC particle and their microstructure. When the WC content was lower than 40 wt.% in the feed powder, the wear rate of the coatings decreased with increasing WC content. The two-body abrasive wear was identified as the main wear mechanisms. For the coatings with WC content higher than 40 wt.% in the feed powder, their wear rate increased with increasing WC content. The three-body abrasive wear and fatigue wear were the main failures. The coating with 40 wt.% WC in the feed powder exhibited the best wear resistance.

Optimization of processing conditions and characterization investigations of ceramic injection molded and sintered ZrO 2/WC composites

In this investigation, 3 mol% Y 2O 3 stabilized ZrO 2-based composites reinforced with 10 vol.%, 20 vol.% and 40 vol.% WC (named as 3Y-TZP/10WC, 3Y-TZP/20WC and 3Y-TZP/40WC) were fabricated by using injection molding and sintering. Mechanical properties of these composites varied due to WC addition and dwelling time. Density, strength and toughness decreased with shorter dwelling time and increasing WC content however a significant enhancement in fracture toughness was obtained by 3Y-TZP/20WC composite which had 9.2 MPa m 1/2 toughness. Severe unlubricated wear tests which were performed under 55 N normal load and 45 km sliding distance showed that 3Y-TZP/20WC composite had the lowest wear rate and wear volume values which are 2 × 10 −8 mm 3/(N m −1) and 0.05 mm 3, respectively.

Microstructure and fracture toughness of Ti(C 0.7N 0.3)-WC-Ni cermets

Mo 2C is normally added to improve the wettability between Ti(C,N) and Ni in Ti(C,N)-based cermets. Due to the increasing price of Mo 2C, much attention has been paid to Ti(C,N)-based cermets with WC addition. In this paper, effect of WC content on the microstructure and properties of Ti(C 0.7N 0.3)-xWC-15wt.%Ni cermets free of Mo 2C was studied. The experimental results show that the microstructure is refined obviously with the increase of WC content. The fracture toughness decreases with the increase of WC content when WC content is 10–25 wt.%, and increases when WC content varies from 25 wt.% to 30 wt.%.

Effect of WC content on the microstructure and mechanical properties of Ti(C0.5N0.5)–WC–Mo–Ni cermets

Abstract Ti(C0.5N0.5)–xWC–Mo–Ni system cermets were studied to investigate the effect of WC content on the microstructure and mechanical properties. The results showed that the lattice constant of Ti(C,N) hard phase in the Ti(C0.5N0.5)–WC–Mo–Ni system increases with the increase of WC content, but it is smaller than that in Ti(C0.7N0.3)–WC–Ni system. The microstructures of the cermets exhibit three kinds of grains: one has black core-grey rim structure, the second has white core-grey rim structure and the third has black core-white rim structure. The thickness of inner rim increases with the increasing of WC content. Additionally, the particle size of black core decreases with the increase of WC content in the range of 0–10 wt.%, and then increases slightly with further increase of WC. The TRS increases with the increase of WC content, but hardness decreases with the increase of WC content.

Effect of WC on the residual stress in the laser treated HVOF coating

HVOF coating of diamalloy 1005 containing WC particles onto steel (304) is considered and laser melting of the coating is carried out. The effect of WC content on the residual stress formed in the coating is examined. Temperature rise and the temperature gradient developed in the coating is modeled and predicted. XRD technique is used to measure the residual stress in the coating while the analytical formulation is used to predict the residual stress at the coating base material interface. The indentation tests are carried out to measure the Young's modulus and fracture toughness of the coating with and without WC content. It is found that existing of WC modifies temperature rise and the temperature gradient in the coating; in which case, increasing WC content reduces the temperature gradient. The Young's modulus, the magnitude of the residual stress, and the fracture toughness of the coating increase with increasing WC content in the coating.

Effect of WC on the microstructure and mechanical properties in the Ti(C0.7N0.3)–xWC–Mo2C–(Co,Ni) system

Abstract This paper reports an investigation of the effect of WC on the microstructure and mechanical properties in the Ti(CN)–xWC–Mo2C–(Co, Ni) system cermets. This paper reports the amount of WC added varied from 0 to 30 wt.%. The result showed that the grain size of hard phase varies little with the content of WC and the contrast difference between the outer rim and the binder phase decreased with the increase of WC content. The bending strength increases but hardness decreases with the increase of WC content. The change of microstructure and mechanical properties are different from the Ti(CN)–xWC–Co/Ni system cermets which was usually studied by others previously.

Effect of adding WC powder to the feedstock of WC–Co–Cr based HVOF coating and its impact on erosion and abrasion resistance

HVOF grade powders are now commercially available and being used in large scale for different components prone to abrasion/erosion. The literature on HVOF coatings based on WC–Co powder shows that there is a huge difference in hardness between the pure WC powder and WC–Co based HVOF coatings. The objective of this study was to improve the hardness of WC based HVOF coatings by adding pure WC powder to the commercially available powder. The hardness data shows that 20% addition of WC powder will improve the hardness of HVOF coating from 1106 to 1395 Hv 0.3. Hardness increase is due to the embedding of tungsten carbide hard metal matrix. This HVOF coated sample was tested for dry sand abrasion and slurry erosion as per ASTM standards. These tests show that abrasion and erosion resistance of HVOF coated samples goes down with the addition of tungsten carbide powder even though coating hardness has gone up. To understand the negative trend, porosity and SEM studies were carried out. SEM studies show that the porosity of the HVOF coating is higher than the conventional HVOF coating. With increase in WC content (30%), the porosity of the HVOF coating increased up to 10%. The higher porosity is believed to be the reason for poor abrasion and slurry erosion resistance.

Effect of WC content on the microstructure and mechanical properties of (Ti,W)(C, N)–Co cermets

Effect of WC addition on the microstructure and mechanical properties of TiC(sub)–TiN(nm)–WC–Co–C system cermets were studied in this work. The microstructure was investigated by means of X-ray diffractometry (XRD), scanning electron microscope (SEM) in combination with energy dispersive spectrometer (EDS). Mechanical properties such as transverse rupture strength, fracture toughness and hardness were also measured. Results show that the microstructures of cermets exist black core–grey rim structure, white core–grey rim structure and no core–rim structure. The microstructure has a trend to become finer with the increase of WC content. Results also show that the transverse rupture strength and the hardness increase with the increase of WC content, the fracture toughness decreases with increasing WC content, but the change is not obvious when WC addition goes from 10 to 20 wt%.

Effect of Secondary Carbide Addition on Properties of Ti(C<sub>0.7</sub>N<sub>0.3</sub>)-Ni Cermets

The effect of WC or NbC addition on various properties of Ti(C0.7N0.3)-Ni cermets was investigated. The microstructure of Ti(C0.7N0.3)-xWC-20Ni showed a typical core/rim structure, irrespective of the WC content, whereas the structure of Ti(C0.7N0.3)-xNbC-20Ni was different and was dependent on the NbC content. The hardness (HV) and the fracture toughness (KIC) had a tendency to increase marginally, while the coercive force (HC) and the magnetic saturation (4πσ) decreased gradually with an increase in WC or NbC content in the systems studied. In addition, increasing WC content in Ti(C0.7N0.3)-xWC-20Ni system, decarburization was retarded, while denitrification was accelerated.

ZrO 2–WC nanocomposites with superior properties

Fully dense ZrO 2-based nanocomposites with 5–40 vol.% WC were produced by hot pressing at 1450 °C for 1 h. The hardness and bending strength of the composites increases with increasing WC content, whereas the toughness hardly changes. An exceptionally high strength of 2 GPa combined with a hardness of 14.80 GPa and an excellent fracture toughness of 9.4 MPa m 1/2 was obtained for the 2 mol% Y 2O 3 stabilised ZrO 2-based composite with 40 vol.% WC. Such an attractive combination of properties is quite unique for a ceramic composite and is only matched by WC–Co cermets. The composites are substantially harder and stronger than the fine-grained Y-TZP, whereas the excellent toughness of Y-TZP is maintained. The strength improvement was accompanied with a change in fracture mode of the ZrO 2 grains from intergranular to transgranular. The ZrO 2–WC nanocomposites were found to slightly plastically deform before fracturing during bending.

ＭＡの応用 メカニカルアロイングを利用したＦｅＡｌ‐ＷＣの作製

FeAl-WC composite was proposed as a potentially novel hard metal. FeAl powder was synthesized in a planetary ball mill under an argon atmosphere. Powder mixtures consisting of FeAl and WC powders were dry blended in an automatic agitator. FeAl-0-65vol%WC composites were consolidated by pulse current sintering in a vacuum under the pressure application of 40MPa. Vickers hardness of the obtained composites increased with increasing WC content and 1075Hv was obtained for FeAl-50vol%WC composite. Transverse rupture strength of the composites was measured to be about 1.8 MPa up to 30vol%WC and abruptly decreased to 1.1 GPa for more than 50vol% WC. Oxidation test at 1173K exhibited weight gain of FeAl-50vol%WC was a one-seventh as much as that of Co-50vol%WC.

Thermal residual stress distribution in WC-Ni composites

The thermal residual stress distributions in a series of WC-Ni composites with WC volume fractions of 0.11, 0.21, 0.41, and 0.60 were measured using neutron diffraction and modeled using finite element (FE) analysis. The FE procedure employed enables the local variation of the residual microstress in a composite microstructure to be studied. The mean (compressive) stresses in WC decrease and the mean (tensile) stresses in Ni increase with increasing WC content. The stress distributions are sufficiently extensive to create regions of tension in the WC and compression in the Ni. The maximum tensile stresses in WC increase in magnitude with WC content. They are located in corners and, for higher WC content, normal to WC/Ni interfaces. High compression occurs in narrow portions of the WC skeleton. Regions of compression in Ni occur at WC/Ni interfaces for low WC content and, for composites of higher WC content, in narrow bands between chains of WC particles. It was also determined that models of actual composite microstructures, rather than geometric arrays, are required in order to properly obtain local residual stress distributions using the finite element analysis procedure.

Influence of intermediate layers and base materials on adhesion of amorphous carbon and metal-carbon coatings

Metal carbon (Me : C) and hydrogen-containing amorphous carbon (a-C : H) layers offer interesting possibilities for coating of tools because of their remarkable tribological features. But normally adhesion to steels used as base materials for tools is very low. A hybrid physical vapour deposition (PVD)-plasma chemical vapour deposition (PCVD) process was used to deposit zirconium (Zr)/intermediate layer/Zr : C. The a-C : H layers were deposited in a parallel plate reactor by PCVD with RF plasma. The graded Zr : C coating adheres well to various steels, very low adhesion is observed to a cobalt-containing steel and to cobalt-based hard metals. a-C : H adheres very well to silicon, glass, and aluminium (Al), but delamination in the bulk of the base material can occur due to high compressive stress. Adhesion to steel can be improved by thin layers of Al and tungsten (W), but different mechanisms seem to be the reasons for the improvement. The adhesion to hard metals increases with increasing WC content.