Influence of VC on the microstructure and mechanical properties of WC–Co sintered cemented carbides (original) (raw)
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International Journal of Refractory Metals and Hard Materials, 2006
Microstructure and mechanical properties of WC-TiC-10 wt%Co cemented carbides fabricated by sintering with hot isostatic pressing (Sinter-HIP) process were investigated. The WC/TiC grain size ratio of WC-TiC-10 wt%Co cemented carbides was controlled by changing the average size of WC powders ranged from 0.5 to 4 lm, with keeping the average size of TiC powder as 1 lm. The microstructures of sintered WC-TiC-10 wt%Co cemented carbides were sensitively dependent on the WC/TiC grain size ratio. In WC-TiC-10 wt%Co cemented carbides with WC/TiC grain size ratio of 0.5, the TiC/(Ti, W)C core-rim phases were distributed in WC/Co matrix. While, in WC-TiC-10 wt%Co cemented carbides with WC/TiC grain size ratio above 0.8, the WC and TiC/(Ti, W)C core-rim phases were surrounded by Co binder phase. Hardness of WC-TiC-10 wt%Co cemented carbide increased with decreasing the WC/TiC grain size ratio from 4 to 0.8 following the modified Hall-Petch type equation. However, the hardness of WC-TiC-10 wt%Co cemented carbides with WC/TiC grain size ratio of 0.5 shows much higher values than that expected by modified Hall-Petch type equation. Transverse rupture strength of WC-20TiC-10 wt%Co cemented carbides increases with decreasing the WC/TiC grain size ratio.
International Journal of Refractory Metals and Hard Materials, 2016
In this paper the influence of the consolidation process and sintering temperature on the properties of near nanoand nano-structured cemented carbides was researched. Samples were consolidated from a WC 9-Co mixture by two different powder metallurgy processes; conventional sintering in hydrogen and the sinter-HIP process. Two WC powders with different grain growth inhibitors were selected for the research. Both WC powders used were near nanoscaled and had a grain size of 150 nm and a specific surface area of 2.5 m 2 /g. Special emphasis was placed on microstructure and mechanical properties; hardness and fracture toughness of sintered samples. Consolidated samples are characterised by different microstructural and mechanical properties with respect to the sintering temperature, the consolidation process used and grain growth inhibitors in starting powders. Increasing sintering temperature leads to microstructure irregularities and inferior hardness, especially for samples sintered in hydrogen. The addition of Cr 3 C 2 in the starting powder reduced a carbide grain growth during sintering, improved microstructural characteristics, increased Vickers hardness and fracture toughness. The relationship between hardness and fracture toughness is not linear. Palmqvist toughness does not change with regard to sintering temperature or the change of Vickers hardness.
International Journal of Refractory Metals & Hard Materials, 1997
As an effort to investigate a possible extent of substitution of W, the metal from strategic mineral, by a less strategic V, phase relations, microstructure, and hardness and fracture strength, of powder metallurgically processed 90 mass% [(l -y)WC-yVC]-10 mass% Co alloys are studied. Throughout the composition eight phases, cc-Co, P-Co, WC, V,C,, V,C,, q3(Co,W,C), q,(Co,W,C) and graphite C(g), were encountered and a distinct microstructural difference existed across midcomposition. On the basis of combined mechanical properties of hardness and fracture strength the alloys between y = 0.2 and 0.4, which correspond to 18-36 mass % VC, were most promising. Contrary to the antagonistic relations between hardness and toughness commonly encountered in cemented carbides and hard materials, the hardness and fracture strength of the present WC-VC-1OCo alloys were nearly parallel. 0 1997 Published by Elsevier Science Limited
International Journal of Refractory Metals and Hard Materials, 2001
Mechanical properties and microstructures of nanocrystalline WC±10Co cemented carbides were investigated. The nanocrystalline WC±10Co cemented carbide powders were manufactured by reduction and carbonization of the nanocrystalline precursor powders which were prepared by spray drying process of solution containing ammonia meta-tungstate (AMT) and cobalt nitrate. The WC powders were about 100 nm in diameter mixed homogeneously with Co binder phase and were sintered at 1375°C under a pressure of 1 mTorr. In order to compare the microstructures and mechanical properties with those of nanocrystalline WC±10Co, commercial WC powders in a diameter range of 0.57±4 lm were mixed with Co powders, and were sintered at the same conditions as those of nanocrystalline powders. TaC, Cr 3 C 2 and VC of varying amount were added into nanocrystalline WC±10Co cemented carbides as grain growth inhibitors. To investigate the microstructure of Co binder phase in the WC±10Co cemented carbides, Co± W±C alloy was fabricated at the temperature of sintering process for the WC±10Co cemented carbides. The hardness of WC±10Co cemented carbides increased with decreasing WC grain size following a Hall±Petch-type relationship. The fracture toughness of WC±10Co cemented carbides increases with increasing HCP/FCC ratio of Co binder phase by HCP/FCC phase transformation. Ó
Effect of Carbon Addition on Microstructure and Properties of WC–Co Cemented Carbides
Journal of Materials Science & Technology, 2012
Based on a unique method to synthesize WC-Co composite powder by in-situ reactions of metal oxides and carbon, the effects of the carbon addition in the initial powders on the phase constitution, microstructure and mechanical properties of the cemented carbides were investigated. It is found that with a suitable carbon addition the pure phase constitution can be obtained in the sintered bulk from the composite powder. The mechanical properties of the cemented carbides depend on the phase constitution and the WC grain structure. To obtain the excellent properties of the WC-Co bulk, it is important to obtain the pure phase constitution from the appropriate carbon addition in the initial powders and a suitable grain size.
Microstructures of cemented carbides
Materials & Design, 2001
An overview is given of the detailed microstructure of cemented carbides of types WC-Co and WC-MC-Co. and of titanium Ž . carbo-nitride based cemented carbides cermets . The manufacturing process is first described, and the changes in composition that occur during manufacturing are discussed. The microstructure and its formation during sintering is then described for the three types of cemented carbides. In particular is treated: Grain boundary segregation in the carbide skeleton: Control of solid solution hardening in the binder; Segregation in the binder; Formation of a core-rim structure in hard phase grains; Formation of an inner rim during solid state sintering; Slow diffusion of metal atoms in hard phase; Retention of phases far from equilibrium; Approach to paraequilibrium during sintering. ᮊ
Analytical modeling to calculate the hardness of ultra-fine WC–Co cemented carbides
Materials Science and Engineering: A, 2008
An analytical model to calculate the hardness of ultra-fine WC-10Co cemented carbides was investigated. The nanocrystalline WC-10Co powders were manufactured using a spray conversion process and sintered at 1375 • C in a vacuum. Varying amounts of TaC, Cr 3 C 2 , and VC were added to nanocrystalline WC-10Co cemented carbides as grain growth inhibitors. The hardness of WC-10Co cemented carbides increased with a decreasing WC grain size from 5 m to 300 nm. An analytical model to calculate the hardness of WC-10Co cemented carbides was proposed under the assumption that the applied load is transferred from the WC to the Co binder phase. The analytically calculated hardness showed good agreement with the experimentally measured hardness of WC-10Co cemented carbides. In the proposed analytical model, the hardness of WC-10Co cemented carbides is similar to that predicted by the Hall-Petch relationship when the WC grain size is large. However, when the grain size is finer than a critical value, the predicted hardness of the WC-10Co cemented carbide becomes saturated.
Oscillatory pressure sintering: A new method for preparing WC-Co cemented carbides
Journal of Alloys and Compounds, 2019
WC-10 wt% Co cemented carbides were prepared by a new oscillatory pressure sintering (OPS) process in the present work, and the influence of sintering temperature on their microstructure and mechanical properties was mainly investigated. The results were also compared to the sample prepared via conventional hot pressing (HP) under a similar consolidation condition. The optimum OPS temperature was 1310 C; the denser sample with uniform microstructure could be obtained; the sample exhibited the highest flexural strength of 2431 MPa, Vickers hardness of 21.1 GPa and fracture toughness of 11.42 MPa m 1/2. Moreover, the OPS-fabricated sample displayed much better mechanical properties than that of HP-fabricated sample, which might greatly be related to the improved grain boundary sliding, plastic deformation and mass diffusion during the OPS process. This work demonstrates a new approach to prepare high-performance cemented carbides.
Tribologia, 2016
This study performs a comprehensive analysis concerning the amount of fine tungsten carbide (WC) grains needed for the appropriate reinforcement of the cobalt (Co) metallic binder in WC-8Co cemented carbides. The goal is to investigate the balance of coarse-to-fine grain distribution to achieve overall improvement of the material’s mechanical and wear properties. All samples possessed the same WC-8Co binder content, therefore, allowing the role of grain size distribution to be tested. It was found that a ratio of 8:1 wt% of coarse to ultrafine grain WC yielded an appropriate balance between material hardness, fracture toughness, and rupture strength. Upon adding grain growth inhibitors vanadium carbide (VC) and chromium carbide (Cr3C2), the overall wear resistance is further improved compared to undoped composites when samples are tested under abrasive wear conditions.
Fracture behaviour of a new submicron grained cemented carbide
In this work, the effect of increasing argon pressure applied on a post-sintering treatment from 3 MPa to 100 MPa on the mechanical properties of a newly developed ha rdmetal grade, namely, hardness, flexural strength and fracture toughness, is reported. The as-received material has been previously sintered at 1460ºC under 2 MPa argon pressure from powder mixtures of WC and 3.5 wt% Co together with minor additions of VC, graphite and a pressing lubricant. By increasing the argon pressure, a significant increase in flexural strength from ≈ 1500 MPa to ≈ 3000 MPa was observed, whilst hardness (HV30≈2000) and fracture toughness (≈8 MN.m-3/2) remained practically unchanged. Both microstructural and fractographic studies revealed that this is f mainly attributed to a decrease in the amount and size of microstructural defects (namely, pores and metallic inclusions). Furthermore, fracture has been found to occur mainly by intrinsic (bulk) defects rather than surface-related ones, suggesting that surface finishing did not affect flexural strength measurements. Hot isostatic pressing has been successfully used to consolidate WC-3.5wt% Co composites with submicron WC grains size confirming that porosity reduction results in flexural strength improvement.