Ultrafine WC - Co Tungsten Carbide Preparation

WC and Co by the composition of tungsten cobalt-based carbide with excellent hardness and wear resistance and other properties, is a widely used tools, structural materials. However, there is a rejection phenomenon between the transverse rupture strength and the hardness in the tungsten-cobalt type cemented carbide, that is, the hoisting strength will damage the hardness, and the hardness will be weakened by the increase of the hardness. This is a technical problem that has been difficult to solve. The results show that the microstructure with ultra-fine grain characteristics of tungsten and cobalt type cemented carbide, can achieve strength and hardness of the synchronous upgrade; general requirements, the grain size of 0.2 to 0.5 microns of tungsten cobalt-based hard alloy can be called super Fine grain hard alloy. However, in the sintering stage of the preparation of WC-Co cemented carbide, grain growth occurs. In order to achieve tungsten cobalt-based carbide fine grain size, generally from two aspects. Conventional method is to WC and Co mixed powder as raw materials, milling after mixing granulation, and then press forming, and then pressure sintering. In order to avoid grain growth, the grain growth inhibitor such as VC and Cr2C3 was added to the mixed powder. Another idea is the use of small grain size of WC-Co composite powder as raw material. The WC-6% Co composite powder prepared by spray-transformation, calcination and low-temperature reduction carbonization process was used as the raw material. The average grain size was below 50 nm and the distribution was uniform. The ultrafine WC-Co tungsten carbide with grain size of about 400 nm was successfully prepared by wet grinding, forming and pressure sintering without adding grain growth inhibitor, and good results were obtained.

The microstructures of the composites prepared by the composite powders show that the size of WC grains is smaller than 0.5 micrometers, and the size distribution of WC grains is uniform. Bonding, bridging phenomenon is greatly reduced, part of the grain edges and corners dissolved dissolved, the edge is more smooth, so that the application of the alloy is not prone to excessive concentration of stress. These are beneficial to improve the mechanical properties of materials. However, the WC grains in the alloy prepared by the traditional method have abnormal growth phenomenon, which will seriously damage the mechanical properties of ultra-fine cemented carbide.

The strength and hardness of ultrafine WC-Co cemented carbide prepared by composite powder were higher than that of the traditional mixed powder preparation. The tensile strength of the composites was 4304N / mm2, which was much higher than that of the samples prepared with mixed powders (3200N / mm2). The hardness of the composite powders was 93.1HRA, which was also superior to that of the mixed powders The hardness of the sample was prepared (91.5 HRA). The results show that the grain size of the composite powder is small, the average grain size is below 50 nm and the distribution is uniform. The component distribution of the composite powder is uniform, and the distribution of W, C and Co is related to the molecular homogeneity. .

Their experiments also found that the composite powder prepared by ultrafine WC-Co cemented carbide prepared with the traditional method of the material in the coercivity value of the significant difference. According to the analysis, when the content of Co in the alloy is the same, as the grain size of WC decreases, the Co phase dispersion increases, the mean free path decreases and the coercive force increases. The coercivity of the composite powder was 34 kA / m, and the sample prepared by the conventional method was 26.7 kA / m. It is also proved that the WC grain size of the ultrafine WC-Co cemented carbide prepared by using composite powder as raw material is smaller than that of the traditional mixed powder.

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