Method for preparing high density nanocrystalline hard alloy by step sintering

Abstract

The invention provides a method for preparing a high density nanocrystalline hard alloy by step sintering, and belongs to the technical field of novel materials and novel powder metallurgy. The method comprises the following steps: firstly determining the dosage of the raw materials according to the requirements on the content of Co in the final hard alloy based on nanoscale purple tungsten oxide, cobaltous oxide, carbon black and mixed powder of vanadium oxide and chromic oxide as raw materials, mixing the raw materials and performing ball milling, then pressing the raw materials to blocks and conveying the pressed raw materials into a vacuum pump to perform a in-situ reaction to prepare nanometer composite powder with uniform distribution and good dispersity; filling the nanometer composite powder into a high density hard alloy mold, performing discharge plasma sintering, and performing segmented heating, heating up and heat preservation processes to obtain a pre-sintered block with controllable length and size of crystalline grain; finally, putting the pre-sintered block in a high-strength graphite mold to perform high temperature instant discharge plasma quick sintering densification to finally obtain a dense nanocrystalline hard alloy block material. The method provided by the invention can be used for effectively improving the density and mechanical properties of the hard alloy block material.

Description

technical field [0001] The invention relates to a preparation method of high-density nanocrystalline WC-Co hard alloy, which reduces the porosity of nanocrystalline hard alloy through step-by-step sintering to obtain high density and mechanical properties, and belongs to new materials and new powder metallurgy technology field. Background technique [0002] In cemented carbide, WC-Co-based cemented carbide has become an indispensable tool material in high-tech fields due to its high hardness, toughness and flexural strength, especially nanocrystalline cemented carbide, which exhibits excellent hardness and Comprehensive properties of toughness. However, the preparation of the existing WC-Co-based nanocrystalline cemented carbide bulk materials is still at the stage of laboratory research. At present, there is still a long way to go to prepare fully dense, high-hardness and high-strength nanocrystalline cemented carbide bulk materials. It is difficult to meet the urgent dem...

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Problems solved by technology

However, the preparation of the existing WC-Co-based nanocrystalline cemented carbide bulk materials is still at the stage of laboratory research. At present, there is still a long way to go to prepare fully dense, high-hardness and high-strength nanocrystalline cemented carbide bulk materials. It is difficult to meet the urgent demand for high-performance nanocrystalline cemented carbide in industry

[0003] In the past, researchers usually prepared nanocrystalline cemented carbide by increasing the amount of grain growth inhibitor added and rapid sintering. Although the expected effect was achieved in reducing the grain size of the hard phase WC in cemented carbide, the sintering The problem of low density of the block has been difficult to break through

[0004] Regardless of whether solid-phase sintering or liquid-phase sintering is used for the preparation of cemented carbide bulk materials, the sintering temperature is above 1000°C. It is an inevitable phenomenon that WC grains grow during the sintering process. It is necessary to control the growth of WC grain size and reduce the sintering temperature. Temperature is an inevitable way, but the lower sintering temperature cannot eliminate the gas adsorbed between the powder particles and the surface of the particles, resulting in higher porosity and low density of the sintered block, and it is impossible to obtain mechanical properties such as high toughness and high strength. Nanocrystalline cemented carbide

In view of the research status of the preparation of nanocrystalline cemented carbide at home and abroad, we have developed a two-step sintering technology that uses high-pressure pre-sintering followed by rapid low-temperature densification to prepare nanocrystalline cemented carbide blocks with high density. Materials, there are no relevant reports at home and abroad

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