Impurity elements will exist in tungsten raw materials in the form of compounds or solid solutions, and interact with tungsten carbide and cobalt, significantly affecting the structure and properties of cemented carbide. It mainly contains impurity elements such as sulfur, calcium, aluminum, molybdenum, manganese, copper and iron.
1. Advantages and disadvantages
During the sintering process, cobalt can improve the wettability of the alloy, improve the interfacial bonding force between tungsten and the matrix phase, and play a role in synergistically strengthening sintering. At the same time, it can achieve the purpose of reducing the sintering temperature and significantly improving the strength and toughness of the alloy. Trace amounts of manganese will generate a stable intermediate phase on the alloy phase boundary, purify the grain boundary, improve the interface strength between the matrix and the bonding phase, and the plasticity and toughness of the alloy.
Some impurity elements (such as calcium and copper) will cause defects such as holes in the alloy. A small amount of impurity iron will cause the grain expansion of tungsten carbide, which is not conducive to further refinement processing and form a compact structure. The trace element phosphorus in the alloy neither honors the bonding phase nor solid dissolves in the tungsten particles, which will hinder the contact connection between the bonding phase and the hard phase, and at the same time reduce the melting point of the alloy, resulting in individual growth of tungsten carbide grains. affect the properties of the alloy.
2. Partial solutions
(1) In the process of preparing cemented carbide, vacuum sintering technology can be used, which can effectively remove trace oxide impurities such as silicon, magnesium and calcium, and gas impurities such as oxygen in the sintered body, so that the cemented carbide and hard alloy can be bonded together. The amount of magazine segregation between the solid phase interface is reduced, and the purity of the cemented carbide is improved.
(2) An appropriate amount of rare earth elements can be added to effectively control the content of impurity elements, which can change the distribution of impurities at the interface, reduce the precipitation of gas and the generation of pores, and make cobalt deposit at the tungsten carbide grain boundary to form dispersed particles, thus playing a role It can refine grains and improve the strength and hardness of cemented carbide.
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