Inhibitor Effect on Tungsten Carbide Button

Theoretically, the smaller granularity, the hardness is higher; and the fracture strength of materials with the increasing hardness. In order to improve the hardness and the strength of tungsten carbide buttons, we have to optimize the sintering process and add grain growth inhibitor properly to inhibit the growth of grains. The common used inhibitor in the sintering process of tungsten carbide powder include TaC, MoC, Cr3C2, VC, NbC and so on, which can be as a single additive can also be a certain percentage of the composition of compound inhibitor. In addition, some researchers add refractory metal carbides into the Co-rich matrix and the resulting solid solution as the inhibitor. It can remarkably decrease the melting point of the base, Co formed in the liquid phase in a stable metal / non-metallic atomic group, and the presence of the radicals will hinder W, C atoms from one grain to another grain adjacent liquid migration, thereby further reducing the WC grain growth rate.

Rare earth elements can also be used as grain growth inhibitors which also inhibit grain growth and improve the performance of tungsten carbide buttons during sintering. There are many rare earth elements such as Y, La, Nd, Pr, Ce, may also be added in the form of rare earth metal oxides and mixed rare earth. The main role of the rare earth element is:
1. Lively nature, a strong affinity to O, S, N, C and other elements, so tungsten carbide button in these impurity elements form a rare earth compound particle and distributed at the grain boundaries. This also effectively prevents the diffusion of dissolved in liquid Co and WC phases of grain boundary migration suppressed uneven WC grain growth;
2. Purify the grain boundaries and remove the impurities, rare earth elements and impurity elements combine to form a spherical compound of the binder phase dispersion strengthening. In the both mechanisms above, the hardness, the bending strength of tungsten carbide button has been significantly strengthened. At the same time, rare earth elements can effectively reduce the sintering temperature of tungsten carbide button, and better solve the contradiction between controlling grain growth and densification.

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