TiC Effect on Tungsten Carbide Button Properties (2/2)

With the increase of the added amount of TiC, its grain refinement, solid solution strengthening effect began to appear, which is beneficial for improving the bending strength of tungsten carbide buttons. And thereafter continue to add TiC, sintered body appeared in the ring structure with non-normal tissue, which is thus the core parts containing lower amounts of solid solution WC and an outer layer containing a high amount of WC solid solution consisting of the ring with will make the structure appear flexural strength decreased more obviously. The variation of fracture toughness is similar to the bending strength.

From the point of view fracture surface, tungsten carbide button after fracture section added TiC is smoother and the distribution is more uniform. And by observing the hard phase of WC and Co binder phase section can be found in WC grains tend to diversify, it also shows that the fracture of the alloy phase is broken along the border and the bonded phase WC grains and binder phase, rarely WC grains through the break, and it is related to the dispersion of fine-grained solid solution with TiC phase of strengthening.

Furthermore, there are some pores in the section, especially the surface of alloy without adding TiC. In the process of solid phase sintering, because of rigid WC skeleton hinder shrinkage during cooling of briquettes contraction and solidification Co generated carbide makes it impossible to completely fill the screen, resulting in the formation of pores shrink tube; on the other hand, uneven distribution and the gas generated during sintering forming agent is one of the reasons. In addition, TiC also has an influence on the routes of cracks expanding. It will have containing and pinning effect on the movements of WC grain boundaries. And owing to a great difference of elastic modulus and coefficient of thermal expansion, the residual stress of TiC and the matrix in the process of sinter cooling, which resulting in cracks in the offset process of moving forward, extending the cracks propagation path.

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