In the commercial production of thick compact for Ti(C, N)-base cermet and WC-base cemented carbide, it is said that sintering crack tends to occur in the former, compared with in the latter. This and the inferior toughness, etc., are main reasons for the minor application of cermet to wear resistant parts that are usually thicker than cutting tools.
In this study, the cause for the sintering crack was firstly investigated from various viewpoints. The sintering crack was shown to occur during de-waxing process of the compact. The main cause was suggested to be the presence of a large amount of fine particles generated by ball-milling particularly in Ti(C, N)-base mixed powders: (1) Under the presence, molten wax makes the pores among particles closed and/or their sizes further smaller, leading to strongly restrict the smooth escape of included gases through pores, and (2) the sintering crack occurs when the gas pressure (the maximum: the equilibrium evaporation pressure) increased by the restriction exceeds the fracture strength of the compact. Based on this suggestion, it was clarified that the sintering crack could be avoided by using hard-to-pulverize Ti(C,N) special-type raw powder with more uniform grain size.