Microstructure And Mechanical Properties Of Ti(C,N)-NiMo-based Cermets And Heat-treated By Gas Pressure Post-sintering

In this paper, Ti(C,N)-based cermets with NiMo-binder are prepared by powder metallurgy in order to obtain better mechanical properties. Effect of NiMo-binder content and sintering temperature on Ti(C,N)-NiMo-based cermets were investigated. Besides, Ti(C,N)-based cermets prepared by vacuum sintering(VS) were heat-treated through gas-pressure post-sintering(GPPS) and vacuum post-sintering(VPS). Effect of post-sintering in argon pressure and vacuum on microstructure and mechanical properties of Ti(C,N)-based cermet was investigated.The study shown that the microstructure of Ti(C,N)-NiMo-based cermets exhibited a typical core-rim structure embedded in binder. Besides, grey phase without core-rim structure were also observed. With the increase of NiMo-binder content, the amount of hard phase particles reunion phenomenon and grey phase were decreased, and black cores became finer. The microstructure also became more homogeneous while core-rim structure became more complete. In addition, transverse rupture strength(TRS) increased while hardness decreased with the increase of binder content. With the increase of sintering temperature, the cores became finer and the rims became thicker. Meanwhile, TRS increased to maximum and then decreased. As to cermets with lower NiMo-binder content, hardness also increased firstly and then decreased with the sintering temperature increased, however, hardness decreased with the sintering temperature increased when the NiMo-binder content was high. The rupture of cermets was a combination of transgranular fracture and intergranular and fracture morphologies of cermets showed flat cleavage planes and pores accompanied by tearing ridges. Besides, white particles were observed at the grain boundary. The cleavage planes in fracture decreased obviously and pores accompanied by tearing ridges increased with NiMo-binder increased.Dissolution-reprecipitation process took place again during the post-sintering, and small cores were vanished obviously. The contrast difference between outer rim and inner rim dropped down after post-sintering which manifested heat-treated make the diffusion process proceed more sufficient. Specially, the amount of big cores and the thickness of rim increased obviously after VS. After GPPS, transverse rupture strength(TRS) of cermet was enhanced distinctly, reaching a maximum value 2433 MPa. Moreover, hardness, fracture toughness(KIC) and density were also improved by GPPS. However, the mechanical properties of cermet deteriorated after VPS.