Effects of metal binder on the microstructure and mechanical properties of Ti(C,N)-based cermets

Abstract

To optimize the mechanical properties of Ti(C,N)-based cermets used as tool materials, the cermets with different Ni–Co binder contents and Co/(Ni+Co) weight ratios were prepared. The effects of metal binder content and Co/(Ni+Co) ratio on the microstructure and mechanical properties of Ti(C,N)-based cermets were investigated by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and measuring the transverse rupture strength (TRS), Vickers hardness (HV) and fracture toughness (KIC). The experimental results reveal that increasing Ni–Co binder content can increase the thickness of rim phases by improving the solid solution reaction and the wetting of hard phases. The cermets with 25wt.% binder addition present good comprehensive mechanical properties, which is attributed to the moderate rim phases and uniformly distributed Ti(C,N) grains. The Co/(Ni+Co) weight ratios in binder have a great influence on the grain sizes and microstructure features of Ti(C,N)-based cermets, in virtue of the synergic effects between the wettability of Co and the solubilizing capacity of Ni on hard phases. The cermets with pure Co as binder exhibit optimal mechanical properties with a TRS of 1767±81MPa, a hardness of 12.26±0.10GPa and a KIC of 8.40±0.47MPam1/2, which meet the requirements for tool materials. And the cermets with a Co/(Ni+Co) ratio of 0.2 have the second best mechanical properties with a TRS of 1848±201MPa, a hardness of 11.12±0.40GPa and a KIC of 9.43±0.54MPam1/2, in which the lower hardness can be further improved by optimizing the compositions and sintering process.