DEVELOPMENT AND CHARACTERIZATION OF HIGH-PERFORMANCE TiC AND TiN CERMETS

Abstract

‘Cermets’ are engineered composites that combine ceramic and metallic phases to generate materials that, typically, exhibit both high hardness and toughness. Because of this combination of constituents, cermets can exhibit a moderately low coefficient of friction combined with good wear resistance. In addition, through careful selection of the actual cermets phase compositions, they can also possess high oxidation resistance and good thermal stability. The development and synthesis of TiC/TiN with novel binder alloys such as stainless steel 316L and PH17-4PH, Ni3Al and additions such as graphene nanoplatelets (GNPs) and Mo2C were developed for applications under extreme wear resistance environments. The effects of incorporating Mo2C additions into TiN-Ni3Al cermets, in terms of their densification response and microstructural development have also been studied. It is demonstrated that an increase in the Mo2C content reduces both the melting and solidification temperature of the Ni3Al-based component of the system, which is initially formed via reaction sintering. The wettability of the Ni3Al binder was improved through additions of Mo2C, enhancing the densification process. The influence of series of post-sinter heat treatments, between 600 and 1340 °C, on atomic ordering of the Ni3Al on the TiC-30Ni3Al were also studied. An increase in Vickers hardness, from 1400 to 1530 HV, is observed as a result of heat treatment at 1200 ºC. Furthermore, the scratch hardness value was improved from 11.89 to 18.12 GPa, with the main wear mechanisms being identified as TiC grain pull out and brittle fracture. Other heat treatments were performed on the TiC-PH 17-4 stainless steel based cermets, evaluating the effects of heat treatments on precipitation hardening steels in comparison with non-heat treatable steel, when used in combination with TiC. Martensitic Cu rich precipitates were identified by X-ray diffraction analysis when TiC-17-4 precipitation hardening steel was heat treated. An increase in Vickers hardness from 1160 to 2342 HV is as a result of a 1150 ºC heat treatment. Moreover, the scratch resistance was significantly improved, dropping from 1.74 to 0.8 μm in scratch depth, when performed at a load of 30N.