Effect of presintering treatments on TiMoCN-Ni based cermets processed from different powder mixtures

Different powder mixtures have been used to analyse the effect of presintering heat treatments on the composition and microstructure of TiMoCN-Ni based cermets. When methane is present in the atmosphere C contents after presintering can be associated to the C activity calculated from the C + 2H2 = CH4 equilibrium. H2 based atmospheres produce high C losses whereas N2-CH4-H2 gas mixtures induce strong carburization of the compacts. When no methane is present in the atmosphere, the C activity could be related to the C content of the compacts by the Boudouard equilibrium. Changes in C and N contents are also observed to depend critically on the phases present in the powder mixtures. Those containing free C, TiC, Mo2C or TiMoC phases show higher C and N changes after presintering than those based on quasi-monophasic TiMoCN powders. These data confirm that presintering treatments can be designed to modify the C/N ratio of TiMoCN-Ni cermets in order to avoid graphite precipitation and to have a closer control on the composition of carbonitride and metallic binder phases after sintering.