On the disappearance of Mo2C during low-temperature sintering of Ti(C,N)-Mo2C-Ni cermets

Abstract

In order to seek a better understanding of the mechanisms leading to the disappearance of Mo2C during the sintering of Ti(C,N)-based cermets at or below 1200 °C, the sintering reactions occurring in ternary phase mixtures Ti(C,N)-Mo2C-Ni and their associated binary counterparts Ni-Mo2C, Ti(C,N)-Mo2C and Ni-Ti(C,N) at 1200 °C were investigated by X-ray diffraction analysis. It was shown that the decrease and disappearance of Mo2C during the sintering of Ti(C,N)-Mo2C-Ni cermet composites at or below 1200 °C are dictated by the relative amount of Mo2C to Ni, through enhanced dissolution of Mo2C in Ni by the presence of Ti(C,N). The reprecipitation of (Ti,Mo)(C,N) onto Ti(C,N) grains does not occur to a large extent under these conditions. On average, when the ratio of Mo2C to Ni is below or around 0.3, all of the Mo2C phases present in the Ti(C,N)-Mo2C-Ni alloys can be dissolved in Ni after 1 h at 1200 °C. However, when the ratio is well over 0.3, only partial dissolution of Mo2C can be observed even when the alloys are sintered at 1200 °C for 10 h. Both Mo2C and Ti(C,N) can be dissolved in Ni in the solid state, but the dissolution of Mo2C in Ni in the Ti(C,N)-Mo2C-Ni alloys is enhanced by the presence of Ti(C,N), hence N, compared to the dissolution of Mo2C in the Ni-Mo2C alloys. Negligible phase interactions are detected between Ti(C,N) and Mo2C when sintered at 1200 °C for up to 5 h, either with or without Ni presence.