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

In order to seek a better understanding of the mechanisms leading to the di sappearance of Mo2C during the sintering of Ti(C,N)-based cermets at or bel ow 1200 degrees C, the sintering reactions occurring in ternary phase mixtu res Ti(C,N)-Mo2C-Ni and their associated binary counterparts Ni-Mo2C, Ti(C, N)-Mo2C and Ni-Ti(C,N) at 1200 degrees C were investigated by X-ray diffrac tion analysis. It was shown that the decrease and disappearance of Mo2C dur ing the sintering of Ti(C,N)-MoC-Ni cermet composites at or below 1200 degr ees C are dictated by the relative amount of Mo-2 to Ni, through enhanced d issolution 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 th ese 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 d issolved in Ni after 1 h at 1200 degrees C. However, when the ratio is well over 0.3, only partial dissolution of Mo2C can be observed even when the a lloys are sintered at 1200 degrees 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 t he 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 d egrees C for up to 5 h, either with or without Ni presence. (C) 1999 Kluwer Academic Publishers.