Sintering of Ti(C,N)-WC/Mo₂C-(Ta,Nb)C-Co/Ni cermets investigated by CO and N₂ outgassing

Abstract

Cermets of the type Ti(C,N)-WC/Mo2C-(Ta,Nb)C-Co/Ni with changing [Mo]/([Mo] + [W]) ratio were subjected to an investigation of outgassing of CO and N2 upon sintering. Quantification of CO and N2 was performed by gas calibration, measurement of masses 12 (12C), 14 (14N) and 28 (28CO and 28N2), as well as C, N, O analysis of the samples before and after sintering. The formation of CO occurs at lower temperatures than that of N2, both gases being completely evolved already at solid-state sintering conditions. If pre-alloyed powders are employed in the starting formulation, the amount of evolved gases is substantially reduced, because part of the formation of mixed hard phases is anticipated. Changing binder composition from Co:Ni = 1:1 to 2:1 and 3:1 does not change the outgassing characteristics, while different batches of nominally the same Ti(C,N) powder can have significant influence. Mass spectrometry is a most valuable in situ tool for getting insight into the metallurgical reactions occurring upon sintering. These reactions result in the typical microstructure and influence the properties of cermets.