Investigations on kinetics of formation of fcc-free surface layers on cemented carbides with Fe–Ni–Co binders

The formation of surface layers free of face centered cubic (Ti,Ta,Nb,W)(C,N) carbonitrides and enriched in ductile binder phase (fcc-free surface layers) was investigated on cemented carbides containing Fe–Ni–Co binders. Cemented carbide alloys with varying Fe–Ni–Co binders were sintered in vacuum atmospheres at 1450 °C for 2, 3 and 5 h. Independent of the binder composition the growth of fcc-free surface layers obeys a parabolic law. For same sintering conditions, fcc-free layer growth kinetics is enhanced by the addition of Fe to Co and Ni binders. Thermodynamic calculations showed that adding Fe to Co and Ni binders increases the solubility of the element nitrogen in the liquid binder phase. The higher solubility of N in Fe-containing binder phases promotes the formation of larger fcc-free surface layers, so that the width of fcc-free surface layers can be modified by controlling the Fe content in the binder phase.

Research Highlights
► Formation of fcc-free layers on hardmetals with Fe–Ni–Co binders was studied.
► Experimental correlations between binder composition and fcc-free layer thicknesses.
► Fcc-free layer growth kinetics is enhanced by addition of Fe to Co and Ni binders.
► Thermodynamic calculations of N solubility in the liquid binder phase.
► Fe-containing binders promote the formation of thicker fcc-free surface layers.