Sintering behavior, microstructure and mechanical properties of NbC-Ni alloys with different carbon contents

Abstract

This work aims to study the influence of the carbon content in a (NbC-3vol%Mo2C)-12vol%Ni-0.5vol%WC alloy on the sintering process, and its resulting effect on the microstructure and mechanical properties. NbC cemented carbides with additions of Mo or C were sintered at 1450 °C for 1 h in the vacuum furnace of a dilatometer and of a TGA (Thermogravimetric Analysis) device. Liquid phase sintering temperature is decreased with addition of Mo or C, leading to an early densification which limits nickel evaporation. Swelling occurs during heating in the 3 phase (NbC + Ni + liquid) domain for the high carbon content alloys. A graphite phase is observed for largest carbon contents. The C/Mo ratio also affects the phase composition and lattice parameters. The lattice parameter variation of the carbide and Ni rich-binder is explained by the variation of the metallic solute contents as a function of the overall composition. Grain growth is globally enhanced by increasing the carbon content. A significant effect of C/Mo ratio on the mechanical properties of the alloy is also observed. The Vickers hardness (HV30) decreases while the toughness (KIc) exhibits a maximum value as the carbon content increases.