Impact of Nb content on the morphology and properties of Ti (C0.5N0.5)-FeCrMo-based green cermets

A series of TiCN-FeCrMo-xNb (x = 2,4,6,8 wt%) was prepared through pressureless vacuum sintering at a sintering temperature of 1500 °C. This study aims to fabricate TiCN-high chromium Fe-based cermets and investigate the effect of incorporating strong carbide-forming elements such as Nb on the microstructure, phase, and mechanical properties. The microstructure and composition of the sintered cermets were investigated by Scanning electron microscope (SEM) in combination with an energy dispersive spectrometer (EDS) respectively, and detailed investigation of phase constitution was carried out using thermodynamic calculations and X-ray diffraction (XRD) measurements. Microstructure tends to become finer with increasing Nb additions (up to 4 wt%); however, when Nb additions increase to 6–8 wt%, ceramic particles become much bigger with a bimodal distribution of Ti(C,N) particle size. Microstructure study reveals that the addition of Nb inhibits the grain growth by diffusion of Nb in the Ti(C,N) during solid-state sintering and leads to refining the microstructure. Based on these findings, optimal Nb addition (up to 4 wt%) in the Ti(C,N)-FeCrMo -based cermets plays the role of an inhibitor in the dissolution-reprecipitation process, inhibiting the precipitation of brittle (Ti, M) C, N rim phases. The mechanical properties of the Ti(C,N)-FeCrMo -based cermet increased with 2–4 wt% Nb addition and decreased sharply with further increasing the Nb content. The maximum hardness and fracture toughness have been achieved for the cermet with 4 wt% Nb with 1322 ± 61 HV30 and 8.56 ± 0.17 MPa m1/2 respectively.