Synthesis of Ti(C,N)w and preparation of whisker-reinforced Ti(C,N)-based cermets

Whisker reinforcement is an effective approach to address the insufficient strength and toughness of Ti(C,N)-based cermets. The incorporation of whiskers homologous to the matrix is crucial for preserving the one-dimensional characteristics. In this study, Ti(C,N) whiskers were synthesized via a fluoride-assisted carbothermal reduction and nitridation method using microcrystalline cellulose as the carbon source. The fluoride resource and synthesis temperature were carefully designed based on the decomposition behaviors of NaF and KF, as well as reaction thermodynamics. Systematic investigation of precursor ratios revealed that the optimal molar ratio of n(TiO₂):n(C):n(KF) = 1:12:5 achieved the highest whisker yield, with the diameter of 2–5 μm. The growth followed a vapor-liquid-solid (VLS) mechanism with the K_xTiF_y as the self-generated catalytic droplets. The effect of varying Ti(C,N) whisker contents on the microstructure and mechanical properties of Ti(C,N)-based cermets was systematically investigated. Similar to Ti(C,N) particles, typical “core-rim” structures can also be observed on undissolved Ti(C,N)_w, ensuring a promising bonding strength. Notably, “tooth-like” inner rims formed on whisker cores, due to the solid-state diffusion with disperse-contacting second carbides. The doping of Ti(C,N)_w resulted in a bimodal grain size feature, thus promoting the dissolution of finer Ti(C,N) particles and the formation of grey particles and white core-grey rim structures. Remarking improvements of fracture toughness with less loss of hardness can be achieved for whisker-reinforced Ti(C,N)-based cermets. When replacing over 30 % Ti(C,N) by Ti(C,N)_w, the cermet exhibited optimal comprehensive performances of 1480 HV10 and a fracture toughness of 11.65 MPa·mm^1/2.