Influence of HfH2 addition on the microstructure and mechanical properties of TiC-NiTi cermets

(Ti,Hf)C-0.7 cermets with different Ti/Hf atomic ratio and 20 vol% NiTi binder were prepared by pressureless liquid-phase sintering at 1380 degrees C for 60 min. The Hf content was modified by adding up to 42.4 wt% HfH2 powder in a TiC0.95+ Ni49.4Ti50.6+ TiH2 starting powder mixture. Upon HfH2 addition, the binder phase changed from austenite to martensite NiTi. The actual Hf content in the (Ti, Hf) C-0.7 at different HfH2 addition was slightly lower than the theoretical value, due to some Hf dissolution in the binder phase. The (Ti, Hf) C-0.7 grain size and binder mean free path length decreased whereas the apparent porosity slightly increased with increasing HfH2 content up to 42.4 wt% HfH2. The hardness increased with increasing HfH2 addition up to 42.4 wt%, while the elastic modulus remained the same. The bending strength and fracture toughness increased with increasing HfH2 addition to 19.9 wt% but decreased upon further increasing the HfH2 content up to 42.4 wt%. (C) 2017 Elsevier Ltd. All rights reserved.