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

• Published in: Materials & design 2017-11, Vol.133, p.30-38
• Main Authors: Liu, Bolu, Huang, Shuigen, Van Humbeeck, Jan, Vleugels, Jef
• Format: Article
• Language: English
• Subjects: Cermet; HfH2; Mechanical properties; Pressureless liquid-phase sintering; TiC-NiTi
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2017.07.044

(Ti,Hf)C0.7 cermets with different Ti/Hf atomic ratio and 20vol% NiTi binder were prepared by pressureless liquid-phase sintering at 1380°C for 60min. The Hf content was modified by adding up to 42.4wt% 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)C0.7 at different HfH2 addition was slightly lower than the theoretical value, due to some Hf dissolution in the binder phase. The (Ti,Hf)C0.7 grain size and binder mean free path length decreased whereas the apparent porosity slightly increased with increasing HfH2 content up to 42.4wt% HfH2. The hardness increased with increasing HfH2 addition up to 42.4wt%, while the elastic modulus remained the same. The bending strength and fracture toughness increased with increasing HfH2 addition to 19.9wt% but decreased upon further increasing the HfH2 content up to 42.4wt%. [Display omitted] •Near fully dense (Ti,Hf)C0.7-NiTi cermets were obtained by pressureless sintering of HfH2/TiC/NiTi/TiH2 powder mixtures.•A martensitic NiTi is formed upon HfH2 addition and a secondary Hf-rich (Hf,Ti)Cx is generated upon 42.4 wt% HfH2 addition.•Increasing HfH2 addition significantly decreases the (Ti,Hf)C0.7 grain size but slightly increases the porosity.•The 19.9 wt% HfH2 cermet has an optimum combination of hardness, fracture toughness, bending strength and elastic modulus.