Improvement in mechanical properties of dental cast Ti-6Al-7Nb by thermochemical processing

Hydrogenation and dehydrogenation, that is, thermochemical processing (THP) and its variation with a post-heat treatment (THPH), are investigated in order to improve the balance of strength, elongation, and fatigue strength of cast Ti-6Al-7Nb and Ti-6Al-4V for dental applications. Microstructures of both cast alloys change from coarse Widmanstatten alpha structure to super fine alpha structure with an average diameter of 3 mum by conducting THP or THPH. Tensile strength and fatigue limit of cast Ti-6Al-7Nb and Ti-6Al-4V increase by around 10 and 40 pet, respectively, as compared with those of both as-cast alloys. The balance of strength and ductility of cast Ti-6Al-7Nb is improved by conducting THPH as compared with the case where THP is conducted. This improvement is due to the plastic deformability of unstable beta phase because the lattice constant of beta phase in each alloy conducted with THPH is much greater than that of each as-cast alloy.