Compositional and microstructural optimization and mechanical-property enhancement of cast Ti alloys based on Ti-6Al-4V alloy

The effects of alloying additions on the microstructure and mechanical properties of cast Ti alloys based on Ti- 6Al-4V were systematically investigated through a combination of thermodynamic calculations and experimental verifications. New cast titanium alloys with significantly improved properties were developed through combining thermodynamic calculations and physical metallurgy principles, which achieve an optimum combination of high strength and high ductility at both room and elevated temperatures. Our analysis indicates that the improved strength is due mainly to the α colony and lath size refinement induced by both macro- and micro-alloying of Cr, Fe, B and C elements, whereas the mechanisms for such property optimization include: (1) an increased volume fraction of ductile β phase in the cast state, (2) a refined α colony and lath size by the Cr, Fe, B and C alloying additions, and (3) an enhanced grain-boundary cohesion and refined grain size of prior-β grains induced by proper amount of B additions. The newly developed cast Ti alloys with substantially enhanced mechanical properties for engineering applications.