Effects of boron addition on the microstructure and mechanical property of as-cast Ti-46.5Al-8Nb alloy

Abstract

Boron addition (≤ 0.7%, atomic fraction) in fully lamellar Ti-46.5Al-8Nb alloys could refine the grain size and the critical content is about 0.5%. The refining mechanism is controlled both by additive composition supercooling induced by boron at the solidification front and the precipitated boride pinning grain boundaries. Interlamellar spacing (λ) increases with more boron added because boron could reduce the undercooling of the lamellar formation, and A value has linear relationship with the grain size d-1/2. The higher the α2 volume fraction in the as-cast alloy, the higher the hardness. The ultimate strength (σb) and elongation (δ) are improved when boron content increases. σb and grain size follows the Hall-Petch relationship.