Effects of Nb addition on micro structure and mechanical property of Ti-48Al-0.7B alloy

Abstract

Ti-48Al-0.7B-xNb (x=0, 3, 5, 8; atomic fraction, %) alloys were centrifugal cast into car exhaust valves and their microstructures and mechanical properties were studied. The results indicate that all the cast alloys possessed the fully lamellar α2+γ structure, and has no β phase. The grain sizes of the alloys with different Nb contents are related to the additive composition supercooling induced by boron at the solidification front area and the grain boundary pinned by the precipitated borides during the solidification process. The interlamellar spacing (λ) has a linear relationship with grain size d-1/2. The σb of the alloy is affected by oxygen and niobium contents and the 5 is directly dominated by the grain size. The Ti-48Al-0.7B-5Nb alloy has the most refined grain size and the optimum combined mechanical property (σb=399.6 MPa, δ=0.26%).