Investigation of the grain size effect on mechanical properties of Ti-6Al-4V alloy with equiaxed and bimodal microstructures

Abstract

In this study, equiaxed microstructures with various grain sizes ranging from 6.0μm to 0.3μm and bimodal microstructures with grain sizes of primary α ranging from 5.0μm to 0.6μm were successfully fabricated by hot deformation and subsequent annealing in α+β two phase region in Ti-6Al-4V alloy having a martensite initial microstructure. The mechanical properties of both microstructures with different grain sizes were tested at room temperature. It was found that the strength (yield and tensile strength) of both microstructures increased with the decrease of the grain size. In the equiaxed microstructure, the uniform elongation gradually decreased with the decrease of the grain size, which was in consistent with the behavior of other metallic materials with ultrafine grains. However, in the bimodal microstructure, relatively large uniform elongation (∼8%) was stably obtained regardless of the grain size. The unique and superior balance between strength and uniform elongation in bimodal microstructures was discussed, considering the contribution of interfaces between primary α grains (α p) and transformed β areas (β trans).