Origins and importance of fine secondary α in slowly cooled Ti6Al4V

Abstract

It has been known for sometime that slowly cooled Ti6Al4V (Ti64) contains only about 10vol% of β and that this β takes three different forms. Firstly, there are thin volumes of interfacial β, between the grains of α, which are clearly the remains of the β present at high temperatures left when α replaces the β present at high temperatures, by diffusion and boundary migration. Secondly, there are regions of roughly equiaxed β at triple points, but some of this β contains very fine secondary α, whereas the other grains are retained β. Analytical transmission electron microscopy has been used in an attempt to understand the origin of these two different types of equiaxed β grains. It has been found that grains, which are retained β contain about 20wt%V, but the β grains that contain secondary α originate from parent β grains that have only about 14wt%V. The origin and the significance of these observations will be discussed in the presentation.