Effect of prior cold rolling on α precipitation in a Ti-15V-3Cr-3Sn-3Al alloy

The effect of prior cold rolling on α(hcp) precipitation from the β(bcc) matrix in a Ti-15V-3Cr-3Sn-3Al alloy has been studied. In the specimen directly aged, α precipitation occurs preferentially at β grain boundaries and proceeds into the interior of β grains. Grain boundary α precipitates tend to form a film-like structure along the grain boundary because of the restriction of crystallographic variants. On the other hand, in the specimens slightly cold rolled and aged, α precipitates form preferentially on the dislocations in the coarse slip bands. In a single slip band, α precipitates exhibit the same morphology and hold a single variant of the Burgers orientation relationship. Furthermore, the intersections of slip bands with the grain boundary act as preferential nucleation sites of α precipitates. The α precipitates formed at the deformed portion of a grain boundary exhibit different crystallographic variants from those at the undeformed portions of the same boundary. In the heavily rolled specimen, a very fine dispersion of α precipitates is obtained, resulting in the (α+β) microduplex structure.