Effects of Cold Deformation on the Morphology of a Precipitates in p Titanium Alloys

Abstract

The effects of cold deformation on the morphology of a precipitates were examined for three [1 titanium alloys which were each mainly deformed by slip, twinning, and stress-induced martensitic transformation. Although a precipitated preferentially at β grain boundaries in the undeformed specimens, slight deformation (5% rolling) added another preferential nucleation site peculiar to the deformation modes, which was clearly reflected by the microstructure after aging at 873 K. In Ti-15V-3Cr-3Sn-3AI, slip brought about a striated structure of planar slip bands caused by the extremely localized dislocations, and consequently led to directionally elongated a precipitates aligned along the striations. In Ti-16V-10Sn, deformation twins were frequently accompanied by the internal twins, and the a phase preferentially precipitated at the twin boundaries, especially at the cross points with the internal twins, to finally form film-like a with occasional a precipitates within the twins. In Ti-16V-4Sn, stress-induced orthorhombic martensite (ce“) tended to be produced in groups of martensite plates aligned in parallel by cold rolling, leading to a banded structure. This martensite substantially reverted to the β phase during the early stages of aging, and the a. phase precipitated preferentially at the interface between the ft phases which were originally the a and the β matrix. During further aging, the a phase coalesced to form film-like a.On the other hand, there was no significant difference reflected by the initial deformation modes in the a. morphology after heavy deformation (60% rolling) among the three alloys, and the microstructures were considered to be of a microduplex structure. © 1992, The Iron and Steel Institute of Japan. All rights reserved.