Effects of working, heat treatment, and aging on microstructural evolution and crystallographic texture of α, α′, α″ and β phases in Ti-6Al-4V wire

Crystallographic texture was measured on Ti-6Al-4V wire at several stages of a process similar to that used in producing titanium products. As-received wire had a moderately strong fiber texture with prism plane normals aligned with the longitudinal wire axis. Wire specimens were cold worked by extrusion, solution heat-treated in the α + β phase field, water quenched, and then aged. Extrusion strengthened the as-received texture. After solutionization and quenching, a secondary fiber with basal plane normals aligned with the wire axis emerged at the expense of the initial texture, indicating that a strongly preferred variant selection occurred during quenching. After artificial aging, α″ and β phases were present, but subsequent natural aging for a year led to elimination of α″ and a reduction in the amount of the β phase. The effect of processing history on the orientations of α, α′, α″, and β (focusing particularly on the effect of extrusion and solutionization time) is discussed in the context of the known physical metallurgy of titanium alloys. The selection of preferred variants in the α → β → α transformation cycles is discussed in relation to shears imposed in the β phase due to differential thermal expansion between misoriented α regions, causing 90° rotations by variant selection.