{332}〈113〉 Twinning system selection in a β-type Ti-15Mo-5Zr polycrystalline alloy

The orientational dependence of {332}〈113〉 twinning and its system was examined in a 4.0% tensile-strained Ti-15Mo-5Zr (mass%) polycrystalline alloy by electron backscatter diffraction analysis combined with Schmid factor analysis. Twinning and system selections were found to obey the Schmid law in grains with tensile axes close to the [1 11] and [001] directions, in which the maximum Schmid factors of an easily operative (233)[311] twinning system were larger than 0.46 and smaller than 0.34, respectively. However, when the maximum Schmid factor ranged from 0.34 to 0.46, both selections became complex and not entirely explainable by the Schmid law around the center of a stereographic triangle. Twinning systems other than (233)[311] were also activated in grains with a Schmid factor even below 0.1 and inside twins with a negative Schmid factor. We conclude that additional factors, specifically local stress concentrations and geometric constraints between neighboring grains, should also be considered in regard to {332}〈113〉 twin formation, even in a polycrystalline β-titanium alloy that has been only slightly deformed.