Microstructure insensitive twinning: A statistical analysis of incipient twins in high-purity titanium

Abstract

Apart from some statistical variation, deformation twins are known to be strongly sensitive to microstructure, particularly grain size and lattice orientation. Here we employ a large-scale statistical analysis of several thousands of preliminary twins in lightly deformed titanium. We show that for the set of preliminary twins, their formation, twin type, response to strain and strain rate, and thickness, have little sensitivity to grain size and grain orientation. We rationalize that these findings reveal that preliminary twin formation is not dictated by the same grain level stress states or grain properties. The early stages of twinning, instead, are heterogeneous stress driven, governed by largely fluctuating stresses, spanning positive and negative stresses, generated by over volumes at least two orders of magnitude smaller than the grain size. These findings can benefit understanding of the behavior of materials that twin even under small strain deformation states, such as fatigue, where structural materials are not intended to deform much beyond yield.