Slip heterogeneity in a colony-structured titanium alloy: Planar versus wavy slip traces

Abstract

Titanium (Ti) alloys with colony microstructures, including many near-α and α + β Ti alloys, are widely used in aerospace components. Although the characteristics of the colony microstructures have been extensively studied, the localized deformation behavior of individual colonies has been less reported. This study investigates the slip behavior of α colonies in a near-α Ti-6.5Al-2Mo-Zr-V alloy through surface slip trace analysis, revealing two distinct deformation modes: (i) homogeneous slips, characterized by dense, uniform, and straight planar slip lines; and (ii) heterogeneous slips, featuring wavy and planar slip traces with varying intensities. The wavy slip traces result from <a>-type screw dislocation cross-slips between basal, prismatic, and pyramidal planes, wherein the screw dislocations are primarily emitted from the stressed α/β interfaces at the colony boundaries. These stress concentrations at α/β interfaces arise from the mismatch of elastic modulus (ΔE > ∼5 GPa) and low geometrical compatibility (m' < ∼0.5) between adjacent colonies. All the planar slip traces are aligned with basal or prismatic planes, but the slip intensity - reflecting a degree of slip localization - varies significantly, and an easy slip transfer across an α/β interface promotes slip delocalization. Pyramidal-I <c+a>-type dislocations are also observed and enhance the slip heterogeneity. These findings provide critical insights into deformation heterogeneity in colony-structured titanium alloys, inspiring new pathways for microstructural design to enhance their mechanical performance for a wide range of applications.