Latest publication – Five-parameter characterization of intervariant boundaries in additively manufactured Ti-6Al-4V

Our latest research publication by Nima, Ryan and Liam is now available online (https://www.sciencedirect.com/science/article/pii/S0264127520307127?via%3Dihub). A brief summary of what the paper is about can be found below.

Ti-6Al-4V undergoes a phase transformation from the body-centered cubic β phase to the hexagonally close-packed α phase (or martensitic α’) during additive manufacturing, which is usually governed by the Burgers orientation relationship. Crystal symmetry allows for twelve possible α orientation variants to transform from one prior β orientation. Not much is known about the character of the boundaries that are created when two different α variants meet during growth (intervariant boundaries) although the character of these boundaries affects the mechanical properties of AM products. The objective of this work was to provide full ‘five-parameter’ crystallographic characteristics of the intervariant boundaries in an additively manufactured Ti-6Al-4V. The results show that the most common α/α intervariant for different Ti-6Al-4V microstructures resulting from changing the AM parameters are 60°/ [1 1 0], and 63.26°/[ 5 5 ]. The extraction of the grain boundary plane distributions enables revealing a high anisotropy in intervariant boundaries plane distribution. Ti-6Al-4V microstructure shows a maximum population of prismatic planes and a minimum population of basal planes, which contrasts with the expected inverse relationship between the plane energy and the plane population. This suggests that, during additive manufacturing of Ti-6Al-4V and irrespective of the α morphology, the crystallographic constraints imposed by the Burgers orientation relationship determine the boundary plane distribution characteristics. These findings make a novel contribution to the understanding of additive manufacturing of titanium alloys.