Five-parameter characterization of intervariant boundaries in additively manufactured Ti-6Al-4V
N. Haghdadi, Ryan DeMott, P.L. Stephenson, Xiaozhou Liao, Simon P. Ringer, Sophie Primig
Abstract
Additive manufacturing has emerged as a promising route to fabricate complex-shaped Ti-6Al-4V parts. The microstructural evolution and variant selection across builds in response to different printing strategies processed by electron beam powder bed fusion has been previously clarified. However, a detailed knowledge of the grain boundary plane characteristics of the α-α intervariant interfaces is still missing. The aim of this study was to reveal the full ‘five-parameter’ crystallographic characteristics of the intervariant boundaries. The most common α-α intervariant for colony and basketweave microstructures was 60°/[1 1 2¯ 0], while in the acicular microstructure, the maximum was at 63.26°/[10¯ 5 5 3¯]. This is discussed in terms of self-accommodation during the β to α phase transformation, and the degree of coherence of the α laths in the as-deposited condition and during further growth. The grain boundary plane distributions reveal a high tendency for intervariant boundaries to terminate on prismatic and pyramidal planes rather than on low-energy basal planes. 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.