Five-parameter intervariant boundary characterization of martensite in commercially pure titanium

Abstract

The intervariant boundary characteristics of a commercially pure Ti microstructure formed by the β→α martensitic phase transformation were described according to the crystallography of the displacive transformation and the boundary plane orientation. The martensitic transformation created a microstructure whose grain boundary misorientation angle distribution had four distinct peaks that were consistent with the misorientations between the variants produced by the Burgers orientation relationship. Interestingly, about 60% of population corresponded to 60°/[112¯0] intervariant boundaries. Three-variant clusters with a triangular morphology were observed frequently. This configuration is consistent with the phenomenological theory of martensite, which predicts that these clusters, separated by 60°/[112¯0] boundaries, have a lower transformation strain than other possible variant cluster arrangements. Other intervariant boundaries resulted from the impingement of different combinations of distinct three-variant clusters. The five-parameter boundary analysis revealed a strong anisotropy in the plane orientation distribution, showing that boundaries have a tendency to terminate on prismatic {hki0} and pyramidal {101¯1} planes, when misorientation was ignored. The dominant 60°/[112¯0] intervariant boundaries had symmetric tilt (1¯101) boundary planes, which are a low energy configuration.