“A Contribution to Anisotropic Deformation Behavior of Alpha+Beta Titanium Alloys Inherent in the Crystallography of the Burgers Orientation Relationship”

Abstract: A new source of anisotropic deformation behavior for alpha and beta titanium aligned according to the Burgers orientation relationship has been understood from the perspective of 2-fold maximum common crystal symmetry. Overlays of stereographic projections viewed along {011} || (0001) and rotated so that <111> || <2-1-10>, establishing a Burgers orientation relationship, revealed the maximum common crystal symmetry between bcc-β and hcp-α phases in the composite α/β material was only 2-fold. This new observation had implications for necessary anisotropy of deformation behavior between and within a-basal, a-prism, a-pyramidal and c+a pyramidal slip systems. Consideration for requirements of 2-fold crystal symmetry, e.g. testing of slip systems at loading orientations within 180° of each other and relative orientation with respect to the {011} || (0001) mirror planes, showed that 3, 6, 6 and 12 unique responses were required when testing hcp-α slip systems at orientations of constant maximum Schmid factor. Calculation showed this contribution to anisotropic deformation behavior resulted from geometrical hardening, i.e. large changes in Schmid factor on mating bcc-β slip systems when testing hcp-α slip systems at orientations of constant maximum Schmid factor. Comparison is made between these calculated results and those obtained during testing of single variant, single colony alpha+beta titanium materials at maximum Schmid factor on hcp-α slip systems.