The crystallography of the β-α transformation in titanium

Abstract

The orientation relationships, habit plane and surface contour associated with the martensitic transformation in iodide titanium were investigated. The transformation markings studied were those on the natural facets of the specimens, which had originally been single crystals of β-phase. The orientation relationship was close to but not quite identical with the Burgers relationship: (0001) β | | {110} β; {H20} α || {lll} β; the deviations were 1 2−1° . The habit plane was close to {8, 9, 12}, to an accuracy of 1°. The orientations associated with individual habit plane variants were analysed and fitted into a consistent scheme which was close to that expected if the transformation mechanism proposed by Burgers operated. Each habit plane was 10° from the variant of {112} predicted as shear plane by Burgers. Data on the surface contour showed that the direction of atom motion was close to the variant of 〈111〉 required by Burgers, though the magnitude of the surface tilt was smaller than predicted. The precise contour of individual plates, as revealed by multiple beam interferometry, showed that accommodation slip had occurred which would reduce the surface tilt. The results could not be satisfactorily interpreted on the basis of Frank's theory of the martensitic transformation, but they provide some support for Geisler's views.