Crystallographic analysis of cubic to orthorhombic martensitic transformation for the formation of the oxide plates in tantalum

摘要

In the theory of martensitic transformations described by Wechsler et al. [1], the total transformation distortion is factorized into a pure distortion, which produces the essential change in crystal structure, and a lattice invariant or inhomogeneous shear. The magnitude of this shear is determined by the condition that a plane of zero distortion exist and this plane is identified as the habit plane separating the two phases. In this manner the crystallographic features of the transformation, viz. the habit plane, the orientation relation-ship between crystal axes, and the macroscopic change in shape, are determined as a function of the lattice parameters of the two phases. In the theory of Bowles and Mackenzie [2], a different factorization of the total distortion and mathematical formulation are used. This theory includes a dilatation parameter, δ, which in effect slightly relaxes the requirements that the habit plane be undistorted. But the two theories yield almost identical results [3].