Landau theory of structural transformations in titanium-nickel and gold-cadmium alloys

We present a rigorous symmetry-based Landau theory of the two martensitic transformations from the cubic B2 (beta(2)) austenite parent phase to the rhombohedral R (zeta(2)') product phase of P3 symmetry and to the orthorhombic B19 (gamma(2)') product phase of Pmma symmetry. Both are improper ferroelastic transformations. their primary order parameters are expressed in terms of the shuffle displacements that correspond to the two [zeta zeta 0] TA(2) modes for zeta = 1/3 and zeta = 1/2, respectively. Numerical agreement with experimental data is exact for the B2-B19 transformation and good/fair for the B2-R transformation in AuCd/TiNi, respectively. (C) 1999 Elsevier Science S.A. All rights reserved.