J. Phys. IV France
Volume 112, October 2003
Page(s) 1091 - 1094

J. Phys. IV France
112 (2003) 1091
DOI: 10.1051/jp4:20031072

Martensitic transformations during ordering in CuAu

N.D. Zemtsova and L.G. Kabanova

Institute of Metal Physics, Ural Branch RAS, 18 S. Kovalevskaya Str., 620219 Ekaterinburg, Russia

It was found that the ordering process in an equiatomic CuAu alloy is nonmonotonic. The initial stage of ordering includes a diffusion nucleation of microdomains of an ordered L10o phase with a high degree of order and a tetragonal lattice axes ratio $\rm c/a = 0.87$. Large elastic anisotropic coherent stresses, which arise in the two-phase ${\rm Al}+L1_0$ structure, suppress the diffusion completion of the ordering process and facilitate relaxation shear processes realized in two stages. The first shear transformation leads to a polytype formation of a metastable Z phase of the martensitic class. The reverse martensitic transformation takes place in plates of the Z martensite and restores the atomic order typical of the L10 phase, but changes the orientation of the c-axis by 90°. The proposed mechanism of ordering, which includes shear processes, explains the cause of formation of a lamellar structure in the CuAu alloy.

© EDP Sciences 2003