Kosogor A.O.,Taras Shevchenko National University |
L'Vov V.A.,6b Academy Vernadsky Blvd
Metallofizika i Noveishie Tekhnologii | Year: 2010
A two-component nonscalar order parameter describing the slow reconfiguration of crystal defects after the martensitic transformation of cubictetragonal type is introduced within the scope of Landau theory of phase transitions. In such a way, the phenomenological theory of martensite aging is developed. The conception of stabilizing internal stress is formulated, and stress-temperature phase diagram of the aged alloy is plotted. The dependences of austenite-start and austenite-finish temperatures on the aging time are derived from this diagram. The influence of aging on the yield stress value inherent to the twinned martensite is estimated. The slow evolution of the crystal-lattice parameters during the martensite aging is expressed through the stabilizing internal stress and shear elastic modulus of tetragonal phase. The applicability of the theory to the aging effects in the Ni-Mn-Ga shapememory alloy is demonstrated.