Special Microstructures and Twin Features in Ti50Ni50-X(Pd,Au)X at Small Hysteresis
The breaking of symmetry due to atomic displacements in the austenite-martensite phase transformation generally leads to their crystallographic incompatibility. Energy minimizing accommodation mechanisms such as martensite twinning have been recently shown to be a source of hysteresis and irreversible plastic deformation. Compatibility between the two phases can however be achieved by carefully tuning lattice parameters through composition change. A dramatic drop in hysteresis and novel microstructures such as a lowering of the amount of twin lamella are then observed. Related theoretical and simulation works also support the existence of such microstructures including peculiar self-accommodating configurations at near-compatibility. We present the transmission electron microscopy (TEM) study of these novel microstructures for the alloy systems Ti50Ni50-xPdx and Ti50Ni50-xAux where the composition was systemically tuned to approach perfect compatibility. High resolution imaging of the interface between austenite and martensite supplies evidences of compatibility at the atomic level.
Yves Bréchet, Emmanuel Clouet, Alexis Deschamps, Alphonse Finel and Frédéric Soisson
R. Delville et al., "Special Microstructures and Twin Features in Ti50Ni50-X(Pd,Au)X at Small Hysteresis", Solid State Phenomena, Vols. 172-174, pp. 105-110, 2011