Resonant ultrasound spectroscopy, differential scanning calorimetry and neutron powder diffraction were employed to analyze the role of defects in a first-order transformation. An anomalous behavior associated with the martensitic transformation in a Cu-Al-Ni shape-memory alloy was observed; the internal friction peak measured during cooling completely disappeared on heating. The elastic constants also showed different behavior on heating and cooling. The different mobility of defects in the two phases, and the simultaneous occurrence of both the defect recovery processes and the martensitic transformation in the same temperature range, were the origin of the observed behavior. These effects showed an exceptional influence of defects on thermo-elastic equilibrium during a first-order structural transition. The proposed mechanism was general and could be applied to transitions other than the one reported here.

Defect Pinning of Interface Motion in Thermoelastic Structural Transitions of Cu-Al-Ni Shape-Memory Alloy. J.I.Pérez-Landazábal, V.Recarte, D.S.Agosta, V.Sánchez-Alarcos, R.G.Leisure: Physical Review B, 2006, 73[22], 224101 (9pp)