The influence of particle size and heat treatments on the transformation energies of a gas atomized Cu-Al-Ni-Mn shape memory alloy

Abstract

Forward and reverse transformation temperatures of shape memory alloys are significantly affected by their thermal and processing history. Controlling these temperatures is of great importance when designing materials displaying shape memory effect. In this direction, the present work shows the influence of particle size and heat treatments on thermodynamic properties of a gas-atomized Cu-Al-Ni-Mn shape memory alloy. Commercially pure elements were used in the gas atomization process and differential scanning calorimetry was used to measure As, Af (austenitic start and final transformation temperatures), Ms, Mf (martensitic start and final transformation temperatures), transformation temperature hysteresis and chemical/non-chemical energies involved in the martensitic-austenitic transformation. The influence of quenched-in defects and annealing was also studied. Results show a correlation between particle size and transformation energies, which can be attributed to atomic ordering in the austenitic phase upon cooling, after the solidification process. This is further confirmed by the increase in the reverse and forward transformation temperatures after thermal cycling and annealing.