Microstructure and Thermo-Mechanical Properties after Recovering Treatments in Aged CuAlNi Shape Memory Alloys

Abstract

In Cu-14.3Al-4.1Ni (wt%) shape memory alloy, aging thermal treatments above room temperature in parent β phase increase martensitic transformation temperatures and decrease transformation stresses, thus affecting Clausius-Clapeyron diagrams. γ phase precipitation and ordering processes (until their culmination) are the most probable phenomena responsible for these modifications. After aging, a recovery thermal treatment was performed, which was able to restore the original martensitic transformation stresses and temperatures of the alloy. However, microstructural observations of samples submitted to the recovery thermal treatment reveal a high density of dislocations, which is evidence that the recovery process was not able to fully restore the material to its initial state. We show how the high density of defects in recovered samples affects electrical resistance measurements, even when macroscopic properties such as transformation temperature and stresses are unaltered.