Up-quenching effect on the stabilization process of a CuZnAl martensite

Abstract

Abstract The correlation between the recovered shape memory capability and the temperature of an up-quenching treatment of a partially stabilized martensite has been studied in a Cu-25.6wt.%Zn-3.94wt.%Al alloy by estimating the transformation temperatures M ∗ and A ∗ , the spacing difference Δd and the mechanical behaviour of tensile testing ( σ y , η an , η tr and η pl ). The effect of a subsequent secondary low temperature aging on the shape memory effect (SME) of an up-quenced stabilized martensite has also been investigated. It is shown that the transformation temperatures M ∗ and A ∗ decrease monotonically with increasing upquenching temperature, and secondary low temperature aging restores M ∗ and A ∗ to their original values with neither a change in Δd nor degradation of the shape recovery capability. It was also discovered that the up-quenched microstructure could change from the parent phase into a martensite phase as the result of a secondary low temperature aging treatment, which is correlated with the degree of short-range disorder in the DO 3 phase. Both the value of Δd and the capacity of the SME of a partially stabilized martensite can be restored by up-quenching in an oil bath with a temperature above 140°C for 3 min. However, up-quenching at 270°C causes a dramatic increase in yielding stress that is seriously detrimental to the SME behaviour of the sample owing the precipitation of α 1 plates.