Marcelo Stipcich

The effect of post-quench aging on stabilization of martensite in Cu–Zn–Al and Cu–Zn–Al–Ti–B shape memory alloys

Abstract The effect of post-quench aging in polycrystalline β Cu–Zn–Al and Cu–Zn–Al–Ti–B on the martensite stabilization has been studied. The samples were heat treated at 1073 K and subsequently quenched into water at 373 K. After the quench, the samples were aged in the β phase, 373 K≤ T ≤ 403 K, during 300 s ≤ t β ≤10 5 s. The stabilization tests were performed by applying compressive stresses at temperatures above the reverse transformation temperature, A f followed by martensite aging under constant strain. When unloading the sample, it recovers its original shape but the reverse transformation stress is shifted to lower values. The magnitude of the stress shift, a measure of martensite stabilization, is a function of the thermal treatment and aging time. The process continues until a saturation is reached. It was found that the stress shift saturation value depends on the temperature and the aging time in the β phase. The results show that the stabilization depends on the vacancy concentration and that dislocations can not be the dominating type of vacancy sinks in martensite.

Influence of Cd addition on the phase transformations of β Cu–Al alloys

Cu–Al alloys in the hyper- and hypoeutectoid region with addition of Cd are studied. The phase transformation sequence during continuous heating and cooling has been followed by resistometry, calorimetry, and optical microscopy.

Calorimetric Study of Avalanche Criticality in the Martensitic Phase Transition of Cu67.64Zn16.71Al15.65

The first-order diffusionless structural phase transition in Cu67.64Zn16.71Al15.65 is characterized by jerky propagation of phase front related to the appearance of avalanches. In this work we describe a full analysis of this avalanche behaviour using calorimetric heat-flux measurements and the results are compared with acoustic emission (AE) measurements.