Martensite-martensite pseudoelastic cycles in CuZnAl - a novel approach to superelasticity

FRANCO DE CASTRO BUBANI; FRANCISCO LOVEY; MARCOS SADE

Florianópolis

Congreso; XI Brazilian MRS Meeting; 2012

SBPMAT - Brazil MRS

The mechanical behaviour of CuZnAl shape-memory alloys is extremely complex and some of the physical phenomena associated with it are not completely understood. Particularly, the 18R-6R martensite-martensite transformation has not received much attention, as most studies focused on different aspects of the 18R phase or the beta-18R transformation. The 18R-6R transition shows a very high hysteresis and a slight dependence on temperature, making it suitable for applications. However, plastic deformation has been reported to coexist with the transformation. This plasticity can be inhibited by the introduction of nanoprecipitates. We have studied the superelastic properties of the 18R-6R transformation under repeated loading conditions (mechanical cycling) in single crystals with nanoprecipitates. At very low cycling frequencies, severe stress-strain cycle degeneration is observed due to 6R martensite stabilization. However, at frequencies above 10-1 Hz, it is possible to reach more than 2000 superelastic cycles with very high hysteresis and relatively little degeneration.  This behaviour is unique and might be beneficial to certain damping applications such as seismic engineering and satellite launches.