Thermal cycling effects in high temperature Cu-Al-Ni-Mn-B shape memory alloys

The effects of thermal cycling through the martensitic transformation have been studied in three Cu-Al-Ni-Mn-B high temperature shape memory alloys. An increase of the martensitic Transformation temperatures with the number of cycles (up to similar to 7 K after 60 cycles) has been generally observed by DSC measurements. The microstructure of these alloys is rather complicated, with the presence of big manganese or aluminum boride particles and small boron precipitates, as well as the formation of dislocations during thermal cycling. By means of aging experiments, it has been shown that the evolution of transformation temperatures during cycling is mainly due to the step-by-step aging in parent phase accompanying the thermal cycling, and that the dislocations formed during cycling have only a very small effect, at least up to 60 cycles.