Microstructural evolution of martensite during deformation in Zr50Cu50 shape memory alloy

The microstructural evolution of deformed martensite in the Zr50Cu50 shape memory alloy was studied by transmission electron microscopy (TEM) and the deformation mechanism was finally clarified. Before deformation, the intervariants in the Zr50Cu50 alloy showed a (021) type I twinrelationship, and the dominant substructures inside the martensite variant were (001) compound twins. Distinct deformation mechanisms were observed at different deformation stages. Detwinning of the (001) compound twins was the dominant mechanism during the primary stage. As the compressive strain increased, the detwinning zone expanded, but did not result in complete detwinning. At higher strain levels, stress induced the formation of many (021) and (201¯) nanoscale deformation twins, originating from 1/10<012> partial dislocations; this was considered to be the dominant deformation mechanism. The irrecoverable strain was closely associated with crossed (021) and (201¯) deformation twins that limited the mobility of martensite during heating.

The deformation of martensite in Zr50Cu50 alloys has been systematically studied. The compressive deformation mechanisms involve the detwinning of (001) compound twins and the forming of deformation twins. With increasing deformation strains, different deformation mechanisms become active. The detwinning of (001) compound twins exist at every strain level and do not progress completely. As the deformation strain increases, profuse nanoscale deformation twins ((021) twins and (201¯)) with a tower shape originate from partial dislocations emissions by steps at the twin interface or the intersection of two set active deformation twins. The (021) deformation micro-twins or stacking faults are responsible for the accommodation plastic deformation in Zr50Cu50 alloys.230