Structure refinement of shape memory alloys under severe electroplastic rolling

It is shown that the deformability of Ti49.2Ni50.8 and Ti50.0Ni50.0 alloys rolled with pulse electric current is considerably greater than that obtained by cold rolling. The influence of true strain and current density on features of the microstructure was investigated. It was demonstrated that severe grain refinement to size of 60120 nm accompanies the electroplastic rolling process. At the same annealing temperature, the alloy with the initial martensitic structure has a larger grain size. These differences can probably be explained by the different recrystallization temperatures of deformed martensite and austenite. The intensity of strain hardening was compared for both alloys after electroplastic rolling (EPR). The reasons for the different behaviour in the EPR process are discussed.