Direct-Current-Assisted Healing for Functional Degradation of Nanocrystalline Superelastic NiTi Shape Memory Alloys

A direct-current-assisted (DC-assisted) healing method is proposed to deal with the functional degradation of nanocrystalline superelastic NiTi shape memory alloys. Based on microstructural observation, we clarify that DC-assisted healing is mainly attributable to the elimination of residual martensite and transformation-induced dislocations via Joule effect. The proposed healing strategy is suitable for nanocrystalline samples with small grain size (less than ~ 30 nm) and high initial dislocation density (~1 × 10 16 m −2 ), and the appropriate healing parameters are determined.