Effect of biaxial cyclic severe deformation on structure and properties of Ti-Ni alloys

In this work, biaxial cyclic severe deformation of Ti-50.0 at.% Ni shape memory alloy was performed using MaxStrain module of Gleeble system at 250 degrees C with ultimately high accumulated true strain of e = 11. The martensitic transformations, structure and crystallographic texture features were studied using DSC, X-ray diffractometry, and TEM from three mutually perpendicular sides. The maximum completely recoverable strain was determined by a thermomechanical method, and the hardness was measured. A true nanocrystalline structure with grain/subgrain size of 50 nm has been formed in bulk Ti-Ni samples for the first time. The resulting structure is crystallographically isotropic and provides the completely recoverable strain of 9.6% that exceeds the best result attained for bulk equiatomic Ti-Ni alloys. The texture factor in a combination with the structure factor contribute to the completely recoverable strain only until accumulated strain reaches e = 9.5 at higher deformation temperatures. (C) 2019 Elsevier B.V. All rights reserved.