Change of Microstructure and Analysis of Fracture of the Ti-50.8 at.% Ni Alloy in the Ultrafine-Grained State after Multiple Martensitic Transformations with a Large Number of Cycles

The microstructure and mechanical properties of the ultrafine-grained Ti–50.8 at.% Ni alloy after thermal cycling treatment with the number of cycles up to 250 was investigated. A fractographic analysis of the samples after tensile tests was carried out. The fracture pattern of the alloy in the UFG state has a viscous character with microdepths on the fracture surface. The average size of microdepths decreases as the number of thermal cycles increases up to n= 250.