Study of the Evolution of the Structure and Kinetics of Martensitic Transformations in a Titanium Nickelide upon Isothermal Annealing after Hot Helical Rolling

Abstract

Differential scanning calorimetry has been used to study the effect of the temperature and holding time upon isothermal annealing on the calorimetric effects of the martensitic transformations (MTs) of an aging Ti–50.7 at % Ni alloy produced by hot helical rolling at a temperature of 850–900°С with subsequent cooling in air. The sequence of the phase transitions upon reverse MT has been determined using X-ray diffractometry. The regularities of the evolution of the characteristic temperatures of martensitic transformations after annealing at temperatures of 400, 430, and 450°С for 1–10 h have been analyzed. The results of electron-microscopic studies of the structure of the alloy in the initial state and after annealing have been presented; the features of the morphology of the Ti₃Ni₄ phase precipitated upon aging have been analyzed. Based on the results of calorimetric and structural studies, the temperature of the highest intensity of the aging processes has been determined.