Features of Changes in the Surface Structure and Phase Composition of the of α + β Titanium Alloy after Electromechanical and Thermal Treatment

Abstract

Changes of structure, phase composition and microhardness in high-strength α + β titanium alloy were investigated after electromechanical treatment (EMT) and subsequent aging. The EMT was performed with alternating current density (j of 300 and 600 A/mm2). The aging was performed upon heating at 600 °C and exposure for 14 h. Methods of scanning electron microscopy, X-ray phase structure, micro X-ray spectral and durometric analyses were used. Modified layers (up to 200–250 µm in depth) on the surface of α + β titanium alloy were formed due to intensive thermo-deformation during the EMT and the following aging. The structure of the surface layer was characterized by high dispersivity (with particle sizes of about 30–500 nm), significant concentration heterogeneity (due to redistribution of the alloying elements and changes in the volume ratio of α- and β-phases), distortions in the crystal structure, increased levels of microstrain and microstress (2–2.5 times as compared to the initial) and increases in microhardness (by 30–40%).