The effect of alpha-case formation on plastic deformation and fracture of near β titanium alloy

The paper studies the effect of oxidation on the plastic deformation and fracture of near beta titanium alloy Ti-5Al-5V-5Mo-1Cr-1Fe produced by radial shear rolling. It is shown that the aging of the rolled titanium alloy in ambient air at 550 degrees C for 3 h leads to the formation of an oxide (alpha-case) layer 1.5-2 mu m thick with a simultaneous decrease in the strength and ductility of oxidized specimens under tension at room temperature. The study of the gauge section surface and fracture behavior revealed that the reason for ductility reduction in alloy specimens with an oxide layer in tension is the development of surface microcracks, whose density and depth increase with strain. The growth of microcracks to a depth exceeding the alpha-case layer thickness causes brittle fracture. The strength decrease of alloy specimens with an alpha-case layer is caused by a decrease in the microhardness of the near-surface layer due to reduced V and Mo concentrations, which influences the solid solution hardening of titanium alloys, as well as by a change in the beta-phase decomposition kinetics due to oxygen diffusion.