The effect of phase transformations on the recovery of pulsed electron beam irradiated Ti-6Al-4V titanium alloy during scratching

The formation of martensitic α′ and α′′ phases in Ti-6Al-4V titanium alloy subjected to low energy high current pulsed electron beam (LEHCPEB)treatment with an energy density of 12–25 J/cm ² was revealed by X-ray diffraction and transmission electron microscopy. It was substantiated that the strain-induced phase transformation is the dominant mechanism underlying the deformation behavior of the melted surface layer of the titanium alloy samples during nanoindentation and scratch testing. It was found that the reverse transformation of the α′′ phase into the more close-packed α phase is responsible for the softening of the uppermost surface layer of the samples subjected to LEHCPEB treatment. The development of the direct and reverse α′′→α→α′′ martensitic transformations in the uppermost surface layer resulted in the improvement in elastic recovery of the treated Ti-6Al-4V samples after scratching.