Stressed State of the Surface Layer of VT6 Titanium Alloy after Copper and Lead Ion Implantation

Background/Objectives: The article describes the results of the experimental measurement of the level of residual stresses in the surface layer of VT6 titanium alloy after ion implantation using polyion beams. Methods/Statistical Analysis: To study the effect of ion implantation on the residual stresses in the surface layer of VT6 titanium alloy, flat sheet samples of 1 mm thick and 10 mm wide were used. Before implantation the samples were annealed in a vacuum furnace to relieve stresses which arose during sheet rolling. The annealing temperature was 750 °C. Cathodes of copper, Cu-Pb monotectic alloy, and monotectic alloy with additional contact doping with tin were used. Findings: As a result of ion implantation in the studied range of doses of irradiation of VT6 titanium alloy, microstructure of its surface layer substantially hardens due to breakage of the particle size and the increase in the dislocation density. After implantation, it was managed to achieve the thickness of the modified layer comprising the actual implanted layer and the layer with changed dislocation structure of about 60...100 microns with an average size of nanoparticles near the surface of 50...100 nm. The dislocation density as a result of plastic deformation reached the values of ρD ≈ (2,7…9,8)·1012 (cm^-2) at the initial value ρDinit ≈ 5·1011 (cm^-2). The regularity of the increase in the residual compressive stresses at the increase in the implantation dose to 5·1017 ion/cm², and then with a further increase of the implantation dose, the residual stresses decrease. In general, the depth of occurence of the residual stresses slightly exceeds the depth of the implanted layer. Applications/Improvements: It is shown that by using beams with two and more ion kinds, residual stresses in the surface layer of VT6 titanium alloy increase.