Thermal relaxation of residual stresses in shot peened surface layer of (TiB + TiC)/Ti–6Al–4V composite at elevated temperatures

As an effective and important surface treatment method, shot peening can introduce high residual compressive stress and microstructure variation at near surface deformation layers. In this work, residual stresses relaxation behaviors of the shot peened layer of (TiB + TiC)/Ti–6Al–4V composite were investigated during thermal exposure, and the microstrain was calculated according to the integral breadth after isothermal annealing. The microstrain decreased fast and reached the minimum at 500 °C, which resulted from the thermal recovery and dynamic recrystallization. At elevated temperatures, the residual compressive stresses were relaxed in the whole deformation layers, which were caused by the thermally activated gliding of dislocations. The processes of relaxation can be described using a Zener–Wert–Avrami function and the activation energy of the residual stresses relaxation was higher than that of titanium self diffusion, which was ascribed to the hindrance effects of reinforcements as sink sources of dislocations during annealing.

► The residual stresses of shot peened samples are relaxed obviously after isothermal annealing.
► The processes of relaxation can be described using a Zener–Wert–Avrami function.
► The thermal relaxation process is caused by the thermally activated gliding of dislocations.
► The activation energy of relaxation is higher than that of both α-Ti and β-Ti self diffusion.
► The increment of activation energy is ascribed to the hindrance effects of reinforcements.