Effect of ultrasonic shot peening on LCF behavior of the Ti-6Al-4V alloy

The effect of ultrasonic shot peening (USSP) was studied on microstructural modification in the surface region and low cycle fatigue (LCF) behavior of the Ti-6Al-4V alloy, at room temperature. Nanostructure of 17-25 nmwas developed in surface region of the alloy by USSP. Fatigue life of the USSPed samples was found to increase progressively with decrease in strain amplitude to much larger extent in comparison with those of the non-USSPed ones. Fatigue life of the USSPed sample was enhanced by four times at the lowest strain amplitude of +/- 0.60%. There was cyclic softening from the beginning until the failure, at the high strain amplitudes (Delta epsilon(t)/2 >= +/- 0.80%) whereas cyclic hardening was exhibited during the initial 100 cycles, followed by softening at the lower strain amplitudes (Delta epsilon(t)/2 >= +/- 0.70%). Deformation structure of the samples, tested at different strain amplitudes was analysed using TEM. The results are discussed in terms of increase in the resistance of the material against crack initiation due to grain refinement in the surface region and the associated compressive stresses induced from USSP. (C) 2017 Elsevier B.V. All rights reserved.