Characterization on surface mechanical properties of Ti-6Al-4V after shot peening

The surface mechanical properties of Ti-6Al-4V after shot peening (SP) were investigated in this work. Firstly, the surface yield strength was obtained from the in-situ X-ray stress analysis method combined with the tensile test technique, and the value was increased to 1080 MPa, which was improved about 27% compared with the unpeened bulk material. It was ascribed to the surface work-hardening during the process of SP. Secondly, after SP, the hardness increased obviously and the compressive residual stress was introduced in the surface layer, which were beneficial to the surface properties of Ti-6Al-4V. Even so, the compressive residual stress was relaxed under cyclic loading. So thirdly, the relaxation of residual stress on the peened surface was studied under cyclic loading. The fast relaxation took place in the first few cycles then became stable gradually in further cycles. When the applied tensile stress was approaching to the yield strength, the relaxation was drastic and distinct. The behaviors of residual stress relaxation under different applied stresses were quantified by a function. The results indicated that the relaxation behavior was mainly influenced by the original magnitude, the applied stress and the cycling numbers. In view of all analysis, it can be found that t he method of combining in-situ X-ray stress analysis and the tensile test is an effective method to characterize the surface mechanical properties of metal materials after SP treatment.