Effect of HIP and Laser Shock Peening Sequence on the Fatigue Behavior of Laser Powder Bed Fused Ti6Al4V

Abstract The fatigue performance of laser powder bed fused Ti-6Al-4V is influenced by process-induced defects, surface condition and the stress state generated by manufacturing and post-processing. This study examined whether reversing the order of hot isostatic pressing (HIP) and laser shock peening (LSP) altered the fatigue response of a deliberately defect-rich LPBF condition. Specimens were subjected to LSP followed by HIP or HIP followed by LSP. X-ray computed tomography was used to quantify the internal defect populations, stress-life testing was conducted between 210 and 380 MPa at R = 0 and 50 Hz, and scanning electron microscopy was used to examine post-test surface features associated with crack initiation. The two hybrid routes exhibited similar defect counts and mean sphericity values, while the HIP + LSP condition contained the largest measured defect and the greatest detected defect volume. Nevertheless, HIP + LSP produced the stronger fatigue response, including two right-censored run-outs at 10 6 cycles, compared with no run-outs for LSP + HIP. The CT descriptors therefore did not account for the observed sequence effect. The results are consistent with, but do not directly prove, the hypothesis that applying LSP after HIP preserves the beneficial final surface state generated by peening, whereas subsequent HIP exposure may modify or relax part of that state. Because residual stress was not measured, this mechanism is presented as a literature-supported interpretation rather than a measured causal relationship. The findings demonstrate that post-processing order can influence fatigue performance even when conventional CT defect metrics do not indicate a superior internal defect population.