Non-uniform surface layer formation in ultrasonic shot peening of VT25U titanium alloy compressor blisk blades: Residual stress and microhardness analysis

Quality control of ultrasonic shot peening on complex aerodynamic surfaces is challenged by the inability of conventional point measurements to capture spatial treatment heterogeneity. This study develops and validates a sacrificial paint-based coverage assessment methodology for rapid quality evaluation on VT25U (Ti-6.5Al-2Mo-1.5Sn-1Zr-0.2Si) titanium alloy compressor blisk blades of the AI-450 gas turbine engine. Coverage was classified into three intensity levels via macrophotographic analysis; characterisation included incremental hole-drilling residual stress measurement at ten locations and Vickers microhardness testing at 27 points. Maximum compressive stresses of MPa at depths up to were recorded in high-intensity zones; suction side magnitudes exhibited a 41 % coefficient of variation. Microhardness increased by 35–45 % in optimally treated zones (515 HV to 521 HV versus 357 HV to 387 HV baseline), whilst edge regions demonstrated up to 20 % reduction. Statistically significant positive correlations between coverage intensity and microhardness ( – , ) validate the methodology as a reliable predictor of mechanical property distribution. The approach enables quality control inspection in approximately 15 minutes per component, compared to 4–6 h for comprehensive X-ray diffraction scanning.