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Chinese Journal of Aeronautics 25 (2012) 650-656 Contents lists available at ScienceDirect Chinese Journal of Aeronautics journal homepage: www.elsev /locate/cja Investigation of Surface Integrity on TC17 Titanium Alloy Treated by Square-spot Laser Shock Peening CAO Ziwen*, XU Haiying, ZOU Shikun, CHE Zhigang National Key Laboratory of Science and Technology on Power Beam Processes,Beijing Aeronautical Manufacturing Technology Research Institute, Beijing 100024, China Received 11 June 2011; revised 29 August 2011; accepted 7 October 2011 Abstract Laser shock peening (LSP) is an innovative surface treatment method, which has been shown to greatly improve the fatigue life of many metallic components. This work investigates surface integrity of TC17 titanium alloy treated by LSP with innova- tive square laser spot. Nd: glass laser with duration of 30 ns and spot size of 4 mm×4 mm is applied. The surface morphology and surface residual stress of the TC17 titanium alloy, treated with varying peening parameters such as laser power density and overlapping ratio, have been studied in detail. The results show that laser pulse energy greatly influences surface morphology and surface residual stress around single-spot treated areas, and compressive residual stresses are saturated as laser pulse energy is over 55 J. There are significantly different surface morphologies and residual stress distributions at the overlapped areas with different overlapping ratios. A relative smooth surface is produced with uniform compressive residual stress distribution at an overlapping ratio of 8 . The experiment of residual