Introduction of compressive residual stresses in Ti-6Al-4V simulated airfoils via laser shock processing

Ti-6Al-4V (Ti-64) simulated airfoils were laser shock processed with two laser power densities (4 and 9 GW/(2)) for each of three pulse repetition treatments (1, 3, and 5 shocks/spot). The microstructural effects of laser shock processing (LSP) on the Ti-64 were studied via scanning electron microscopy (SEM). Ultrasonic nondestructive inspection (NDI) was conducted to ensure that the LSP treatments resulted in no internal damage to the simulated airfoils. In-depth residual stress and cold work measurements were made using x-ray diffraction. No substantial changes due to LSP were found in the microstructure, and no internal damage was detected during NDI or metallographic sectioning. It was found that the in-depth residual stress and cold work states induced by LSP were a function of laser power density and pulse repetition. It was possible to induce compressive residual stresses in the direction most critical for the prevention of fatigue-crack growth throughout the thickness of the simulated airfoil leading edge.