Effects of water-guided laser surface strengthening on surface properties and fatigue life of TC4 titanium alloy in tension-tension fatigue tests

Abstract

In this study, we introduce a novel surface strengthening technique known as Water-Jet Guided Laser (WJGL) strengthening. This method is investigated for its impact on the surface properties of TC4 titanium alloy, highlighting its effectiveness in enhancing material performance and extending service life. WJGL strengthening influences material characteristics by adjusting jet velocity and laser overlap ratio.Surface roughness increases with higher jet velocities, and residual stress distribution is similarly affected. Specifically, at a 30 % overlap ratio, surface roughness values rise by 0.0562, 0.2551, and 0.6634 μm as jet velocity increases from 300 to 400 mm/s. Residual compressive stress initially increases with jet velocity, reaching peaks of 827.5, 1018.8, and 1003.3 MPa, before declining.The technique shows consistent effects on maximum residual compressive stress across various overlap ratios, with jet velocity being the primary factor affecting residual stress distribution. WJGL strengthening significantly improves high-cycle fatigue life and thermo-mechanical fatigue performance under tensile-tensile loading conditions. Higher jet velocities correlate with an increased number of cycles to failure in high-cycle fatigue testing. The fracture-prone area initially contracts and then expands, likely due to changes in residual stress.In thermo-mechanical fatigue tests, the central region exhibits a reduced lifespan, indicating a concentrated stress distribution. Fatigue cycle counts show a consistent pattern across different overlap ratios and jet velocities, with higher overlap ratios contributing to longer fatigue life.Compared to traditional techniques such as Water-Jet (WJ) and Laser Shock Peening (LSP), WJGL strengthening demonstrates superior performance and presents a promising approach for material enhancement.