Strengthened and hydrophobic surface of titanium alloy by femtosecond laser shock peening without a protective or sacrificial layer

Titanium alloys are widely used for aviation and other structural components. Their reliability pertains to their main economic value and safety characteristics under extreme conditions such as extremely high or low temperatures, high loads and complex liquid conditions. We applied femtosecond laser shock peening to collaboratively regulate the surface structure, element composition and functional properties including the residual stress, surface hardness and hydrophobic properties of Ti-6.5Al-2Zr-1Mo-1 V (TA15) alloy. The alloy's original tensile stress was converted into compressive stress, and its hardness increased by up to 20%. We also converted the alloy's hydrophilic surface, which has a contact angle of 70°, into tunable hydrophobic micro/nano structures with a maximum contact angle of 111° through one-step laser irradiation without chemical treatments. Different strengthening mechanism under low and high level of laser fluence were revealed. The comprehensive properties of the alloy could be adjusted by regulating the applied double-pulse delay, which was closely related to a laser-induced shockwave.