Altering the surface wettability of copper sheet using overlapping laser shock imprinting

Abstract Overlapping laser shock imprinting (LSI) is proposed to alter the surface wettability of copper sheet. By using a micro-die with rough concave texture, under the action of laser shock waves, multiscale surface microstructures can be accurately fabricated. The homogeneity of the micro-pattern array under different overlap rates were investigated. The radial expansion effect can reduce the inhomogeneity, but the shock pressure induced by the radial expansion effect in the non-irradiated area is weaker than that in laser irradiated area. Observed contact angle result is in accord with theoretical Cassie-Baxter mode, and it increases first and then tends to be stable when the number of laser pulse ranges from 2 to 6. Multiscale surface microstructures can be observed in 4 and 6 laser pulses cases. LSI can reduce the surface free energy by decreasing its polar component, and it sharply decreases first and then tends to be stable when the number of laser pulse ranges from 2 to 6. The grain size of protruding feature decreases with laser pulse numbers. And nano-scale grains are observed on the surface layer, which is caused by the material flowing on the rough surface of micro-die. The nano-indentation tests indicated that mechanical properties are enhanced.