Melt flow and ripple formation induced by continuous wave laser irradiating of copper foil at 10 Pa

Abstract

Continuous wave laser (CW laser) ablation morphology of copper foil in low pressure environment is very different from that in atmospheric environment. In low pressure environment, there are few splashes on the surface of molten region. Ring ripples are also observed on the surfaces of molten region after laser irradiation. A 2D axisymmetric model considering temperature dependent surface tension and condensation coefficient is established to investigate the molten flow behavior in molten pool during laser ablation in the environment of 10 Pa. The results show that Marangoni effect caused by temperature gradient is the main driver of fluid flow during laser irradiation. Ring ripples are formed by Marangoni effect and capillary force during cooling process. Compared with those in atmospheric environment, the recoil pressure in 101 Pa environment is smaller and the evaporation rate is higher at the same temperature. For foils with different thicknesses, the differences in temperature gradient make the distribution of ripples different. The mechanisms of the ripple formation on metal foil induced by CW laser irradiation are revealed for the first time.