Melt instabilities during laser surface alloying

The depth of the melt layer during laser surface alloying plays a significant role in the shape of the melt pool. There appear to be critical depths at which the molten layer becomes unstable and alters its shape in response to convective flow patterns. The Marangoni number provides an understanding of the influence of the material properties on convection and subsequently the melt shape, being inversely proportional to depth squared, viscosity, and thermal diffusivity, and directly proportional to the surface tension gradient. The laser processing parameters affect the melt shape through their influence on depth. The current research sought to influence the Marangoni flow and control the shape of the melt pool using a rectangular beam. (C) 2002 Laser Institute of America.