Rapid melting and solidification of a surface layer

A one-dimensional computer heat flow model is used to investigate the effect of high intensity heat fluxes,e.g. those achieved via continuous CO2 laser radiation, on the important surface layer melting and subsequent solidification variables of three substrate materials: aluminum, iron, and nickel. Temperature profilesvs time, melting, and solidification interface velocities, heating, and cooling rates in the surface layers of the three metals are calculated. Results are presented in a general form to permit determination of these variables for large ranges of absorbed heat fluxes and times. General trends established show that temperature gradients in the liquid and solid phases and interface velocities are directly proportional to the absorbed heat flux, whereas melt depth is inversely proportional to the absorbed heat flux. Average cooling rates comparable to splat cooling can be achieved by increasing the heat flux and reducing the dwell time of the incident radiation. An order of magnitude increase in the absorbed heat flux results in a corresponding two orders of magnitude increase in average cooling rates in the liquid during solidification of crystalline and noncrystalline structures.