The influence of Soret and Dufour cross-effects on laser surface treatment of metal accompanied by solid-phase chemical reaction

Abstract

The paper presents a mathematical model of the process of heat treatment of surface of solid material by short thermal impulse, corresponding to laser developed in the line. The absorption and reflection of the laser beam according to the Lambert-Bouguer law, the Soret and Dufour cross effects, which appear due to high temperature and concentration gradients, and possible chemical transformations due to impurity diffusion into the material, are taken into account. The dimensionless variables are used for the problem solution. The temperature and concentration fields in solid materials are calculated analytically and numerically. For analytical solution, Laplace transform method is used. Numerically, the problem is solved using finite differences method. For the first time in such a problem, both possible chemical transformations and cross effects are simultaneously taken into account. It is found that, in the region of the high temperature and composition gradients, the Soret and Dufour effects lead to a decrease in temperature near the surface and a decrease in concentration at a certain distance from the surface both during heating and after the termination of the pulse. In the case of an exothermic reaction that converts a reactant into a product, cross effects lead to an increase in the concentration of the reaction product in the heated zone outside the region with the high concentration gradient.