Modeling in Laser Materials Processing: Melting, Alloying, Cladding
With the advent of high power lasers, the laser technology has taken an important place in the areas of manufacturing and materials processing. To utilize this technology in the economical and efficient ways, a proper understanding of the phase changes occurred during laser processing is required. Both theoretical and experimental studies are required to achieve this goal. This paper presents several mathematical models for various types of laser processing. Most of the laser processing involves the melting, vaporization, and solidification of materials. Due to the inherent rapid cooling rate, novel microstructures with metastable phases are produced during laser processing. Laser cladding is a technique to coat a substrate with a thick layer of other materials to improve the surface properties of the substrate. If the cladding powder is a mixture of more than one type of materials, the resulting coating is usually found to have metastable phases with nonequilibrium compositions. The solidification rate, which affects the composition of the nonequilibrium alloys, is obtained by solving the energy conservation equations in the melt, solidified clad, and substrate regions. Also, the mass transfer equation is solved to determine the distribution of solute atoms in the liquid and solid regions. Finally, the model is used to obtain the nonequilibrium phase diagrams for Ni-Al, Ni-Hf, and Nb-Al systems. The partition coefficient is found to be an important parameter for this model, and for this reason, an expression for the nonequilibrium partition coefficient for the concentrated binary systems is also presented in this paper.
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