Laser Processing: Surface Treatment and Film Deposition

Synthesis of nonequilibrium metallic phases has been an area of great interest to the materials processing community since early 1960. Inherent rapid cooling rates in laser processing are being used to engineer non-equilibrium microstructures which cannot be rivaled by other processes. This lecture will discuss the phenomena involved and its application in designing materials with tailored properties. What is non-equilibrium Synthesis? This is a synthesis method to produce binary or higher order materials where kinetics of the pro­ cess affects the transport of the constituent elements during phase transformation resulting in a composition or crystallographic configuration which is different from what is observed when the elements arranges themselves with the lowest possible Gibbs Free energy, which is the equilibrium condition. Figure 1 illustrates the phenomena. Phase diagram under equilibrium condition is illustrated by the solid line whereas the no-equilibrium phase diagram is represented by the dotted line. One can observe the shrinkage of the phase field under non-equilibrium condition. Any alloy composition between the solidus lines of the equilibrium and non-equilibrium phase diagram will be a non­ equilibrium alloys with extended solid solution.