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.

To understand how the substrate temperature influences the deposition rate and spatial profile of deposits formed using laser chemical vapor deposition (LCVD), spatially resolved multi-wavelength pyrometry measurements of the substrate temperature have been made during LCVD of titanium nitride (TiN) on Ti-6Al-4V substrates. The precursors that have been used are TiCl$sb4,$ N$sb2,$ and H$sb2.$ Also, deposition has been studied as a function of the N$sb2$:H$sb2$ gas ratio, the TiCl$sb4$ partial pressure, the total chamber pressure, and the laser power. Also, film thickness has been measured by stylus profilometry, and film composition and microstructure have been determined by Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES), and X-ray Photoelectron Spectroscopy (XPS). While the substrate temperature and the gas composition have the greatest influence on TiN film growth, H$sb2$ exerts the greatest influence on TiN film growth. Also, enhanced mass transport associated with localized laser beam heating has led to film growth rates on the order of 1 $mu$m/sec; however, there is still evidence of reactant depletion at the center of the laser heated spot. In addition to calculating film growth rates based on film height, two new methods of characterizing the film growth rate have been developed. Using these growth rates, three insights have been obtained. First, the film growth rates are 1-1/2 orders of magnitude greater than typical CVD deposition rates. Second, radial growth of the films continues after reactant depletion occurs at the center of the deposit. Third, comparison of the growth rates with LIF measurements supports the concept of a temperature-dependent sticking coefficient. Based on the experiments, reaction rate equations have been postulated as a function of N$sb2$/H$sb2$ gas ratio and TiCl$sb4$ partial pressure. Also, the apparent activation energy for deposition is 108.9 kJ/mol when one calculates the deposition rate based on film height. Using alternate definitions of film growth rates, the apparent activation energies are 65.2 and 81.4 kl/mol. The discrepancy in these activation energies has occurred because part of the measured film volume is actually TiCl$sb4$ rather than TiN.