TECHNICAL: A run of metal alloy of given bulk composition may be processed along any one of many pyrometallurgical pathways. Elemental composition may exhibit position dependence specific to the processing pathway; surface segregation by constituent elements is a long-standing example. Transport properties are sensitively affected by the structure of the elemental composition profile and therefore become dependent of processing history. The literature is filled with examples of widely varying numerical values for a given property, such as spectral emissivity and thermal diffusivity. This state of affair has persisted for two basic reasons: one, there has not been any robust development of a theoretical framework in mesoscopic scales that bridges the microscopic lattice-level analysis and the macroscopic thermo-chemical models; and two, there had not been any commensurate experimental methodologies for composition profile based characterization of thermophysical properties until now. The high-risk/high payoff and transformative project brings to the table a new measurement methodology and requisite instrumentation, which can provide measures of selected transport properties and local elemental composition simultaneously by time-resolved spectroscopy of laser-produced plasma (LPP) plume emissions. The project is supported by a body of evidence that the composition profiles of a given alloy specimen can be modified thermally in a reproducible manner; disparate thermal transport of constituent atoms can incur significant modifications of near-surface composition profiles. The goal of the project is to demonstrate that the modification is causal by characterizing the imposed thermal drive and examining the movement of the elemental composition profile by direct position-resolved measurement. Several different schedules of thermal cycling will be applied to the specimens and the composition profiles will be analyzed by the LPP methodology. The study will be focused initially on a nickel-chromium binary alloy. The project research has high risk in that the above-generalized picture of the ways an alloy responds to thermal cycling may not bear out over wider ranges of alloy systems. The primary system used in the study (low-melting point four-element Wood's alloy) as a model system could prove to be an exception, rather than a representative system for a wide class of alloys. We reason that use of simpler systems, such as two-element alloys, will be an effective approach to examine the potential uncertainty. NON-TECHNICAL: The phenomenon of near-surface composition anomaly suggests a potential for active modification of the alloy surface properties in a predictable manner by intentionally changing the alloy's near-surface composition. It may be to enhance material's corrosion resistance, scratch resistance or magnetic and electrical properties at material surfaces. Rigorous understanding of the relevant atom transport mechanisms will help formulate the predictive models to achieve these goals. The impact of such capability will provide a number of new development options to metals industries in the U.S. The broader impact will also be to help develop mesoscopic models of materials processing for functionality-specific alloys. The research once proven will have a transformative impact on the alloy design and processing fields; it will provide a basis for quantitative modeling. The investigation will also help produce a new generation of experts from the ranks of graduate students; during the one-year SGER project period a M.S. degree work will be completed. First-principle based understanding of the atom transport processes will be crucial to design of new materials and cost-effective management of materials utilization.
