Yong W. Kim

By Ryan P. Cress and Yong W. Kim

The great majority of metallic alloys in use are disordered. The material property of a disordered alloy changes on exposure to thermal, chemical, or mechanical forcing; the changes are often irreversible. We present a new first principle method for modeling disordered metallic alloys suitable for predicting how the morphology, strength, and transport property would evolve under arbitrary forcing conditions. Such a predictive capability is critically important in designing new alloys for applications, such as in new-generation fission and fusion reactors, where unrelenting harsh thermal loading conditions exist. The protocol is developed for constructing a coarse-grained model that can be specialized for the evolution of thermophysical properties of an arbitrary disordered alloy under thermal, stress, nuclear, or chemical forcing scenarios. We model a disordered binary alloy as a randomly close-packed (RCP) assembly of constituent atoms at given composition. As such, a disordered alloy specimen is an admixture of nanocrystallites and glassy matter. For the present purpose, we first assert that interatomic interactions are by repulsion only, but the contributions from the attractive part of the interaction are restored by treating the nanocrystallites as nanoscale pieces of a single crystalline solid composed of the same constituent atoms. Implementation of the protocol is discussed for heating of disordered metals, and results are compared to the known melting point data.

Part of the book: Progress in Metallic Alloys

By Eric R. Kaiser and Yong W. Kim

Structural disorder is ubiquitous for a large class of metallic alloys. Such an alloy’s transport properties are highly susceptible to change when the disorder is modified. A first-principle method has been developed for modeling of disorders in metallic alloys. In this approach, an alloy specimen is regarded as a randomly close-packed mixture of a population of nanocrystallites and constituent atoms in glassy state. The disorder is then represented by the size distribution function of the nanocrystallites. Under sustained exposure to thermal, stress, nuclear or chemical forcing at an elevated temperature, the distribution function becomes modified, and this process is predictable for a given forcing condition, and thus controllable. Transport of excitations is affected by the detail of the distribution function, making it possible to control transport properties, all at a fixed alloy composition. The modeling and experimental support will be presented.

Part of the book: Thermophysical Properties of Complex Materials

By Yong W. Kim

The great majority of metallic materials in use are not single crystals but disordered. We model such a material specimen as being composed of nanoclusters, each cluster being a small mutually interacting cluster of atoms. In this modeling, a material specimen is then treated as a mixture of nanocrystalline and glassy-state atoms. If we define the degree of crystallinity of the object by the probability that an atom is a member of a crystallite existing within the specimen, the probability would be smaller than unity. Structural disorder in such metallic alloys affects thermophysical properties of the alloy specimen in myriad ways. Transport properties in turn impact material utilization in significant ways to the extent that the specimen could behave as possessing completely different alloy properties. This approach to changing alloy properties can serve useful purposes. We show how one might approach such modification of alloy properties without changing alloy composition with a sample of copper-nickel alloy.

Part of the book: Copper