A Diffusion Multiple Approach for the Accelerated Design of Structural Materials
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A Diffusion Multiple
Approach for the Accelerated Design of Structural Materials
Ji-Cheng Zhao, Melvin R. Jackson, Louis A. Peluso, and Luke N. Brewer Abstract A diffusion multiple is an assembly of three or more different metal blocks, in intimate interfacial contact, that is subjected to a high temperature to allow thermal interdiffusion. The power of using a diffusion multiple approach in the efficient mapping of phase diagrams and materials properties for multicomponent alloy systems is illustrated in this article using several examples. It is now possible to map phase diagrams and materials properties at an efficiency some 3 orders of magnitude higher than the conventional one-alloy-at-a-time approach. With this high efficiency, many critical materials data that otherwise would be too time-consuming and expensive to acquire can be obtained and employed to accelerate our understanding of a system’s materials physics and chemistry. It is postulated that coupling the diffusion multiple approach with the CALPHAD (calculation of phase diagrams) method will have a significant impact on the computational design of materials. Keywords: combinatorial methods, diffusion, elastic properties, mechanical properties, nanoindentation, phase equilibria, structural materials.
Introduction Structural alloys usually consist of several alloying elements and multiple phases in order to simultaneously achieve and balance several properties such as strength, ductility, modulus, fatigue resistance, and environmental resistance. The fundamental questions facing alloy designers are (1) which elements will be most effective for strengthening, (2) how can the precipitation of desirable phases be induced to strengthen the alloy while avoiding the formation of detrimental phases, and (3) how stable will the precipitates and microstructure be against coarsening and long-term exposure? Addressing these questions requires information such as phase diagrams, solutionhardening effects, and kinetic data. As more advanced alloys are required for more de-
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manding applications, alloy developers are resorting to the addition of more alloying elements to achieve the required properties. For instance, advanced Nibased superalloys have 8–11 elements. As the number of elements increases, the amount of information required to predict the phases and properties of a multicomponent alloy also rapidly increases. The traditional one-alloy-at-a-time approach for measuring phase diagrams and composition–property relationships is too slow for the alloy development process. The desire for rapid mapping of phase diagrams and materials properties dates back a long way. A brief history can be found in the introductory article in this issue of MRS Bulletin. Metallurgists have
been using diffusion couples for more than a century to evaluate diffusion coefficients and phase diagrams by taking advantage of the local equilibrium at the phase interfaces. However, the composition variations generated in the diffusion couples were generally not exploited. Part of
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