Realistic simulations reveal atomic-scale details responsible for superalloy properties
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Realistic simulations reveal atomic-scale details responsible for superalloy properties
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recent study of nickel-aluminum superalloys has given researchers their first glimpse of the atomic-scale details responsible for the phenomenal properties of superalloys. By performing molecular dynamics simulations based on realistic, experimentally informed structures, the researchers were able to observe the interactions of defects and precipitate phases in nickel-aluminum superalloys under stress. The results will help inform efforts to make increasingly high-temperature superalloys with less dependence on strategic elements like rhenium. Superalloys are of tremendous industrial importance. Found in the blades of all gas turbines for airplane engines and power plants, single crystal nickel-base superalloys provide excellent mechanical strength and stability at high temperatures. In these materials, precipitate impurity phases impede the movement of dislocation defects, which tend to be responsible for plasticity. These interactions have not yet been observed experimentally, however, which fundamentally limits an understanding of superalloys and hinders the ability to engineer evergreater superalloys. Now, a team of researchers have illuminated some of the critical atomicscale details of superalloys through atomistic simulations. The team, hailing from Friedrich-Alexander-Universität Erlangen-Nürnberg, The Ohio State University, and the Max-PlanckInstitut für Eisenforschung, published their findings in the June 15 issue of Acta Materialia (DOI: 10.1016/j.actamat.2015.03.050; p. 33). “This was the first time someone has taken experimental microstructures, put them in a computer, and simulated what happens in this process of dislocation/ precipitate interaction, which is one of the most important strengthening mechanisms in these superalloys,” says Erik Bitzek, lead author of the study. “We did all this at high temperatures and could
Superalloy simulations provide an unprecedented view into the interactions of dislocations and precipitates in these technologically critical materials. Credit: Acta Materialia.
directly observe a lot of processes which had been postulated before on the basis of individual post-mortem [transmission electron] micrographs,” says Bitzek. Up until now, simulations have been limited to quasi-two dimensions with idealized configurations. These have yielded insight and valuable quantitative information, but the studies are fundamentally limited. Here, the researchers made two important advances: simulating the system in three dimensions, and starting from realistic structures determined through atom probe tomography. Bitzek and colleagues initiated their simulations with morphologies acquired through atom probe tomography of superalloy specimens that were first subjected to heat cycles to simulate aging. From these data, the researchers extracted information about the boundaries between the matrix phase (γ) and the precipitate phase (γ'). Having determined the shape and location of those boundaries
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