Atomistic Studies of Concentrated Multicomponent Nickel-Based Alloys Utilizing Atom-Probe Tomography and Vacancy-Mediated Lattice Kinetic Monte Carlo Simulations

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Non-Technical AbstractThis research program is focused on how phase separation occurs in nickel-aluminum based alloys, which are the physical bases of all nickel-based superalloys and which may contain up to 12 different alloying elements, with each element serving a particular purpose. Nickel-based superalloys are utilized for turbine blades and disks, which are at the heart of both military and commercial jet engines as well as natural gas-fired turbine engines that produce electricity, and which operate at extremely elevated temperatures. To study these materials at an atomic scale in this technologically important class of alloys, extensive utilization will be made of the Northwestern University Center for Atom-Probe Tomography. Atom-Probe Tomography is a unique technique that allows characterizing materials at the sub-nano to nanoscale. Applying this technique to nickel-aluminum based alloys will allow understanding the development of the final microstructure, which is of great significance and technological importance for controlling the physical and mechanical properties of a material at microscopic and macroscopic length scales. This work will help train the next generation of materials scientists in this state of the art technique. Technical AbstractThe kinetic pathways in the different stages of alloy phase separation (nucleation, growth and coarsening) of concentrated multicomponent nickel-based supersaturated solid-solutions are critical for understanding the development of the final microstructure, which is of great significance and technological importance for controlling the physical and mechanical properties of a material at microscopic and macroscopic length scales. To study the temporal evolution of phase separation, the PI will perform correlative experiments utilizing ultraviolet laser-assisted atom-probe tomography (APT) and vacancy-mediated lattice-kinetic Monte Carlo (LKMC) simulations, which permit understanding this evolution on an atomic scale. This work will also employ microhardness measurements and transmission electron microscopy experiments. The temporal evolution is studied starting with the clustering of atoms to form embryos exhibiting short-range order (SRO), which are the precursors of stable nuclei (precipitates); thus, allowing study of SRO and then precipitates with long-range order (LRO) and observation of growth and coarsening. All of the 10 plus physical parameters, for describing the temporal evolution, are measured via APT and simulated via LKMC simulations. Additionally, the PI will study the evolution during the quasi-steady coarsening regime and compare these results with the Philippe-Voorhees (P-V) mean-field modeling of multicomponent alloys (2013) for selected ternary and quaternary nickel-based alloys, which involves the use of both thermodynamic and mobility data bases. This will yield a realistic approach to quasi-stationary coarsening of a polydispersed distribution of precipitates embedded in a matrix. This multipronged experimental and simulation approach yields information at the atomic scale through the continuum length scale.