Date of Award

Fall 11-16-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials and Infrastructure Systems

First Advisor

Collin Wick

Abstract

A high-throughput parameterization of modified embedded atom model (MEAM) interatomic potentials for combinations of Cu, Ti, Ni, Cr, Co, Al, Fe, and Mn was carried out using a genetic algorithm. Unary systems were parameterized based on DFT calculations and experimental results. MEAM potentials for 28 binary and 56 ternary combinations of the elements were parameterized to DFT results that were carried out with semi-automated frameworks. Specific attention was made to reproduce properties that impact compositional segregation, material strength, and mechanics. Utilizing the MEAM interatomic potentials and a Monte Carlo scheme, phase segregation in the CrNiCo, CuNiCr and CuNiCo fcc alloys was investigated. It was shown that while CrNiCo remained single phase, CuNiCr and CuNiCo segregated to a considerable degree. Calculating the probability distribution of minimum energy structures demonstrated that the CuNiCr and CuNiCo had two sharp peaks including a Cu-poor hard phase and Cu-rich soft phase. This specific behavior of identified CCAs in phase segregation provides an extra pathway to tailor the mechanical properties of CCAs and predicting phase transformation from single phase to dual phase at high temperatures. The results of the new models were validated against CALPHAD predictions and experimental measurements. The effects of W content on phase segregation and the shear strength of CrNiCo were studied using a set of newly developed MEAM interatomic potentials. The models were fit to the physical and mechanical properties of unary, binary, and ternary systems to reproduce experiment and density functional theory results. Calculations showed that phase segregation occurred at 6-10% W content, consistent with experiment. For fully mixed systems, the simulations demonstrated that W content had little impact on the shear strength of crystals without dislocations. However, in the cases with a dislocation, a small amount of W significantly increased the shear strength in a similar manner as experiment. The presence of W was shown to cause dislocation pinning effects that hindered shear displacement. The CuNiCr alloy was observed to compositionally segregate into two fcc phases, one that was Cu rich soft phase, while the other was Cu poor hard phase. The soft phase was found to have lower shear strength than the hard phase by a modest degree for systems without dislocations present. When dislocations were introduced, the difference between the soft and hard phases was much greater. Simulations revealed that when the matrix is hard with a soft precipitate containing a dislocation, the shear strength is comparable to the fully mixed system with the same composition. In contrast, a soft matrix containing a dislocation with a hard precipitate enhances the system’s strength significantly in comparison to a fully mixed system with the same composition. These were found to be a consequence of the hard phase hindering dislocation movement. These observations align well with experimental data from literature.

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