Caleb Yenusah: https://orcid.org/0000-0002-4926-6569
Mississippi State University
Stone, Tonya W.
Date of Degree
Dissertation - Open Access
Doctor of Philosophy (Ph.D)
James Worth Bagley College of Engineering
Department of Mechanical Engineering
The continual research and development of nickel-based superalloys is driven by the global demand to improve efficiency and reduce emissions in the aerospace and power generation industries. Integrated Computational Material Engineering (ICME) is a valuable tool for reducing the cost, time, and resources necessary for the development and optimization of the mechanical properties of materials. In this work, an ICME approach for understanding the microstructure development and optimizing the mechanical properties in nickel-based superalloys is employed. Most nickel-based superalloys are precipitate strengthened by either the γ’ phase, γ” phase, or both. Therefore, understanding the precipitation kinetics and morphological evolution of these phases is critical for evaluating their hardening effects during heat treatment and degradation of the microstructure during high temperature service. To this end, a phase-field model has been developed to analyze the nucleation, growth and coarsening kinetics during isothermal and non-isothermal aging conditions. Utilizing the phase-field model, the γ” phase microstructure development and its coherency strengthening effect in Inconel 625 is studied. A novel multistage aging strategy to optimize the γ” phase strengthening effect and reduce aging times for Inconel 625 is proposed. Secondly, the coarsening kinetic and microstructure development of γ’ strengthening phase in nickel-based superalloys is studied, with the goal of understanding the effect of elastic inhomogeneity on the microstructure evolution at high volume fractions of the γ’ phase. The result shows deviation of the coarsening kinetics from the classical Lifshitz-Slyozov-Wagner (LSW) due to the effect of elastic inhomogeneity, highlighting the need for incorporating elastic energy into coarsening theories.
Yenusah, Caleb O., "Phase-field simulations of the precipitation kinetics and microstructure development in nickel-based superalloys" (2022). Theses and Dissertations. 5506.