Thesis Committee
Ian Baker, Ph.D. (Chair)
Harold Frost, Ph.D.
Jifeng Liu, Ph.D.

Abstract

Within the past few decades, high-temperature intermetallics have been extensively researched as structural materials for aerospace and automotive applications. Due to their corrosion resistance and strength retention at elevated temperatures, TiAl-based alloys are currently used in aircraft engines and turbine blades. However, such intermetallics are brittle at room-temperature. Therefore, developing advanced structural materials that can perform at both ambient and high temperatures is crucial. Fe30Ni20Mn35Al15, Fe29Ni19Mn38Al14, Fe36Ni18Mn33Al13 are lamellar two-phase alloys comprised of a hard, NiAl-rich B2 phase and a ductile, FeMn-rich f.c.c. phase. For this system, the room-temperature elongation to fracture drops by ~20% as the f.c.c. lamellae width (λ) decreases from 1 μm in Fe36Ni18Mn33Al13 to 500 nm in Fe30Ni20Mn35Al15. For the alloy containing the highest aluminum content (15 at. %), the ductility further decreases from 6.5 to 0.7% when tested at a slow strain rate (10-6 s-1).

The objective of the present project is to determine whether a slow strain rate affects the ductility of Fe36Ni18Mn33Al13 and to optimize its room-temperature and high-temperature mechanical performance through cold-working and various heat treatments. The microstructural transformations that occur upon thermo-mechanical processing (recovery and recrystallization) are then compared with similarly-processed Fe29Ni19Mn38Al14 and Fe30Ni20Mn35Al15. The resulting microstructures exhibit recrystallized, discrete f.c.c. and B2 grains that correspond to enhanced room-temperature strength and almost full restoration of the as-cast alloys’ ductility.