Abstract: The performance of metallic materials in demanding and physiological environments is strongly influenced by their composition, microstructure, and phase stability. This work explores how chemical complexity and temperature-driven microstructural changes affect both corrosion behavior and deformation-induced phase transformation, with relevance to structural and biomedical applications.

The first part of this study examines the corrosion performance of two high-entropy alloys (HEAs), Fe₄₀.₄Ni₁₁.₃Mn₃₄.₈Al₇.₅Cr₆ with 1.1 at% carbon (CHEA) and Fe₄₂Mn₂₈Co₁₀Cr₁₅Si₅ (DP-5Si-HEA), as potential alternatives to conventional biomedical metals. Corrosion testing was conducted at room temperature and 40 °C in simulated physiological and acidic environments, including Ringer’s solution with lactate, sulfuric acid, and acetic acid. Surface morphology following exposure was analyzed using scanning electron microscopy. Results indicate that DP-5Si-HEA consistently exhibited lower corrosion rates and more stable surface passivation than CHEA, particularly under near-physiological conditions.

The second part of this work investigates how temperature influences the transformation of austenite to martensite in SS316L stainless steel during tensile deformation. Specimens were strained to fracture at −15, 0, 10, and 20 °C using a temperature-controlled experimental setup. Digital image correlation and thermal imaging were used to capture strain localization and thermal response at 0 °C and above. The results show that lower temperatures promote martensitic transformation, highlighting the importance of thermal conditions in controlling phase stability during deformation.

Together, these studies demonstrate how composition, microstructure, and temperature can be used as design variables to guide the development of alloys with improved mechanical performance and environmental resistance.

Thesis Committee: Ian Baker (Chair), Doug Van Citters, Will Scheidler