"The Influence of Composition on Modern High Temperature Alloy Design" 

Victoria Tucker, MSE PhD Candidate 

Advisor: Professor Micheal Titus

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ABSTRACT

The foundation of materials engineering lies in identifying and understanding the relationships between structure, properties, and performance. In metals, particularly in superalloys, a critical link exists between structure and properties— deformation mechanisms. It is well documented that these alloys change deformation mechanisms across temperatures and strain rates. At elevated temperatures, where diffusion occurs, solute segregation to planar faults can alter the active deformation mechanisms, with some elements and mechanisms accelerating deformation, while others enhance creep resistance. Only recently have we begun to comprehend how the underlying thermodynamics and kinetics of this phenomenon can be leveraged as a tool for alloy design. In this context, Haynes® 244® alloy stands out for its distinctiveness as a superalloy. The precipitate-matrix structure relationships and complex dislocation pathways in this alloy are so dominant that deformation twinning begins at the onset of deformation and remains the primary deformation mechanism across all tested temperatures and strain rates, prevailing over any other mechanism. As a result, this alloy's deformation mechanisms are not altered by diffusion or thermal energy. Instead, its unique structure—comprising a body-centered orthorhombic (BCO, 𝜸’’’) precipitate and a disordered face-centered cubic (FCC, 𝜸) matrix—leads to strain rate insensitivity at both room temperature and 649°C. Regardless of the microstructure, a high-temperature alloys efficacy depends on understanding its mechanical properties under specific temperatures and stresses, which are directly tied to the dominant deformation mechanisms. This work concludes by describing a novel testing technique developed to extract creep performance across vast temperature and stress ranges in a fraction of the time compared to traditional creep testing and electron microscopy.