Strain rate and temperature dependence on the constitutive behavior of advanced structural alloys for aerospace systems
Titanium alloys and Nickel-based superalloys are omnipresent in advanced aerospace and terrestrial systems due their combination of specific material properties (normalized by density) and superb performance at elevated temperatures. Although found in automotive, biomedical and sporting goods industries the materials high costs impede their widespread usage. When applicable, Additive Manufacturing (AM) technologies such as Electron Beam Melting (EBM) and Selective Laser Melting (SLM) could alleviate production costs by reducing the amount of raw material needed, machining processes and personnel. While the aerospace-grade structural materials market has been traditionally dominated by conventional alloys such as the above described High Entropy Alloys (HEAs) have emerged as potential candidates given their combination of excellent stability, high strength, corrosion and fatigue resistance. HEAs are loosely defined as alloys containing five or more principal elements, each with a concentration between 5-35 at. %. Notwithstanding its complex chemical arrangement, a multiplicity of reports in the open literature identified the formation of solid solution phases consisting, generally, of simple FCC and/or BCC crystal structures. The foundation of this doctoral dissertation lays at the intersection of material science and mechanical engineering. Is on the basis of the correlation between processing physical descriptors, materials structure and properties that an engineer can design an industry or application specific component with predictable performance. Consequently, this document summarizes a comprehensive investigation of the microstructural features (initial state and deformed) and first tier mechanical properties of current and potential aerospace-grade alloys, i.e., EBM Ti6Al4, SLM IN718 and as-cast HEAs. Particular emphasis was placed on documenting the high deformation rate (103-105 s-1) plastic response. The body of knowledge on quasi-static behavior (10-4-10-1 s-1) is vast, however, the scientific literature is, at most limited, in reporting mechanical properties on the high rate domain.