No description available.

No description available.

Bulk metallic glasses and multi-principal element alloys represent relatively new classes of multi-component engineering materials designed for satisfying multiple functionalities simultaneously. Correlating the microstructure with mechanical behavior (at the microstructural length-scales) in these materials is key to understanding their performance. In this study, the structure evolution and nano-mechanical behavior of these two classes of materials was investigated with the objective of fundamental scientific understanding of their properties. The structure evolution, high temperature nano-mechanical behavior, and creep of two Zr-based alloys was studied: Zr41.2Ti13.8Cu12.5Ni10.0Be22 (Vitreloy1) and Zr52.5Ti5Cu17.9Ni14.6All0 (Vitreloy105). Devitrification was found to proceed via the formation of a metastable icosahedral phase with five-fold symmetry. The deformation mechanism changes from inhomogeneous or serrated flow to homogenous flow near 0.9Tg, where Tg is the glass transition temperature. The creep activation energy for Vitreloy1 and Vitreloy105 were 144 kJ/mol and 125 kJ/mol, respectively in the range of room temperature to 0.75Tg. The apparent activation energy increased drastically to 192 kJ/mol for Vitreloy1 and 215 kJ/mol for Vitreloy105 in the range of 0.9Tg to Tg, indicating a change in creep mechanism. Structure evolution in catalytic amorphous alloys, Pt57.5Cu14.7Ni5.3P22.5 and Pd43Cu27Ni10P20, was studied using 3D atom probe tomography and elemental segregation between different phases and the interface characteristics were identified. The structure evolution of three multi-principal element alloys were investigated namely CoCrNi, CoCrFeMnNi, and Al0.1CoCrFeNi. All three alloys formed a single-phase FCC structure in as-cast, cold worked and recrystallized state. No secondary phases precipitated after prolonged heat treatment or mechanical working. The multi-principal element alloys showed less strain gradient plasticity compared to pure metals like Ni during nano-indentation. This was attributed to the highly distorted lattice which resulted in lesser density of geometrically necessary dislocations (GNDs). Dislocation nucleation was studied by low load indentation along with the evaluation of activation volume and activation energy. This was done using a statistical approach of analyzing the "pop-in" load marking incipient plasticity. The strain rate sensitivity of nanocrystalline Al0.1CoCrFeNi alloy was determined by in situ compression of nano-pillars in a Pico-indenter. The nanocrystalline alloy demonstrated a yield strength of ~ 2.4 GPa, ten times greater than its coarse grained counterpart. The nanocrystalline alloy exhibited high strain rate sensitivity index of 0.043 and activation volume of 5b3 suggesting grain boundary dislocation nucleation.

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<p dir="ltr">Advancements in material science are accelerating technological evolution, driven by initiatives like the Materials Genome Project, which integrates computational and experi- mental strategies to expedite material discovery. In this work, we focus on the reliability of advanced materials under extreme conditions, a critical area for enhancing their technological applications.</p><p dir="ltr">Multi-principal component alloys (MPEAs) exhibit remarkable properties under extreme conditions. However, their vast compositional space makes a brute-force exploration of potential alloys prohibitive. We address this challenge by employing a Bayesian approach to explore the oxidation resistance of hundreds of alloys, applying computational techniques to accurately calculate and quantify errors in the melting temperatures of MPEAs, and investigating the compositional biases and short-range order in their nucleation behaviors.</p><p dir="ltr">Furthermore, we scrutinize the role of wide bandgap semiconductors, which are essential in high-power applications due to their superior breakdown voltage, drift velocity, and sheet charge density. The lack of lattice-matched substrates often results in strained films, which enhances piezoelectric effects crucial for device reliability. Our research advances the pre- diction of piezoelectric and dielectric responses as influenced by biaxial strain and doping in gallium nitride (GaN). Additionally, we delve into how various common defects affect the formation of trap states, significantly impacting the electronic properties of these materials. These studies offer significant advancements in understanding MPEAs and wide bandgap semiconductors under extreme conditions. We also provide foundational insights for developing robust and efficient materials essential for next-generation applications.</p>