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TY  - THES
AU  - Wu, Chengguang
TI  - Role of interstitial atoms in microstructures and mechanical properties of TiNbZr and TiNbZrHfTa complex concentrated alloys
PB  - Rheinisch-Westfälische Technische Hochschule Aachen
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2025-06056
SP  - 1 Online-Ressource : Illustrationen
PY  - 2025
N1  - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University
N1  - Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2025
AB  - To address the growing global demand for transportation and energy, the development of more efficient turbine engines and power generators capable of operating at higher temperatures and tolerating extreme conditions (e.g., H2 exposure) is essential. Over the past decade, refractory complex concentrated alloys (RCCAs), consisting of three or more transition elements from groups IV, V, and VI, have emerged as promising materials due to the vast compositional versatility and superior mechanical properties at elevated temperatures compared to the conventional refractory alloys. However, the brittleness of RCCAs at room temperature significantly limits their practical applications. Recent findings indicate that interstitial elements contribute to the brittle behavior of RCCAs at ambient conditions. Moreover, the strong affinities between interstitials and refractory elements underscore the influence of these small atoms on microstructure and phase stability, which, in turn, alter macroscopic mechanical performances. This thesis seeks to offer an in-depth understanding of the interplay between interstitial atoms (especially H) and RCCAs, focusing on their effects on microstructure, phase stability, and consequent mechanical properties, to advance the design of RCCAs with optimized performance under extreme conditions: (1) Hydrogen Accommodation in TiNbZr RCCA: In-situ synchrotron high-energy X-ray diffraction combined with density functional theory reveal hydrogen-induced lattice expansion (holding at 500 °C) and transformation (body-centered cubic to body-centered tetragonal cubic structure upon cooling) in a TiNbZr RCCA. Hydrogen prefers to accommodate at tetrahedral sites, while the ordered distribution of hydrogen solutes results in the occurrence of tetragonality. (2) Hydrogen-Assisted Spinodal Decomposition: In a TiNbZrHfTa RCCA, hydrogen modulates nanoscale spinodal decomposition, creating chemical fluctuations and enhancing hardness. A thermodynamic model demonstrates the role of hydrogen in destabilizing single-phase structures, enabling novel microstructure tailoring strategies. (3) Boron Effects on Grain Boundary Chemistry: Boron segregation alters grain boundary chemistry in a TiNbZrHfTa RCCA, reducing yield strength and enabling grain boundary shear localization. Enhanced slip transfers upon boron doping highlight the role of segregation engineering in optimizing mechanical performance. (4) Ductilization via Oxygen-Induced Nanoscale Chemical Heterogeneity: The incorporation of oxygen interstitials in a TiNbZr RCCA induces the formation of nanoscale chemical heterogeneity, characterized by Ti concentration fluctuations. The presence of Ti-enriched regions strongly pins dislocation, resulting in an increase in strain-hardening rate and strain rate sensitivity, accompanied by the refinement of deformation bands. These microstructural characteristics collectively contribute to improved ductility while preserving yield strength, offering a promising strategy for overcoming the strength-ductility trade-off in RCCAs. These findings highlight the critical role of interstitial atoms in influencing microstructure and phase stability, ultimately shaping macroscopic mechanical performance, and providing a foundation for designing RCCAs with tailored properties for demanding applications.
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2025-06056
UR  - https://publications.rwth-aachen.de/record/1014386
ER  -