Investigation and Analysis of Slip and Microstructural Deformation Behavior of Binary Tantalum-Tungsten Alloy During Rolling and Influence of Deformed Microstructure on Recrystallization Behavior During Annealing

다국어 초록 (Multilingual Abstract)

This dissertation presents a comprehensive study on the crystallographic orientation-dependent deformation and recrystallization behavior of Ta–10W alloys under extreme thermomechanical conditions. Through the integration of in-depth experimental characterization and computational modeling, five independent but thematically connected chapters explore the underlying mechanisms of non-Schmid plasticity, stored energy evolution, recrystallization kinetics, viscoplastic deformation, and texture-based design strategies in body-centered cubic (BCC) refractory metals. In Chapter 1, the non-Schmid plasticity effects of Ta–10W alloy are elucidated through a combination of uniaxial compression tests and crystal plasticity simulations. Unlike conventional FCC metals, the BCC Ta–10W alloy exhibits strong orientation- and temperature-dependent deviations from Schmid’s law. Experimental results showed a pronounced asymmetry in yield stress and slip system activation depending on the loading direction, especially at cryogenic temperatures. A modified constitutive framework incorporating non-glide stress components was developed and successfully reproduced the observed plastic anisotropy, confirming the critical role of non-Schmid effects in accurately predicting the mechanical response of BCC systems. Chapter 2 focuses on the orientation-dependent accumulation of stored energy and microstructural evolution during 80% cold rolling of Ta–10W sheets at room and cryogenic temperatures. EBSD-based metrics, including kernel average misorientation (KAM), grain orientation spread (GOS), grain average misorientation (GAM), and statistically estimated stored energy (SE), were used to quantify the deformation-induced microstructures. The analysis revealed that orientations along γ-fiber and Rotated Cube accumulated higher internal strains, while Cube-oriented grains exhibited low stored energy but distinctive grain boundary characteristics. Notably, cryogenic rolling promoted a higher degree of strain partitioning and dislocation accumulation, contributing to finer subgrain structures and heterogeneous energy storage across orientations. In Chapter 3, the recrystallization behavior of cold-rolled Ta–10W alloy was examined after annealing at multiple temperatures (1100–1500 °C). Grains were classified into six representative orientation types (Ori1–Ori6), and their recrystallization fraction and grain size evolution were quantitatively analyzed using EBSD and grain boundary misorientation-based segmentation. The results showed that Cube (Ori1) and near-γ (Ori6) grains exhibited the highest nucleation and growth contributions, especially under cryogenic rolling conditions, while α-fiber (Ori3) grains showed the lowest recrystallization tendency. The differences in behavior were attributed to a combination of stored energy magnitude, boundary configuration, and neighbor conditions. This chapter provides direct microstructural evidence for orientation-selective recrystallization pathways in BCC alloys. Chapter 4 employs a viscoplastic self-consistent (VPSC) polycrystal model to simulate the development of deformation texture and slip system activity during cold rolling of Ta–10W. The simulations reproduce the experimentally observed texture evolution and strain partitioning among differently oriented grains. VPSC predictions confirmed the dominant activation of {110}<111> and {112}<111> slip systems and explained the delayed rotation of certain orientations due to geometrical hardening and intergranular constraints. The modeling further highlighted the connection between slip system asymmetry and macroscopic texture development, especially under cryogenic deformation. These results strengthen the mechanistic understanding of crystallographic rotation and substructure evolution in severely deformed BCC alloys. In Chapter 5, insights from experimental and modeling studies are synthesized to propose a crystallographic strategy for microstructure optimization in Ta–10W alloys. By controlling deformation temperature and annealing conditions, the selective promotion of favorable orientations (such as Cube and near-γ) can enhance recrystallization kinetics and grain refinement. The study concludes that cryogenic rolling enables uniform and high dislocation storage across orientations, which, when followed by controlled annealing, results in a refined, recrystallized texture with improved mechanical uniformity. This orientation-engineering approach provides a viable path toward the design of next-generation high-temperature materials for nuclear, aerospace, and defense applications.

목차 (Table of Contents)

• I. CHAPTER1 1
• 1.1 Introduction 1
• 1.2 Experimental 4
• 1.3 Resutls & Discussion 8
• 1.4 Conclusion 30
• 1.5 Reference 32
• II. CHAPTER2 37
• 2.1 Introduction 37
• 2.2 Experimental Procedure 43
• 2.3 Microstructure Analysis 48
• 2.4 Results & Discussion 56
• 2.5 Conclusion 91
• 2.6 Reference 93
• III. CHAPTER3 102
• 3.1 Introduction 102
• 3.2 Experimental Procedure 106
• 3.3 Microstructure Analysis 110
• 3.4 Results & Discussion 118
• 3.5 Conclusion 145
• 3.6 Reference 147
• IV. CHAPTER4 157
• 4.1 Introduction 157
• 4.2 Experimental & Simulation Method 160
• 4.3 Results & Discussion 165
• 4.4 Conclusion 173
• 4.5 Reference 174
• V. CHAPTER5 178
• 5.1 Introduction 178
• 5.2 Experimental and Calculation Methos 181
• 5.3 Results & Discussion 187
• 5.4 Conclusion 201