검색 상세

Influence of lightweight alloying elements on the microstructural evolution and thermodynamic complexity of powder metallurgy high-entropy alloys

  • 이한성 (Hansung Lee, 아주대학교 일반대학원)

초록/요약

High-entropy alloys (HEAs) are an innovative class of materials formed by alloying five or more elements in nearly equiatomic or similar proportions. This innovative approach surpasses traditional alloy paradigms, offering superior mechanical properties and unique features. HEAs are known for their flexible design and exceptional properties, including high strength and high-temperature stability, making them suitable for extreme environments and refractory applications. The four core effects of HEAs make differences compared to conventional alloys. To design these advanced materials, it is crucial to consider thermodynamic complexity and satisfy various thermodynamics. Despite these challenges, HEAs exhibit high specific strength, toughness, excellent high-temperature stability, fatigue resistance, and corrosion resistance, making them ideal for aerospace, nuclear fusion, and high-pressure turbine applications. This study aims to stably incorporate lightweight elements with distinct thermodynamic characteristics into HEAs based on thermodynamic complexity, using powder metallurgy (PM). By analyzing the microstructure and mechanical properties, the study seeks to elucidate the strengthening mechanisms and explore the effects of microstructural changes induced by the addition of lightweight elements. The research explores the thermodynamic complexity and examines how the addition of non-metallic silicon influences phase formation, lattice structure, and mixed bonding in FeCoNiAlSi system HEAs. The findings indicate that silicon addition leads to significant lattice distortion, changes in valence electron concentration (VEC), and mixed bonding effects, influencing the microstructural evolution from FCC + BCC to BCC/B2 phases. Mechanical properties vary with microstructure, showing increased hardness and strength but reduced fracture strain with higher Si content. The study identifies optimal compositions, such as FeCoNiAlSi0.2, which balances strength and ductility. In a parallel effort, the research investigates FeMnAlTiSiMg system ultra-lightweight HEAs to explore the effects of lightweight elements on specific strength. Results show that these alloys, fabricated via PM, achieve high specific strength (up to 480 MPa·m³/kg), comparable to conventional titanium alloys. The optimal composition, FeMnAlTiSiMg0.25, exhibits a refined BCC/B2 structure with enhanced mechanical properties due to grain refinement and maximized lattice distortion. Overall, this dissertation demonstrates the potential of HEAs designed with thermodynamic complexity and lightweight elements for use in extreme environments. The findings contribute to advancing the understanding of HEAs to enhance the mechanical properties of HEAs developed through PM.

more

목차

Chapter 1. Introduction 1
1. 1. Thermodynamic complexity for understanding high-entropy alloys 1
1. 2. Effect of lightweight elements on high-entropy alloys fabricated via powder metallurgy 4
Chapter 2. Research background 6
2. 1. High-entropy alloys 6
2. 1. 1. Definition 6
2. 1. 2. A different paradigm from conventional alloys 9
2. 1. 3. Four core effects 11
2. 1. 3. 1. High-Entropy Effect - Thermodynamics 12
2. 1. 3. 2. Severe Lattice Distortion - Structure 14
2. 1. 4. Thermodynamic complexity 22
2. 1. 5. Mechanical properties and application 28
2. 2. Alloying of lightweight elements in high-entropy alloys 30
2. 2. 1. Literature review 30
2. 2. 2. Author's previous studies 33
2. 2. 3. Challenges and difficulties 34
2. 3. Powder metallurgy process for high-entropy alloys 36
2. 3. 1. Mechanical alloying 36
2. 3. 2. Densification (Spark plasma sintering) 38
2. 3. 3. Advantages of applying PM process to HEAs fabricating 40
2. 4. Objective 43
2. 4. 1. Impact of adding lightweight and non-metallic bonded Si to high-entropy alloys 43
2. 4. 2. Designing high-entropy alloy with four lightweight elements to improve specific strength 45
Chapter 3. Effects of mixed atomic bonding on FeCoNiAlSi system lightweight high-entropy alloys 47
3. 1. Introduction 47
3. 2. Experimental procedure 49
3. 3. Results and discussion 56
3. 3. 1. Thermodynamic parameters of FeCoNiAlSi system HEAs 56
3. 3. 2. Phase predict using CALPHAD 59
3. 3. 3. Microstructure and phase transformation 62
3. 3. 4. Thermal properties 81
3. 3. 5. Magnetic properties 86
3. 3. 6. Mechanical properties 90
3. 3. 6. 1. Micro-Vickers hardness 90
3. 3. 6. 2. Compressive properties and fracture surface 92
3. 3. 6. 3. Strengthening mechanisms 96
3. 3. 6. 4. Wear behavior 103
3. 4. Conclusions 124
Chapter 4. Designing FeMnAlTiSiX system lightweight high-entropy alloys to improve specific strength 126
4. 1. Introduction 126
4. 2. Experimental procedure 130
4. 3. Results and discussion 134
4. 3. 1. FeMnAlTiSi0.75CuX (X = 0, 0.25, 0.5, 0.75, 1) HEAs 134
4. 3. 1. 1. Thermodynamic parameters 134
4. 3. 1. 2. MA of the HEA powders 137
4. 3. 1. 3. Microstructure of the densified HEAs 142
4. 3. 1. 4. Mechanical properties 151
4. 3. 2. FeMnAlTiSiMgX (X = 0, 0.25, 0.5, 0.75, 1) LW HEAs 166
4. 3. 2. 1. Thermodynamic complexity 166
4. 3. 2. 2. Microstructure evolution after addition of Mg 169
4. 3. 2. 3. Densities and mechanical properties 179
4. 3. 3. Comparison properties of previously studied HEAs and conventional alloys 187
4. 4. Conclusions 191
Chapter 5. Overall conclusions and future works 193
Acknowledgment - Korean 195
References 197

more
반출 Meta View 목록