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Title page
Abstract
Contents
Chapter I. General Introduction 8
1. Introduction 8
2. Trends in technology 9
3. Research objectives 14
Reference 16
Chapter II. Theoretical Background 17
1. History of dispersion strengthened Al alloys 17
2. Rapid solidification 23
2.1 Melt spinning 27
2.2 Gas atomization 28
2.3 Spray forming 29
3. Consolidation 30
4. Strengthening mechanisms in dispersion strengthened Al alloys 32
4.1 Solid solution hardening 32
4.2 Grain boundary and sub-grain boundaries strengthening 32
4.3 Particle strengthening 33
5. Amorphous Al based alloys 41
Reference 43
Chapter III. Microstructure and Mechanical Properties of Al-Fe-TM Based Alloys Produced by Melt Spinning and Hot Extrusion Process 46
1. Introduction 46
2. Experimental procedure 47
3. Results and discussion 52
3.1 Microstructure of melt spun ribbons 52
3.2 Microstructure of extruded Al-Fe-TM based bulk alloys 59
3.3 Phase analysis 66
3.4 Mechanical properties 72
4. Summary 79
Reference 81
Chapter IV. Microstructure Control of the Al-8Fe-TM Based Bulk Alloys Produced by Various Rapid Solidification Processes 83
1. Introduction 83
2. Experimental procedure 84
3. Results and discussion 86
3.1 Microstructure of extruded Al-8Fe-TM based bulk alloys 86
3.2 Phase analysis 92
3.3 Mechanical properties 96
4. Summary 103
Reference 105
Chapter V. Relationship between Microstructures and Mechanical Properties of Al-Fe-TM Based Bulk Alloys 106
1. Introduction 106
2. Experimental procedure 106
3. Results and discussion 107
3.1 Room temperature deformation behavior 107
3.2 Effect of grain size on mechanical properties 113
3.3 Effect of particle size on mechanical properties 115
4. Summary 126
Reference 128
Chapter VI. Fabrication and Mechanical Properties of Amorphous/Nanocrystalline Al-Ni-Ce Bulk Alloy and Amorphous/Crystalline Composites 129
1. Introduction 129
2. Experimental procedure 129
3. Results and discussion 132
3.1 Effect of forging temperature on microstructure and property of amorphous/nanocrystalline Al-10Ni-6Ce monolithic bulk alloy produced by a powder forging 132
3.2 Effect of volume fraction of crystalline Al-8Fe-TM based alloy on compressive strength of amorphous/crystalline composites 138
4. Summary 147
Reference 148
Chapter VII. Conclusion 149
Effect of Fe content on microstructure and mechanical properties of Al-Fe-TM based alloys produced by melt spinning and hot extrusion 149
Microstructure control of the Al-8Fe-TM based bulk alloys produced by various rapid solidification processes 150
Relationship between microstructures and mechanical properties of Al-Fe-TM based bulk alloys 151
Fabrication and mechanical properties of amorphous/nanocrystalline Al-Ni-Ce bulk alloy and amorphous/crystalline composites 152
Appendix : Research achievements 153
Publication in International Journal 153
Presentation of International Conference 155
Presentation of Domestic conference 157
감사의 글 158
Table 1-1. Property of high strength precipitate Al alloys 9
Table 1-2. Properties of nanocrystalline Al alloys 10
Table 1-3. Processing, shape, phase, and properties of amorphous Al alloys 11
Table 1-4. Processing and properties of dispersion strengthened Al-Fe based alloys 12
Table 2-1. Interdiffusion coefficients of various transition elements in aluminum at 450℃ 20
Table 2-2. Properties of dispersion strengthened P/M alloy 22
Table 2-3. Extension of solid solubility for binary aluminum alloy 26
Table 3-1. Phase, shapes, and sizes of dispersoids for the Al-Fe-TM based bulk alloys produced by melt spinning and subsequent hot extrusion 71
Table 4-1. The phases, the sizes, and shapes for dispersoids of Al-8Fe-TM based bulk alloys produced by various rapid solidification techniques and hot extrusion processes 95
Table 5-1. Average spacing between the dispersoids, average dispersoid size, their volume fraction, grain size, and compressive yield strength of the present alloys 119
Fig. 1-1 Properties of amorphous Al alloy, nano-crystalline Al alloy, precipitate hardened Al alloys, and dispersion strengthened Al alloy 13
Fig. 2-1 Variation of strength and elongation according to Fe content in Al-Fe binary alloys produced by the gas atomization process 21
Fig. 2-2 Tensile strength values of Al-8Fe-X(wt.%) alloys at room temperature and at 250℃ 22
Fig. 2-3 Relationship between cooling rates and various rapid solidification process 26
Fig. 2-4 Schematic diagram of single-roll melt spinning process 27
Fig. 2-5 Schematic diagram of atomization process 28
Fig. 2-6 Schematic diagram of spray forming process 29
Fig. 2-7 The behavior of surface oxide film on high strength Al alloy powder upon degassing at typical temperatures 31
Fig. 2-8 The behavior of the residual oxide film during extrusion or rolling process 31
Fig. 2-9 Dislocation moving over a field of randomly spaced "weak" point-obstacles by the Friedel process (a), and over"strong" pointobstacles-pointobstacles[원문오류;p.27] 34
Fig. 2-10 Schematic of particle strengthening for alloys containing small volume fractions according to the Fleischer-Friedel approximation 40
Fig. 3-1 External view of single melt spinner used in this study 49
Fig. 3-2 Morphology of melt spun ribbon prepared by single melt spinner with copper roll speed of 42㎧ 49
Fig. 3-3 External view of speed rotor mill used for pulverizing of melt spun ribon 50
Fig. 3-4 Morphology of pulverized melt spun ribbon powder prepared by speed rotor mill 50
Fig. 3-5 External view of 50ton vertical type press used in this study 51
Fig. 3-6 External view of rectangular-shaped bar having width of 15 mm and thickness of 4 mm extruded at 420℃ with extrusion ratio of 25 to 1 51
Fig. 3-7 Digital microscope images(a~e) and cross sectioned OM images(f~j) for Al-Fe-TM melt spun ribbons : (a, f) 2 wt.%Fe, (b, g) 4 wt.%Fe, (c, h) 6 wt.%Fe, (d, i) 8 wt.%Fe, 55
Fig. 3-8 Micro-hardness variation with Fe content for the melt spun ribbon 56
Fig. 3-9 TEM micrographs of as-melt spun Al-XFe-TM alloy ribbons : (a) 2wt.% Fe, (b) 4wt.% Fe, (c) 6wt.% Fe, (d) 8wt.% Fe, and (e) 10wt.% Fe 57
Fig. 3-10 X-ray diffraction profiles of Al-XFe-TM (wt.%) melt spun ribbon alloys 58
Fig. 3-11 Lattice parameter plotted as a function of Fe content in Al-XFe-TM (wt.%) melt spun ribbon alloys 58
Fig. 3-12 Optical micrographs for the Al-8Fe-TM based bulk alloys extruded at 420℃ with extrusion ratio of 5 to 1(a) and 25 to 1(b) 60
Fig. 3-13 TEM micrographs for Al-XFe-TM based bulk alloys produced by melt spinning and subsequent hot extrusion at 420℃ with extrusion ratio of 25 (a~d) and 5 (e) : (a) 2wt.%Fe, (b) 4wt.% Fe, 61
Fig. 3-14 The size distribution of dispersoids for the Al-XFe-TM based bulk alloy produced by melt spinning and subsequent hot extrusion; (a) 2wt.%Fe, (b) 4wt.%Fe, (c) 6wt.% Fe, 62
Fig. 3-15 The variation of average dispersoids size with Fe content for the Al-Fe-TM based bulk alloys produced by melt spinning and subsequent hot extrusion 63
Fig. 3-16 The variation of average grain size with Fe content for the Al-Fe-TM based bulk alloys produced by melt spinning and subsequent hot extrusion 63
Fig. 3-17 The change of lattice parameter values between the as-melt spun ribbons and the extruded Al-Fe-TM based bulk alloys 64
Fig. 3-18 The variation of average grain size with Fe content for the Al-Fe-TM based bulk alloys produced by melt spinning and subsequent hot extrusion 65
Fig. 3-19 TEM-EDS mapping images for the Al-Fe-TM based bulk alloys produced by melt spinning and subsequent hot extrusion at 420℃ with extrulsion ratio of 25 to 1(a~d) and 69
Fig. 3-20 X-ray diffraction profiles of the Al-Fe-TM based bulk alloys produced by melt spinning and subsequent hot extrusion (ER : extrusion ratio) 70
Fig. 3-21 The variation of hardness values with Fe content for the Al-Fe-TM based bulk alloys produced by melt spinning and hot extrusion 72
Fig. 3-22 The true stress-true strain curves for the Al-Fe-TM based bulk alloys tested at room temperature in initial strain rate of 10- /s 75
Fig. 3-23 Ultimate tensile strength, tensile/compressive yield strength and elongation of the extruded alloys at room temperature with initial strain rate of 10- /s 76
Fig. 3-24 Temperature dependance of ultimate tensile strength and yield strength for the Al-Fe-TM based bulk alloys produced by melt spinning and hot extrusion (ER : Extrusion 77
Fig. 3-25 Tensile fracture surface images for the Al-2Fe-TM (a), the Al-4Fe-TM (b), the Al-6Fe-TM (c), and the Al-8Fe-TM based bulk alloy and the compression fracture surface 78
Fig. 4-1 External view of the as received spray formed and hot extruded rod 85
Fig. 4-2 Powder morphology of gas atomized powder with chemical composition of Al-8Fe-2Mo-2V-1Zr(wt.%) 85
Fig. 4-3 TEM micrographs for the spray formed and extruded Al-8Fe-TM based bulk alloy (a), the atomized and extruded Al-8Fe-TM based bulk alloy (b), and the melt spun and 88
Fig. 4-4 The average grain size of Al-8Fe-TM based bulk alloys produced by various rapid solidification techniques and subsequent hot extrusion process 89
Fig. 4-5 The size distribution for the dispersoids of the spray formed and extruded Al-8Fe-TM, the atomized and extruded Al-8Fe-TM, and the melt spun and extruded Al-8Fe-TM 90
Fig. 4-6 The average dispersoids diameter for the the Al-8Fe-TM based bulk alloys produced by various rapid solidification techniques and subsequent extrusion process 91
Fig. 4-7 The volume fraction of dispersoids for the Al-8Fe-TM based bulk alloys produced by various rapid solidification techniques and subsequent extrusion process 91
Fig. 4-8 TEM-EDS mapping images for the spray formed and extruded Al-8Fe-TM (a), the atomized and extruded Al-8Fe-TM (b), and the melt spun and extruded Al-8Fe-TM based 94
Fig. 4-9 X-ray diffraction profiles of the spray formed and extruded Al-8Fe-TM, the atomized and extruded Al-8Fe-TM, and the melt spun and extruded A1-8Fe-TM based bulk 95
Fig. 4-10 The hardness test results for the Al-8Fe-TM based bulk alloys which were produced by various rapid solidification techniques and subsequent hot extrusion process. 96
Fig. 4-11 The true stress-true strain curves for Al-8Fe-TM based bulk alloys produced by various rapid solidification techniques and hot extrusion process at room temperature in 98
Fig. 4-12 The true stress- true strain curves for Al-8Fe-TM based bulk alloys produced by various rapid solidification techniques and hot extrusion process at room temperature in intial strain rate of 10- /s 99
Fig. 4-13 Temperature dependance of ultimate tensile strength(UTS) and yield strength (YS) for Al-8Fe-TM based bulk alloys produced by various rapid solidification techniques 100
Fig. 4-14 Fracture surface images for the spray formed and extruded Al-8Fe-TM (a), the atomized and extruded Al-8Fe-TM (b), and the melt spun and extruded Al-8Fe-TM based bulk alloy after 102
Fig. 5-1 True stress-true strain curves taken from the compressive test at room temperature with initial strain rate of 10- /s 110
Fig. 5-2 True stress-true strain curves for the melt spun and extruded Al-8Fe-TM based alloy taken from compressive test at room temperature with various strain rates 111
Fig. 5-3 Climb of an edge dislocation over a spherical particle 111
Fig. 5-4 Threshold stress τth, c for the climb over particles as a function of climb resistance R 112
Fig. 5-5 TEM image for the deformed Al-8Fe-TM based alloy produced by melt spinning and extrusion 112
Fig. 5-6 Relation between yield strength and grain size for the present alloys 114
Fig. 5-7 Relation between the yield strength and the particle spacing 120
Fig. 5-8 Change in shear stress with increasing particle radius 121
Fig. 5-9 Dynamic Young's Modulus Resonance vibration method 122
Fig. 5-10 An array of particles in a cubic arrangement (a), dislocation at two successive positions A to B (b), dislocation shearing particle 123
Fig. 5-11 Comparison of the theoretical particle radius and the experimental particle radius which the hardening mechanism changes from particle shear to particle bypass 124
Fig. 5-12 TEM image for the deformed Al-2Fe-TM based alloy 125
Fig. 6-1 Schematic diagram of isothermal forging system 131
Fig. 6-2 DSC result of amorphous Al-10Ni-6Ce ribbon alloy 134
Fig. 6-3 OM micrographs taken from the preform of monolithic Al-10Ni-6Ce alloy 134
Fig. 6-4 OM micrographs of the monolithic Al-10Ni-6Ce bulk specimen forged at (a) 250℃, (b) 290℃, (c) 375℃, and (d) 550℃ 135
Fig. 6-5 Porosity of the bulk specimens forged at different temperatures 135
Fig. 6-6 XRD patterns of the monolithic Al-10Ni-6Ce bulk specimens forged at different temperatures 136
Fig. 6-7 Bright-field and selected area diffraction patterns of the monolithic Al-10Ni-6Ce bulk specimens forged at (a) 375℃ and (b) 550℃ 136
Fig. 6-8 Vickers hardness and compressive fracture strength for the monolithic Al-10Ni-6Ce bulk specimens forged at different temperatures 137
Fig. 6-9 OM micrographs of the bulk monolithic (a-e) and composites(Vf of Al-8Fe-TM based alloy : 0.3) (f-j) forged at 350℃(a, f), 375℃(b, g), 400℃(c, h), 450℃(d, i) and 550℃(e, j) 141
Fig. 6-10 XRD patterns for monolithic Al-10Ni-6Ce bulk alloy(a), Al-8Fe-TM based bulk alloy(b) and composites with Vf =0.3(c) forged at 400℃ 142
Fig. 6-11 Nominal stress-strain curves at room temperature for the Al-10Ni-6Ce bulk monolithic (a) and composites with Vf =0.3 (b) forged at different temperatures. 143
Fig. 6-12 Variation of the ultimate compressive strength (a) and compressive plastic strain (b) with forging temperature for bulk monolithic and composites with Vf =0.3 144
Fig. 6-13 SEM fractographs for the bulk Al-10Ni-6Ce monolithic (a) and composites with Vf =0.3 (b) forged at 375℃ 145
Fig. 6-14 Variation of the ultimate compressive strength (a) and compressive plastic strain (b) with the volume fraction of Al-8Fe-TM based alloy (Vf) for forged materials. 146
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