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Title Page

Abstract

Contents

CHAPTER 1. INTRODUCTION 11

CHAPTER 2. THEORETICAL BACKGROUND 13

2.1. Particulate Reinforced Metal Matrix Composites 13

2.1.1. Processing Techniques for Particle Reinforced Metal Matrix Composites 17

2.1.2. Mechanical properties of PMMCs 19

2.2. Mechanical Milling and Mechanical Alloying 21

2.3. Mechanochemical processing 25

2.4. Spark plasma Sintering (SPS)SPS) 28

2.4.1. Principles of SPS process 28

2.4.2. Sintering mechanism 29

CHAPTER 3. EXPERIMENTAL PROCEDURE 32

3.1. Starting powders 32

3.2. Preparation of Fe-TiB₂ nanocomposite powder 34

3.3. Spark plasma sintering of Fe-TiB₂ nanocomposite powder 37

3.4. Analysis 39

CHAPTER 4. RESULTS AND DISCUSSION 42

4.1. Synthesis of Fe-TiB₂ nanocomposite powder 42

4.2. Spark plasma sintering of Fe-TiB₂ nanocomposite powder 57

4.2.1. Shrinkage behavior during spark-plasma sintering 57

4.2.2. Morphology of bulk samples after 5 hours synthesis 59

4.2.3. Fracture analysis 62

4.2.3. Micro-hardness and density of SPS sintered samples 64

CHAPTER 5. CONCLUSIONS 67

I. Powder synthesis 67

II. Sintering 67

III. Properties 67

References 68

List of Publications 72

Acknowledgements 73

List of Tables

Table 2.1. Mechanical properties of the ceramic typically used as reinforcement in PRMMCs. 16

Table 2.2. Suitable materials for SPS Processing 31

Table 3.1. Characters of raw powders 32

Table 3.2. Parameters of mechanical. pre-milling of FeB 36

Table 3.3. Parameters of mechanical. post-milling of TiH₂ and FeB 36

Table 4.1. Phase fraction of synthesis Fe-TiB₂ composite powders 51

Table 4.2. Theoretical density of synthesis Fe-TiB₂ composite powders 52

List of Figures

Figure 2.1. (a): Schematic view of the different MMC systems, from [1]; (b): Definition of particle morphologies from [13]. 15

Figure 2.2. Some microstructures of PRMMCs produced via various processing techniques, illustrating some typical features and/or defects inherent to the processing route. References are indicated between brackets. 19

Figure 2.3. Early stage of processing. Particles are layered composites of starting constituents 21

Figure 2.4. Intermediate stage of processing: particles consist of convoluted lamellae. It is also possible to get some short-range inter-diffusion of constituents and new phase formation. 22

Figure 2.6. Completion of processing. Each powder particle composition is equivalent to starting powder blend and contains a uniform distribution of dispersoids. 22

Figure 2.7. Schematic drawing of ball-powder-ball collision 24

Figure 2.8. Scheme of the morphological transformation of powder grains induced by milling. D-ductile powder, B-brittle powder, C-Composite grains. 24

Figure 2.9. Schematic of the chemical reaction occurring between two components-metal oxide (MO) and reductant R in the mechanochemical reactions. The product phases (M and RO) from at the interface between the reactants and prevents further reaction from taking place since the reactants are not in contact with each other. 26

Figure 2.10. Typical classification for powder sintering processing. 28

Figure 2.11. Comparison of SPS and HP sintering characteristics. 28

Figure 2.12. SPS system configuration 30

Figure 2.13. ON-OFF pulsed current path. 30

Figure 2.14. Material transfer path during sintering. 30

Figure 3.1. Schematic illustration of experimental procedure 33

Figure 3.2. Structure of planetary high energy ball mill (AGO-2) 34

Figure 3.3. ThermVAC tube furnace 35

Figure 3.4. Tabular 3D mixer 36

Figure 3.5. General view of SPS apparatus 38

Figure 3.6. Parameters of graphite die and punches 38

Figure 3.7. The JSM-6500F field emission scanning electron microscope (FE-SEM) 39

Figure 3.8. Electronic densimeter SD-120L 40

Figure 3.9. Malvern Mastersizer 2000 particle size distribution instrument 40

Figure 3.10: Mitutoyo MVK-H1 Hardness Testing Machine 41

Figure 4.1. XRD patterns of TiH₂ starting powder, FeB powder after crushing, FeB powder after milling for 2 hours, 300 rpm, BPR 20:1 and milled powder mixture of TiH₂ and FeB after milling for 1 hour, 400 rpm, BPR 40:1. 44

Figure 4.2. FE-SEM micrographs of TiH₂ (a), FeB after crushing (b), FeB after pre-milling (c), TiH₂-FeB mixture after post-milling (d). 45

Figure 4.3. EDS profile of TiH₂-FeB mixture after post-milling. 46

Figure 4.4. Elemental composition mapping of TiH₂-FeB mixture after post-millingmilling. 47

Figure 4.5. Particle size distributions TiH2, FeB mixed powder after post-milling at particle number percent (a) and volume percent (b) 48

Figure 4.6. XRD patterns of the TiH₂-FeB post-milled powder after heating in the tube furnace to 1200˚C under Ar atmosphere,heating rate of 5˚C/min and holding time of 1 (a) ,3 (b) ,5 hours (c). 50

Figure 4.7. Particle size distributions of TiH₂, FeB -1200˚C -1(a), 3(b), 5(c) hours holding time 53

Figure 4.8. FE-SEM micrograph of Fe-TiB₂ composite powders after synthesis in the tube furnace for 5 hours holding time. 54

Figure 4.9. Back-scattering electron SEM micrographs of cross-sections of Fe-TiB₂ composite powders after synthesis in the tube furnace for 5 hours holding time. 54

Figure 4.10. Elemental composition mapping of Fe-TiB₂ composite powders after synthesis in the tube furnace for 5 hours holding time. 55

Figure 4.11. EDS profile of Fe-TiB₂ composite powders after synthesis in the tube furnace for 5 hours holding time. 56

Figure 4.12. Change in shrinkage and densification rate of Fe-TiB₂ composite powder compacts during a SPS sintering process at 1150˚C under pressure of 5˚MPa, heating rate of 20˚C/min, olding time of 15 min. 58

Figure 4.13. Optical micrographs of polished surface of Fe-TiB₂ sintered samples after spark-plasmasintered at (a) 1150, (b) 1100, (c) 1030, (d) 980˚C under pressure of 50MPa, heating rate of 20˚C/min and holding time of 15 min. 59

Figure 4.14. FE-SEM microstructure images of polished surface of Fe-TiB₂ sintered samples after spark-plasma sintered at (a) 1150, (b) 1100, (c) 1030, (d) 980˚C under pressure of 50MPa, heating rate of 20˚C/min and holding time of 15 min. 60

Figure 4.15. EDS profile of FeFe-TiB₂ powder compact sintered at 1030℃ 61

Figure 4.16. Fracture surface of Fe-TiB₂ composite powder compacts during a SPS sintering process at optimal conditions. 63

Figure 4.17. Effect of sintering temperature on relative density and hardness of Fe-TiB₂ composite after synthesis for an hour synthesis 65

Figure 4.18. Effect of sintering temperature on relative density and hardness of Fe-TiB₂composite after synthesis for 3 hours synthesis 65

Figure 4.19. Effect of sintering temperature on relative density and hardness of Fe-TiB₂composite after synthesis for 5 hours synthesis 66

Figure 4.20. Effect of synthesis time on hardness of Fe-TiB₂ composites 66

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