氏名　WAN NUR AZRINA BINTI WAN MUHAMMAD
学位の種類　博士（工学）
学位記番号　博甲第589号
学位授与の日付　平成23年6月30日
学位論文題目　Development of Magnesium Based Composites using Spark Plasma Sintering Technology　（スパークプラズマ焼結法を用いたマグネシウム複合材の開発）
論文審査委員
　主査　教授　武藤　睦治
　副査　教授　福澤　康
　副査　教授　岡崎　正和
　副査　准教授　宮下　幸雄
　副査　特任講師　大塚　雄市

• 論文目次
• 論文要旨
• 論文審査の結果の要旨

［平成23（2011）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

TABLE CONTENTS　PAGE
ABSTRACT　p.ii
ACKNOWLEDGEMENT　p.iv
TABLE OF CONTENTS　p.v
LIST OF FIGURES　p.ix
LIST OF TABLES　p.xvi
LIST OF PUBLICATIONS　p.xvii

CHAPTER1:　INTRODUCTION AND SCOPE OF THIS WORK
　1.1　Introduction　p.1
　1.2　Review of Literature　p.2
　1.2.1　Metal Matrix Composites （MMCs）　p.2
　1.2.2　Particulate Reinforced MMCs　p.3
　1.2.3　Magnesium Based Composites　p.5
　1.2.4　Manufacturing Processes for Magnesium Based Composites　p.7
　1.2.4.1　Spark plasma sintering （SPS）　p.9
　1.2.4.2　Spark plasma sintering mechanism　p.10
　1.2.4.3　Features and Applications of Spark Plasma Sintering Technology　p.13
　1.2.5　High temperature properties of Magnesium based composites　p.16
　1.3　Scope of Present Work　p.16
　References　p.18
CHAPTER2:　MICROSTRUCTURE AND MECHANICAL PROPERTIES OF MAGNESIUM PREPARED BY SPARK PLASMA SINTERING （SPS） AND PRESSURELESS SINTERING （PLS）
　2.1　Introduction　p.22
　2.2　Experimental Procedure　p.23
　2.3　Characterization　p.25
　2.4　Mechanical tests　p.25
　2.5　Result and discussion
　2.5.1　Microstructure　p.30
　2.5.2　Average gain size　p.35
　2.5.3　Relative density　p.36
　2.5.4　Hardness　p.37
　2.5.5　Tensile properties　p.38
　2.6　Conclusion　p.45
　References　p.45
CHAPTER3:　MICROSTRUCTURE AND MECHANICAL PROPERTIES OF MAGNESIUM BASED COMPOSITES BY SPARK PLASMA SINTERING （SPS）
　3.1　Introduction　p.48
　3.2　Experimental procedure　p.50
　3.3　Characterization　p.52
　3.4　Mechanical tests　p.52
　3.5　Result and discussion
　3.5.1　Microstructure　p.53
　3.5.2　Relative density　p.55
　3.5.3　Hardness　p.56
　3.5.4　Tensile properties　p.57
　3.6　Conclusion　p.64
　References　p.65
CHAPTER4:　EFECT OF MIXING CONDITIONS ON THE MECHANICAL PROPERTIES OF MAGNESIUM BASED COMPOSITES
　4.1　Introduction　p.71
　4.2　Experimental Procedure　p.72
　4.3　Characterization　p.73
　4.4　Mechanical tests　p.73
　4.5　Result and discussion
　4.5.1　Effect of mixing speed　p.74
　4.5.1.1　Microstructures　p.74
　4.5.1.2　Relative density　p.77
　4.5.1.3　Hardness　p.77
　4.5.1.4　Tensile strength　p.78
　4.5.2　Effect of mixing time　p.81
　4.5.2.1　Microstructures　p.81
　4.5.2.2　Relative density　p.85
　4.5.2.3　Hardness　p.86
　4.5.2.4　Tensile strength　p.87
　4.6　Conclusion　p.89
　References　p.89
CHAPTER5:　HIGH TEMPERATURE PROPERTIES OF MAGNESIUM BASED COMPOSITES PREPARED BY SPARK PLASMA SINTERING （SPS）
　5.1　Introduction　p.92
　5.2　Experimental Procedure　p.93
　5.3　Mechanical tests　p.94
　5.4　Result and discussion
　5.4.1　Tensile properties　p.95
　5.4.2　Elongation and reduction of area　p.97
　5.4.3　Fracture behaviour　p.99
　5.5　Conclusion　p.102
　References　p.102
CHAPTER6:　MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AZ31 COMPOSITES PREPARED BY SPARK PLASMA SINTERING （SPS）
　6.1　Introduction　p.105
　6.2　Experimental Procedure　p.106
　6.3　Characterization　p.107
　6.4　Mechanical test　p.108
　6.5　Result and discussion
　6.5.1　Monolithic AZ31 alloy　p.108
　6.5.1.1　Relative density　p.111
　6.5.1.2　Hardness　p.111
　6.5.1.3　Tensile properties　p.112
　6.5.2　AZ31-SiC composites　p.116
　6.5.2.1　Relative density　p.117
　6.5.2.2　Hardness　p.117
　6.5.2.3　Tensile properties　p.118
　6.6　Conclusion　p.122
　References　p.123
CHAPTER7:　OVERALL CONCLUSION AND FUTURE PROSPECTS
　7.1　Overall Conclusions　p.125
　7.2　Future Recommendations　p.128

Lightweight magnesium based composites are demanded especially in automotive, electronics and aerospace industries. No research work has been done on the magnesium and its composites prepared by spark plasma sintering techniques and there does exist a critical need to determine and understand the effect of SPS processing conditions and silicon carbide content on microstructure and mechanical properties of magnesium based composites. This thesis includes seven chapters, which are shown below.

Chapter 1 “Introduction”: Chapter one provided an introduction of magnesium based composites and spark plasma sintering process. This introductory chapter presented the background and motivation for this research. Then the objective and scope of this work were addressed.

Chapter 2 “Microstructure and mechanical properties of magnesium prepared by spark plasma sintering （SPS） and pressureless sintering PLS”: In this chapter, monolithic magnesium was fabricated by SPS as well as a conventional pressureless sintering. The processing parameters, i.e; sintering temperature and loading pressure were investigated. The experimental results showed that high dense magnesium could be fabricated by a using spark plasma sintering technique compared to that fabricated by conventional pressureless sintering at the same sintering temperature. The magnesium samples prepared by SPS showed better mechanical properties than those prepared by PLS. The microstructure observations revealed that the grain growth was not significant in SPS process compared to PLS, which would enhance the mechanical properties of the SPS sintered magnesium.

Chapter 3 “Microstructure and mechanical properties of magnesium based composites prepared by spark plasma sintering”: In this chapter, magnesium matrix composites reinforced with SiC particles were successfully fabricated by the spark plasma sintering method at sintering temperatures of 585°C. A uniform distribution of SiC particles was observed along the boundary between matrix particles. The mechanical properties, i.e. hardness and tensile strength increased with increasing SiC content up to 10wt%. However, when the SiC content was larger than 10wt%, the tensile strength decreased due to the agglomeration of SiC particles.

Chapter 4 “Effect of mixing condition on the mechanical properties of magnesium based composites” : In this chapter, the effect of mixing speed and mixing time on the mechanical properties of magnesium based composites were investigated. It was found that increase of mixing speed and mixing time can improved the distribution of SiC particle and mechanical properties of magnesium based composites.

Chapter 5 “High temperature properties of magnesium based composites prepared by spark plasma sintering”: In this chapter, high temperature tensile test was conducted to study high temperature properties of the magnesium based composites reinforced with SiC particulates and the monolithic magnesium as well. It was found that tensile strength of monolithic magnesium and Mg-SiC composites decreased with an increase in testing temperature. The elongation was increased when increasing temperature
for both samples. At all testing temperatures, the tensile strength of the composite sample was found to be superior compared to monolithic magnesium due to presence of SiC particulates.

Chapter 6 “Microstructure and mechanical properties of AZ31 composites prepared by spark plasma sintering”: In the previous chapters, the applicability and effectiveness of spark plasma sintering （SPS） for fabricating magnesium and magnesium composites reinforced with SiC have been confirmed. Magnesium and Mg-SiC composites sintered by an SPS method exhibited fine microstructures and excellent mechanical properties. In this chapter, AZ31 magnesium alloy matrix composites reinforced with SiC particles were fabricated by an SPS method and the effects of sintering temperature and SiC content on microstructure and mechanical properties were investigated. It was found that the sintering temperature of 552oC was the most suitable sintering temperature for AZ31 alloy. AZ31 alloy matrix composites reinforced with SiC particles were then successfully fabricated by SPS at 552oC. Hardness and tensile strength increased with increasing SiC content up to 8wt%. However, when the SiC content was larger than 8wt%, the tensile strength decreased due to the agglomeration of SiC particles that could lead the degradation of the interfacial bonding strength between matrix and reinforcement.

Chapter 7 “Overall conclusions and Future prospects” : Based on the above results and discussion, magnesium based composites reinforced with silicon carbide were fabricated by spark plasma sintering technique and their mechanical properties as well as high temperature properties were summarized. The significant research results of the magnesium based composites prepared by spark plasma sintering were described. Future researches to be developed were also suggested.

　本論文は、「Development of Magnesium Based Composites Using Spark Plasma Sintering Technology （スパークプラズマ焼結法を用いたマグネシウム複合材の開発）」と題し、7章より構成されている。
　第1章「Introduction」では、本研究に関わる研究動向を概説するとともに、本研究の目的と範囲を述べている。
　第2章「Microstructure and mechanical properties of magnesium prepared by spark plasma sintering （SPS） and pressureless sintering （PLS）」では、純マグネシウム粉末を用い、従来の常圧焼結（PLS）とスパークプラズマ焼結（SPS）を行い、SPSにより微細な組織の焼結体が得られ、引張強度などの機械的特性にも優れていることを明らかにするとともに、SPSの最適焼結条件などを明らかにしている。
　第3章「Microstructure and mechanical properties of magnesium based compositesprepared by spark plasma sintering」では、マグネシウム粉末に強化粒子としてSiC粉末を添加し、SPSにより複合材を作製している。SiC粉末の添加により強度は顕著な増加が認められ、約10％のSiC粉末の添加で最大の強度が得られること、それ以上の添加により強度は低下するが、それがSiC粒子の偏析によることなどを明らかにしている。
　第4章「Effect of mixing condition on the mechanical properties of magnesium based composites」では、前章までに用いた通常の粉末混合条件では偏析を生じるため、複合材作製のためのより適切な粉末混合条件について検討し、より均一な混合と、優れた機械的特性の得られる混合条件などを明らかにしている。
　第5章「High temperature properties of magnesium based composites prepared byspark plasma sintering」では、SiC粒子強化マグネシウム複合材の高温強度を調べ、SiC粒子の添加により、室温の強度のみならず、高温においても高い強度を示すことなどを明らかにしている。
　第6章「Microstructure and mechanical properties of AZ31 composites prepared by spark plasma sintering」では、マグネシウム合金AZ31粉末にSiC強化粒子を添加した複合材をSPSにより作製し、優れた強度を示すこと、添加量が8％を超えるとSiC粒子の偏析により強度が低下することなどを明らかにしている。
　第7章「Overall conclusions and Future prospects」では、以上の研究の結果を総括的にまとめるとともに、将来の展望について述べている。よって、本論文は工学上及び工業上貢献するところが大きく、博士（工学）の学位論文として十分な価値を有するものと認める。