Ti3Al基介金屬合金因其具有優異的高溫性質，因此是目前航太工業上倍受矚目的材料。本Ti-25Al-10Nb-3V-1Mo合金在高溫950-1000oC及低應變速率10-4-10-5 s-1下具有相當卓越之高溫超塑性，伸長率高達1000%以上，低溫則在850oC (0.57 Tm) 及5x10-4 s-1的應變速率下可獲得330%的低溫超塑性。本研究係探討Ti3Al合金之低溫超塑性質，並針對本研究中之重要發現，超塑性應變所誘發的相變化行為，做一整合性之分析及探討，進而建立低溫超塑性之變形機制，此發現將有助於Ti3Al合金低溫超塑性之開發。

本合金乃經由熱機處理所製成具有雙相(

Ti3Al based intermetallic alloys are attractive for aerospace and aircraft applications due to their superior high temperature properties. Excellent high temperature superplasticity in the Ti3Al-Nb based alloy has been widely published. However, the alloys become brittle and hard to deform at temperatures below 600oC so that low temperature superplasticity is difficult to develop. In the current super

TABLE OF CONTENTS……..……………………………………………….……………….i
LIST OF TABLES……..……………………………………………….………….………….iv
LIST OF FIGURES……..……………………………………………….……………………vi
ABSTRACT……..……………………………………………….………………………….xiii
中文提要…………………………………………………………………………………….xv
致謝…………………………………………………………………………………………xvi
CHAPTER 1 Background and Research Motive…….....……………………………………1
1.1 Introduction to Ti3Al intermetallic compounds………………………….………...1
1.1.1 The characteristics of Ti3Al………………………….…………….………1
1.1.2 The structures and properties of Ti3Al…………………………….………1
1.2 Processing for producing fine-grained Ti3Al alloys……..……….…………………3
1.3 Introduction to superplasticity and deformation mechanisms..……………………..6
1.3.1 Introduction to superplasticity……………………….…………….………6
1.3.2 Deformation mechanisms………………………………………….……11
1.4 Superplastic behavior in Ti3Al alloys……………………………………….……13
1.4.1 HTSP in Ti3Al alloys………………………………………...…….……..13
1.4.2 LTSP in Ti3Al alloys……………………………………………….……17
1.4.3 LTSP and HSRSP in other Ti based alloys……………………….………19
1.5 Phase transformation phenomena…………………………………………...……21
1.6 Anisotropy during superplastic deformation………………………………………23
1.7 The texture analyses on Ti3Al alloys………………………………………..……24
1.8 Introduction to electron back scatterred diffraction (EBSD) ……………..………28
1.8.1 Advantages of EBSD……………………………………………...……28
1.8.2 The basic principles and set-up of a typical EBSD system………………29
1.9 Motive of the research………………………….……………………………...…31
CHAPTER 2 Experimental Methods…….....…………………………………………..…33
2.1 Materials………………………….……….. ……………………………….……33
2.2 Mechanical tests….…………………………………………………….…….……33
2.3 Anisotropic tests…..………………………………………………………….……34
2.4 Retention of microstructure for tensile specimens………………………….……35
2.5 Microstructure characteristics……………………………………………………35
2.5.1 OM and SEM observations………………………………………..……35
2.5.2 TEM observations………………………….………………………...…36
2.6 Volume fraction determinations………………………….………………………36
2.7 Texture analyses………………………….………………………………………37
CHAPTER 3 Experimental Results…….....………………………………………….……39
3.1 Microstructure characterization of the as-received materials……………………39
3.2 Mechanical tests…..………………………….……………………………………40
3.2.1 Room temperature properties…………………………………….………40
3.2.2 Elevated temperature properties…………………………….….………...40
3.3 Anisotropic tests…………………………………………………………………41
3.4 Microstructure evolutions………………………….……………………………42
3.4.1 Static annealing………………………………………………….……….42
3.4.2 The crystal relationship between

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