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博碩士論文 etd-0724102-172139 詳細資訊
Title page for etd-0724102-172139
論文名稱
Title
純鋁經等徑轉角擠形之變形組織
Deformation Structure in Aluminum Processed by Equal Channel Angular Extrusion
系所名稱
Department
畢業學年期
Year, semester
語文別
Language
學位類別
Degree
頁數
Number of pages
162
研究生
Author
指導教授
Advisor
召集委員
Convenor
口試委員
Advisory Committee
口試日期
Date of Exam
2002-07-03
繳交日期
Date of Submission
2002-07-24
關鍵字
Keywords
塑性變形、細晶粒、變形組織、等徑轉角擠形、鋁、晶界結構
boundary structure, aluminum, deformation structure, plastic deformation, ECAE, fine grain
統計
Statistics
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The thesis/dissertation has been browsed 5679 times, has been downloaded 2245 times.
中文摘要
等徑轉角擠形可對材料施予一簡單剪變形而改變材料內部結構,但並不改變其尺寸大小,因此可得到累積大量塑性應變之中塊材,對於工業應用上提供了一具高潛力的變形方式。等徑轉角擠形之通道交角及擠製路徑均為變形時的重要參數,會影響材料內部結構的發展。近來對於等徑轉角擠形的研究頗多,但卻沒有提供一完整的資訊。因此本研究對於經等徑轉角擠形後之變形組織做定量化的分析,得到其次晶粒之形態、大小、形狀及次晶界之方位差角的資訊。AA1050商用純鋁不同的等徑轉角擠形擠製路徑變形至應變量為8,可以發現產生高角晶界的路徑是route A與Bc相似,route C最差(A~Bc>C)。而在晶粒的細化上是route Bc最好,A次之,C最差。此外經等徑轉角擠形,route A產生最長的次晶粒,Bc產生最接近等軸的次晶粒。
等徑轉角擠形之通道交角決定其每道擠製應變量及剪切面之方位,為了簡化通道交角的效應,本研究使用route C來觀察每道擠製應變量對變形的影響。經研究發現,每道擠製應便量對於產生高角晶界的比例影響並不大,但對於高角晶界的分布有影響。此外發現每道擠製應變量較小之變形路徑產生較長之晶粒且等軸晶之比例較小。


Abstract
Equal channel angular extrusion (ECAE) has attracted a substantial attention for it provides the opportunity to introduce large plastic strain into the material in the bulk form. Both die angles and processing routes have been recognized as the important parameters in applying ECAE to fabricate ultrafine-grained materials. Unfortunately, studies of different group provided inconsistent conclusions on the effectiveness of processing routes, which are believed to be due to the incomplete microstructural information obtained in each investigation. In the present work, quantitative analysis of the microstructure developed by different processing conditions were conducted using transmission electron microscopy (TEM), in which the morphology, size, and shape of subgrains as well as boundary misorientation were fully characterized.
A commercial pure aluminum (AA 1050) was deformed by ECAE to strain of ~ 8 with different routes (A, Bc and C, in terms of reorientation angle 0o, 90o, and 180o respectively of the billet between two extrusion passes) and die angles. The results show that the effectiveness of high angle boundary (HAB) formation is in the sequence of route A≒Bc>C. However, in terms of grain refinement, the effectiveness is in the order of route Bc>A>C. In addition, route A produces subgrains with the most elongated shape, while route Bc produces subgrains with the most equiaxed shape. These results may be attributed to the different shear pattern introduced in each route.
ECAE die angle determines both the strain per pass and the shear plane orientation. In route C, the shear is maintained in the same plane and the effect of strain per pass can be studied. With route C, both the 90o and 120o die produce microstructure with similar HAB proportions, but they result in different arrangement of HABs. The 120o die produces subgrains with larger size and higher aspect ratio than the 90o die does in route C. Generally speaking, for the die angle range studied, the different values of strain per pass used in ECAE mainly affect the morphology of the subgrains. On the other hand, the effect of die angle is weakened with route Bc as compared to route C, which may be attributed to the intersection of shear planes involved in route Bc.



目次 Table of Contents
CONTENTS

CONTENTS……………………………………………………………………… i
List of Tables……………………………………………………………… iv
List of Figures…………………………………………………………… vi
Acknowledgement…………………………………………………………… xiv
Abstract…………………………………………………………………… xvi

Chapter I Introduction………………………………………… 1

Chapter II Literature Review
2-1 Microstructure evolution during large strain deformation…………4
2-1-1 Grain subdivisions………………………………………………… 4
2-1-2 High angle boundaries formation by grain subdivision…………… 9
2-1-3 Microstructure evolution in shear band…………………………… 10
2-2 Methods for large strain deformation………………………………… 11
2-2-1 Redundant strain processes…………………………………………… 11
2-2-2 Directional strain processes……………………………………….….. 12
2-2-3 Equal channel angular extrusion…………………………………..….. 12
2-3 Characteristics of ECAE deformation………………………………... 12
2-3-1 The friction and homogeneity in ECAE……………………………… 14
2-3-2 The effect of deformation route in ECAE……………………………. 17
2-3-3 The effect of die angle in ECAE……………………………………… 19
2-3-4 The other parameters in ECAE……………………………………….. 20
2-3-5 Tentative model for the microstructure evolution in ECAE……… 21
2-4 Microstructure characterization………………………………………… 23
2-4-1 SAD for misorientation measurement…………………………..……. 23
2-4-2 EBSD for misorientation measurement………………………………. 24
2-4-3 Kikuchi pattern for misorientation measurement….………………… 25

Chapter III Experimental
3-1 Material……………………………………………………………….…… 26
3-2 ECAE deformation………………………………………………………... 26
3-3 Optical Microscopy (OM)………………………………………….…….. 27
3-4 Microhardness measurement…………………………………...………… 28
3-5 Texture analysis…………………………………………………………… 29
3-6 Electron Backscattered Diffraction (EBSD)……………………….. 29
3-7 Transmission Electron Microscopy (TEM)……………………………… 30
Chapter IV Results
4-1 Macroscopic observations…………………………………………………. 34
4-1-1 Optical microscopy…………………………………………………... 34
4-1-2 Hardening due to large strain deformation…………………………… 35
4-1-3 Texture evolution in route C………………………………………….. 36
4-2 The effect pf strain per pass…………………………………………… 37
4-2-1 Results provided by EBSD analysis………………………………….. 37
4-2-2 Morphology of deformation structure………………………………... 38
4-2-3 Size and shape of subgrains………..…………………………….…... 40
4-2-4 Boundary misorientations obtained by TEM………………………… 43
4-2-5 Microtexture analysis………………………………………………… 45
4-2-6 Summary………………………………………………………….….. 46
4-3 Changing strain path in redundant deformation……………………… 47
4-3-1 Morphology of deformation structure………………………………... 47
4-3-2 Size and shape of subgrains………………………………………….. 49
4-3-3 Boundary misorientations obtained by TEM………………………… 52
4-3-4 Microtexture analysis………………………………………………… 54
4-3-5 Summary………………………………………………………….….. 55
4-4 The effect of processing route………………………………………… 56
4-4-1 Morphology of deformation structure………………………………... 56
4-4-2 Size and shape of subgrains………………………………………….. 56
4-4-3 Boundary misorientation obtained by TEM…………………………. 58
4-4-4 Microtexture analysis………………………………………………… 59
4-4-5 Summary……………………………………………………………... 60
4-5 HABs formation by grain subdivision…………………………………… 61

Chapter V Discussion
5-1 TEM Kikuchi pattern analysis……………………………………………. 63
5-2 Effect of deformation route……………………………………………… 65
5-2-1 Formation of HABs…………………………………………………... 65
5-2-2 Morphology, size and shape of subgrains……………………….…… 69
5-2-3 Comparison with previous reports…………………………………… 71
5-3 Effect of die angle………………………………………………………… 73
5-3-1 Boundary misorientation and distribution……………………………. 73
5-3-2 Subgrain size and shape………………………………………………. 74

Chapter VI Conclusions……………………………………………………… 77

Reference……………………………………………………………………………... 79

Appendix A Definitions of dislocation arrangements…………………………… 158
Appendix B List of symbol…………………………………………………………... 160
Appendix C TEM picture number...…………………………………………………... 161
List of Tables

Table 3-1 Chemical composition of AA1050aluminum (in wt%)……………………. 26

Table 3-2 Design of experimental conditions………………………………………… 28

Table 4-1 Microstructure characteristics of all measured subgrains in samples processed by route C…………………………………….…………………………….. 41

Table 4-2 Microstructure characteristics of equiaxed subgrains in samples processed by route C………………………………………..…………………………….. 41

Table 4-3 Microstructure characteristics of elongated subgrains in samples processed by route C………………………………………..…………………………….. 41

Table 4-4 The comparison of the microstructure produced by different die angles with route Bc and C……………………………………………………………... 47

Table 4-5 Microstructure characteristics of all measured subgrains in samples processed by route Bc and C………………………………………………………….. 50

Table 4-6 Microstructure characteristics of equiaxed subgrains in samples processed by route Bc and C….………………………………………………………….. 51

Table 4-7 Microstructure characteristics of elongated subgrains in samples processed by route Bc and C…….……………………………………………………….. 52

Table 4-8 Microstructure characteristics of all measured subgrains in samples processed by various routes with the 90o die………………………………………….. 57

Table 4-9 Microstructure characteristics of equiaxed subgrains in samples processed by various routes with the 90o die……………….…………………………….. 57

Table 4-10 Microstructure characteristics of elongated subgrains in samples processed by various routes with the 90o die……………………………………………... 58

Table 4-11 The comparison of the microstructure produced by different routes with the 90o die……………………………………………………………………… 60
Table 5-1 The shear strains developed by different ECAE routes during the first 4 passes………………………………………………………………………. 67

Table 5-2 Angular range of slip traces of F=90o after 5 passes with different routes... 69




List of Figures

Fig. 2-1 A mechanism interpreted for microstructure evolution in cold rolling or plane-strain compression (Humphreys 1999a)………………………………. 87

Fig. 2-2 TEM micrograph of a pure aluminum single crystal shows grain subdivision at two levels by GNBs and IDBs forming cell blocks (Hughes et al. 1998)…… 87

Fig. 2-3 The distribution of boundary orientation results from (a) microstructural evolution and (b) texture evolution (Hughes 1997)…………………………. 88

Fig. 2-4 A model for microstructure evolution in adiabatic band (Hine et al. 1998)…. 88

Fig. 2-5 The model for shear localization and recrystallization in high-strain, high-strain-rate deformation of tantalum (Nesterenko et al. 1997)………….. 89

Fig. 2-6 The geometry of ECAE (Iwahashi et al. 1997)……………………………… 89

Fig. 2-7 Traces of deformed grids from the center plane of the middle sections of billets that have been extruded halfway through a 120o die under different conditions (Bowen et al. 2000)………………………………………………………….. 90

Fig. 2-8 Different deformation routes of ECAE (Iwahashi et al 1998b)…………….... 91

Fig. 2-9 The shear pattern of ECAE (F=90o) (Iwahashi et al. 1998b)………………... 91

Fig. 2-10 The proposed model of ECAE deformation of pure Al and Al-5%Zn at 298K (Berbon et al. 2000)………………………………………………………….. 92

Fig. 2-11 The shear bands intersection of (a) route A and (b) route B (Segal 1999)….... 92

Fig. 3-1 The principle of EBSD (Randle 1992)………………………………………. 93

Fig. 3-2 The Kikuchi pattern solved by personal computer……………………..……. 93

Fig. 3-3 The relationship between a reference orthogonal coordinate and the double tilt holder (Liu 1994)…………………………………………………………….. 94

Fig. 3-4 Sample worksheet used to collect orientation data during TEM experiment (Agnew 1998)………………………………………………………………... 94

Fig. 3-5 A map of several subgrains with relative boundary misorientation angles determined by the method modified by Liu (1994), is adopted in the present study. Kikuchi patterns for each subgrain obtained at zero tilting condition are shown………………………………………………………………………… 95

Fig. 4-1 Optical micrographs on (a) X-, (b) Y- and (c) Z-plane of a sample deformed by the 120o die (route C, N=1). The reference coordinate for ECAE processed billet is shown in (d)……………………………………………………………….. 96

Fig. 4-2 Optical micrographs on (a) X-, (b) Y- and (c) Z-plane of a sample deformed by the 90o die (route C, N=1)…………………………………………………… 97

Fig. 4-3 Optical micrographs on (a) X-, (b) Y- and (c) Z-plane of a sample deformed by the 120o die (route C, N=2)………………………………………………….. 98

Fig. 4-4 Optical micrographs on (a) X-, (b) Y- and (c) Z-plane of a sample deformed by the 90o die (route C, N=2)…………………………………………………… 99

Fig. 4-5 Optical micrographs on (a) X-, (b) Y- and (c) Z-plane of a sample deformed by the 120o die (route C, N=6)………………………………………………….. 100

Fig. 4-6 Optical micrographs on (a) X-, (b) Y- and (c) Z-plane of a sample deformed by the 90o die (route C, N=4)…………………………………………………… 101

Fig. 4-7 Optical micrographs on (a) X-, (b) Y- and (c) Z-plane of a sample deformed by the 120o die (route C, N=12)………………………………………………… 102

Fig. 4-8 Optical micrographs on (a) X-, (b) Y- and (c) Z-plane of a sample deformed by the 90o die (route C, N=8)…………………………………………………… 103

Fig. 4-9 Optical micrographs of a sample deformed to a strain of ~8 by using the 90o die and route A. (a) X-plane and (b) Y-plane……………………………………. 104

Fig. 4-10 Variation of microhardness with increasing strain (route C)………………… 105

Fig. 4-11 Variation of microhardness value with increasing strain for samples deformed by route Bc and C……………………………………………………………….. 106

Fig. 4-12 (111) X-ray pole figure of a sample in the initial condition…………………. 107

Fig. 4-13 (111) X-ray pole figures of specimens deformed by the 90o die with route C. (a) N=1 and (b) N=4……………………………………………………………... 108

Fig. 4-14 (111) X-ray pole figures of specimens deformed by the 120o die with route C. (a) N=1 and (b) N=6……………………………………………………………... 109

Fig. 4-15 Distribution of misorientation angles of specimens deformed by the 120o die with route C. (a) N=1 (b) N=2 (c) N=4 (d) N=6, where the measurements were obtained by EBSD along the Z-direction on the X-plane……………………. 110

Fig. 4-16 Distribution of misorientation angles of specimens deformed by the 90o die with route C. (a) N=1 (b) N=2 (c) N=4, where the measurements were obtained by EBSD along the Z-direction on the X-plane…………………………………. 111

Fig. 4-17 Variation of average misorientation angle determined by EBSD with increasing strain (route C), (a) LABs and (b) HABs……………………………………. 112

Fig. 4-18 Proportion of HABs determined by EBSD is shown as a function of strain (route C)…………………………………………………………………………….. 113

Fig. 4-19 Spacing of HABs determined by EBSD is shown to decrease with increasing strain (route C)……………………………………………………………….. 113

Fig. 4-20 Typical microstructures observed on the X-plane of specimens produced by the 90o die at a strain of ~4 (route C). (a) Banded structure consists of elongated cells and subgrains, and (b) nearly equiaxed subgrains……………………… 114

Fig. 4-21 (a) Typical microstructures observed on the Y-plane of specimens produced by the 90o die at a strain of ~4 (route C), and (b) the mosaic structure observed on the Y-plane of a specimen produced by the 120o die at a strain ~4 (route C)... 115

Fig. 4-22 Microstructure observed on the X-plane of specimens deformed to a strain of ~8 by (a) the 120o die (route C, N=12), and (b) the 90o die (route C, N=8)…….. 116

Fig. 4-23 Microstructure observed on the Y-plane of specimens deformed to a strain of ~8 by (a), (b) the 90o die (route C, N=8), and (c) (d) the 120o die (route C, N=12)…………………………………………………………………..…... 117

Fig. 4-24 (a) Subgrain size and (b) aspect ratio of subgrains are shown as function of strain and die angle (route C)………………………………………………… 119

Fig. 4-25 (a) TEM micrograph showing the microstructure of a sample deformed by the 120o die (route C, N=6). (b) The misorientation angles, which were determined by the use of Kikuchi pattern analysis, are marked on each boundary in the sketch………………………………………………………………………… 120

Fig. 4-26 Distribution of misorientation angles on the Y-plane of specimens deformed to a strain of ~4 by (a) the 90o die (route C, N=4), and (b) the 120o die (route C, N=6)………………………………………………………………………….. 121

Fig. 4-27 Distribution of misorientation angles in the LABs area on the Y-plane of specimens to a strain of~4 by (a) the 90o die (route C, N=4) and (b) the 120o die (route C, N=6) measured by TEM…………………………………………… 122

Fig. 4-28 Distribution of LABs and HABs on the Y-plane of a sample deformed to a strain of ~4 by the 90o die (route C, N=4). (a) TEM micrograph, and (b) a sketch to reveal the distribution of LABs and HABs of the microstructure shown in (a). The thick and thin lines indicate HABs and LABs, respectively, and the dotted lines indicate those boundaries, which were not analyzed……………….….. 123

Fig. 4-29 Distribution of LABs and HABs on the Y-plane of a sample deformed to a strain of ~4 by the 120o die (route C, N=6). (a) TEM micrograph, and (b) a sketch to reveal the distribution of LABs and HABs of the microstructure shown in (a). The thick and thin lines indicate HABs and LABs, respectively, and the dotted lines indicate those boundaries, which were not analyzed……………….….. 124

Fig. 4-30 Distribution of misorientation angles on the Y-plane of specimens deformed to a strain of ~8 by (a) the 90o die (route C, N=8), and (b) the 120o die (route C, N=12)………………………………………………………………………… 125

Fig. 4-31 Distribution of LABs and HABs on the Y-plane of a sample deformed to a strain of ~8 by the 90o die (route C, N=8). (a) TEM micrograph, and (b) a sketch to reveal the distribution of LABs and HABs of the microstructure shown in (a). The thick and thin lines indicate HABs and LABs, respectively, and the dotted lines indicate those boundaries, which were not analyzed…………………... 126

Fig. 4-32 Distribution of LABs and HABs on the Y-plane of a sample deformed to a strain of ~8 by the 120o die (route C, N=12). (a) TEM micrograph, and (b) a sketch to reveal the distribution of LABs and HABs of the microstructure shown in (a). The thick and thin lines indicate HABs and LABs, respectively, and the dotted lines indicate those boundaries, which were not analyzed……………….….. 127

Fig. 4-33 Microtexture revealed by (100) pole figures obtained from different regions in samples deformed by the 90o die to a strain of ~4 (route C, N=4). The pole figures were determined by TEM Kikuchi pattern analysis……………….… 128

Fig. 4-34 Microtexture revealed by (100) pole figures obtained from different regions in samples deformed by the 120o die to a strain of ~4 (route C, N=6). The pole figures were determined by TEM Kikuchi pattern analysis…………………. 129

Fig. 4-35 Microtexture revealed by (100) pole figures obtained from different regions in samples deformed by the 90o die to a strain of ~8 (route C, N=8). The pole figures were determined by TEM Kikuchi pattern analysis…………………. 130

Fig. 4-36 Microtexture revealed by (100) pole figures obtained from different regions in samples deformed by the 120o die to a strain of ~8 (route C, N=12). The pole figures were determined by TEM Kikuchi pattern analysis…………………. 131

Fig. 4-37 TEM micrographs of a specimen deformed by the 90o die (route Bc, N=4). (a) X-plane and (b) Y-plane……………………………………………………… 132

Fig. 4-38 TEM micrographs of a specimen deformed by the 90o die (route Bc, N=8). (a) X-plane and (b) Y-plane……………………………………………………… 133

Fig. 4-39 TEM micrographs of a specimen deformed by the 120o die (route Bc, N=12). (a) X-plane and (b) Y-plane……………………………………………………... 134

Fig. 4-40 (a) Subgrain size and (b) aspect ratio of subgrains in different die angles and routes are shown……………………………………………………………… 135

Fig. 4-41 Distribution of misorientation angles on the Y-plane of specimens deformed to a strain of ~4 by the 90o die (route Bc)………………………………………... 136

Fig. 4-42 Distribution of LABs and HABs on the Y-plane of a sample deformed to a strain of ~4 by the 90o die (route Bc, N=4). (a) TEM micrograph, and (b) a sketch to reveal the distribution of LABs and HABs of the microstructure shown in (a). The thick and thin lines indicate HABs and LABs, respectively, and the dotted lines indicate those boundaries, which were not analyzed…………………... 137

Fig. 4-43 Distribution of misorientation angles measured on the Y-plane of specimens processed by route Bc to a strain of ~8. (a) the 90o die (N=8) and (b) the 120o die (N=12)………………………………………………………………….… 138

Fig. 4-44 Distribution of LABs and HABs on the Y-plane of a sample deformed to a strain of ~8 by the 90o die (route Bc, N=8). (a) TEM micrograph, and (b) a sketch to reveal the distribution of LABs and HABs of the microstructure shown in (a). The thick and thin lines indicate HABs and LABs, respectively, and the dotted lines indicate those boundaries, which were not analyzed…………………... 139

Fig. 4-45 Distribution of LABs and HABs on the Y-plane of a sample deformed to a strain of ~8 by the 120o die (route Bc, N=12). (a) TEM micrograph, and (b) a sketch to reveal the distribution of LABs and HABs of the microstructure shown in (a). The thick and thin lines indicate HABs and LABs, respectively, and the dotted lines indicate those boundaries, which were not analyzed…………………... 140

Fig. 4-46 Cumulative distribution of boundary misorientation angles for specimens processed by different die angles with route Bc and C……………………… 141

Fig. 4-47 Microtexture revealed by (100) pole figures obtained from different regions in samples deformed by the 90o die to a strain of ~4 (route Bc, N=4). The pole figures were determined by TEM Kikuchi pattern analysis…………………. 142

Fig. 4-48 Microtexture revealed by (100) pole figures obtained from different regions in samples deformed by the 90o die to a strain of ~8 (route Bc, N=8). The pole figures were determined by TEM Kikuchi pattern analysis…………………. 143

Fig. 4-48 Microtexture revealed by (100) pole figures obtained from different regions in samples deformed by the 90o die to a strain of ~8 (route Bc, N=8). The pole figures were determined by TEM Kikuchi pattern analysis…………………. 144

Fig. 4-50 TEM micrographs of a sample deformed to a strain of ~8 by using the 90o die (route A). (a) X-plane and (b) Y-plane……………………………………….. 145

Fig. 4-51 (a) Subgrain size and (b) aspect ratio of subgrains in different routes are shown……………………………………………...…………………………. 146

Fig. 4-52 Distribution of misorientation angles measured on the Y-plane of specimens processed by the 90o die to a strain of ~8 (route A)………………………….. 147

Fig. 4-53 Distribution of LABs and HABs on the Y-plane of a sample deformed to a strain of ~8 by the 90o die (route A, N=8). (a) TEM micrograph, and (b) a sketch to reveal the distribution of LABs and HABs of the microstructure shown in (a). The thick and thin lines indicate HABs and LABs, respectively, and the dotted lines indicate those boundaries, which were not analyzed…………………... 148

Fig. 4-54 Cumulative distribution of boundary misorientation angles for different ECAE conditions. The results for random grain orientation (Mackenzie, 1958) are also included in the plot for comparison………………………………………….. 149

Fig. 4-55 Microtexture revealed by (100) pole figures obtained from different regions in samples deformed by the 90o die to a strain of ~8 (route A, N=8). The pole figures were determined by TEM Kikuchi pattern analysis…………………. 150

Fig. 4-56 An example observed in specimen C-4-90-Y. It shows alternating of the orientations of subgrains in a region and the axis of rotation is close to the Y-axis (TD)…………………………………………………………………... 151

Fig. 4-57 The change of orientations of subgrains along a line indicated in (a) is revealed by the (100) pole figure. The example is taken from the specimen of C-4-90-Y……………………………………………………………………... 152

Fig. 4-58 (a) Subgrains arrange along a line indicated with orientations shown in (b). This sample is taken from C-12-120-Y………………………………………. …... 153

Fig. 4-59 (a) Subgrains arrange with orientations shown in (b). This sample is taken from C-4-90-Y……………………………………………………………………... 154

Fig. 5-1 Shearing patterns for a die angle of F=90o and rotation around the X-axis: (a) route A, (b) route C and (c) route Bc…………...………………………..…... 155

Fig. 5-2 The comparison of cumulated percentage of boundary misorientation angles for ECAE route C and CEC (Richert et al. 1999)……………………………….. 157



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