Effect of Large Shear Deformation on Rail Steels and Pure Metals

More documents

Recommendations

Info

$dissertation global and local fracture properties of metal matrix ...$

3 3 Results and Discussion Figure 3.9: TEM bright field micrographs <strong>of</strong> (a) initial microstructure <strong>of</strong> 900A, (b) HPT deformed 900A, ɛeq = 8 and (c) HPT deformed HSH, ɛeq = 8. Figure 3.10: TEM micrographs <strong>of</strong> (a)HPT deformed HSH, ɛeq = 2, bright field (b) corresponding dark field image and (c)HPT deformed HSH, ɛeq = 8, dark field. ford 52, 53 investigated the microstructural evolution in wire drawing <strong>of</strong> pearlitic steels and the resulting changes in strength. The results presented in these papers are very similar to the present findings. Also in wire drawing an intensive alignment <strong>of</strong> the lamellae in the drawing direction is observed. The main mechanism for the increase in strength was found to be the decreasing lamellae distance, this was confirmed by many studies, see for instance. 54, 55 Later investigations 56–60 revealed that also in drawn pearlitic wires dissolution <strong>of</strong> cementite can be observed. Two reasons for this dissolution are discussed in the literature: Firstly, it is assumed that the binding energy <strong>of</strong> carbon atom to a dislocation is larger than the binding energy <strong>of</strong> the carbon in the carbide. Therefore, carbon atoms are dragged out <strong>of</strong> the carbide by crossing dislocations. Secondly, it is assumed that the very fine carbides resulting from this deformation become thermodynamical unstable due to the Gibbs Thomson effect. A comprehensive discussion about the different mechanisms is given by Gavriljuk. 61 There is even less agree- 20
3.2 Structural Evolution <strong>of</strong> Rail Steels during Severe Plastic <strong>Deformation</strong> Figure 3.11: (a) Measured EEL spectra <strong>of</strong> ferrite and carbide in the initial microstructure (b) Fe-L2/L3 area and peak high ratio for various measurements in the initial microstructure (c) FWHM for various measurements in the initial microstructure and (d) Comparison <strong>of</strong> the Fe-L3/Fe-L2 ratio <strong>of</strong> undeformed and deformed samples. The black lines mark the average values in the initial microstructure, the gray lines mark the highest and lowest observed values in the initial microstructure. ment about the question, where the carbon is situated after the dissolution. Ivanisenko et al. 62 and Sauvage 63 reported that a dissolution <strong>of</strong> the cementite lamellae can occure after HPT. The microstructures, the mechanical properties and the observed dissolution <strong>of</strong> carbide seem to be in good agreement with the present finding. Nevertheless it has to be noted that the strains needed to reach this results are much higher in their investigations. 3.2.2 Cyclic High Pressure Torison The microstructure resulting from Cyclic High Pressure Torsion is depicted in Figure 3.13. Similar as in pure metals, also the microstructure <strong>of</strong> the rail steels is strongly influenced by the strain per cycle. After CHPT with a small ∆ɛ the main feature are severely fragmented carbides that are aligned parallel to the shear plane. There are no indications that something like a dissolution <strong>of</strong> the carbon from the carbides has occured. After CHPT with a large ∆ɛ the microstructure is quite similar like in a monotonic deformed sample, but the strains needed for a 21 3
Page 1 and 2: University of Leob
Page 3: ASTRID, LÄTITIA
Page 7 and 8: Danksagung Die hier vorliegende Arb
Page 9 and 10: Summary The investigation o
Page 11 and 12: Kurzfassung Die Untersuchung der Au
Page 13 and 14: Sobald jemand in einer Sache Meiste
Page 15 and 16: Contents 1 Introduction 1 1.1 Motiv
Page 17 and 18: Contents E.3.2 Mechanical strengths
Page 19 and 20: 1.1 Motivation 1 Introduction Today
Page 21 and 22: 1.2 Objectives The aim of</
Page 23 and 24: 2 Methods of Sever
Page 25 and 26: 2.2 Equal Channel Angular Pressing
Page 27 and 28: 2.2 Equal Channel Angular Pressing
Page 29 and 30: 3 Results and Discussion In the fol
Page 31 and 32: 3.1 Structural Evolution of
Page 37: 3.2 Structural Evolution of
Page 45 and 46: 3.3 Mechanical Properties In contra
Page 47 and 48: 3.3 Mechanical Properties Figure 3.
Page 49 and 50: 3.3 Mechanical Properties Figure 3.
Page 51 and 52: 3.3 Mechanical Properties can be se
Page 53 and 54: 4 Conclusions The methods o
Page 55 and 56: [1] G. Baumann, H.-J. Fecht, and S.
Page 57 and 58: Bibliography [36] T. Hebesberger, H
Page 59 and 60: 5 List of appended
Page 61 and 62: A Structural Refinement of<
Page 63 and 64: A.1 Introduction A.1 Introduction K
Page 65 and 66: A.3 Results Figure A.2: Micrograph
Page 67 and 68: A.4 Discussion Figure A.3: Microgra
Page 69 and 70: Bibliography to paper A [1] W. Lojk
Page 71 and 72: B Structural Changes of</st
Page 73 and 74: B.1 Introduction B.1 Introduction D
Page 75 and 76: B.3 Results and Discussion after a
Page 77 and 78: Figure B.5: 2Θ scans of</s
Page 79 and 80: B.4 Conclusion B.4 Conclusion • T
Page 81 and 82: Bibliography to paper B [1] G. Baum
Page 83 and 84: C Strain Hardening during High Pres
Page 85 and 86: C.1 Introduction C.1 Introduction R
Page 87 and 88: C.3 Results With this equation it i
Page 89 and 90:
C.4 Discussion Figure C.4: SEM micr
Page 91 and 92:
Bibliography to paper C [1] T. Hebe
Page 93 and 94:
D Formation of sur
Page 95 and 96:
D.1 Introduction D.1 Introduction T
Page 97 and 98:
D.3 Results D.3.1 Monotonic <strong
Page 99 and 100:
D.3 Results Figure D.4: SEM microgr
Page 101 and 102:
D.4 Discussion Figure D.6: SEM micr
Page 103 and 104:
occurring on the surface of
Page 105 and 106:
Bibliography to paper D [1] Y. K. C
Page 107 and 108:
E High Pressure Torsion of<
Page 109 and 110:
E.1 Introduction E.1 Introduction T
Page 111 and 112:
E.3 Results Figure E.2: SEM microgr
Page 113 and 114:
E.3.2 Mechanical strengths E.4 Disc
Page 115 and 116:
Bibliography to paper E [1] L. Wang
Page 117 and 118:
F TEM Investigation of</str
Page 119 and 120:
F.1 Introduction F.1 Introduction C
Page 121 and 122:
F.4 Discussion see Figure F.2b. The
Page 123 and 124:
Figure F.3: In-situ measured torque
Page 125 and 126:
F.4 Discussion Figure F.6: Comparis
Page 127 and 128:
F.6 Appendix • Electron energy-lo
Page 129 and 130:
[1] M. Zelin. Acta Mater., 50(17):4
Page 131 and 132:
G Fracture Processes in Severe Plas
Page 133 and 134:
G.2 Introduction G.2 Introduction T
Page 135 and 136:
G.4 Results toughness test. It can
Page 137 and 138:
G.5 Discussion Figure G.3: (a) Load
Page 139 and 140:
G.5.2 Fracture G.5 Discussion Fract
Page 141 and 142:
Bibliography to paper G [1] J. D. E
Page 143 and 144:
H Cyclic High Pressure Torsion <str
Page 145 and 146:
H.1 Introduction H.1 Introduction I
Page 147 and 148:
Figure H.2: Sample preparation for
Page 149 and 150:
H.3 Results With increasing ∆ɛ a
Page 151 and 152:
H.3 Results Figure H.7: SEM microgr
Page 153 and 154:
H.3 Results between 2°and 15°, th
Page 155 and 156:
H.4 Discussion comparable to ECAP R
Page 157 and 158:
H.5 Conclusions bon steels as a fun
Page 159 and 160:
H.5 Conclusions • The steady stat
Page 161 and 162:
Bibliography to paper H [1] Y. T. Z
Page 163 and 164:
Bibliography to paper H [33] C. Buq
Page 165 and 166:
I Structural Evolution during Cycli
Page 167 and 168:
I.1 Introduction I.1 Introduction T
Page 169 and 170:
I.3 Results Figure I.2: SEM microgr
Page 171 and 172:
I.4 Discussion be seen that saturat
Page 173 and 174:
I.5 Conclusions structure size is a
Page 175:
[1] H. Mughrabi. Mater. Sci. Eng.,
show all

Effect of Large Shear Deformation on Rail Steels and Pure Metals

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?