Structural Investigation of Size Effects in Plasticity using Indentation ...

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

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Abstract It was found, that contrary to the predictions of classic continuum plasticity theory, the plastically deformed zone below nano-, micro- and macroindentations is not selfsimilar. Rather, different stages of deformation associated with varying sizes of the deformed regions were detected. Examining cross-sections through nanoindentations in copper by means of electron backscatter diffraction (EBSD) technique, show that different characteristic deformation patterns occur. For large nanoindentations (2.5 mN–10 mN) a plastically deformed zone, which consists of three characteristic regions is found, while for shallow nanoindentations (≤ 1 mN) only two characteristic sections appear. Due to these findings it can be assumed, that a change in the deformation mechanism between large and shallow nanoindentations takes place. Analysis of the corresponding hardness data in terms of geometrically necessary dislocations (GNDs) using the Nix-Gao model, supports the assumption of a “mechanism change”. To explain the observed behavior, two models based on possible dislocation arrangements are suggested and compared to the experimental findings. The model presented for large imprints is similar to the dislocation pile-up model explaining the Hall-Petch effect, while the model for shallow nanoindentations uses far-reaching dislocation loops to accommodate the shape change caused by the indenter. Further evidence for a change of the deformation mechanism were delivered by additionally performed transmission electron microscopy (TEM) experiments. As the TEM experiments show, the plastically deformed zone of large nanoindents consists of high density dislocation networks, intermitted by almost dislocation free regions. The deformation zone found for small nanoindentations, however, looks somewhat different. Instead of dense networks of dislocations, the plastically deformed zone is built up by single dislocation loops surrounding the imprint. The plastic deformation zone below microindentations (> 10 mN–300 mN) can as well be divided into three characteristic regions. Noticeable is, that the dimension of the zone where significant changes of the orientation occur, is proportional to the size of the imprint. For macroindentations (> 300 mN–100 N) the plastically deformed zone consists of only two characteristic regions. The identified regions exhibit a structure, which is typical for low and medium deformed face-centered cubic single crystals of pure metals. With increasing load, dislocation substructures which exhibit orientation IX
Page 1 and 2: University of Leoben Dissertation S
Page 3: To my family
Page 7: Acknowledgements I would like to ex
Page 11 and 12: Istud, quod tu summum putas, gradus
Page 13 and 14: Contents Affidavit V Acknowledgemen
Page 15 and 16: 1.1 A short review on indentation s
Page 17 and 18: 1.1 A short review on indentation s
Page 19 and 20: 1.3 Summary of the thesis volumes,
Page 21 and 22: 1.3 Summary of the thesis stress wh
Page 23 and 24: Bibliography [1] Mott BW. Micro-Ind
Page 25 and 26: Bibliography [41] Fleck NA, Muller
Page 27 and 28: 2 List of appended papers Paper A M
Page 29 and 30: A Microstructural investigation of
Page 31 and 32: A.2 Experimental details and materi
Page 33 and 34: A.3 Results Figure A.3: Misorientat
Page 35 and 36: A.3 Results surface, shows a rotati
Page 37 and 38: A.3 Results profiles are presented
Page 39 and 40: A.3 Results Figure A.9: Application
Page 41 and 42: A.4 Discussion majority of the disl
Page 43 and 44: A.4 Discussion the experimental obs
Page 45: A.5 Summary and conclusions The dif
Page 48 and 49: Bibliography to paper A [20] Viswan
Page 50 and 51: B The deformation-induced zone belo
Page 58 and 59:
B The deformation-induced zone belo
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C Where are the geometrically neces
Page 63 and 64:
C.2 Experimental planes that are ar
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C.3 Comparison - Single crystal and
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C.4 Hardness in the proximity of a
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C.5 Summary and conclusions Of cour
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D Microstructural investigation of
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D.3 Results and discussion between
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D.3 Results and discussion the defo
Page 79 and 80:
τβ = τsource + τback = Gb 2πs
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[1] Gane N, Cox JM. Philos Mag A 19
Page 84 and 85:
E Stacking fault energy and indenta
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Bibliography to paper E [19] Gottst
Page 94 and 95:
F Indentation across size scales -
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Bibliography to paper F [1] Tabor D
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G TEM sample preparation using the
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G.2 Specimen preparation method Fig
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G.3 Results and discussion 180 to e
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G.4 Conclusions Figure G.4: Cross-s
Page 114:
Bibliography to paper G [18] Massl
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