Experimental study of the microstructural evolution of chemical vapour deposited nickel upon ...

113 Pages·2011·6.88 MB·English

Experimental study of the microstructural evolution of
chemical vapour deposited nickel upon annealing
by
Chichi Chen
A thesis submitted in conformity with the requirements
for the degree of Master of Applied Science
Materials Science and Engineering
University of Toronto
© Copyright by Chichi Chen 2011
Abstract

Experimental study of the microstructural evolution of chemical
vapour deposited (CVD) nickel upon annealing
Chichi Chen
Master of Applied Science
Materials Science and Engineering
University of Toronto
2011
The effect of annealing conditions on the microstructure evolution of CVD nickel was
investigated systematically in the present study by differential scanning calorimetry, optical
microscopy and transmission electron microscopy (TEM), upon both ex-situ and in-situ
annealing. TEM observation revealed the as-deposited CVD nickel possessed a bi-modal grain
structure, with large columnar grains embedded in nanocrystalline matrix. Ultrafine and nano
growth twins were present as well as multiply twinned grains with five-fold symmetry.
Microstructure observation upon annealing showed that grain growth did not occur until
annealing at 400ºC. Detwinning was observed at 400ºC and higher temperatures. The ultrafine
and nano twins tended to transform into dislocation cell structures and this phenomenon was
driven by the excess free energy associated with the high density of grown-in twin boundaries.
The five-fold twinned grains were found to be thermally stable up to 600ºC. The hardness was
observed to decrease with increasing annealing temperature.
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Acknowledgements

I would like to take this opportunity to acknowledge all the people who have showed their
support throughout this project. First and foremost, I would like to give many thanks to my
supervisor Professor Zhirui Wang. This thesis would not have been possible without his expert
professional guidance, patience and encouragement in all aspects of this project. Furthermore,
my gratitude is extended to Mike Mei and Sal Boccia for their helpful suggestions and technical
assistance with Electron Microscopy, Srebri Petrov and John Graydon for their professional
analysis and suggestions during my experiment and all my colleagues Zongshu Li, Jean Hsu,
Jun Huang for their helpful discussions and technical support. Finally, the material supply from
Weber Manufacturing Technologies Inc. is highly appreciated.

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Table of contents
Contents
Abstract ........................................................................................................................................... ii
Acknowledgements ........................................................................................................................ iii
Table of contents ............................................................................................................................ iv
List of Tables ................................................................................................................................. vi
List of Figures ............................................................................................................................... vii
List of Appendices ........................................................................................................................ xii
1 Introduction ............................................................................................................................. 1
1.1 Nanocrystalline materials .................................................................................................. 2
1.1.1 Definition ................................................................................................................... 2
1.1.2 Preparation of bulk nanocrystalline materials ............................................................ 4
1.1.3 Mechanical properties of nanocrystalline materials .................................................. 7
1.2 Chemical vapor deposition ............................................................................................... 9
1.2.1 Introduction ................................................................................................................ 9
1.2.2 Nickel Vapour Deposition ......................................................................................... 9
1.2.3 Structure and grain morphology of CVD nickel ...................................................... 13
1.2.4 Mechanical properties of CVD nickel ..................................................................... 17
1.2.5 Advantages of nickel vapor deposition over electroforming ................................... 21
1.3 Thermal stability of nanocrystalline materials ................................................................ 22
1.3.1 Thermal stability of cold worked materials ............................................................. 22
1.3.2 Thermal stability of nanocrystalline nickel .............................................................. 26
1.4 Twinning and detwinning in FCC materials ................................................................... 31
1.4.1 Twinning and its effect on materials properties ....................................................... 31
1.4.2 Stability of nanotwins in FCC materials .................................................................. 31
2 Experimental .......................................................................................................................... 36
2.1 Material ........................................................................................................................... 36
2.2 Thermal stability analysis via DSC ................................................................................. 37
2.3 Microstructure evolution investigation ........................................................................... 38
2.3.1 Optical microscopy .................................................................................................. 38
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2.3.2 Grain boundary tracking via semi in-situ optical microscopy ................................. 39
2.3.3 Transmission electron microscopy (TEM) .............................................................. 39
2.3.4 Hot stage In-situ TEM ............................................................................................. 39
2.4 Microhardness and Rockwell hardness testing ............................................................... 40
3 Results ................................................................................................................................... 41
3.1 Thermal stability investigation using DSC ..................................................................... 41
3.2 Preliminary analysis using Optical Microscopy ............................................................. 42
3.2.1 Characteristics of as-received CVD nickel .............................................................. 42
3.2.2 Microstructure evolution upon annealing ................................................................ 43
3.2.3 Grain boundary tracking by Semi in-situ OM ......................................................... 45
3.3 Detailed analysis using Transmission Electron Microscopy .......................................... 47
3.3.1 Characteristics of as-deposited CVD nickel ............................................................ 47
3.3.2 Microstructure evolution upon annealing ................................................................ 53
3.4 Hot stage In-situ TEM .................................................................................................... 68
3.5 Mechanical properties of CVD nickel upon annealing ................................................... 70
4 Discussions ............................................................................................................................ 72
4.1 Grain growth behaviour of CVD nickel upon annealing ................................................ 72
4.2 Thermal stability of ultrafine and nano twins in CVD nickel ......................................... 74
4.3 Thermal stability of five-fold twinned structures ........................................................... 78
4.4 Analysis on the stable structure in hot stage in-situ TEM .............................................. 81
4.5 Thermal stability of CVD nickel in terms of mechanical properties .............................. 83
5 Conclusions ........................................................................................................................... 84
6 Future Work ........................................................................................................................... 86
7 Appendices ............................................................................................................................ 87
8 References ............................................................................................................................. 96
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List of Tables
Table 1.1 Properties summary of CVD nickel, conventional nickel and electrodeposited
nickel……………………………………………………………………………………………..18
Table 1.2 Chemical composition of CVD nickel………………………………………………...18
Table 1.3 Mechanical properties of Ni and Ni-B alloys………………………………………....20

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List of Figures

Figure 1.1 Atomic structure of a two dimensional nanocrystalline material……………………...2
Figure 1.2 Schematic illustrations of four types of nanocrystalline materials showing structure in
different numbers of dimensions……………………………………………………………….….3
Figure 1.3 Schematic representations of severe plastic deformation setup……………...…….….6
Figure 1.4 A schematic diagram of Hall-Petch relation and inverse Hall-Petch relation………....8
Figure 1.5 Schematic representations of the CVD reactor…………………………………….…10
Figure 1.6 Schematic of three types of structures obtained by CVD…………………………….14
Figure 1.7 Optical image showing typical grain structure of pure CVD nickel…………………15
Figure 1.8 Microstructure of a CVD pure nickel………………………………………………...15
Figure 1.9 (a) Five <011> subgrains meet to form a pentagon (b) zone axis diffraction pattern of
the pentagon in (a)………………………………………………………………………………..16
Figure 1.10 (a) A regular decahedron consisting of five irregular tetrahedrons (b) Relationship
between the fcc and bco structure………………………………………………………………..17
Figure 1.11 Micro-hardness as a function of boron content for as deposited and Ni and Ni-B
alloys……………………………………………………………………………………………..19
Figure 1.12 (A) Electroformed nickel (B) CVD nickel………………………………………….21
Figure 1.13 Various stages involved in the recovery of a plastically deformed material………..23
Figure 1.14 Polygonization of the bent crystal containing edge dislocations……………………24
Figure 1.15 Mechanism of subgrains rotation and coalescence………………………………….25
Figure 1.16 Schematic representation of grain growth through atomic diffusion……………….26

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Figure 1.17 DSC scan of a 20 nm grain sized Ni deposits at heating rate of 10K/min……….…27
Figure 1.18 Bright field TEM micrographs of electrodeposited nickel in as-received condition.28
Figure 1.19 Optical micrograph of the nanocrystalline nickel after annealing at 773K for 8
hours………………………………………………………………………………………….…..30
Figure 1.20 XTEM and cross-sectional HRTEM micrographs of epitaxial nanotwinned Cu films
at the tip of a nanoindentor……………………………………………………………………....33
Figure 1.21 Snapshots of in-situ TEM micrographs of Σ3{112} ITBs before indentation…..….34
Figure 1.23 Schematics of three proposed detwinning processes…………………………….….35
Figure 2.1 Bulk nickel prepared by nickel carbonyl vapour deposition with 16 mm
thickness……………………………………………………………………………..……….…..36
Figure 2.2 Schematic representation of bulk CVD nickel on the substrate with the growth
direction indicated…………………………………………………………………………….….36
Figure 2.3 Schematic of a heat flux DSC with disk-type measuring system………………….…37
Figure 3.1 Thermal stability investigation of CVD nickel through Differential Scanning
Calorimetry at a heating rate of 20°C/min…………………………………………………….…41
Figure 3.2 Optical micrographs showing the microstructure of as-received CVD nickel…….…43
Figure 3.3 Grain morphology of CVD nickel at planar view after isothermal annealing for 45
minutes at various temperatures…………………………………………………………….……44
Figure 3.4 Grain morphology of CVD nickel at transverse view after isothermal annealing for 45
minutes at various temperatures…………………………………………………………….……45
Figure 3.5 Semi in-situ tracking of grain growth under optical microscope…………………….46
Figure 3.6 Ultrafine and nano grains surrounding the large columnar grains in as-deposited CVD
nickel in the transverse direction………………………………………………………………...48

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Figure 3.7 TEM micrographs showing the morphology of large columnar grains in as-deposited
CVD nickel………………………………………………………………………………………49
Figure 3.8 (a) High density of growth twins inside the large columnar grains (b) Distribution of
twin thickness showing all the twins are in the ultrafine and nano size range……………….….50
Figure 3.9 TEM images showing five-fold twinned structures embedded in the bi-modal grains
of as-deposited CVD nickel……………………………………………………………………...52
Figure 3.10 Microstructure evolution of CVD nickel upon annealing at 200ºC, 400ºC, 600ºC and
800ºC in the planar direction observed under TEM……………………………………………..54
Figure 3.11 Microstructure evolution of CVD nickel upon annealing at 200ºC, 400ºC, 600ºC and
800ºC in the transverse direction observed under TEM…………………………………………55
Figure 3.12 (a) Twin receding in the form of step movement (b) Dislocation configuration at the
migrating step fronts……………………………………………………………………………..56
Figure 3.13 Receding of growth twins took place in a five-fold twinned grain…………………57
Figure 3.15 Partial dislocations formed at both the end of twins and the misfitted sites traversed
by dislocation lines……………………………………………………………………………….57
Figure 3.16 Tangled dislocations along twin boundaries with some of them extending into the
lattice…………………………………………………………………………………………….58
Figure 3.17 Twin boundaries transformed into dislocation array structures…………………….58
Figure 3.18 (a) Twin boundaries turned into dislocation lines and disappeared (b) dislocations
emitted from twin boundaries into the twinned crystal…………………………………………..59
Figure 3.19 Dislocation cell structures formed in the cleared grain interior after detwinning; twin
boundaries became darker and blurred full of tangled dislocations……………………..……….60
Figure 3.20 (a) One grain with half of the growth twins transformed into dislocation cells (b)
Dislocation cells were formed both at the detwinning front and directly at twin boundaries..….60
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Figure 3.21 (a) Dislocation arrays formed at the end of twins and along twin boundaries (b)
detwinning by migration of dislocation arrays and dislocation emission………………………..62
Figure 3.22 Morphology of nanotwins inside the large grains traversed by dislocation walls after
annealing at 600 ºC……………………………………………………………………………....63
Figure 3.23 (a) Dislocation cell walls formed at the moving steps of a twin lamella (b) Non-
uniform size distribution of dislocation cells at 800 ºC………………………………………….64
Figure 3.24 Schematic demonstration of the formation of dislocation cells at the tip of a receding
twin lamella. Traces of dislocations left from detwinning became part of a dislocation cell
wall……………………………………………………………………………………………….65
Figure 3.25 Five-fold twinned structures in CVD Ni of as-deposited condition and after
annealing at 400ºC and 600ºC……………………………………………………………………66
Figure 3.26 In-situ TEM images showing the microstructure of the same location upon annealing
up to 661ºC…………………………………………………………………………………….…68
Figure 3.27 Morphology of a five-fold twinned grain upon annealing from room temperature up
to 655ºC in hot stage TEM……………………………………………………………………….70
Figure 3.28 Microhardness of CVD nickel on planar and transverse direction upon
annealing………………………………………………………………………………………....71
Figure 3.29 Rockwell hardness of CVD nickel on planar and transverse direction upon
annealing…………………………………………………………………………………………71
Figure 4.1 Model of grain rotation and growth induced by deformation in nanocrystalline Ni…74
Figure 4.2 Proposed possible detwinning mechanisms for CVD nickel upon annealing………..76
Figure 4.3 Strain energy density of twin boundaries and dislocations in polycrystalline copper..78
Figure 4.4 HREM image of the central area of the five-fold twinned grain……………………..79

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