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  • 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

  • ii

    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.

  • iii

    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.

  • iv

    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

  • v

    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