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Phase Transformation in High Entropy Bulk Metallic Glass (HE-BMG) and Lamellar Structured-High Entropy Alloy (HEA)

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Phase Transformation in High Entropy Bulk Metallic Glass (HE-BMG) and Lamellar Structured-High Entropy Alloy (HEA) Phase transformation in High Entropy Bulk Metallic Glass (HE-BMG) and Lamellar Structured-High Entropy Alloy (HEA) Norhuda Hidayah Binti Nordin A thesis submitted for the degree of Doctor of Philosophy Department of Materials Science and Engineering The University of Sheffield 2018 To my late father for his encouragement, Hj Nordin Bin Saad 1 DECLARATION I hereby declare that I have conducted, completed the research work and written the dissertation entitles “Phase transformation in High Entropy Bulk Metallic Glass (HE- BMG) and Lamellar structured -High Entropy Alloys (HEA)”. I also declare that it has not been previously submitted for the award of any qualification or other similar title of this for any other examining body or University. This dissertation contains fewer than 40,000 words including appendices, bibliography, footnotes, equations and tables and has fewer than 80 figures. 2 ACKNOWLEDGEMENTS Thanks God for his blessing I can finish my PhD journey successfully. I owe a debt of gratitude to the people around me for their support and kindness during my PhD studies. First and foremost, I would like to express my sincere gratitude to my supervisors, Prof Iain Todd and Dr Russell Goodall for their guidance, immense knowledge, endless support and treasured suggestions while allowing me to work on my own way. I would also like to say special thanks to the members in Mercury centre, Sorbey centre and technical staff especially Dean Haylock, Dawn Bussey, Joanne Sharp and Ben Palmer for their skill in guiding me to operate the machines confidently and never hesitate to help me in anyway. My sincere thanks also go to all the postdocs and colleagues, Dr Zhao Y Leong, Dr Philips Mahoney, Yuhe, Dr Dikai and Dr Gao that always share their knowledge and skill with me during my PhD programme. I would also like to acknowledge my sponsors, Ministry of High Education Malaysia (MoHE) and International Islamic University Malaysia (IIUM) for the financial support that without which my time in UK would not have been possible. To my dearest husband, Mohd Haikal Idris, thank you for your endless support despite the thousands of miles we have been apart during my final year. Your positive words and your faith in me and ever failed to give me strength to raise our ‘PhD daughter’, Aisya Insyirah on my own while doing this research. I have experienced a tough life when it comes to both studies and parenting responsibilities. But it is become a driving force for me to strive for the best in my studies. I also owe my mother, Mrs Fatimah Arshad and my parent in law, Mr Idris and Mrs Jamilah for their support and prayers for my success. To all my family members, thank you for always support me through my ups and downs life in the UK. To my amazing best friends, Fadhilah, Aina and Atiqah who I shared the goods and tough times and always cherish my life. Thank you for always be there for me and lastly let’s finish whatever we have started! ii 3 TABLE OF CONTENTS 1 DECLARATION ...................................................................................................... i 2 ACKNOWLEDGEMENTS .................................................................................... ii 3 TABLE OF CONTENTS ....................................................................................... iii 4 LIST OF TABLES ................................................................................................ vii 5 LIST OF FIGURES .............................................................................................. viii 6 ABSTRACT ......................................................................................................... xiii 1 CHAPTER 1 - INTRODUCTION .......................................................................... 1 Introduction ................................................................................................. 1 2 CHAPTER 2 - LITERATURE REVIEW .............................................................. 4 High entropy alloys ..................................................................................... 4 2.1.1 A new concept of alloy design ......................................................... 4 2.1.2 Scientific approach to design HEA .................................................. 7 2.1.3 Validity of empirical parameters to the formation of phases........... 9 2.1.4 Four core effects of HEA ............................................................... 14 1. High Entropy effect ......................................................... 14 2. Severe lattice distortion ................................................... 15 3. Sluggish diffusion ............................................................ 16 4. Cocktail effect .................................................................. 17 Phase formation tendency in High Entropy Alloys ................................... 18 2.2.1 Solid solution ................................................................................. 18 2.2.2 Intermetallic ................................................................................... 19 2.2.3 Amorphous .................................................................................... 22 The Metastability of Liquid in High Entropy Alloys ................................ 26 2.3.1 Phase transformation in HEAs ....................................................... 30 2.3.2 Crystallisation kinetics in HE-BMGs ............................................ 32 Alloys design and properties of HEAs with secondary phases ................. 37 iii 2.4.1 Mechanical properties .................................................................... 38 Summary of literature review .................................................................... 49 3 CHAPTER 3 - METHODOLOGY ...................................................................... 51 Introduction ............................................................................................... 51 Materials preparation ................................................................................. 51 3.2.1 Arc melting and casting ................................................................. 51 3.2.2 Melt spinning ................................................................................. 56 Annealing process ..................................................................................... 58 Characterisation techniques ....................................................................... 59 3.4.1 Phase analysis ................................................................................ 59 3.4.1.1 X-Ray diffraction (XRD) ................................................. 59 3.4.1.2 Determination of Phase Fraction by Rietveld refinement 60 3.4.2 Thermal analysis ............................................................................ 61 3.4.2.1 Differential Scanning Calorimetric (DSC) ...................... 61 3.4.2.2 Differential Thermal Analysis (DTA) ............................. 62 3.4.3 Microscopy .................................................................................... 62 3.4.3.1 Scanning Electron Microscopy (SEM) ............................ 62 3.4.3.2 Transmission Electron Microscopy (TEM) ..................... 62 Mechanical Testing.................................................................................... 63 3.5.1 Compression testing ....................................................................... 63 3.5.2 Hardness testing ............................................................................. 64 3.5.2.1 Micro indentation tests .................................................... 64 3.5.2.2 Nano indentation tests ..................................................... 64 4 CHAPTER 4 .......................................................................................................... 66 Crystallisation Kinetics and Thermal Stability of TiZrHfNiCu High Entropy Bulk Metallic Glass by Differential Scanning Calorimetry (DSC) .................................... 66 Abstract ...................................................................................................... 66 Introduction ............................................................................................... 67 Theoretical background ............................................................................. 69 Experimental procedure ............................................................................. 71 4.4.1 Characterisations ............................................................................ 72 4.4.2 Crystallization kinetics experiments .............................................. 72 iv Result and Discussion ................................................................................ 73 4.5.1 Alloys design ................................................................................. 73 4.5.2 Non-isothermal annealing .............................................................. 79 4.5.3 Isothermal annealing ...................................................................... 94 Conclusions ............................................................................................. 101 5 CHAPTER 5 ........................................................................................................ 102 Design of Lamellar-structured High Entropy Alloys with the Addition of Boron Content ..................................................................................................................... 102 Abstract ...................................................................................................
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