REFRACTORY COATINGS FOR CONTAINMENT OF MOLTEN REACTIVE METALS AND THEIR ALLOYS Hui Su B.E. Northeast University of Technology, Shenyang, China, 1984 M.E. Northeast University of Technology, Shenyang, China, 1987 A dissertation submitted to the faculty of the Oregon Graduate Institute of Science & Technology in partial fulfillment of the requirements for the degree Doctor of Philosophy in Materials Science October 1996 The Dissertation "Refractory Coatings for Containment of Molten Reactive Metals and Their Alloys" by Hui Su has been examined and approved by following Examination Committee: Milton R. Scholl, ~hesisAdvisor Assistant Professor James T. ~tanle~;~hesi;p".&r . President, Material Soft ,& David G. Atteridge Professor - - Jack H. Devletian Professor ACKNOWLEDGMENT I would like to express my sincerest appreciation to my thesis advisors, Dr. Milton Scholl and Dr. James T. Stanley, for their guidance, support and patience through this work. I also wish to thank the other members of my dissertation committee, Dr. David Atteridge and Dr. Jack H. Devletian for their time and effort spent as committee members and examining my dissertation and sharing their professional opinions. I am grateful to Dr. Don Mc Murchie for his invaluable help in the plasma spraying laboratory. I would also like to acknowledge Dr. Jack Mccarthy and Mr. Steven Brooks for their help and cooperation in SEM and TEM analysis and melting experiments. I would like to express my appreciation to Dr. Paul Clayton, my four year SPC chairman, for his invaluable advice and help in my course curriculum. I also would like to thank Department Head Dr. Bill Wood for his help, especially for the final year financial support. I would like to thank my fellow students at OGI: Hua Li, Youping Gao, Xihong Wang, Shiliang Ding, Lu Fang, Xiaoyen Su, W.Y. Shen, Jun Ding, Nong Jin, Badih J. Rask, Cangsang Zhao, Dawei Shen, Wei Su, Xiao Chen for their help and friendship. I would like to thank Oregon Metallurgical Corporation and the Oregon Metal Initiative for sponsoring this projects. Finally I would like to thank my wife Ding Ding for her love, never ending support, encouragement and patience, and my parents for their spiritual and emotional support. TABLE OF CONTENTS TITLE PAGE .................................................................................................................. i .. APPROVAL PAGE ........................................................................................................ n ... ACKNOWLEDGMENT ................................................................................................. m TABLE OF CONTENTS ................................................................................................ iv LIST OF TABLES .......................................................................................................... vi LIST OF FIGURES ........................................................................................................ vii ABSTRACT .................................................................................................................... x CHAPTER 1 INTRODUCTION ................................................................................... 1 CHAPTER 2 LITERATURE REVIEW ........................................................................ 11 TITANIUM CHARACTERISTICS AND CRUCIBLE REQUIREMENTS ........... 11 CERAMIC CRUCIBLES FOR MELTING OF TITANIUM AND ALLOYS ........ 12 COATED CRUCIBLES FOR TITANIUM AND ITS ALLOYS ............................ 33 COATED CRUCIBLES FOR OTHER REACTIVE METALS .............................. 35 CONTINUOUS CASTING OF TITANIUM AND ITS ALLOYS .......................... 38 SUMMARY OF PREVIOUS RESEARCH ............................................................. 43 EXISTING PROBLEMS .......................................................................................... 46 SELECTION OF REFRACTORY MATERIALS ................................................... 47 SELECTION OF FABRICATION METHOD ......................................................... 47 General Introduction of Coating Technologies .................................................. 47 Thermal Spray Processes .................................................................................... 50 CHAPTER 3 EXPERIMENTAL APPROACH ............................................................ 55 EXPERIMENTAL PROCEDURE ........................................................................... 55 Experimental Equipment ..................................................................................... 55 Experimental Materials ....................................................................................... 55 Plasma Spray Process .......................................................................................... 58 Melting Process ................................................................................................... 58 MICROSCOPY ANALYSIS .................................................................................... 60 Optical Microscopy ............................................................................................ 60 Scanning Electron Microscopy ........................................................................... 61 Transmission Electron Microscopy ................................................................... 61 CHAPTER 4 EXPERIMENTAL RESULTS ................................................................ 62 DEVELOPMENT OF OPTIMUM PLASMA SPRAYING PARAMETERS ......... 62 PHYSICAL CONTAINMENT OF MOLTEN TITANIUM .................................... 62 CHEMICAL COMPATIBILITY OF MOLTEN ALLOYS AND COATINGS ...... 72 Single Oxide Crucibles ....................................................................................... 72 Complex Oxide Crucibles ................................................................................... 74 INDUCTION MELTING RESULTS ....................................................................... 89 MELTING OF TITANIUM ALUMINIDE COMPOUND ...................................... 90 BOND LAYER AND INTERMEDIATE LAYER .................................................. 95 TEM ANALYSIS OF COATINGS .......................................................................... 101 CHAPTER 5 THERMODYNAMIC STUDY RESULTS AND DISCUSSION ........... Ill SOLUBILITY OF SINGLE OXIDES IN MOLTEN TITANIUM .......................... Ill SOLUBILITY OF COMPLEX OXIDES IN MOLTEN TITANIUM ...................... 120 THE OXYGEN ACTIVITY DEPENDENCE OF INTERFACE REACTION BETWEEN MOLTEN TITANIUM AND OXIDE .................................................. 129 CHAPTER 6 COMPARISON OF EXPERIMENTAL RESULTS AND THEORETICAL ANALYSIS AND DISCUSSION ...................................................... 133 DISCUSSION OF THERMODYNAMIC ANALYSIS ........................................ 133 THERMODYNAMIC ANALYSIS IN SINGLE OXIDE CRUCIBLES ................. 135 THERMODYNAMIC ANALYSIS IN COMPLEX OXIDE CRUCIBLES ............ 140 DEGRADATION MECHANISMS OF CRUCIBLE COATINGS .......................... 142 A GENERAL APPROACH FOR SELECTION OF REFRACTORY COMPOUND ............................................................................................................ 143 COMMERCIALIZATION OF CONTINUOUS CASTING ..................................... 144 FUTURE WORK ....................................................................................................... 145 CHAPTER 7 CONCLUSIONS ..................................................................................... 147 REFERENCES ................................................................................................................ 149 BIOGRAPHICAL NOTE ............................................................................................... 155 LIST OF TABLES Reaction couples ................................................................................................. 15 Comparison of crucible performance for yttrium oxide crucibles ...................... 22 Contamination of Ti.2.7Be melts made in ceramic crucibles ............................. 23 Chemical composition of remelted Mar M-247 using various crucibles ............ 28 Gas content in target alloys for recording film using the calcia refining process ................................................................................................................. 28 Impurities in target alloys for read/write head using the calcia refining process ................................................................................................................. 29 Comparison of size distribution of inclusions distribution in a 3.5 GPa Maraging steel between normal and calcia melting ............................................ 29 Free energy and solubility data of various compounds ....................................... 49 The thermal and mechanical properties of graphite ............................................ 56 Optimized spray parameters for original gun anode ........................................ 63 Optimized spray parameters for replacement gun anode .................................... 68 List of the melt experiments ................................................................................ 69 Free energy of formation of complex oxides for one mole oxygen .................... 120 Free energy of formation from the constituent oxides to complex oxides .......... 121 Experimental and theoretical results of solubility product of Y203in liquid titanium ..............................................................................................................