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Ann Arbor, MI 48106 THE DEVELOPMENT AND PERFORMANCE OF CHROMIDM/REACTIVE ELEMENT-MODIFIED ALUMINIDE DIFFUSION COATINGS BY CHLORIDE- ACTIVATED PACK CEMENTATION DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University by Robert Bianco, B.S., M.S. ***** The Ohio State University 1992 Dissertation Committee: Approved by R.A. Rapp S.A. Dregia Advisor G.W. Powell Program in Metallurgical Engineering To Susan, the best is yet to be! 11 ACKNOWLEDGMENTS I wish to thank Prof. Robert A. Rapp for his assistance and encouragement during this investigation and for giving me the opportunity to attend and present this study at several technical conferences in my field. I would also like to thank the financial support from the Office of Naval Research (A.J. Sedriks) and the Naval Air Development Center (T.A. Kircher). Technical assistance and coating evaluation from the NASA Lewis Research Center especially Drs. James L. Smialek and Nathan S. Jacobson, who initiated me into this challenging field, is gratefully appreciated. In addition, the assistance of Dr. Rex Hussey of the National Research Council, Ottawa, Canada with the SIMS study is also recognized. I would like to offer a special thanks to the members of my dissertation committee: Profs. Dregia and Powell. Their comments and criticism were quite helpful in clarifying this document. I wish to thank my fellow graduate students for their friendship and generosity: Mike Antony, Tom Broderick, Dan Evans, Andy Gordon, Karthick Gourishankar, Brent Harle, Chungwei Hsia, Patrick LeBlanc, Greg Meszaros, Jim Moore, iii Jon Papal, John Naizer, and Craig Miller. I would also like to thank the members, past and present, of the high temperature coatings group; Denis O'Connell, Ed Naylor, Fred Geib, Brian Cocheram, Mark Harper, and Drs. Choquet, Ravi, Wang, and Strawbridge. I wish them all much future success. A special thanks to my good friends: Jeff Moser, Drew Mueller, and Dave Miller; whose early morning golf outings will never be forgotten. The assistance of Dorothy Savely, Clare McDonald, David Little, Jack Kocka, Gary Dodge, and Bud Farrar has been essential and greatly appreciated. Finally, I wish to thank my parents and family for their constant love and encouragement throughout my life. Without their support, all this work and effort would not have been possible. For this, I am eternally grateful and indebted. Lastly, I wish to thank the most important person in my life, my wife Susan. Her love and support will always be remembered. The best is yet to be! IV VITA June 3, 1966 Born-Indiana, Pennsylvania December 1988 B.S. Metallurgical Engineering The Ohio State University Columbus, Ohio. August 1991 M.S. Metallurgical Engineering The Ohio State University Columbus, Ohio. August 1991-present Graduate Research Associate Department of Materials Science and Engineering The Ohio State University Columbus, Ohio. PUBLICATIONS *R. Bianco, J. Electrochem. Soc.. 136 (1989) 265C. *R. Bianco and N.S. Jacobson, J. Mater. Sci.. 24 (1989) 2903. *R. Bianco and R.A. Rapp, "Simultaneous Chromizing- Aluminizing of Nickel-Base Superalloys with Reactive Element Additions," in High Temperature Chemistrv V . W.B. Johnson and R.A. Rapp (Eds.), The Electrochemical Society, Inc., Pennington, NJ (1990) 211. *R. Bianco, M.A. Harper, and R.A. Rapp, J. Metals. 43 No. 11 (1991) 68. V FIELDS OF STUDY Major Field: Metallurgical Engineering Studies in: Chemical Metallurgy R.A. Rapp, G.R. St. Pierre, Y. Sahai, E. Nygren Physical Metallurgy P.G. Shewmon, G. Meyrick, S.A. Dregia Mechanical Metallurgy R.H. Wagoner, P. Anderson, G.S. Daehn Corrosion R.A. Rapp, B.E. Wilde, S. Smialowska Solidification C.E. Mobley Solid-State Physics R. Sooryakumar Electron Microscopy W.A.T. Clark VI TABLE OF CONTENTS ACKNOWLEDGMENTS................................... Ü i VITA ............................................................ V LIST OF TABLES ..................................... ix LIST OF FIGURES................................... xiii ABSTRACT ........................................ xxiii CHAPTER PAGE I. INTRODUCTION................................... 1 II. LITERATURE SURVEY ........................... 14 2.1 Halide-Activated Pack Cementation Diffusion Coatings........................ 14 2.1.1 Aluminizing...................... 14 2.1.2 Chromizing........................ 26 2.1.3 Siliconizing...................... 29 2.1.4 Deposition of a Reactive Element. 31 2.1.5 Codeposition...................... 33 2.2 Thermodynamics and Kinetics of Pack Cementation.......................... 37 2.2.1 Single Element Deposition .......... 37 2.2.2 Codeposition........................ 49 2.3 Degradation of Pack Cementation Diffusion Coatings........................ 54 2.3.1 Interdiffusion.................... 55 2.3.2 Oxidation........................ 56 2.3.3 Fused Salt Attack (Hot Corrosion) . 63 2.4 Reactive Element (RE) Effect............... 68 2.4.1 Observations........................ 69 2.4.2 Mechanical Behavior ............... 71 2.4.3 Chemical Behavior ................. 72 2.4.4 New Theories........................ 75 III. EXPERIMENTAL PROCEDURES ..................... 79 3.1 Materials ................................ 79 3.2 Diffusion Coating Procedures............... 82 3.3 Characterization of the Diffusion Coatings..................................86 Vll 3.4 Analysis of Vapor Species Evolved from Pack Mixtures ............................ 89 3.5 Environmental Durability Testing........... 91 3.5.1 Oxidation .......................... 91 3.5.2 Hot Corrosion...................... 92 IV. VOLATILE SPECIES IN CHLORIDE-ACTIVATED DIFFUSION COATING PACKS ..................... 97 4.1 ITSOL Computer Program.................... 97 4.2 Pack Equilibrium Calculations ........... 99 4.2.1 Sample Inputs ...................... 99 4.2.2 Sample Outputs..................... 106 4.3 ITSOL Calculations With a RE Source . .Ill 4.3.1 RE Oxide Source ................... Ill 4.3.2 RE Activator Salt ..................118 4.3.3 Masteralloy Combination ............ 121 4.4 Mass Spectrometer Measurements............ 125 V. RESULTS AND DISCUSSION....................... 134 5.1 Coating Development for Nickel-Base Alloys...................................134 5.1.1 Chromium/RE-Modified Aluminide Coatings........................... 134 5.1.2 RE-Doped Aluminide Coatings ........ 160 5.1.3 Chromium/Silicon-Modified Aluminide Coatings..................167 5.2 Kinetics and Formation Mechanisms of Al, Cr, RE C o a t i n g s ..................... 175 5.2.1 Contacting Powder Arrangement . .175 5.2.2 "Above Pack" Arrangement............ 185 5.3 Environmental Durability of Aluminide Coatings................. .............. 189 5.3.1 Cyclic Oxidation................... 193 5.3.2 Isothermal Oxidation................ 211 5.3.3 Hot Corrosion (Fused Salt (Attack) Studies................... 217 VI. SUMMARY AND CONCLUSIONS...................... 233 VII. FUTURE WORK ................................. 238 APPENDICES A. ITSOL CALCULATIONS: CONSTANT PRESSURE VERSUS CONSTANT VOLUME................................. 239 REFERENCES ........................................ 242 Vlll LIST OF TABLES TABLE PAGE 1. Summary of interdiffusion studies on the nickel-aluminum system ....................... 18 2. Nominal compositions of nickel-base alloys coated (at.%)..................................80 3. Composition of the chromium-aluminum binary masteralloy powders............................ 80 4. Properties of the chloride activator salts used in this investigation.................... 81 5. Standard Gibbs energies of formation for the aluminum species used as input for the ITSOL program...................................... 101 6. Standard Gibbs energies of formation for the chromium