ISOTHERMAL OXIDATION COMPARISON OF THREE Ni-BASED SUPERALLOYS By MALLIKARJUNA HEGGADADEVANAPURA THAMMAIAH A thesis submitted to The Faculty of Graduate Studies In partial fulfillment of the requirement for the degree of MASTER OF SCIENCE Department of Mechanical Engineering The University of Manitoba Winnipeg, Manitoba May 2016 Copyright © 2016 by Mallikarjuna Heggadadevanapura Thammaiah DEDICATION To My Parents Mr. Thammaiah (late) and Mrs. Asha And My Brother, Vinod Kumar H. T. TABLE OF CONTENTS LIST OF FIGURES ..................................................................................................................................... i LIST OF TABLES ..................................................................................................................................... vi ACKNOWLEDGEMENTS ..................................................................................................................... vii ABSTRACT .............................................................................................................................................. viii 1. INTRODUCTION ................................................................................................................................... 1 1.1 Application of nickel-based superalloys ............................................................................................. 1 2.1 Superalloys – General remarks ....................................................................................................... 4 2.1.1 Cobalt-base superalloys ............................................................................................................... 5 2.1.2 Iron-base superalloys ................................................................................................................... 6 2.1.3 Nickel-base superalloys ................................................................................................................ 6 2.2 Nickel-base superalloys: chemistry and microstructure. .............................................................. 7 2.2.1 Gamma phase (γ): ........................................................................................................................ 9 2.2.2 Gamma prime phase (γ'): ............................................................................................................. 9 2.2.3 Carbides (MC and M23C6): ......................................................................................................... 11 2.2.4 Topologically close packed (TCP) phases: ................................................................................ 12 2.3 Strengthening mechanism of nickel-base superalloys ................................................................. 12 2.3.1 Solid solution strengthening....................................................................................................... 12 2.3.2 Precipitation hardening .............................................................................................................. 13 2.3.3 Grain boundary strengthening by carbides ................................................................................ 14 2.4 Development of Ni-base superalloys processing ........................................................................... 14 2.4.1 Physical metallurgy of IN738LC ............................................................................................... 16 2.4.2 Physical metallurgy of single crystal N5 ................................................................................... 17 2.4.3 Physical metallurgy of modified IN600 (TAS) .......................................................................... 17 2.5 Oxidation ......................................................................................................................................... 18 2.5.1 Theory of oxidation .................................................................................................................... 19 2.5.2 General formation of metal oxides ............................................................................................. 19 2.5.3 Thermodynamics of oxidation ................................................................................................... 20 2.6 Structural properties of oxides ...................................................................................................... 22 2.6.1 Point defect structures and mechanism of lattice diffusion ........................................................ 23 2.6.2 Line defect structures, plane defect structures and short-circuit diffusion................................. 25 2.7 Kinetics of oxidation ....................................................................................................................... 26 2.7.1 Parabolic oxidation rate ............................................................................................................. 27 2.7.2 Logarithmic oxidation rate ......................................................................................................... 29 2.7.3 Linear oxidation rate .................................................................................................................. 30 2.8 Wagner’s theory of parabolic oxidation ....................................................................................... 31 2.9 Breakaway oxidation due to depletion of alloying elements ....................................................... 33 2.10 Effect of alloying elements on oxidation of superalloys ............................................................. 34 2.11 Oxidation of alloys ........................................................................................................................ 38 2.11.1 High-temperature oxidation of chromia-forming nickel-base superalloys .............................. 39 2.11.2 High-temperature oxidation of alumina-forming nickel-base superalloys............................... 43 2.12 Pettit’s oxidation groups ............................................................................................................... 46 2.13 Phase transformation during high-temperature oxidation ....................................................... 47 2.13.1 Formation of new phase ........................................................................................................... 49 2.13.2 Phase dissolution ...................................................................................................................... 50 2.13.3 Void formation ......................................................................................................................... 52 2.15 Summary of literature review ...................................................................................................... 54 2.16 Scope of project ............................................................................................................................. 55 3. EXPERIMENTAL PROCEDURES ................................................................................................... 54 3.1 Introduction ..................................................................................................................................... 54 3.2 Materials .......................................................................................................................................... 54 3.3 Heat treatment ................................................................................................................................ 55 3.4 Sample preparation ........................................................................................................................ 56 3.4.1 Electrical discharge machining-wire cutting (EDM-WC) ......................................................... 56 3.4.2 Polishing, dimensioning and weighing ...................................................................................... 57 3.5 Isothermal oxidation ....................................................................................................................... 58 3.6 Oxidized specimen characterization .............................................................................................. 59 3.6.1 Cold mounting sample preparation of oxidized specimens ....................................................... 59 3.6.2 Etching for alloy microstructure characterization ...................................................................... 60 3.6.3 Optical microscope .................................................................................................................... 60 3.6.4 Scanning electron microscopy (SEM) / EDS analysis ............................................................... 60 3.6.5 Electron probe microanalysis (EPMA) ...................................................................................... 61 3.6.6 Auger electron spectroscopy (AES) ........................................................................................... 61 3.6.7 Atomic force microscopy (AFM) .............................................................................................. 62 3.7 Hardness measurement .................................................................................................................. 62 4. RESULTS .............................................................................................................................................. 63 4.1 Introduction ....................................................................................................................................