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«THERMOMECHANICAL FATIGUE CRACK FORMATION IN A SINGLE CRYSTAL NI-BASE SUPERALLOY A Dissertation Presented to The Academic Faculty By Robert Lewis ...»

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THERMOMECHANICAL FATIGUE CRACK FORMATION IN A SINGLE

CRYSTAL NI-BASE SUPERALLOY

A Dissertation

Presented to

The Academic Faculty

By

Robert Lewis Amaro

In Partial Fulfillment

Of the Requirements for the Degree

Doctor of Philosophy in the

George W. Woodruff School of Mechanical Engineering

Georgia Institute of Technology

December, 2010

THERMOMECHANICAL FATIGUE CRACK FORMATION IN A SINGLE

CRYSTAL NI-BASE SUPERALLOY

Approved by:

Dr. Stephen D. Antolovich, Co-Advisor Dr. Richard W. Neu, Co-Advisor School of Materials Science and George W. Woodruff School of Engineering, Mechanical Engineering, George W. Woodruff School of School of Materials Science and Mechanical Engineering Engineering Georgia Institute of Technology Georgia Institute of Technology Dr. David L. McDowell Dr. W. Steve Johnson George W. Woodruff School of School of Materials Science and Mechanical Engineering, Engineering, School of Materials Science and George W. Woodruff School of Engineering Mechanical Engineering Georgia Institute of Technology Georgia Institute of Technology Dr. Preet M, Singh Date Approved: December XX, 2010 School of Materials Science and Engineering, Georgia Institute of Technology

ACKNOWLEDGEMENTS

First and foremost, I would like to acknowledge my wife, Erika Stinson, for her patience and support during this arduous process; and for putting so much faith into a high school dropout. Thank you.

I am also grateful to my advisers Dr. Richard Neu and Dr. Stephen Antolovich for their vital guidance and dedicated mentorship. Furthermore, I am greatly appreciative of my dissertation reading committee Dr. David McDowell, Dr. W. Steve Johnson and Dr.

Preet Singh who have provided experimental and technical support; without which this work would not have been possible.

I would like to acknowledge Pratt & Whitney for their financial support of this research. I am particularly grateful to Raymond Keith Kersey and Dr. Alexander Staroselsky of Pratt & Whitney for their technical support.

Dr. Blaine Reely, P.E., my professional mentor, has invested countless hours of his time to ensuring my success. I will be forever grateful for his guidance and friendship. Moreover, to name just a few of my academic mentors who were there long before this doctoral journey began, and without whom I would never have come so far in my studies: Dr. Ken Cunefare of Georgia Tech, and Professor Julie Tarr from Pima Community College in Tucson, AZ. Thank you for believing in me.

Finally, I would be remiss to not acknowledge my fellow researchers and associates at the Georgia Institute of Technology who have provided help, input or general support with regard to either my personal development or the development of this work: Mike Hirsch, Patxi Fernandez-Zelaia, Rob Kopkovits, Ben Beck, Nick Earnhart,

–  –  –

ACKNOWLEDGMENTS……………………………………………. ………………….iii LIST OF TABLES ………………………………………………………………………..ix LIST OF FIGURES……………………………………………………………………….xi SUMMARY……………………………………………………………………………..xxi CHAPTER 1. INTRODUCTION

1.1 RESEARCH MOTIVATION

1.2 RESEARCH OBJECTIVES

1.3 OVERVIEW OF DISSERTATION

CHAPTER 2. LITERATURE REVIEW

2.1 INTRODUCTION

2.2 DESCRIPTION OF PWA 1484

2.3 GENERAL PLASTICITY AND SLIP BAND SPACING

2.3.1 Fundamentals of Inelastic Deformation

2.3.2 Classical Plasticity Rate Equations

2.3.3 Slip Band Spacing

2.4 DEFORMATION MECHANISMS

2.4.1 γ-γ’ Interaction- influence of γ’ precipitates on deformation.................. 23 2.4.2 Orientation effects- anisotropic behavior of single crystal superalloys.. 27 2.4.3 Strain amplitude and strain rate effects

2.4.4 Temperature Effects

2.4.5 Influence of Coatings

2.5 OXIDATION OF NI-BASE SUPERALLOYS

2.5.1 Introduction

2.5.2 General Superalloy Oxidation

v 2.5.3 γ’ Depletion

2.5.4 Fatigue-Oxidation Interaction

2.6 GAMMA-PRIME (Γ’) COARSENING AND RAFTING

2.7 DAMAGE MECHANISMS IN NI-BASE SUPERALLOYS

EXPERIENCING TMF

2.8 THERMOMECHANICAL FATIGUE (TMF) LIFE PREDICTION

METHODOLOGIES

2.9 SUMMARY

CHAPTER 3. THERMOMECHANICAL FATIGUE - EXPERIMENTAL PROCEDURE

AND RESULTS

3.1 INTRODUCTION

3.2 SPECIMENS

3.3 EQUIPMENT

3.4 VERIFICATION OF ADHERENCE TO TMF TEST STANDARDS...... 76 3.4.1 ASTM TMF test criteria

3.4.2 Procedures employed to ensure test validity per ASTM

3.5 TESTING/CONTROL/PROGRAMS

3.6 TMF TEST MATRICES

3.7 CRACK INITIATION CRITERIA

3.8 FATIGUE TEST RESULTS

3.9 PLOTS

3.10 DOMINANT DAMAGE MECHANISM CHARACTERIZATION....... 94 3.10.1 Baseline TMF Tests





3.10.2 Baseline BiF Tests

3.10.3 TMF versus BiF

3.11 ORIENTATION EFFECTS

3.12 DISCUSSION

CHAPTER 4. ENVIRONMENTAL EFFECTS

4.1 INTRODUCTION

4.2 MATERIAL

4.3 EXPERIMENTAL PROCEDURES AND RESULTS

4.3.1 Sensitivity of Surface Roughness

4.3.2 Kinetics of γ’ Depletion

vi 4.3.3 Oxide Characterization

4.3.4 Measurements of γ’ Depletion

4.4 ANALYSIS

4.4.1 Sensitivity of Surface Roughness

4.4.2 Non-Stressed Oxidation

4.5 COUPLED FATIGUE-OXIDATION

4.6 DISCUSSION

CHAPTER 5. SLIP BAND SPACING

5.1 INTRODUCTION

5.2 SLIP BAND SPACING HYPOTHESIS

5.3 EXPERIMENTAL PROCEDURE

5.3.1 Test Matrix

5.3.2 Test Equipment

5.4 EXPERIMENTAL RESULTS

5.4.1 Measurement of Slip Band Spacing

5.4.2 Cyclic Slip Results

5.4.3 Monotonic Slip Results

5.5 MATHEMATICAL RELATIONSHIPS

5.6 SUMMARY

CHAPTER 6. CRACK INITIATION LIFE MODELING

6.1 INTRODUCTION

6.2 NEU-SEHITOGLU MODEL

6.2.1 Neu-Sehitoglu Model Implementation

6.2.2 Parametric Sensitivity Analysis

6.3 LIFE MODEL DEVELOPMENT

6.4 DISCUSSION

CHAPTER 7. CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK

7.1 CONCLUSIONS

7.2 RECOMMENDATION FOR FUTURE WORK

APPENDIX

vii A.2 MATERIAL TRACKING DOCUMENTS

A.3 LAUE RESULTS

A.4 TEST MATRICES

A.5 TMF/BIF START-UP-PROCEDURE

A.6 TMF/BIF TEST DATA SHEET

A.7 TEST CONTROL ALGORITHMS

A.8 OXIDE EDS RESULTS

REFERENCES………………………………………………………………………….301

–  –  –

Table 2-1: a) Nominal Chemical Composition of Superalloys by Generation (top) [2]; b) Role of Alloying Elements (bottom) [2, 21]

Table 2-2: Nominal Chemical Composition of PWA 1480 and PWA 1484 (wt %) [7].. 13 Table 2-3: Schmid Analysis for FCC Crystal Loaded in [001] Direction

Table 2-4: Schmid Analysis for FCC Crystals- Active Slip Systems

Table 2-5: SXSA Temperature-Deformation Response [1, 3, 7, 17]

Table 2-6 Nominal Chemical Composition (in Weight Percent) of Representative Single Crystal Superalloys [11]

Table 3-1 Specimen Temperature Gradient Test Results

Table 3-2 Fatigue Test Results (Tests marked with an * will be used as Baseline tests in Chapter 6)

Table 4-1 Nominal composition of PWA 1480 and PWA 1484 (wt %) [7]

Table 4-2 Surface Preparation Oxidation Test Schedule, All Tests Performed at 1050° C

Table 4-3 Surface Roughness Values for Various Levels of Specimen Preparation...... 134 Table 4-4 Final Polish Schedule (Struers Products)

Table 4-5 Results Evaluating Sensitivity of Surface Roughness

Table 4-6 Furnace Oxidation Test Matrix

Table 4-7 Average γ’ Depletion Values

Table 4-8 γ' Depletion Time Exponent Values: Determined for PWA 1484 and Taken from Literature, GTD 111 [59], Rene N4 [62], CM247LC DS [64]

Table 4-9 γ' Depletion Kinetics Prefactor and Activation Energy: Determined for PWA 1484 and Taken from Literature, GTD 111 [59], MAR-M247 [67], CM247LC DS [64]

Table 4-10 Chemical Compostion of Superalloys for which γ' Depletion Kinetics are Known

Table 4-11 PWA 1484 TMF and BiF Test Data

Table 5-1 Slip Band Spacing as a Function of Inelastic Strain and Temperature [31]... 176

–  –  –

Table 5-3 Room Temperature Cyclic Slip Band Spacing Results

Table 5-4 Slip Band Spacing as a Function of Inelastic Strain and Temperature.......... 193 Table 6-1 Fatigue and Environmental Fatigue Module Constants

Table 6-2 Results of Variation of Parameters Study- Calibration Using Baseline PWA 1484 OP TMF Data

Table 6-3 Parameter Values From Correlation of Eq 6-26 to all 001 PWA 1484 OP TMF and BiF Results

Table 6-4 Parameter Values From Correlation of Eq 6.33 to all 001 PWA 1484 OP TMF and BiF Results. Value of r0 from [7]

Table A-1 Matrix of OP TMF and BiF Tests

–  –  –

Figure 2-1: Typical Two Phase Superalloy Microstructure [19]

Figure 2-2: Schematic of a Basic Turbojet Gas Turbine Engine [2]

Figure 2-3: Evolution of Take-Off TET Capability for Rolls-Royce Civil Aero Engines [2]

Figure 2-4: Superalloy Creep Response as a Function of Year. Originally from [2]....... 10 Figure 2-5: (a) Illustration of Equiaxed Polycrystalline, (b) Directionally Solidified, and (c) Single Crystal Alloys Used for Turbine Blade Airfoils [2]

Figure 2-6: Superalloy Material Properties as a Function of Crystalline Structure [17].. 12 Figure 2-7 Slip Systems for FCC Crystal- Single Slip Plane Left, Tetrahedron Created by Four {111} Planes [41]

Figure 2-8 Schmid Analysis for FCC Crystal for Different Loading Directions: 001 Top Left, 011 Top Right, 111 Bottom Left and 123 Bottom Right

Figure 2-9 Loading Direction of Interest Plotted on Standard Stereographic Triangle.... 16 Figure 2-10 Dependence of Slip Band Spacing on Grain Size for Polycrystalline Copper [29]

Figure 2-11: Yield Stress as a Function of Temperature and γ’ Volume Fraction (%) in Ni-Cr-Al Ternary Alloys [2]

Figure 2-12 Creep Rupture Life of a representative Superalloy as a Function of γ’ Volume Fraction (%) for a Fixed γ’ Size [2]

Figure 2-13 Theoretical Relationship Between γ’ Particle Size and Alloy Strength [32] 26 Figure 2-14 Experimental Relationship Between Particle Size and Alloy Strength in a NiCr Base Alloy [32]

Figure 2-15 Variation in γ' Particles Size for PWA 1484 in Full Heat Treat Condition:

Primary and ultra fine (A) γ' [7]

Figure 2-16: Elastic Modulus as a Function of Crystallographic Orientation for PWA 1480 [35]

Figure 2-17 Variations with Temperature of Critical Resolved Shear Stress for γ’ Single Crystals [2]

xi Figure 2-18 Sketch of Macroscopic “Cube” Slip composed of Cross Slip on Octahedral Planes [39]

Figure 2-19 PWA 1493 649 ° C LCF Data: Resolved Shear Stress Range on Most Active Slip System versus Cycles to Failure [5]

Figure 2-20: Tensile Yield Strength and Ductility as a Function of Temperature in PWA 1484 Loaded in [001] Direction [7]

Figure 2-21 Comparison of Superalloy Coatings: Temperature Range vs. Life [2]......... 38 Figure 2-22 SEM Image of Coating Cracks in Pt-Modified NiAl Diffusion Coated PWA 1484 [47]

Figure 2-23 Effect of Oxidation Rate Constant, Kp, on the Growth of the γ Region [51] 42 Figure 2-24 Schematic Diagram of Oxides Formed on Ni-Cr-Al Ternary Alloys. (a) Group I, (b) Group II and (c) Group III [50]

Figure 2-25 Example of “Transition Alloy” oxidation, presented in [52] at higher quality, originally from [37]

Figure 2-26 Effect of γ’ Volume Fraction on (a) Monotonic and (b) Cyclic Response at 950° C [51]

Figure 2-27 Comparison of Accumulated Inelastic Strain With and Without Oxidation After 400 hr at 950 °C [51]

Figure 2-28 Fatigue Crack Initiation From Oxide Pits in Uncoated René N4 [62].......... 55 Figure 2-29 Micrograph of Rafting in a Single Crystal Superalloy [19]

Figure 2-30 Temperature and Strain Waveforms: (a) OP TMF, (b) OP BiF

Figure 2-31 Comparison of Isothermal LCF, IP BiF and OP BiF for Bare and Coated PWA 1484 [79]

Figure 3-1: Fatigue Specimen Drawing

Figure 3-2: TMF Experiment

Figure 3-3 Induction Coil Verification: 6 Thermocouples Welded longitudinally along Gage Section

Figure 3-4: Induction Coil Verification: 4 Thermocouples Welded Circumferentially Around Center of Gage Section

Figure 3-5 OP TMF Temperature-Time and Mechanical Strain-Time waveforms.......... 80

–  –  –

Figure 3-7: OP BiF Temperature-Time and Load-Time Waveforms

Figure 3-8: Requested Material Orientation on Stereographic Triangle

Figure 3-9: Schematic of Crack Initiation Criteria

Figure 3-10: PWA 1484 Dendrite Spacing

Figure 3-11 Fatigue Test Results (OP TMF and BiF): Inelastic Strain Range versus Cycles to Crack Initiation, 001 Specimens

Figure 3-12 Fatigue Test Results (OP TMF and BiF) Delineated By Effective Temperature, 001 Specimens

Figure 3-13 Fatigue Test Results (OP TMF and BiF)- Dominant Damage Mechanisms, 001 Specimens

Figure 3-14 Deformation Mechanism Map for OP BiF and TMF

Figure 3-15 Baseline OP TMF and BiF Tests, 001 specimens

Figure 3-16 ∆εmech = 0.5%, OP TMF Baseline Test Hysteresis Loops- Ni=1810 Cycles

Figure 3-17 ∆εmech = 0.5%, OP TMF Baseline Test Stress Evolution- Ni=1810 Cycles

Figure 3-18 ∆εmech = 0.9%, OP TMF Baseline Test Hysteresis Loops- Ni=471 Cycles

Figure 3-19 ∆εmech = 0.9%, OP TMF Baseline Test Stress Evolution- Ni=471 Cycles 99 Figure 3-20 ∆εmech = 1.3%, OP TMF Baseline Test Hysteresis Loops- Ni=80 Cycles

Figure 3-21 ∆εmech = 1.3%, OP TMF Baseline Test Stress Evolution- Ni = 80 Cycles



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