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Thermal Spraying of Polymer-Ceramic Composite Coatings with Multiple Size

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Thermal Spraying of Polymer-Ceramic Composite Coatings with Multiple Size Thermal Spraying of Polymer-Ceramic Composite Coatings with Multiple Size Scales of Reinforcements A Thesis Submitted to the Faculty of Drexel University by Varun Gupta in partial fulfillment of the requirements for the degree of Master of Science in Materials Engineering April, 2006 i © Copyright 2006 Varun Gupta. All Rights Reserved. ii DEDICATION To my parents iii ACKNOWLEDGEMENTS I would like to express my gratitude to my primary advisor, Dr. Richard Knight, for his guidance, constant support and advice in many aspects of my graduate studies and research work but especially for the invaluable insights into thermal spray technology and a great influence on my professional development. I would like to thank my co-advisor, Dr. Richard Cairncross, for his always constant motivation, understanding, trust and support given throughout the course of my graduate studies. I deeply appreciate the friendship, assistance and practical help of Mr. Dustin Doss and Mr. Milan Ivosevic in working with me on this project, especially for the hands-on introduction to thermal spraying. I would also like to extend my thanks to Ms. Dee Breger for all her help during the SEM analysis and to Mr. Kishore Kumar Tenneti for assistance with the TGA analysis during the course of this project. I would like to give my special thanks to Mr. Ranjan Dash, Ms. Maria Pia Rossi, Mr. Davide Mattia, Mr. Brandon McWilliams and Mr. Stephen Niezgoda for their constant motivation and help. I also wish to thank all my friends, colleagues, faculty and staff members in the Department of Materials Science and Engineering who gave me the opportunity to learn from their advice and who have made my stay here at Drexel unforgettable. I would also like to thanks Dr. Thomas E. Twardowski for his valuable contribution during the project. Above all, my deepest gratitude goes to my parents and my sister for their continued moral support and endurance in helping me in accomplishing my goal. iv This work was made possible with support from National Science Foundation (NSF) under the Grant Number: DMI-0209319. Any opinions, findings, and conclusions or recommendations expressed in this thesis are those of the author and do not necessarily reflect the views of NSF. v TABLE OF CONTENTS LIST OF TABLES viii LIST OF FIGURES ix LIST OF EQUATIONS xiv LIST OF ABBREVIATIONS xv ABSTRACT xvii CHAPTER 1: INTRODUCTION 1 CHAPTER 2: BACKGROUND AND LITERATURE REVIEW 5 2.1. Particulate Reinforced Polymer Matrix Composites 5 2.2. Multi-scale Particulate Reinforcement 10 2.3. Thermal Spray Processing 12 2.3.1. Thermal Spray “Family” Tree 13 2.3.2. High Velocity Oxy-Fuel Combustion Spray 16 2.3.3. Thermal Spraying of Polymers and Polymer-Matrix Composites 18 CHAPTER 3: EXPERIMENTAL PROCEDURE 28 3.1. Materials Selection 29 3.1.1. Substrate Material 29 3.1.2. Feedstock Powders 29 3.1.2.1. Matrix Material: Pure Nylon-11 29 3.1.2.2. Reinforcing Phase: Ceramic Powders 30 3.2. Characterization of Feedstock Materials 31 3.2.1. Density 31 vi 3.2.2. Powder Feed Rate Calibration 32 3.3. Production of Composite Feedstock Powders 33 3.4. Coating Procedure 36 3.4.1. HVOF Spray System 36 3.4.2. Spray Setup and Substrate Preheating 37 3.5. Characterization Techniques: Powders and Sprayed Coatings 39 3.5.1. Morphology and Coating Microstructure 39 3.5.2. Elemental Analysis 40 3.5.3. Particle Size Distribution (PSD) 40 3.5.4 Thermal Properties 41 3.5.4.1. Ashing and Thermo Gravimetric Analysis (TGA) 41 3.5.4.2. Differential Scanning Calorimetry (DSC) 41 3.5.5. Scratch Testing 42 CHAPTER 4: RESULTS-FEEDTSOCK MATERIALS 44 4.1. Pure Nylon-11 Powder 44 4.2. Reinforcements: Ceramic Powders 45 4.3. Effect of Ball-milling on Particle Size Distribution 48 4.4. Morphology of the Ball-milled Composite Powders 50 4.5. Ashing and Thermo Gravimetric Analysis of Feedstock Powders 54 4.6. Measurements of Melting Point: Differential Scanning Calorimetry (DSC) 57 CHAPTER 5: RESULTS-SPRAYED COATINGS 58 5.1. Coating Production 58 5.1.1. HVOF Sprayed Pure Nylon-11 Coatings 58 vii 5.1.2. Composite Coating Formation 59 5.1.3. Nano and Multi-scale Reinforced Coatings 62 5.2. Coating Microstructure and Elemental Analysis 63 5.2.1. Nano-scale (7 nm silica) Reinforced Coatings 63 5.2.2. Multi-scale Coatings 65 5.3. Ashing and Thermo Gravimetric Analysis of Composite Coatings 69 5.4. Differential Scanning Calorimetry (DSC) 71 5.5. X-ray Microtomography of Coatings 72 5.6. X-ray Diffraction of Coatings 73 5.7. Mechanical Properties: Scratch Resistance 75 CHAPTER 6: SPLATTING OF NYLON-11 PARTICLES 79 6.1. Splat Tests 79 6.2. Splatting of Nylon-11 on Smooth Surfaces 80 6.3. Splatting of Nylon-11 on Non-smooth Surfaces 82 6.4. Modeling Predictions 84 6.5. Experimental Results 85 CHAPTER 7: SUMMARY AND CONCLUSIONS 90 Suggestions for future work 93 APPENDIX A 94 Powder Feed Rate Calibration 94 LIST OF REFERENCES 96 viii LIST OF TABLES Table 2.1: HVOF process and deposit characteristics [modified from Smith, 1992]....... 17 Table 2.2: Thermally sprayed polymers and polymer composites57 [modified from Petrovicova et al., 2002]. .................................................................................................. 24 Table 3.1. Composition of blended polymer/ceramic powders prepared for ball-milling.34 Table 3.2. HVOF spray parameters used for the deposition of pure Nylon-11 and polymer-ceramic composite coatings. .............................................................................. 37 Table 4.1. Reinforcement content in composite powders as calculated from ashing and TGA. ................................................................................................................................. 55 Table 5.1. Reinforcement content in composite coatings as determined from ashing and TGA. ................................................................................................................................. 69 Table 5.2. Comparison of reinforcement content in composite powders and sprayed coatings, as determined by TGA....................................................................................... 71 Table 7.1: Summary of the key results of ashing, TGA and scratch resistance for the composite powders and sprayed coatings......................................................................... 92 ix LIST OF FIGURES Figure 2.1: Ashby diagram showing the strength vs. density for various engineered materials18, 19. ...................................................................................................................... 6 Figure 2.2: Stress-strain curve for a particle-reinforced polymeric material. The experimental observations show increasing yield stress, tensile strength and strain to failure32. .............................................................................................................................. 9 Figure 2.3: Schematic of load transfer between multi-scale reinforcing particles within a polymer matrix composite (a) a likely composite structure with varying ceramic sizes and (b) the transmission of load in compression or impact moderated by nano-size particles and micron-size particles. ................................................................................................. 12 Figure 2.4: Overview of the major thermal spray coating processes [extended and modified by Knight, 2002; from Smith, 1992]. ................................................................ 14 Figure 2.5: Temperature-Velocity envelope of thermal spray processes9. ....................... 15 Figure 2.6: Schematic of coating deposition, depicting the major microstructural features found in thermal spray coatings50. .................................................................................... 15 Figure 2.7: Schematic of the Jet-Kote II® high velocity oxy-fuel (HVOF) thermal spray gun, including main stages of a feedstock particle transport53. ........................................ 18 Figure 2.8: Predicted velocities of Nylon-11 particles in an HVOF jet53 and effect of particle diameter and speed on the calculated degree of melting of Nylon-11 in an HVOF jet57.................................................................................................................................... 21 Figure 2.9: General influence of molecular weight on (a) polymer properties and (b) viscosity60, 61...................................................................................................................... 22 Figure 3.1: Molecular structure of polyamide Nylon-1182. .............................................. 30 Figure 3.2: Schematic of a pressurized volumetric powder feeder................................... 32 Figure 3.3: Schematic showing the embedding of hard ceramic particles into the surface of a polymer particle during ball-milling, resulting in core-shell structure...................... 33 x Figure 3.4: Ball-milling Process (a) Schematic (side view) and (b) Norton Ball-mill used in this study....................................................................................................................... 35 Figure 3.5: Schematic of the Jet Kote II® high velocity combustion spray system50. ...... 36 Figure 3.6: Spray setup with Jet-Kote II® high velocity oxy-fuel (HVOF) in operation, showing the deposition of coatings onto a substrate......................................................... 38 Figure 3.7: Scratch testing set up (a) BYK Gardner SG-8101 balance beam scrape adhesion and mar tester (ASTM D 5178-9137) and (b) schematic of a typical scratch profile...............................................................................................................................
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