Klaus Erich Schneider, Vladimir Belashchenko, Marian Dratwinski, Stephan Siegmann, Alexander Zagorski

Thermal Spraying for Power Generation Components

WILEY- VCH

WILEY-VCH Verlag GmbH & Co. KGaA Contents

Preface V

The Authors of this Book VII

1 Introduction 1 1.1 Requirements for Materials and in Powcrplants 1.2 Examples of Coatings in Turbines 2 1.3 Definition of Thermal Spraying (THSP) 5 1.4 Thermal-Spraying Systems 5 1.5 Coatings for Power-Generation Components 6 1.6 The Complete Manufacturing and Process 7 1.7 Coating-Process Development 12 1.8 Tasks for "Target" Readers 35

2 Practica I Experience Today 17 2.1 Coating Processes J7 2.2 Basics of Thermal Spraying 21 2.3 Feedstock 23 2.3.1 Wire 23 2.3.2 Powder 24 2.3.2.1 Powder Types 24 2.3.2.2 Powder-Production Processes and Morphologies 27 2.3.2.3 Powder Characterization 33 2.3.2.4 Powders for Power-Generation Applications 36 2.4 Thermal-Spraying Equipment 40 2.4.1 Example of a Low-Pressure -Coating System 41 2.4.2 Flame and Are Spray Torches 43 2.4.3 HVOF Process 45 2.4.3.1 Comparison of HVOF 47 2.4.3.2 A Brief Overview of the Major Existing HVOF Systems 2.4.3.3 Possible [mprovements of HVOF Systems 51 2.4.4 Plasma Process 54 2.4.4.1 A Brief Overview of Plasma Torches 58

Thermal Spraying for Power Generation Components '{. E. Schneider, V. Bdashchfriko, M, Dratwinski, S. Siegrmnn, A. Zagorski Copyright © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 3-527-31337-0 X Contents

2.4.4.2 Possible Improvements of Plasma Systems 63 2.5 Work Flow and Important Coating Hardware 65 2.5.1 Powder Preparation and Powder-Dclivery System 68 2.5.1.1 Powder Preparation 68 2.5.1.2 Powder Delivery and Injection System 68 2.5.1.3 Powder Injection and Plasma/Hot Gas Jet 73 2.5.1.4 Injector Plugging and "Spitting" 75 2.5.1.5 Powder Buildup at the Front Nozzle Wall 77 2.5.2 Cooling System 77 2.5.3 Power-Supply System 79 2.5.4 Gas Supply and Distribution System 80 2.5.5 Manipulation Systems 81 2.5.6 Fixtures and Masking 83 2.6 Examples of Coated Power-Generation Components 84 2.7 Production Experience 86 2.7.1 Surfate Preparation 87 2.7.1.1 Internal Plasma and Transferred Are 89 2.7.2 Process and Systems 91 2.7.2.1 Tbe Programming of fhe Coating Process 94 2.7.3 Finishing 95 2.7.4 Repair of Turbine Parts 95 2.7.4.1 Coating Removal, Stripping 97 2.7.4.2 Restoration of the Base Materials 98 2.7.4.3 Refurbisbing, Recoating 98 2.8 Commercial 99 2.8.1 General 99 2.8.2 Surfa.ee Preparation 103 2.8.3 Coating Equipment 103 2.8.4 Finishing 104

3 Quality and Process Capability 705 3.1 Quality Assurance 105 3.2 Sources of Process Variations 105 3.2.1 Special Causesof Coating-Process Variation 107 3.2.2 Stochastic Nature of a Spray Process 108 3.2.2.1 Are and Jet Pulsations 108 3.2.2.2 Powder-Size Distribution 109 3.2.2.3 Powder Injection 110 3.2.2.4 Powder Sbape 110 3.2.2.5 Particle Bonding 110 3.2.2.6 Gun and Component Motion and Positioning HO 3.2.3 Drifting 7 77 3.2.4 S tability of the Quality Control 7 7 2 3.3 Process Capability and Stable Process 115 3.3.1 Definition of Process Capability 115 3.3.2 Definition ofa Stahle Coating Process 117 3.3.3 Operational Window 1J8 3.3.4 What Process Capability is Required? 122 3.3.5 Additional Factors that Affect the Process Capability 124 3.3.6 Case Study: Achievable Process Capability 125 3.3.6.1 Part Complexity 125 3.3.6.2 Mutual Position of the Gun and Component Fixtures 125 3.3.6.3 Powder Quality 125 3.3.6.4 Torch Pulsations and Drifting 126 3.3.6.5 lnstability of the Quality-Control Process 128 3.3.6.6 Surface Preparation and the Part Temperature 128 3.3.6.7 Conditions of the Powder-Injection System 129 3.3.6.8 Process Capability 129 3.4 Maintenance 130

4 Theory and Physical Trends 133 4.1 Coating Formation from Separate Particles: Particle Impact, Spreading and Bonding 133 4.2 Physics of Plasma Torches 138 4.2.1 Plasma Properties 139 4.2.2 Gas Dynamics of Plasma Torch 145 4.2.3 Energy Balance of the Plasma Gun 147 4.2.4 Major Trends 149 4.2.4.1 Variation of the Gun Power; the Gas Flow Rates and Composition Unchanged 149 4.2.4.2 Variation of the Plasma Composition at the Same Specific Plasma Enthalpy 149 4.2.4.3 Variation of the Plasma Flow Rate at Unchanged Gun Power and Gas Composition 150 4.2.4.4 Effect of Nozzle Diameter 151 4.2.5 Plasma Swirl 151 4.3 Structure of Plasma Jets 757 4.3.1 APS Jet 151 4.3.2 S tructure ofLPPSJet 153 4.4 Particles in Plasma 155 4.4.1 Particles at APS 156 4.4.2 Particle at LPPS 158 4.4.2.1 Particle Acceleration and Heating in the LPPS Free Jet 158 4.4.2.2 Particle Acceleration and Heating Inside the Nozzle 160 4.5 Spray Footprint (Spray Pattern) 161 4.6 Influenceof Particles on Plasma Flow 164 4.7 Substrate Surface Temperature 165 4.8 Formation of the Coating Layer 167 4.9 Useof Different Plasma 168 4.10 Some Distinguishing Features ofHVOF Physics 169 XII Contents

5 Offline Simulation of a Thermal-Spray Process 171 5.1 Simulation in Production 171 5.2 Physical Background of Simulation Package 275 5.2.1 Viscoplasticity Model of a Splat and Particle Bonding 175 5.2.2 Thermodynamic and Transport Properties of / Mixtures 176 5.2.3 Modeling of the Plasma Gun 176 5.2.4 Modeling of the Plasma Jets 176 5.2.4.1 APS Jet 177 5.2.4.2 LPPSJet 177 5.2.5 Acceleration and Heating of Parti des in Plasma 779 5.2.6 Surface Thermal Conditions 180 5.3 Spray Pattern 182 5.3.1 Calibration of the Bonding Model and Sensitivity of a Spray Pattern to the Process Parameters, Spray Angle and Bonding Model 182 5.3.2 Coating Porosity and Roughness 185 5.4 Modeling of Turbine Blades 187 5.5 Coating Thickness Optimization and Stochastic Modeling Tools 189 5.6 Simulation ofHVOF Process 195 5.7 Use of Offline Simulation in Coating Development 199 5.7.1 Application Areas of Modeling in the Coating Process 199 5.7.1.1 Coating Definition and Design for Coating 199 5.7.1.2 Coating-Process Development 199 5.7.1.3 Part Development 200 5.7.1.4 Physical Modeling and Offline Simulation as Process-Diagnostic Tools 201 5.7.1.5 Simulation as a Numerical Experiment 201 5.7.1.6 When the Offline Simulation Should Be Used 202

6 Standards and Training 205 6.1 Standards, Codes 205 6.1.1 Introduction to Standards 205 6.1.2 Quality Requirements for Thermally Sprayed Structures and Coating Shops 206 6.1.3 QuaKfication and Education of Spraying Personnel 209 6.2 Special Case: Spraying for Power-Generation Components 211 6.2.1 Coating-Process Development 212 6.2.2 Coating Production 213 6.2.3 Genera] Requirements for Coating-Shop Personnel 213

7 Monitoring, Shopfloor Experience and Manufacturing Process Development 215 7.1 Monitoring, Sensing 215 7.1.1 Introduction of Monitoring 215 7.1.2 Particle-Monitoring Devices 217 Contents XIII

7.1.3 Influence of Spray Parameters on Particle Speed and Tcmperature 218 7.1.4 Influence of Particle Velocity and Tempcrature on Microstructure 219 7.2 How to Use Monitoring for Process Control 222 7.2.1 Monitoring, Sensing from a Job Shop Point of View 222 7.2.2 Vision for Future Coating Control and Monitoring 224 7.3 Manufacturing Coating Development 228 7.3.1 Coating Development Process 229 7.3.2 Coating Definition and Coating Specification; Design for Coating 230 7.3.3 Process Development 233 7.3.3.1 Powder Selection 234 7.3.3.2 Torch Parameters 234 7.3.3.3 Spray Pattern and Standoff Distance 234 7.3.3.4 Coating Mono-Layer; Powder Feed Rate and Traverse Gun Speed 235 7.3.3.5 Spray Trials and Coating Qualification 235 7.3.3.6 Sensitivity Checks 236 7.3.4 Part Development 236 7.3.4.1 Coating Program 236 7.3.4.2 Process Qualification and Preserial Release 237 7.3.5 Serial Release 239

8 Outlook, Summary 241 8.1 Thermal Spray Torches 242 8.2 Future Offline Programming and Monitoring in Process Development and Production 244

References 245

Subject Index 261