ELECTRICAL CONTACTS FUNDAMENTALS, APPLICATIONS AND TECHNOLOGY MlLENKO BRAUNOVIC MB Interface, Scientific Consultants Montreal, Quebec, Canada VALERY V. KONCHITS National Academy of Sciences of Belarus Belarus, Russia NIKOLAI K. MYSHKIN National Academy of Sciences of Belarus Belarus, Russia (g) CRC Press Taylor &. Francis Group Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business
Table of Contents Parti Fundamentals of Electrical Contacts 1 Milenko Braunovic, Valery V. Konchits, and Nikolai K. Myshkin Chapter 1 Introduction to Electrical Contacts 3 1.1 Introduction 3 1.2 Summary of Basic Features 6 Chapter 2 Contact Mechanics 9 2.1 Surface of Solids 9 2.2 Surface Topography 11 2.3 Modern Techniques of Measuring Surface Parameters 17 2.4 Contact of Smooth Surfaces 21 2.4.1 Plastic and Elastoplastic Contacts 23 2.5 Contact between Rough Surfaces 27 2.5.1 Greenwood-Williamson Model 27 2.5.2 Multilevel Model 29 2.5.3 Transition from Elastic to Plastic Contact 33 Chapter 3 Tribology 35 3.1 Friction 35 3.1.1 Laws of Friction 35 3.1.2 Real Contact Area 38 3.1.3 Interfacial Bonds (Adhesion Component of Friction) 38 3.1.4 Deformation at Friction 41 3.1.5 Friction as a Function of Operating Conditions 42 3.1.6 The Preliminary Displacement 44 3.1.7 Stick-Slip Motion 46 3.2 Wear 47 3.2.1 Stages of Wear 48 3.2.2 Simple Model of Wear 48 3.2.3 Basic Mechanisms of Wear 50 3.2.4 Abrasive Wear 52 3.2.5 Adhesive Wear 56 3.2.6 Prow Formation 57 3.2.7 Fatigue Wear 57 3.2.8 Corrosive Wear 59 3.2.9 Fretting Wear 59 3.2.10 Delamination 62 3.2.11 Erosion 64 3.2.12 Combined Wear Modes 64 3.3 Lubrication 65 3.4 Current Trends in Tribology 67
Chapter 4 Contact Materials 71 4.1 Metallic Contact Materials 71 4.1.1 Properties of Contact Materials 71 4.1.1.1 Copper 71 4.1.1.2 Aluminum 75 4.1.1.3 Silver 76 4.1.1.4 Platinum 78 4.1.1.5 Palladium 78 4.1.1.6 Gold 79 4.1.1.7 Rhodium 79 4.1.1.8 Tungsten 79 4.1.1.9 Nickel 80 4.1.2 Metals and Alloys for Heavy- and Medium-Duty Contacts 80 4.1.3 Metals and Alloys for Light-Duty Contacts 83 4.1.4 Materials for Liquid-Metal Contacts 85 4.1.5 Spring Contact Materials 87 4.1.6 Shape-Memory Alloys and Their Applications in Electrical Contacts 88 4.2 Coatings for Electrical Contacts 89 4.2.1 Basic Requirements 89 4.2.2 Surface Engineering Technologies 91 4.2.2.1 Surface Segregation 92 4.2.2.2 Ion Implantation 94 4.2.2.3 Electroplating 94 4.2.2.4 Electroless Plating 97 4.2.2.5 Cladding 97 4.2.2.6 Chemical Deposition 99 4.2.2.7 Plating by Swabbing 99 4.2.2.8 Physical Vapor Deposition Technology 99 4.2.2.9 Electro-Spark Deposition (ESD) 100 4.2.2.10 Intermediate Sublayers 101 4.2.2.11 Multilayered Contacts 101 4.2.3 Coating Materials 102 4.2.3.1 Coatings for Power Connectors (Copper and Aluminum Joints) 102 4.2.3.2 Coatings for Electronic/Electrical Applications 104 4.3 Composite Contact Materials 111 4.3.1 Composite Materials for Contacts of Commutating Apparatuses 111 4.3.2 Self-Lubricating Composites for Sliding Contacts 118 4.4 Nanostructured Materials 125 4.4.1 "Bulk" Properties Nanomaterials 127 4.4.2 Mechanical Properties 127 4.4.3 Electrical Properties 131 4.4.4 Magnetic Properties 136 4.4.4.1 Giant Magnetoresistance (GMR) 136 4.4.4.2 Ballistic Magnetoresistance (BMR) 138 4.4.5 Nanotubes 140 4.4.6 Thermal Stability 142 4.4.7 Characterization Techniques for Nanostructured Materials 143 4.4.7.1 Nanoindentation 143 4.4.7.2 Scanning Probe Microscopes 144
Chapter 5 Current and Heat Transfer across the Contact Interface 149 5.1 Contact Resistance 149 5.1.1 Circular and Noncircular a-spots 149 5.1.2 Effect of Signal Frequency 154 5.1.3 Size Effects, Nanocontacts 157 5.1.4 Effect of Surface Films 160 5.1.5 Effect of Contact Geometry 166 5.1.6 Conductivity of Rough Contact 172 5.2 Interfacial Heating 180 5.2.1 Principles of Heat Conduction Theory 181 5.2.2 Simple Problems of Heat Conduction Theory 183 5.2.3 Contact Spots Heated by Electrical Current 188 5.2.3.1 Film-Free Metal Contact 188 5.2.3.2 Heating of Contact Spots Having Surface Films 190 5.2.3.3 Field Intensity in the Contact Clearance with Tunnel-Conductive Films 194 5.2.4 Formulation of Heat Problem with Friction 195 5.2.5 Flash Temperature of Electrical Contact 198 5.2.6 Thermal Instability of Friction Contact 200 5.2.6.1 Thermoelastic Instability 201 5.2.6.2 Instability Caused by Temperature-Dependent Coefficient of Friction 202 5.2.6.2 Instability Related to Friction Mode Variation 202 Chapter 6 Reliability Issues in Electrical Contacts 205 6.1 Significance of Electrical Contacts Reliability 205 6.2 Electrical Contact Requirements 206 6.3 Factors Affecting Reliability 206 6.4 Connection Degradation Mechanisms 208 6.4.1 Contact Area 209 6.4.2 Oxidation 211 6.4.3 Corrosion 212 6.4.4 Fretting 214 6.4.4.1 Mechanisms of Fretting 217 6.4.4.2 Factors Affecting Fretting 219 6.4.4.3 Fretting in Electrical Contacts 219 6.4.4.4 Contact Load 221 6.4.4.5 Frequency of Motion 223 6.4.4.6 Slip Amplitude 224 6.4.4.7 Relative Humidity 224 6.4.4.8 Temperature 226 6.4.4.9 Effect of Current 226 6.4.4.10 Surface Finish 228 6.4.4.11 Hardness 229 6.4.4.12 Metal Oxide 230 6.4.4.13 Coefficient of Friction 230 6.4.4.14 Electrochemical Factor 230 6.4.5 Intermetallic Compounds 230
6.4.5.1 Effect of Electrical Current 232 6.4.6 Electromigration 237 6.4.7 Stress Relaxation and Creep 240 6.4.7.1 Nature of the Effect of Electric Current 241 6.4.7.2 Effect of Electric Current on Stress Relaxation 242 6.4.8 Thermal Expansion 247 6.5 Impact of Connection Degradation 248 6.5.1 Prognostic Model for Contact Remaining Life 250 6.5.2 Economical Consequences of Contact Deterioration 256 6.5.3 Power Quality 258 Part II Applications of Electrical Contacts 261 Milenko Braunovic, Valery V. Konchits, and Nikolai K. Myshkin Chapter 7 Power Connections 263 7.1 Types of Power Connectors 263 7.2 Design Features and Degradation Mechanisms 263 7.2.1 Bolted Connectors 263 7.2.1.1 Fretting in Bolted Connectors 269 7.2.1.2 Fretting in Aluminum Connections 271 7.2.1.3 Intermetallics 272 7.2.1.4 Creep and Stress Relaxation 275 7.2.2 Bus-Stab Contacts 276 7.2.3 Compression Connectors 279 7.2.3.1 Degradation Mechanisms in Compression Connectors 281 7.2.3.2 Corrosion 282 7.2.3.3 Fretting in Compression Connectors 283 7.2.4 Mechanical Connectors 284 7.2.4.1 Binding-Head Screw Connectors 285 7.2.4.2 Insulation Piercing Connectors 289 7.2.4.3 Wedge Connectors 289 7.2.5 Welded Connectors 290 7.3 Mitigating Measures 292 7.3.1 Contact Area-Connector Design 292 7.3.2 Contact Pressure 294 7.3.3 Surface Preparation 296 7.3.4 Mechanical Contact Devices 297 7.3.4.1 Retightening 300 7.3.4.2 Bimetallic Inserts 301 7.3.4.3 Transition Washers 301 7.3.4.4 Multilam Contact Elements 302 7.3.4.5 Shape-Memory Alloy Mechanical Devices 302 7.3.4.6 Self-Repairing Joints 303 7.3.5 Lubrication: Contact Aid Compounds 304 7.4 Installation Procedures 306
Chapter 8 Electronic Connections 309 8.1 Types of Electronic Connections 309 8.2 Materials for Electronic Connections 309 8.2.1 Solder Materials 310 8.2.2 Lead-Free Solders 312 8.2.2.1 Tin 312 8.2.2.2 Tin-Silver 312 8.2.2.3 Tin-Silver-Bismuth 313 8.2.2.4 Tin-Silver-Copper 313 8.2.2.5 Tin-Silver-Copper-Antimony 314 8.2.2.6 Tin-Silver-Antimony 314 8.2.2.7 Tin-Bismuth, 314 8.2.2.8 Tin-Copper 315 8.2.2.9 Tin-Indium 315 8.2.2.10 Tin-Indium-Silver 316 8.2.2.11 Tin-Zinc 316 8.2.2.12 Tin-Zinc-Silver 316 8.2.2.13 Tin-Zinc-Silver-Aluminum-Gallium 317 8.3 Degradation Mechanisms in Electronic Connections 317 8.3.1 Porosity 319 8.3.2 Corrosion/Contamination 322 8.3.2.1 Pore Corrosion 322 8.3.2.2 Creep Corrosion 323 8.3.2.3 Tarnishing 324 8.3.3 Fretting 327 8.3.4 Frictional Polymerization 334 8.3.5 Intermetallic Compounds 336 8.3.6 Creep and Stress Relaxation 348 8.3.7 Electromigration 353 8.3.8 Whiskers 357 8.4 Mitigating Measures 361 8.4.1 Effect of Coating 361 8.4.1.1 Gold Coatings 361 8.4.1.2 Palladium and Palladium Alloys 362 8.4.1.3 Tin Coatings 364 8.4.1.4 Nickel and Nickel-Base Alloys 364 8.4.2 Effect of Lubrication 364 Chapter 9 Sliding Contacts 369 9.1 Tribology of Electrical Contacts 369 9.1.1 Interrelation of Friction and Electrical Processes 370 9.1.2 Role of Boundary Films 371 9.1.3 Main Means of Improving Reliability of Sliding Contacts 371 9.1.4 Tribophysical Aspects in the Development of Sliding Contacts 373 9.2 Dry Metal Contacts 376 9.2.1 Low-Current Contacts 376 9.2.1.1 Effects of Low Current and Electrical Field on Friction 377 9.2.1.2 Effect of Interfacial Shear 378
9.2.1.3 Adhesion, Transfer, Wear Debris Formation, and Surface Transformation 380 9.2.2 High-Current Contacts 386 9.2.2.1 Effects of Electrical Current on Tribological Behavior 386 9.2.2.2 Influence of Electric Fields 390 9.2.2.3 Effect of Velocity 392 9.2.2.4 Effect of Material Combination of Contacting Members 393 9.2.2.5 Electroplastic Effect in Sliding Contact 394 9.2.2.6 Friction and Current Transfer in Metal Fiber Brush Contacts 396 9.2.3 Stability of the Contact Resistance. Electrical Noise 400 9.2.3.1 Contact Noise in Closed Connections 400 9.2.3.2 Electrical Noise in Sliding Contacts 402 9.3 Lubncated Metal Contacts 414 9.3.1 Introduction. Lubrication Factors 414 9.3.2 Electrical Properties of Lubricating Boundary Layers 415 9.3.3 Conductivity of Lubricated Contacts 419 9.3.3.1 Effect of Lubricant on Conductivity near the Contact Spots 419 9.3.3.2 Effect of Lubricant on Conductivity of Contact Spots 420 9.3.3.3 Experimental Studies of Electric Conductivity of Lubricated Contacts 427 9.3.3.4 Contact Resistance between Very Smooth Lubricated Surfaces 430 9.3.3.5 Temperature Dependencies of Contact Conductivity 431 9.3.4 Lubrication Factors in Sliding Contacts 433 9.3.4.1 Effect of Lubricant Origin 434 9.3.4.2 Lubricant Durability 435 9.3.4.3 Tribochemical Aspects of Lubrication 438 9.3.4.4 Effect of Velocity in Light-Current Contacts 441 9.3.4.5 Effects of Lubricant Contact Properties 442 9.3.4.6 Current Passage and Friction in High-Current Lubricated Contacts 444 9.3.5 Lubricants for Electrical Contacts 449 9.3.5.1 Lubricants for Sliding Electric Switch Contacts 450 9.3.5.2 Lubricants for Sliding Contacts of Sensors 451 9.3.5.3 Selection of Contact Lubricants 454 9.4 Composite Contacts 454 9.4.1 Effect of Intermediate Layers on Electrical Characteristics 455 9.4.1.1 Structure and Electrical Properties of Intermediate Films 456 9.4.1.2 Mechanism of Current Passage through the Contact with Intermediate Films 460 9.4.1.3 Influence of Polarity on Conductivity in Composite-Metal Contact 467 9.4.2 The "Lubricating" Effect of Electrical Current 471 9.4.2.1 Effect of Current on Friction Characteristics 471 9.4.2.2 Mechanism of the "Lubricating" Action of the Electric Current 473 9.4.2.3 Effect of Brush Material on Friction Behavior with Electric Current 477 9.4.3 Electrical Wear 479 9.4.3.1 Wear of Currentless Contacts 479 9.4.3.2 Effect of Current on Wear 480 9.4.3.3 Factors Leading to Electrical Wear in the Absence of Sparking 483
9.4.3.4 Influence of the Electric Field in the Clearance 489 9.4.3.5 Wear with Sparking and Arcing 491 9.4.3.6 Some Ways to Reduce Electrical Wear 493 Part III Diagnostic and Monitoring Technologies 495 Milenko Braunovic, Valery V. Konchits, and Nikolai K. Myshkin Chapter 10 Electrical Methods in Tribology 497 10.1 Surface Characterization 497 10.2 Diagnosis of Contact Area and Friction Regimes 503 10.2.1 Formation of Contact Area 503 10.2.2 Control of Sliding Contact with the Presence of Oxide Films 508 10.2.3 Experimental Study of Metallic Contact Spots Formation 509 10.3 Evaluation of Tribological Performance of Materials and Lubricants 511 10.3.1 Evaluation of Load-Bearing Capacity and Lubricity of Surface Films 511 10.3.2 Estimation of Lubricant Interlayer Shear Strength under Imperfect Lubrication 515 10.3.3 Evaluation of Thermal Stability of Materials and Lubricants by Electrical Methods 517 10.3.4 Control of Surface Coatings and Films 519 10.3.5 Novel Systems for Measuring and Analysis of Contact Characteristics 521 10.3.5.1 Method of "Triboscopy" 523 Chapter 11 Monitoring Technologies 529 11.1 Thermal Measurements 530 11.1.1 Infrared Thermography 532 11.1.2 Basic Features of Infrared Thermography 532 11.1.3 Types of Infrared Thermal Systems 534 11.1.4 SME Temperature Indicators 538 11.1.5 Temperature Stickers (Labels) 540 11.1.6 Remote Temperature Sensors 541 11.2 Resistance Measurements 542 11.3 Monitoring Contact Load (Pressure) 545 11.4 Ultrasonic Measurements 546 11.5 Wireless Monitoring 548 11.6 Cost Benefits of Monitoring and Diagnostic Techniques 552 Appendix 1: Methods of Description of Rough Surface 555 Appendix 2: Shape-Memory Materials 565 Appendix 3: Electrical Contact Tables 585 References 599 Index 641