Powder Metallurgy Science, Technology and Materials Anish Upadhyaya Associate Professor Department of Materials Science and Engineering Indian Institute of Technology Kanpur, India G S Upadhyaya Former Professor Department ofmaterials and Metallurgical Engineering Indian Institute of Technology Kanpur, India Foreword by Prof. Dr Ken-ichi Takagi, Tokyo City University, Tokyo
Contents Foreword Preface About the series v vii ix 1 INTRODUCTION 1 1.1 Production and Characterisation of Powders 6 1.2 Treatment of Powder 7 1.3 Compaction of Powder 7 1.4 Sintering 8 1.5 Full Density Processing 8 1.6 Secondary Treatment 10 1.7 Applications 10 1.8 Holistic View of PM Science and Technology 12 2 POWDER PRODUCTION 15 2.1 Chemical Methods 15 2.1.1 Solid-state reduction 17 2.1.2 Hydro-metallurgical reduction 20 2.1.3 Ion exchange method 23 2.1.4 Direct synthesis 24 2.1.5 Some specific powders produced by chemical method 25 2.2 Electrolytic Method 39 2.2.1 Some specific powders produced by electrolysis 41 2.3 Atomisation Method 45 2.3.1 Gas atomisation 52 2.3.2 Water atomisation 53 2.3.3 Liquid gas atomisation 55 2.3.4 Centrifugal atomisation 56 2.3.5 Vacuum atomisation 58 2.3.6 Ultrasonic gas atomisation 58 2.3.7 Chill methods 60 2.3.8 Some specific atomised metal and alloy powders 61 2.4 Evaporation Methods 63 2.5 Mechanical Methods 64 3 POWDER CHARACTERISATION 79 3.1 Powder Sampling 79 3.2 Chemical Composition and Structure 80
xii Contents 3.3 Particle Size 82 3.3.1 Sieving method 83 3.3.2 Permeability method 84 3.3.3 Light scattering method 85 3.3.4 Sedimentation method 86 3.3.5 Turbidimetry method 86 3.3.6 Crystallite size measurement 88 3.4 Particle Surface Topography 88 3.5 Surface Area 88 3.6 True, Apparent and Tap Density 88 3.7 Flow Rate 92 3.8 Compressibility 92 3.9 Green Strength 93 3.10 Pyrophoricity and Toxicity 93 4 POWDER TREATMENT 98 4.1 Particle 99 Separation 4.2 Annealing and Diffusion Alloying 99 4.3 Powder Mixing 100 4.3.1 Lubricant additive 102 4.3.2 Binder additive 104 4.3.3 Equipments 106 4.4 Granulation 109 4.5 Coating on Metal Powders 112 4.5.1 Electroplating 112 4.5.2 Electroless deposition 112 4.5.3 Coating by hydro-metallurgical process 4.6 Powder Degassing 114 113, POWDER COMPACTION 118 5.1 Basic Aspects 118 5.1.1 Powder packing 118 5.1.2 Powder bed under load 120 5.1.3 Type of material 123 5.2 Die Compaction 124 5.2.1 Pressing operation 125 5.2.2 Compaction presses 127 5.2.3 Press selection 128 5.2.4 Factors affecting tooling design 129 5.2.5 Tooling materials 132
Contents xiii 5.2.6 Part classification 133 5.2.7 Guidelines for part geometry 136 5.3 Warm Compaction 138 5.4 Wet Compaction 140 5.5 Cold Isostatic Compaction 140 5.5.1 Isostatic press equipment and pressing operation 141 5.6 Powder Roll Compaction 146 5.7 Powder Extrusion 148 5.8 Injection Moulding 150 5.8.1 PIM part design 152 5.9 Green Part Material Handling 153 6 PRESSURELESS POWDER SHAPING 158 6.1 Slip Casting/Slurry Moulding 158 6.1.1 Viscosity of a slurry 160 6.1.2 Drying 160 6.2 Tape Casting 162 6.3 Electrophoretic Deposition 164 6.4 Spray Deposition/Forming 164 6.5 Solid Freeform Fabrication 166 7 SINTERING THEORY 171 7.1 Solid-state Sintering: Pressureless 173 7.1.1 Analytical approach to sintering: Stages in sintering 174 7.1.2 Non-isothermal sintering 181 7.1.3 Microstructural evolution 183 7.1.4 Numerical simulation of sintering 186 7.1.5 Phenomenological approach to sintering 188 7.1.6 Sintering maps or diagrams 189 7.1.7 Sintering of nanopowders 189 7.1.8 Solid-state sintering of premixed/pre-alloyed powders 193 7.2 Liquid Phase Sintering 194 7.2.1 Stages of liquid phase sintering 195 7.2.2 Wetting aspects of liquid phase sintering 197 7.2.3 Microstructural evolution during liquid phase sintering 198 7.2.4 Supersolidus sintering 202 7.3 Activated Sintering 203 7.4 Pressure-assisted Sintering 208 7.4.1 Plastic yielding mechanism 210 7.4.2 Creep mechanisms 210
xiv Contents 7.4.3 Viscous flow mechanism 213 7.5 Electronic Theory of Sintering: A Unified Approach 214 7.5.1 Liquid phase sintering 215 7.5.2 Activated sintering 217 7.5.3 Case study: Sintering of refractory compounds 217 8 SINTERING TECHNOLOGY 228 8.1 Debinding 229 8.2 Loose Sintering 229 8.3 Sintering Furnaces 230 8.3.1 Batch-type furnace 230 8.3.2 Continuous furnace 231 8.3.3 Vacuum furnace 236 8.3.4 Electric furnace heating elements 237 8.3.5 Furnace connectivity and control 238 8.4 Sintering Zones 239 8.4.1 Burn-off and entrance zone 239 8.4.2 High-temperature zone 241 8.4.3 Cooling zone 241 8.5 Rapid Sintering Processes 242 8.5.1 Induction sintering 242 8.5.2 Microwave sintering 243 8.6 Sintering Atmosphere 243 8.6.1 Hydrogen 244 8.6.2 Reformed hydrocarbon gases 244 8.6.3 Nitrogen and nitrogen-based atmospheres 251 8.6.4 Dissociated ammonia 252 8.6.5 Argon and helium 253 8.6.6 Vacuum 253 8.7 Sintering Atmosphere Analysis and Control 254 8.7.1 Gas analysis 254 8.7.2 Specific gravity analysis 256 8.7.3 Moisture determination 257 8.7.4 Carbon potential control 257 8.8 Process Variables 259 8.9 Material Variables 261 8.10 Dimensional Changes 261 8.11 Microstructural Changes 263 8.12 Infiltration 264 8.13 Sintered Parts Material Handling 265
Contents xv 9 FULL DENSITY CONSOLIDATION 271 9.1 Dynamic Powder Compaction 271 9.2 Hot Pressing 272 9.2.1 Process and equipment 273 9.3 Hot Isostatic Pressing (HIP) 275 9.3.1 Equipment and process variables 275 9.3.2 Sinter-HIP or overpressure sintering 277 9.4 Powder Hot Extrusion 278 9.4.1 Process 280 9.5 Powder Hot Forging 282 9.5.1 Preform manufacturing and forging 284 9.6 Hot Rolling of PM Preforms 289 9.7 Spark Sintering 292 10 SECONDARY TREATMENTS 298 10.1 Sizing and Coining 298 10.2 Machining 299 10.2.1 Machining practice 301 10.3 Impregnation 301 10.4 Surface Engineering 303. 10.4.1 Steam treatment 303 10.4.2 Coating 304 10.4.3 Shotpeening 308 10.5 Heat Treatment 308 10.5.1 Hardening and tempering 308 10.5.2 Case hardening 313 10.5.3 Age hardening 315 10.6 Joining 318 11 TESTING AND QUALITY CONTROL OF PM MATERIALS AND PRODUCTS 323 11.1 Sampling 323 11.2 Density 324 11.3 Sintered Porosity and Pore Distribution 325 11.4 Structure of PM Materials 326 11.4.1 Qualitative metallography and ceramography 327 11.4.2 Quantitative metallography 332 11.4.3 X-ray analysis 333 11.5 Differential Thermal Analysis 336 11.6 Thermal Expansion 337 11.7 Thermal Shock Resistance 338
xvi Contents I 1.8 Thermal Conductivity 338 11.9 Optical Properties 339 11.9.1 Roughness 339 11.10 Hardness 340 11.10.1 Brinell hardness test 340 11.10.2 Vickers hardness test 340 11.10.3 Rockwell hardness test 341 11.10.4 Microhardness test 342 11.11 Strength 343! 1.11.1 Tensile strength 343 11.11.2 Compressive strength 343 11.11.3 Transverse rupture strength (Bending strength) 345 11.11.4 Modulus of elasticity 345 11.11.5 Effect of grain size and dispersed hard particles 346 11.12 Impact Test 347 11.13 Fracture Toughness 348 11.14 Fatigue Behaviour 349 11.15 Creep Behaviour 350 11.16 Fracture Behaviour 351 11.17 Wear Resistance 351 11.18 Machinabilty 353 11.19 Electrical Resistivity 355 11.20 Magnetic Properties 355 1 1.21 Corrosion Resistance 356 11.22 Quality Control of PM Parts 358 11.22.1 Filters 360 11.22.2 Porous bearings 360 11.22.3 Structural parts 361 11.22.4 Cemented carbide cutting tools 367 11.23 Non-destructive Testing 367 11.24 Statistical Quality Control 368 12 METALLIC AND CERAMIC PM MATERIALS 376 12.1 Low-alloy Ferrous Materials 376 12.1.1 Fe-C alloys 378 12.1.2 Copper-and nickel-containing steels 380 12.1.3 Manganese- and chromium-containing steels 381 12.1.4 Phosphorus-containing alloys 384 12.2 High-alloy Steels 385 12.2.1 High-speed steels 385 12.2.2 Stainless steels 386
Contents xvii 12.3 Copper Alloys 390 12.4 Aluminium Alloys 393 12.5 Silver Alloys 397 12.6 Nickel Alloys 399 12.7 Titanium Alloys 401 12.8 Refractory Metals 402 12.8.1 Copper-containing alloys 403 12.8.2 Precipitation/Dispersion-strengthened refractory metals 403 12.8.3 Tungsten heavy alloys 407 12.8.4 Tantalum 409 12.9 Intermetallics 411 12.9.1 Silicides 411 12.9.2 Aluminides 411 12.9.3 Rare earth intermetallics 412 12.10 Ceramic Systems 412 12.10.1 Porcelain (Whiteware) 412 12.10.2 Alumina, magnesia and zirconia 415 12.10.3 Barium titanate 417 12.10.4 Ferrites 418 12.10.5 Oxide superconductors 419 12.10.6 Oxide nuclear fuels 420 12.10.7 Silicon carbide 420 12.10.8 Silicon nitride 421 12.10.9 Refractory compounds 421 12.11 Cermets 422 12.11.1 Oxide-based cermets 422 12.11.2 Non-oxide-based cermets including cemented carbides 422 12.12 Ceramic-Ceramic Composites 425 12.13 Sintered Nanocrystalline Metals and Ceramics 426 12.14 Functionally Graded Materials 426 12.15 MPIF PM Material Code 427 13 APPLICATIONS OF PM PRODUCTS 445 13.1 Structural Applications 445 13.1.1 Automotive applications 446 13.1.2 Aerospace applications 452 13.1.3 Ordnance applications 454 13.2 Machine Tools 455 13.2.1 Cutting applications 455 13.2.2 Non-cutting applications 457 13.3 Power Generation 459
xviii Contents 13.3.1 Applications based on fossil fuels 459 13.3.2 Applications based on nuclear fuels 461 13.3.3 Fuel cells 462 13.4 Porous PM Products 464 13.5 Friction Elements 465 13.6 Electrical Materials 466 13.6.1 Electrical contact materials 466 13.6.2 Electric lamps 469 13.6.3 Dielectrics 472 13.6.4 Capacitors 473 13.7 Magnetic Materials 474 13.7.1 Soft magnetic materials 474 13.7.2 Hard magnetic materials 474 13.8 Oxygen Sensor 475 13.9 Thermal Management Materials 476 13.10 Hardfacing Rods 477 13.11 Metal Foams 478 13.12 Bio-implants 479 14 TECHNO-ECONOMICS OF PM PROCESSING 485 14.1 Cost of Metal and Ceramic Powders 485 14.2 Techno-economics of Metal Powder Production 487 14.2.1 Pyro-metallurgical methods 487 14.2.2 Hydro-metallurgical methods 487 14.2.3 Electrolytic methods 488 14.2.4 Melt atomisation 488 14.2.5 Mechanical milling 489 14.3 Techno-economic Aspects of Sintered Parts 490 14.4 Energy Saving in Powder Metallurgy 492 14.5 Techno-economic Aspects of Full Density Consolidation 496 14.6 Techno-economic Aspects of Powder Injection Moulding 497 14.7 Techno-economic Aspects of Secondary Treatments 498 14.8 Recycling of PM Materials 500 14.9 Strategy for PM Part Business 501 Index 509