An Introduction to Powder Metallurgy

Transcription

1 An Introduction to Powder Metallurgy F. THÜMMLER Dr.-Ing.habil, FIM Professor Emeritus for Materials University and Nuclear Research Centre Karlsruhe and R. OBERACKER Dr.-Ing., Central Laboratory Institute for Ceramics in Mechanical Engineering University of Karlsruhe Series Editors I.JENKINS and J.V. WOOD THE INSTITUTE OF MATERIALS

2 Contents Preface 1 Introduction (Dr I. Jenkins) 1 2 Powder Production Techniques Metal Powders Mechanical Processes Grinding and Milling 7 - Principal Aspects 7 - Equipment 9 - Mechanical Alloying 15 - Processing of Metal Chips Atomisation 17 - Principal Aspects 17 - Methods Based on Capillary Drop Formation 18 - Atomisation by Liquids 20 - Gas Atomisation 23 - Centrifugal Atomisation 25 - Vacuum Atomisation 26 - Ultrasonic Atomisation 26 - Solidification and Cooling 27 - Trends for Future Development Chemical Processes Reduction 30 - Principal Aspects 30 - Hydrogen Reduction 30 - Hydrochemical Reduction 34 - Carbon Reduction 37 - Reduction by Metals Carbonyl Processes Hydride-Dehydride Processes Electrochemical Processes 44 - Principal Aspects 44 - Electrolysis of Aqueous Solutions 45 ~- - Fused Salt Electrolysis 48 xi

3 An Introduction to Powder Metallurgy 2.2 Transition Metal Carbide, Nitride, Boride, and Suicide Powders Carbide Powders Nitride, Boride and Suicide Powders Ceramic Powders Principal Aspects Powders from Solutions Oxide Ceramic Powders Non-Oxide Ceramic Powders Ultrafine Powders (Nanocrystals) Whiskers and Short Fibres 59 Further Reading 63 Powder Properties and Characteristics Terminology Particle Size Distribution Specific Principal Aspects Common Types of Distribution Function Sampling of Powders Methods of Particle Size Analysis Sieve Analysis Microscopy Sedimentation Analysis - Gravitational Sedimentation Analysis - Centrifugal Sedimentation Analysis Fluid Classification Electrical Sensing Zone Analysis (Coulter Principle) Light Scattering and Diffraction Methods - Theoretical Background - Measurement Techniques Other Methods Surface Surface Analysis by Permeametry Surface Analysis by Gas Adsorption Technological Properties Powder Flowability Apparent and Tap Density Compactibility Powder Impurities Standards Further Reading

4 Contents vii 4 Powder Conditioning and Heat Treatment Principal Aspects and Alloying Techniques Mixing, Blending, Segregation Agglomeration Heat Treatment 115 Further Reading Health and Safety Toxicity of Powders Pyrophoricity and Explosivity of Powders 119 Further Reading Compaction and Shaping Pressure Assisted Shaping Cold Compaction Fundamental Aspects Cold Pressing Principal Aspects Practice of Axial Cold Pressing Compacting Sequence and Tooling Compaction Presses Limiting factors in Axial Pressing Practice of Isostatic Cold Pressing Pressing Equipment Tooling Advantages, Disadvantages, Practical Applications Powder Injection Moulding Principal Aspects Processing Principles Feedstock Rheology Base Powders Binder Systems Moulding Debinding Practice of Powder Injection Moulding Feedstock Preparation Injection Moulding Debinding and Sintering Application Aspects Cold Powder Extrusion Metal Powder Rolling (Roll Compaction) Hot Compaction Fundamental Aspects 155

5 Vlll An Introduction to Powder Metallurgy Practical Aspects of Axial Hot Pressing Practical Aspects of Isostatic Hot Pressing HIP Process Variants HIP Process Equipment Encapsulation Technology Containerless HIP Processing Sequence and Parameters Application of HIP Powder Forging Ferrous Structural Parts Л 66 - Forging, Rolling and Extrusion of Billets High Compaction Rate Processes Explosive Compaction Electrical Discharge Compaction Rotary Swaging Pressureless Shaping Powder Filling and Vibration Slip Casting Electrophoretic Forming Spray Forming 177 Further Reading Sintering Principal Aspects Scope and Definition Driving Force and Objective Stages of Sintering Single Component Sintering Mechanisms of Material Transport Attempts to Define the Sintering Mechanism The Two-Particle Model The Three- and Multi-particle Model The Role of Dislocations and Decreased Neck Viscosity Experiments with Pore Models Powder Shrinkage Experiments Sintering Diagrams Sintering Phenomena in Practice Parameter Dependence and Properties Development Sintering Anomalies Activating and Inhibiting Influences Processing of Ultrafine (Nanosized) Powders Sintering of Covalent Materials 212

6 Contents ix 7.3 Multicomponent Sintering Principal Aspects Solid Phase Sintering Without Solid Solubility With Mutual Solid Solubility Liquid Phase Sintering Principal Aspects Stages and Kinetics Infiltration Reaction Sintering Pressure Sintering (Hot Compaction) (cf ) Special Sintering Procedures Rate Controlled Sintering (RCS) Induction Sintering Plasma and Microwave Sintering Cold Sintering Experimental Investigation of Sintering Processes Dimensional Changes Mass and Physico-Chemical Changes Computer Simulation and Modelling 238 Further Reading Sintering Atmospheres and Equipment Functions and Reactions of Atmospheres Sintering Atmospheres in Practice Sintering Equipment 248 Further Reading Porosity and Pore-Related Properties Definition and Measurement of Porosity and Pore Structures Mechanical Properties Physical Properties Characterisation of Permeable Sintered Materials 259 Further Reading Production Routes in Practice 262 Further Reading The Products of Powder Metallurgy and their Applications Iron and Steel Plain Iron Alloyed Steels Alloying Techniques Strengthening Mechanisms 269

7 x An Introduction to Powder Metallurgy Low Alloy Steels High Alloy Steels Copper and Copper Alloys Nickel and Cobalt Alloys (Superalloys) Light Metals Aluminium Alloys Titanium and Titanium Alloys Beryllium and Magnesium High Melting-Point Metals Tungsten and Molybdenum Tantalum and Niobium Chromium Hard Metals (Cemented Carbides) Transition Metal Hard Phases Conventional Hard Metals Coated Hard Metals Recent Developments Applications Magnetic Materials Soft Magnetic Materials Hard (Permanent) Magnetic Materials High Porosity Materials Composites Principal Aspects Cermets Dispersion Strengthened Metals and Alloys Fibre-and Whisker-Reinforced Metals Infiltrated Alloys Others Advanced Ceramics Principal Aspects Magnetic and Electronic Ceramics (Functional Ceramics) Structural (Engineering) Ceramics Bioceramics Intermetallics and Miscellaneous 317 Further Reading 318 Index 320