Chemistry and Physics of Mechanical Hardness

Preface xi

1 Introduction 1

1.1 Why Hardness Matters (A Short History) 1

1.2 Purpose of This Book 5

1.3 The Nature of Hardness 7

2 Indentation 11

2.1 Introduction 11

2.2 The Chin-Gilman Parameter 14

2.3 What Does Indentation Hardness Measure? 14

2.4 Indentation Size Effect 20

2.5 Indentation Size (From Macro to Nano) 22

2.6 Indentation vs. Scratch Hardness 23

2.7 Blunt or Soft Indenters 24

2.8 Anisotropy 24

2.9 Indenter and Specimen Surfaces 25

3 Chemical Bonding 27

3.1 Forms of Bonding 27

3.2 Atoms 28

3.3 State Symmetries 29

3.4 Molecular Bonding (Hydrogen) 31

3.5 Covalent Bonds 36

3.6 Bonding in Solids 41

3.7 Electrodynamic Bonding 45

3.8 Polarizability 47

4 Plastic Deformation 51

4.1 Introduction 51

4.2 Dislocation Movement 52

4.3 Importance of Symmetry 55

4.4 Local Inelastic Shearing of Atoms 56

4.5 Dislocation Multiplication 57

4.6 Individual Dislocation Velocities (Microscopic Distances) 59

4.7 Viscous Drag 60

4.8 Deformation-Softening and Elastic Relaxation 62

4.9 Macroscopic Plastic Deformation 63

5 Covalent Semiconductors 67

5.1 Introduction 67

5.2 Octahedral Shear Stiffness 69

5.3 Chemical Bonds and Dislocation Mobility 71

5.4 Behavior of Kinks 75

5.5 Effect of Polarity 77

5.6 Photoplasticity 79

5.7 Surface Environments 80

5.8 Effect of Temperature 80

5.9 Doping Effects 80

6 Simple Metals and Alloys 83

6.1 Intrinsic Behavior 83

6.2 Extrinsic Sources of Plastic Resistance 85

7 Transition Metals 99

7.1 Introduction 99

7.2 Rare Earth Metals 101

8 Intermetallic Compounds 103

8.1 Introduction 103

8.2 Crystal Structures 104

8.3 Calculated Hardness of NiAl 112

8.4 Superconducting Intermetallic Compounds 113

8.5 Transition Metal Compounds 115

9 Ionic Crystals 119

9.1 Alkali Halides 119

9.2 Glide in the NaCl Structure 120

9.3 Alkali Halide Alloys 123

9.4 Glide in CsCl Structure 124

9.5 Effect of Imputities 124

9.6 Alkaline Earth Fluorides 126

9.7 Alkaline Earth Sulfi des 128

9.8 Photomechanical Effects 128

9.9 Effects of Applied Electric Fields 129

9.10 Magneto-Plasticity 129

10 Metal-Metalloids (Hard Metals) 131

10.1 Introduction 131

10.2 Carbides 132

10.3 Tungsten Carbide 134

10.4 Borides 136

10.5 Titanium Diboride 137

10.6 Rare Metal Diborides 138

10.7 Hexaborides 138

10.8 Boron Carbide (Carbon Quasi-Hexaboride) 140

10.9 Nitrides 141

11 Oxides 143

11.1 Introduction 143

11.2 Silicates 143

11.3 Cubic Oxides 147

11.4 Hexagonal (Rhombohedral) Oxides 152

11.5 Comparison of Transition Metal Oxides with "Hard Metals" 155

12 Molecular Crystals 157

12.1 Introduction 157

12.2 Anthracene 158

12.3 Sucrose 159

12.4 Amino Acids 159

12.5 Protein Crystals 160

12.6 Energetic Crystals (Explosives) 161

12.7 Commentary 161

13 Polymers 163

13.1 Introduction 163

13.2 Thermosetting Resins (Phenolic and Epoxide) 164

13.3 Thermoplastic Polymers 165

13.4 Mechanisms of Inelastic Plasticity 166

13.5 "Natural" Polymers (Plants) 166

13.6 "Natural" Polymers (Animals) 168

14 Glasses 171

14.1 Introduction 171

14.2 Inorganic Glasses 172

14.3 Metallic Glasses 176

14.3.1 Hardness—Shear Modulus Relationship 177

14.3.2 Stable Compositions 180

15 Hot Hardness 183

15.1 Introduction 183

15.2 Nickel Aluminide versus Oxides 184

15.3 Other Hard Compounds 184

15.4 Metals 185

15.5 Intermetallic Compounds 187

16 Chemical Hardness 189

16.1 Introduction 189

16.2 Defi nition of Chemical Hardness 190

16.3 Physical (Mechanical) Hardness 192

16.4 Hardness and Electronic Stability 193

16.5 Chemical and Elastic Hardness (Stiffness) 194

16.6 Band Gap Density and Polarizability 194

16.7 Compression Induced Structure Changes 195

16.8 Summary 196

17 "Superhard" Materials 197

17.1 Introduction 197

17.2 Principles for High Hardness 197

17.3 Friction at High Loads 198

17.4 Superhard Materials 199

References 200

Index 203