The Superalloys: Fundamentals and Applications

Cover......Page 1
Half-title......Page 3
Title......Page 5
Copyright......Page 6
Contents......Page 9
Foreword......Page 13
Preface......Page 15
Acknowledgements......Page 17
1.1.1 Characteristics of high-temperature materials......Page 19
1.1.2 The superalloys as high-temperature materials......Page 20
1.1.3 Instances of superalloy component failures......Page 23
1.2 The requirement: the gas turbine engine......Page 26
Example question......Page 29
1.3.1 Larson–Miller approach for the ranking of creep performance......Page 32
1.3.2 Historical development of the superalloys......Page 36
1.3.3 Nickel as a high-temperature material: justification......Page 43
1.4 Summary......Page 46
Questions......Page 47
References......Page 49
2 The physical metallurgy of nickel and its alloys......Page 51
2.1 Composition–microstructure relationships in nickel alloys......Page 52
2.1.1 The FCC phase......Page 53
2.1.2 The gamma prime phase......Page 58
A The gamma double prime phase......Page 67
B The TCP phases......Page 69
C Carbide and boride phases......Page 71
B Line defects – dislocations......Page 73
C Point defects – vacancies......Page 77
A Planar defects – the anti-phase boundary......Page 83
B Line defects – dislocations......Page 88
C Point defects......Page 89
2.3 Strengthening effects in nickel alloys......Page 91
2.3.1 Strengthening by particles of the gamma prime phase......Page 92
A The case of weakly coupled dislocations......Page 93
B The case of strongly coupled dislocations......Page 96
2.3.2 Temperature dependence of strengthening in the superalloys......Page 99
2.3.3 The anomalous yielding effect in gamma prime alloys......Page 104
2.4 The creep behaviour of nickel alloys......Page 108
2.4.1 The creep behaviour of nickel......Page 109
2.4.2 Creep strengthening in nickel alloys by solid-solution strengthening......Page 113
2.4.3 Creep strengthening in nickel alloys by precipitation hardening......Page 117
2.5 Summary......Page 119
Appendix. The anisotropic elasticity displayed by nickel......Page 121
Questions......Page 126
References......Page 132
3 Single-crystal superalloys for blade applications......Page 139
3.1.1 The practice of investment casting: directional solidification......Page 140
3.1.2 Analysis of heat transfer during directional solidification......Page 148
A Treatment of infinite rod – estimation of withdrawal velocity......Page 149
B Comparison of axial and transverse contributions to heat transfer......Page 153
C Effects of quenching medium – liquid metal cooling......Page 154
3.1.3 Formation of defects during directional solidification......Page 157
Case study: The freckle defect......Page 158
3.1.4 The influence of processing conditions on the scale of the dendritic structure......Page 161
3.2 Optimisation of the chemistry of single-crystal superalloys......Page 165
3.2.1 Guideline 1......Page 170
3.2.2 Guideline 2......Page 172
3.2.3 Guideline 3......Page 175
3.2.4 Guideline 4......Page 180
Case study – hot corrosion......Page 183
3.3 Mechanical behaviour of the single-crystal superalloys......Page 188
3.3.1 Performance in creep......Page 189
A Tertiary creep regime......Page 190
B Primary creep regime......Page 194
C Rafting regime......Page 198
3.3.2 Performance in fatigue......Page 205
A Low-cycle fatigue......Page 207
B High-cycle fatigue......Page 209
3.4 Turbine blading: design of its size and shape......Page 212
3.4.1 Estimation of the length of the turbine aerofoils......Page 214
Example calculation......Page 215
3.4.2 Choice of mean radius for turbine blading......Page 216
Example calculation......Page 218
Appendix. Growth of an isolated dendrite, using hemispherical needle approximation......Page 220
Questions......Page 221
References......Page 229
4.1 Processing of the turbine disc alloys......Page 235
A Vacuum arc remelting......Page 240
Case study. Melt-related ‘white spot’ defects......Page 242
B Electro-slag remelting......Page 245
D Open- and closed-die forging......Page 247
4.1.2 Processing by the powder route......Page 249
4.2 Composition, microstructure and properties of turbine disc alloys......Page 254
4.2.1 Guideline 1......Page 256
4.2.2 Guideline 2......Page 264
4.2.3 Guideline 3......Page 270
Case study. The design of turbine disc alloys......Page 274
4.3.1 Stress analysis of a turbine disc of simplified geometry......Page 277
A The life-to-first-crack approach......Page 278
B Damage-tolerant lifing......Page 279
C The probabilistic approach to lifing......Page 282
4.3.3 Non-destructive evaluation of turbine discs......Page 289
Questions......Page 292
References......Page 296
5 Environmental degradation: the role of coatings......Page 301
5.1.1 Electron beam physical vapour deposition......Page 303
5.1.2 Plasma spraying......Page 306
5.1.3 Pack cementation and chemical vapour deposition methods......Page 311
Example calculation......Page 315
5.2.2 The choice of ceramic material for a TBC......Page 316
5.2.3 Factors controlling the thermal conductivity of a ceramic coating......Page 319
5.3 Overlay coatings......Page 323
5.3.1 Oxidation behaviour of Ni-based overlay coatings......Page 325
5.3.2 Mechanical properties of superalloys coated with overlay coatings......Page 330
5.4 Diffusion coatings......Page 335
5.5.1 Introduction......Page 342
5.5.2 Observations of failure mechanisms in TBC systems......Page 343
5.5.3 Lifetime estimation models......Page 349
5.5.4 The role of imperfections near the TGO......Page 351
5.6 Summary......Page 353
Questions......Page 355
References......Page 358
6 Summary and future trends......Page 369
6.1 Trends in superalloys for turbine blade applications......Page 371
6.2 Trends in superalloys and processes for turbine disc applications......Page 375
6.3 Concluding remarks......Page 379
References......Page 380
Index......Page 381