Foreword by Dr Mike Hicks ................................... xi
Preface ................................................... xiii
Acknowledgements ............................................ xv
1 Introduction ................................................. 1
1.1 Background: materials for high-temperature
applications ............................................ 1
1.1.1 Characteristics of high-temperature materials .... 1
1.1.2 The superalloys as high-temperature materials .... 2
1.1.3 Instances of superalloy component failures ....... 5
1.2 The requirement: the gas turbine engine ................. 8
1.3 The selection of materials for high-temperature
applications ........................................... 14
1.3.1 Larson-Miller approach for the ranking of
creep performance ............................... 14
1.3.2 Historical development of the superalloys ....... 18
1.3.3 Nickel as a high-temperature material:
justification ................................... 25
Mi Summary .................................................. 28
Questions ................................................... 29
References .................................................. 31
2 The physical metallurgy of nickel and its alloys ............ 33
2.1 Composition-microstructure relationships in nickel
alloys ................................................. 34
2.1.1 The FCC phase ................................... 35
2.1.2 The gamma prime phase ........................... 40
2.1.3 Other phases in the superalloys ................. 49
2.2 Defectfe m nickel and its alloys ....................... 55
2.2.1 Defects in the gamma (FCC) phase ................ 55
2.2.2 Defects in the gamma prime phase ................ 65
2.3 Strengthening effects in nickel alloys ................. 73
2.3.1 Strengthening by particles of the gamma prime
phase ........................................... 74
2.3.2 Temperature dependence of strengthening in the
superalloys ..................................... 81
2.3.2 The anomalous yielding effect in gamma prime
alloys .......................................... 86
2.4 The creep behaviour of nickel alloys ................... 90
2.4.1 The creep behaviour of nickel ................... 91
2.4.2 Creep strengthening in nickel alloys by
solid-solution strengthening .................... 95
2.4.3 Creep strengthening in nickel alloys by
precipitation hardening ......................... 99
Appendix. The anisotropic elasticity displayed by nickel ... 103
Questions .................................................. 108
References ................................................. 114
3 Single-crystal superalloys for blade applications .......... 121
3.1 Processing of turbine blading by solidification
processing ............................................ 122
3.1.1 The practice of investment casting:
directional solidification ..................... 122
3.1.2 Analysis of heat transfer during directional
solidification ................................. 130
3.1.3 Formation of defects during directional
solidification ................................. 139
3.1.4 The influence of processing conditions on
the scale of the dendritic structure ........... 143
3.2 Optimisation of the chemistry of single-crystal
superalloys ........................................... 147
3.2.1 Guideline 1 .................................... 152
3.2.2 Guideline 2 .................................... 154
3.2.3 Guideline 3 .................................... 157
3.2.4 Guideline 4 .................................... 162
3.3 Mechanical behaviour of the single-crystal
superalloys ........................................... 170
3.3.1 Performance in creep ........................... 171
3.3.2 Performance in fatigue ......................... 187
3.4 Turbine blading: design of its size and shape ......... 194
3.4.1 Estimation of the length of the turbine
aerofoils ...................................... 196
3.4.2 Choice of mean radius for turbine blading ...... 198
3.4.3 Estimation of exit angle from blade cross-
section ........................................ 200
Appendix. Growth of an isolated dendrite, using
hemispherical needle approximation .................... 202
Questions .................................................. 203
References ................................................. 211
4 Superalloys for turbine disc applications .................. 217
4.1 Processing of the turbine disc alloys ................. 217
4.1.1 Processing by the cast and wrought route ....... 222
4.1.2 Processing by the powder route ................. 231
4.2 Composition, microstructure and properties of
turbine disc alloys ................................... 236
4.2.1 Guideline 1 .................................... 238
4.2.2 Guideline 2 .................................... 246
4.2.3 Guideline 3 .................................... 252
4.3 Service life estimation for turbine disc
applications .......................................... 259
4.3.1 Stress analysis of a turbine disc of
simplified geometry ............................ 259
4.3.2 Methods for lifing a turbine disc .............. 260
4.3.3 Non-destructive evaluation of turbine discs .... 271
Questions .................................................. 274
References ................................................. 278
5 Environmental degradation: the role of coatings ............ 283
5.1 Processes for the deposition of coatings on the
superalloys ........................................... 285
5.1.1 Electron beam physical vapour deposition ....... 285
5.1.2 Plasma spraying ................................ 288
5.1.3 Pack cementation and chemical vapour
deposition methods ............................. 293
5.2 Thermal barrier coatings .............................. 297
5.2.1 Quantification of the insulating effect ........ 297
5.2.2 The choice of ceramic material for a TBC ....... 298
5.2.3 Factors controlling the thermal conductivity
of a ceramic coating ........................... 301
5.3 Overlay coatings ...................................... 305
5.3.1 Oxidation behaviour of Ni-based overlay
coatings ....................................... 307
5.3.2 Mechanical properties of superalloys coated
with overlay coatings .......................... 312
5.4 Diffusion coatings .................................... 317
5.5 Failure mechanisms in thermal barrier coating
systems ............................................... 324
5.5.1 Introduction ................................... 324
5.5.2 Observations of failure mechanisms in TBC
systems ........................................ 325
5.5.3 Lifetime estimation models ..................... 331
5.5.4 The role of imperfections near the TGO ......... 333
5.6 Summary ............................................... 335
Questions .................................................. 337
References ................................................. 340
6 Summary and future trends .................................. 351
6.1 Trends in superalloys for turbine blade applications .. 353
6.2 Trends in superalloys and processes for turbine
disc applications ..................................... 357
6.3 Concluding remarks .................................... 361
References ................................................. 362
Index ...................................................... 363
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