ABSTRACT
The failure of a relatively small component in a plant can have catastrophic results. In 1969, a blade failed in one of the turbines at Hinkley Point A Power Station during a routine overspeed test [1]. Figure 13.1 shows the resultant devastation, with components having passed through all the outer
13.1 Introduction ......................................................................................................................... 389 13.1.1 Strength of Materials .............................................................................................390 13.1.2 Failure Mechanisms ............................................................................................... 391 13.1.3 Segregation............................................................................................................. 391 13.1.3.1 Thermal ................................................................................................. 391 13.1.3.2 Irradiation Assisted ............................................................................... 395 13.2 Analytical Methods for Determining Grain Boundary Segregation .................................. 396 13.2.1 Introduction ............................................................................................................ 396 13.2.2 Metallographically Polished Specimens ................................................................ 397 13.2.2.1 Chemical Etching .................................................................................. 397 13.2.2.2 SIMS ...................................................................................................... 397 13.2.2.3 Autoradiography .................................................................................... 398 13.2.2.4 Auger Electron Spectroscopy ................................................................ 399 13.2.3 Intergranular Fracture ............................................................................................400 13.2.3.1 Impact at Low Temperature .................................................................. 401 13.2.4 Transmission Electron Microscopy .......................................................................408 13.2.4.1 Production of a Thin Foil ......................................................................408 13.2.4.2 Field Emission Gun STEM....................................................................409 13.2.4.3 Time-of-Flight Atom Probe ................................................................... 413 13.3 Cracks in Metals and Alloys ............................................................................................... 413 13.4 Conclusion ........................................................................................................................... 416 References ...................................................................................................................................... 417 Appendix ........................................................................................................................................ 418 A.1 Introduction ......................................................................................................................... 418 A.2 ISO Technical Committee 201 on Surface Chemical Analysis .......................................... 418 A.2.1 Scope ...................................................................................................................... 419 A.2.2 Structure of ISO Technical Committee 201 .......................................................... 419
casings and the roof of the turbine hall and some parts ending up several hundred meters distant. Fortunately, there were no injuries to personnel but the cost of repair and prevention ran into millions of dollars. It is therefore important to be able to predict how a metal or alloy will behave in service. Despite all the knowledge concerning embrittlement, examples continue to occur where components have failed as the result of segregation of trace elements in alloys. There is also the important problem of intergranular stress corrosion cracking where components under load in an aggressive environment can fail because small cracks are opened up by the combined effects of stress and oxidation. Knowledge of the grain boundary chemistry can assist in reducing or eliminating both these and other problems. There are many ways in which a metal or alloy can be characterized and the structure and composition of the grain boundaries determined. Some techniques analyze the internal surface that has rst been exposed, others analyze the internal surface in thin sections of the material, while others section slowly through the material until a boundary is encountered. This chapter outlines some techniques and methods for determining the grain boundary chemistry and hence the properties of metals and alloys.
