Trace Elements and Residual Elements in Superalloys,
NATIONAL AERONAUTICAL ESTABLISHMENT OTTAWA (ONTARIO)
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This paper is a sequel to an earlier review 1 entitled Impurities and Trace Elements in Nickel Base Superalloys and covers work performed in this field from 1976 to present. Improvements in refinement technology are discussed. This includes evaluation of refractory materials to ensure minimal accumulation of inclusions. The following section on detrimental or tramp elements covers 1 residual gases and porosity, 2 non-metallic inclusions with particular emphasis on fatigue crack formation in inclusions which can lead to premature failure and 3 residual elements such as sulfur, phosphorus and other tramp elements primarily those in AMS 2280 which segregate to grain boundaries. Since this segregation can lead to intergranular fracture, these elements have been the subject of several studies by Auger Electron Spectroscopy AES. There is also a section on beneficial elements which are added in small amounts to counteract the effect of the tramp elements. Some of those beneficial elements in small residual amounts may also help with grain size control. Finally, some recent work on the processing of scrap is discussed, with particular reference to minimizing the inclusion and trace element content of the alloys.