Impurities and trace elements in nickel-base superalloys

Abstract

This review is concerned with the effects of harmful impurities and beneficial trace (and minor alloying) elements on the properties of nickel-base superalloys. The impurities, treated under the headings: (i) residual gases, (ii) residual non-metals, (iii) residual metals and metalloids, and (iv) silicon and manganese, may be present in the charge material, picked up during processing, or picked up during service. Trace and minor alloying elements which are deliberately added during processing are listed under the headings: (i) boron and zirconium, (ii) calcium and magnesium, (iii) hafnium, (iv) rare-earth metals, and (v) carbon. In many cases these elements counteract the injurious elements by grain-boundary refinement. As far as possible, each section covers the effect of the elements on properties and microstructure, and in the case of harmful ingredients, their removal and control. Vacuum-melting practice is covered and some specifications and analytical techniques are included in the concluding section.