Industrial casting of superalloys

Abstract

The current status of precision vacuum casting technology is reviewed in outline and the historical background of the subject is briefly covered. Particular reference is made to its application to the manufacture in nickel-base superalloys of aerofoil and associated components for gas turbine engines, and possible directions for further development of the process and ancillary technology are examined. The current state of progress in both alloy technology and casting process development is reviewed. In connection with the latter, both the scope of currently available product geometries, from small solid equiaxed components through complex hollow shapes to integrally cast multi-aerofoil components, and the extension of the technology to include large, integrally cast, near-net-shape structural components, are discussed. Specific brief reference is made to the main contributory changes and developments which have taken place in each sector of the process from pattern technology to post-casting processing. The more recently adopted and now increasing utilization of multi- and monocrystalline directionally solidified aerofoils in gas turbine engines is addressed with reference to its impact on alloy chemistry and to the conflicting opinions on the relative merits of the diverse process technology. Also addressed are the increasingly important favourable effects on product quality and casting design flexibility of post-casting coating processes, thermal and thermomechanical treatments, advances in non-destructive testing, and the steady trend of progressively improving product quality assurance technology. Finally, consideration is given to the degree to which the casting of superalloys has reached maturity, and what, if any, prospective further improvements may be developed from which gas turbine engines could derive benefits in performance, weight, or operating efficiency in the future.MST/243