Superalloy: Processing and Performance

Abstract

Superalloy represents a class of high temperature / high performance material, which became available shortly before the Second World War.The concurrent development of gas turbine technology led to a rapid expansion in the use of such alloys. The growing demand for higher temperature capability for the turbine material so as to allow higher operating temperature and higher thrust to improve efficiency has been the main impetus for its development. The initial years were devoted to alloy chemistry whereas the subsequent years have seen more emphasis on process improvement. From a modest beginning of 10 % of the total weight of the engine in 1950'x, use ofsuperalloys has now reached a level of around 60 %. This was possible because of simultaneous availability of a variety of newer processes to produce better alloys and defect free prod-ucts. This includes vacuum melting and refining, invest-ment casting, directional solidification and single cry-stal technology. The performance of an engineering mate-rial to a great extent is determined by the processing technique that is followed. The paper describes how our knowledge on structures of material and its correlation with properties and performance has guided adoption of newer technology in the processing of superalloys.