Superalloys made by conventional vacuum melting and a novel spray forming process

Abstract

Wrought Ni-base superalloys used in modern gas turbine engines are typically produced by vacuum induction melting (VIM) plus consumable remelting (ESR and/or VAR). For the more advanced alloys, these processes have certain limitations; namely, the ability to produce sound ingots of a reasonable size, free of harmful segregation related defects, which can readily be converted into wrought product. Powder metallurgy processes have been developed to overcome these problems but substitute another problem: high cost. To address these concerns, a clean, ceramicless spray forming process has been developed which uniquely combines electroslag remelting (ESR), bottom pouring through a cold induction guide (CIG) and spray forming (Osprey Metals Ltd). This paper discusses some of the issues encountered in current superalloy manufacturing processes and describes the clean metal spray forming (CMSF) plant which has been constructed to address them.