DEFORMATION PROCESSING IN SUPERPLASTICITY REGIME-PRODUCTION OF AIRCRAFT ENGINE COMPRESSOR DISCS OUT OF TITANIUM-ALLOYS

Superplastic deformation (SPD) that utilizes the inherent superplastic ity in suitable alloys has been employed for developing compressor dis cs for a jet engine in a titanium alloy equivalent to IMI-685. Deforma tion in the SPD regime by appropriate modification of the microstructu re of the workpiece has enabled forming to near-net shape at comparati vely lower forming loads. The equipment used for the deformation proce ssing includes an electric furnace with robotic handling of heated bil lets, a 2000 ton isothermal forging press with numerical controls for speed and load, and a cooling station for controlled cooling of forged discs. The starting microstructure of the forging stock consisting of mainly alpha laths within prior beta boundaries was refined to fine e quiaxed alpha grains by appropriate deformation in the alpha + beta re gime. The refined structure enabled isothermal forging in the alpha beta phase field at low deformation loads. The effect of SPD and subse quent thermal treatment on the isotropy of properties in discs has bee n studied. The forging characteristics, and the microstructure and mec hanical properties realized in the discs are presented. It is seen tha t SPD is a practical method which enables high quality items to be mad e that are unique in form and reliable in use. The process can be used in a serial production of parts of specified metallurgical properties . (C) 1998 Elsevier Science S.A. All rights reserved.