Superplastic roll forming of Ti alloys

Abstract

The high cost of aerospace alloys and their components makes them prime candidates for net-shape manufacturing techniques. Conventional processes for manufacturing disk components include hammer, hot die, and isothermal forging. This paper will examine the potential of a revolutionary approach for the manufacture of aircraft engine disks, superplastic roll forming. The process of superplastic roll forming, developed at the Institute for Metals Superplasticity Problems, Ufa, employs pairs of small opposed rollers to shape a cylindrical workpiece into a complex axisymmetric shape by simultaneously adjusting the roll gap and by moving the rolls radially outward on the workpiece while it is rotated about its axis of symmetry. Both the workpiece and the rolls are maintained at temperatures close to the beta transus. This paper will describe metallurgical evaluations of superplastically roll formed disks of alloy VT25. The evaluations of the disks included microstructure, crystallographic texture, heat treatment response, tensile strength, stress rupture resistance, and ultrasonic characteristics. The disk microstructures were found to be uniform and without any strongly textured colonies. Mechanical properties of the roll formed VT 25 were compared with those of Ti-6242S, IMI834, and conventionally forged VT25. The RF VT25 disk was found to possess low ultrasonic noise and high inspectability, which provided an increase in signal to noise for synthetic flaws.