Superplastic forming: Evolution from metallurgical curiosity to major manufacturing tool?

Abstract

Superplastic deformation of certain metallic alloys was first observed almost a century ago but simply remained an interesting metallurgical curiosity until the revelation, in 1962, of work in the former Soviet Union. This led to western research and the suggestion by Backofen that the phenomenon could be practically exploited for the manufacture of sheet components. In turn, this resulted in major work to develop new superplastic alloys, forming machinery and forming techniques. Although superplastic behaviour has now been developed in a wide range of materials, its exploitation has been confined to niche applications. It is only the superplastic alloys of titanium and aluminium that have achieved significant commercial markets. The fact that titanium alloys can combine superplastic forming with diffusion bonding to manufacture multisheet structures has assured the material a secure and growing role in aerospace applications. The high basic cost of titanium has precluded significant use in other markets although this could change if current developments in the titanium extraction process are successful. Superplastically formed aluminium components find application in a far wider range of niche applications. It is suggested that the more recent demonstration of superplastic behaviour at much higher strain rates (HSRS) could allow superplastic forming of aluminium alloys to break out of its niche role. However, significant development would be required to combine the existing fundamental knowledge of HSRS with engineering to define a practical, economic manufacturing route for volume production of the new material.