Phase reversion-induced nanostructured austenitic alloys: an overview

The potential of the concept of phase reversion process to obtain nanograined (NG) structure with high strength–high ductility combination and to fundamentally understand the deformation and fracture mechanisms is described. Deformation studies conducted as a function of grain size suggested that there was a clear distinction and fundamental transition in the deformation behaviour of NG and CG austenitic alloy such that ‘deformation twinning’ contributed to the excellent ductility of ‘high strength’ NG alloy, while in the ‘low strength’ CG alloy, ductility was also good but because of strain-induced martensite nucleation at shear bands. It was postulated that in a given austenitic stainless steel used for biomedical devices, the decrease in grain size from the CG to NG regime increases the stability of austenite. The change in the deformation mechanism impacted the mode of fracture such that it was striated fracture in NG alloy and microvoid coalescence in CG counterpart.