Extraordinary superplasticity at low homologous temperature and high strain rate enabled by a multiphase nanocrystalline network

Abstract

Superplasticity is a highly sought-after property of components manufactured with complex geometries in metal forming processes. However, superplasticity usually occurs at high temperatures and/or low strain rates, which entails high energy consumption, long processing time, and severe surface oxidation. Herein, we have developed a multiphase nanocrystalline network (MPNN) in a Ti6Al4V5Cu model alloy, where the grain boundary β phases promote the sliding and rotation of ultrafine α grains, while the nanosized Ti2Cu particles pin down the α/β boundaries to maintain the thermostability of the nanostructure. Results show that the onset temperature for superplasticity of the model alloy is 250 °C lower than that of the Ti6Al4V alloy at the strain rate of 10−4s − 1. Remarkably, superplasticity was also observed at an extremely high strain rate of 1 s − 1 at 750 °C, which is 2–4 orders of magnitude larger than conventional superplastic metals. The present work is of great significance in developing more economical and efficient superplastic deformation processes.