Deformation-induced grain boundary segregation mediated high-strain rate superplasticity in medium entropy alloy

Superplasticity refers to extremely high plastic deformation of crystalline materials at homologous temperature. In particular, high-strain rate superplasticity (HSRS) at a strain rate equal to or higher than 10(-2) s(-1) draws great technological interest in the shape-forming of engineering materials. Besides primary mechanism as grain boundary sliding, the formation of liquid phase at grain boundaries/interfaces can assist HSRS. With the advent of multi-principle element alloys (MPEAs), designing grain boundary segregation of a low melting temperature element with the appropriate choice of composition can bring the possibility to produce the HSRS accommodated by the partial melting in MPEAs. Here, we show the trace of the liquid phase in Al0.3CoCrNi MPEA at the homologous temperature of 0.65. Careful microstructural examination reveals for the first time that deformation-induced Al-segregation occurs at grain boundaries/interfaces. The present work expedites a new path to tailoring microstructure for promoting the HSRS in high-strength materials by grain boundary segregation engineering. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Superplasticity, especially high-strain rate superplasticity (HSRS) at a strain rate equal to or higher than 10(-2) s(-1), shows significant technological potential in the shape-forming of engineering materials. The formation of liquid phase at grain boundaries/interfaces can assist HSRS, and designing grain boundary segregation of a low melting temperature element in multi-principle element alloys (MPEAs) can promote HSRS by partial melting. This study demonstrated the trace of liquid phase in Al0.3CoCrNi MPEA and the possibility of tailoring microstructure for promoting HSRS in high-strength materials by grain boundary segregation engineering.