Remarkable ductility in metastable refractory high entropy alloys via BCC-FCC/α″ martensitic transformations

Abstract

Designing metastable refractory high entropy alloys (RHEAs) with transformation induced plasticity (TRIP) effects is an effective approach for solving the low ductility of RHEAs. However, the traditional martensitic transformations (MTs) in RHEAs generally result in limited ductility improvement. In the present work, we designed a metastable RHEA Zr2Hf4Nb0.5Ta (Nb7Ta13) with severe lattice distortion, and two MTs, BCC-to-FCC/α″, were found in Nb7Ta13. During tension deformation, BCC-to-FCC/α″ MTs appeared after yielding, causing the TRIP effect; after the MTs are completed, the FCC martensite showed excellent deformability and effectively promoted the following deformation of Nb7Ta13. Finally, Nb7Ta13 RHEAs show a remarkable ductility (∼60%). By analyzing the variation of interplanar spacing and interatomic spacing during DIMTs, we believed that the FCC martensite is generated by relaxing the lattice distortion.