Nanolamellar medium entropy alloy composites with high strength and large plasticity

Abstract Single phase coarse-grained medium entropy alloys (MEA) generally possess a low yield strength and high plasticity at macroscopic scale, but strain hardening/softening behavior of nanocrystalline MEA still remains unknown. Here we design and prepare the nanolamellar CoCrNi MEA with heterogeneous interfaces by inserting a hard Ta thin layer. Interestingly, the CoCrNi/Ta pillars have an excellent combination with high yield strength and large uniform plastic strain as compared to single phase MEA when the layer thickness is below 50 nm. Moreover, the strength and strain hardening rate simultaneously increase with decreasing layer thickness in CoCrNi/Ta specimens. Strong constrain effect and the heterogeneous interface by the hard layer effectively suppress the propagation of major shear banding, which is responsible for the enhanced strain hardening.