Low modulus-yet-hard, deformable multicomponent fibrous B2-phase making a medium-entropy alloy ultra-strong and ductile

Introducing inclusions as the strength enhancer is an effective method to develop ultrastrong-yet-ductile metallic composites. However, the widely used high modulus hard-and-brittle inclusions in the low modulus matrix for strengthening often cause hetero-phase cracking and resultant reduced ductility of inclusion-reinforced composites. Here we present a novel strategy to design ultrastrong and ductile heterogeneous NiCoCr-based medium-entropy alloy uniting high modulus-yet-soft equiaxial-grained matrix combined with low modulus-yet-hard fibrous B2-inclusions. The image stress effect induced by the modulus mismatch can weaken the matrix/B2 interfacial resistance for dislocation transmission into the hard B2-phase, thus promoting their plasticity. Meanwhile, the strong matrix can effectively arrest cracks in B2-inclusions nucleated at their ideal strength to realize large ductility and great fracture resistance of composites. The fracture behavior of our designed alloys related to the fibrous B2-inclusions was rationalized in terms of the stress transfer theory. This work provides a novel pathway for designing high-performance multicomponent alloys even metallic composites utilizing the ideal strength of low modulus-yet-hard inclusions.