Ultrastrong 42CrMo/CoCrNi multilayer composites at cryogenic temperatures

High-strength materials generally suffer low ductility due to poor strain-hardening, especially at low temperatures. Laminated composites that integrate high-strength and high-toughness materials provide a promising solution to this strength-ductility trade-off. Here we fabricate a multilayer composite comprising 42CrMo steel and CoCrNi medium-entropy alloy via hot-rolling. The resulting composite achieves an ultra-high yield strength of 1.61 GPa, tensile strength of 1.99 GPa, and ductility of 4.9 % at 93 K. The CoCrNi layers significantly enhance ductility by activating extensive twinning and stacking faults, which alleviate stress concentrations around 42CrMo layers while preserving their high strength. Moreover, optimizing the layer thickness and grain size further improves strength and ductility.