Superior cryogenic tensile properties by constructing multilayer laminates with two-scale heterogeneous interfaces in multi-principal element alloys

A novel dual-heterogeneous laminate with two-scale heterogeneous interfaces, i.e., micro-scale coordinated multilayer interfaces and nano-scale precipitation interfaces, has been designed and fabricated. Then, the effects of layer thickness and deformation temperature on the tensile properties have been investigated in these multilayer laminates with alternating CoCrNi and (CoCrNi) 94 Al 3 Ti 3 layers. The yield strength and the uniform elongation are observed to simultaneously increase with decreasing layer thickness and lower deformation temperature. Hetero-deformation-induced hardening (HDI) is found to be higher for the laminates with smaller layer thickness, and HDI hardening becomes ever higher at cryogenic temperature as compared to that at room temperature. Micro-hardness measurements prior to and after tensile testing reveal that larger hardness increments can be observed in the laminates with decreasing layer thickness and lower deformation temperature. The enhanced tensile properties with decreasing layer thickness and lower deformation temperature can be attributed to the higher HDI hardening. Multiple deformation mechanisms, such as stacking faults, deformation twins, Lomer-Cottrell locks, 9R structures and ɛ -martensite transformation, are observed to be activated at cryogenic temperature, and high density coherent L1 2 nanoprecipitates with interspacing of several tens of nm are found to be sheared by defects, resulting in strong precipitation hardening for better tensile ductility.