Remarkable strengthening of nanolayered metallic composites by nanoscale crystalline interfacial layers

Strengthening of metallic materials has been a long-standing scientific issue. Recent experiments have shown that the introducing of nanoscale amorphous interfacial layers is capable of providing effective strengthening in metallic materials. However, the above strategy is subject to the complexity of the composition and structure in the amorphous layers that usually contains at least two elements with significant concentration variation along the interfacial thickness. Here in this paper it is demonstrated by experiments that significant strengthening can be achieved in a Cu/Ni nanolayered metallic composite by architecting nanoscale single-elemental crystalline (instead of amorphous) interfacial layers into the layered interfacial region. The results show that the hardness of the composite with individual layer thickness of 40 nm exhibits a first-increase-and-then-decrease trend with the decreasing of the thickness of the crystalline (aluminum as an example) interfacial layer from 40 to 2 nm, leading to a maximum value of 5.67 GPa, which is around 22% higher than that of the normal sample without the interfacial layers (4.66 GPa). Further molecular dynamics simulations revealed that the strength enhancement originated from the increase in the lattice mismatch of the layered interfaces due to the addition of crystalline interfacial layers. The interfaces with larger lattice mismatch possess more dense dislocation networks, which relieves the stress concentration at interfaces. Hence, dislocations are much harder to nucleate, resulting in a substantial strengthening in the nanolayered composite. As a result, this work provides a simple effective strengthening strategy by inserting nanoscale crystalline interfacial layers to increase the lattice mismatch of nanolayered interfaces.