Strong and ductile nanolaminate composites combining metallic glasses and nanoglasses

Abstract

The proven superior ductility of nanoglasses (NGs) makes them a promising second phase for metallic glass (MG) matrix composites. Here we evaluate the mechanical properties of MG-NG nanolaminate composites by performing molecular dynamics simulations of tensile loading. We focus on the effects of NG layer thickness and separation as well as the loading direction on the predicted strength and inelastic deformation profile. Our results reveal that nanolaminates with NG layers separated by more than 50 nm fail by shear banding. Meanwhile, the predicted nanolaminate strength versus MG volume fraction follows an inverse Hall-Petch relationship rather than the linear rule-of-mixtures. In contrast, by closely packing NG layers to 4.8 or 6.5 nm, the nanolaminates exhibit enhanced tensile ductility for tensile loading perpendicular or parallel to the MG-NG interfaces, respectively. Our results further reveal that the change in the loading direction causes the differences not only in the location of SB initiation but also the critical distance between NG layers for failure mode transition. Finally, the MG-NG nanolaminate structure with NG layers closely packed and interfaces oriented parallel to the loading direction is identified as the most effective heterostructure, which preserves superplasticity while producing a maximum strength of 2.35 GPa, a value 15% greater than that of monolithic NG with a grain size of 5 nm. Our work demonstrates that a nanolaminate combining MG and NG layers of suitable thicknesses is able to withstand large plastic deformations while maintaining the structural stability, and we expect that these results will inspire the development of novel strong and superplastic MG matrix composites that will broaden the possible applications of MGs.