Improvement of plastic property of Ti/Al nanowires by designing the core–shell structures

Abstract

Ti alloy has the disadvantages of low elastic modulus, high yield ratio, and low plasticity, therefore, improving its plasticity is very important to promote their use. In this study, the tensile behavior of Ti/Al core–shell nanowires (NWs) in the z-axis direction of single-crystal Ti with [0001] grain-oriented HCP structure and single-crystal Al with [001] grain-oriented FCC structure was investigated using molecular dynamic (MD) simulations to explore the mechanism of enhanced ductility in Ti alloy. The results indicate that the shell thickness may significantly affect the mechanical behaviors of the NWs. For the mechanical properties of core–shell NWs, Young’s modulus, ultimate tensile strength (UTS), Specific modulus, Specific strength, flow stress, and fracture strain showed sensitivity to shell thickness. Compared with core–shell NWs, single crystal Ti NW has greater strength and higher Young’s modulus, Specific strength and UTS. By contrast, core–shell NWs have better Specific modulus and plastic properties, their flow stress and fracture strain are higher than those of single crystal Ti NW. For the single crystal Ti NW, the main plastic deformation mechanisms are shear band nucleation and recrystallization. For Ti/Al core–shell NWs with shell thicknesses of 1and 2 nm, the nucleation of the twin variants replaces the dominant position of the shear bands. As the twin boundaries (TBs) expand, the dislocation slip is activated, and grain reorientation occurs, inducing the superior plastic properties of NWs. As the shell thickness increases to 3–5 nm, the interaction between the twin variants and shear bands reduces the expansion rate of the TBs, resulting in increased flow stress and fracture strain of the NWs. This study can provide theoretical guidance for the experimental study and preparation of core–shell NWs.