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• The 〈1 1 2〉 and 〈1 1 0〉 dislocations are mostly formed in the Cu layers. • The defects occur in the interface and then extend towards the Cu layers. • For the horizontal layers specimens, the defects also appear in the Ta layers. The deformation behavior, the fracture mechanism, and the mechanical properties of the Cu/Ta nanoscale metallic multilayers (NMMs) with the vertical and horizontal layers under the tension process are meticulously studied using molecular dynamics (MD) simulations. The influences of the various temperatures, strain rates and modulation periods (λ) are evaluated in detail through the dynamic responses, the stress-strain relationships, and the dislocation density diagrams of the Cu/Ta NMMs. The results reveal that the phase transitions from the FCC structures into the HCP, BCC, and amorphous structures mainly occur in the Cu layers. Only a small amount of the BCC structures transforms into the amorphous structures in the Ta layers. In the Cu layers, the 〈1 1 2〉 and 〈1 1 0〉 dislocations are mostly formed, while the 〈1 1 1〉 dislocations are mostly found in the Ta layers. The defects occur in the interface and then extend towards the Cu layers for the vertical layers specimens. For the horizontal layers specimens, the defects appear both in the Ta layers and in the interface. The tensile strength of the vertical layers specimens is lower than that of the horizontal layers specimens under the same testing conditions. As increasing temperature, the tensile strength and the dislocation density reduce. However, the tensile strength and the dislocation density increase with an increase in strain rate. The tensile strength slightly changes with the different λ. The dislocation density is higher with a larger λ. [ABSTRACT FROM AUTHOR]