Strain rate sensitivity and related plastic deformation mechanism transition in nanoscale Ag/W multilayers

Nanoscale metallic multilayers are a promising structural material for fabricating the next generation of nanoscale devices. Even though the mechanical properties of the multilayers have been extensively studied, the interpretation for the strain rate sensitivity of the multilayers is still lacking. In present study, the hardness and strain rate sensitivity of Ag/W multilayers with a wide range of modulation period Λ and modulation ratio η deposited by d.c. sputtering deposition were evaluated by nanoindentation testing. X-ray diffraction and transmission electron microscopy were carried out to investigate the texture and microstructure of the multilayers. Experimental results indicated that a mechanism transition occurred as the plastic deformation of the Ag/W multilayers was accommodated by the two constituent layers together at Λ ≤ 50 nm, while the plastic deformation localized mainly in Ag layers when Λ > 50 nm. A modified rule of mixture and plastic deformation localization model was proposed to describe the variation of strain rate sensitivity for the multilayers with smaller and larger Λ, respectively.