Indentation depth dependence of nanoscale Al/W multilayers on strain rate sensitivity

While strain rate sensitivity (SRS) is a well-documented parameter to interpret the plastic deformation mechanism of metallic materials, a large inconsistency still exist in its determination in nanoscale metallic multilayers. For example, both positive and negative SRSs have previously been reported. The present study evaluates the effects of both individual layer thickness and penetration depth on the SRS of Al/W nanomultilayers by nanoindentation testing. Varying the layer thickness showed an unusual dependence of indentation penetration depth on SRS. The gradually changed interface direction and the interface density within the plastic zone upon penetration are proposed to be the two crucial parameters that determine the depth dependence of SRS in nanomultilayers, and might be the reason behind the inconsistency of SRS in nanomultilayers.