Structure-dependent size effects in CuTa/Cu nanolaminates

CuTa monolayers with different Ta contents (34 at% and 37 at%) and CuTa/Cu multilayers with varying nanoscale Cu layer thickness (3-24 nm) were prepared by magnetron sputtering. Their microstructure and mechanical properties were investigated by means of high resolution transmission electron microscopy (HRTEM) and nanoindentation testing. The microstructure of CuTa34 was pure amorphous phase while that of CuTa37 was amorphous phase embedded with nanoparticles. Adding Cu layers into the two different CuTa monolayers led to CuTa-Cu interfaces with different microstructures. For CuTa34/Cu, the interface was relatively straight and the Cu layers exhibited textured growth. For CuTa37/Cu, the interface was wavy and GBs (grain boundaries) were formed in the Cu layers. To investigate the influence of the two different microstructures on multilayer deformation, the residue indentation morphologies of CuTa/Cu were observed under scanning electronic microscope (SEM). For both CuTa34/Cu and CuTa37/Cu, SBs (shear bands) could be effectively inhibited if the Cu layers had a proper thickness. Dominant deformation mechanisms and size effects were proposed and discussed for CuTa/Cu thin films possessing different interfaces and Cu layer structures.