Abstract
Cyclic depth-sensing nanoindentation tests are carried out to unravel the effect of monolithic and multilayer thin coatings on load-bearing capacity and stress distribution in the coating-Zr-based metallic glass systems. Thin films of TiN, CrN, and Ti/TiN multilayer, having thickness of 300 nm, are deposited on Zr60Ni10Cu20Al10 and Zr50Cu40Al10 metallic glasses by RF sputtering technique. Strain softening occurs over several cycles in Zr-based metallic glasses, CrN, and TiN films as evidenced by a disparity between the unloading and reloading sequences. However, the cyclic nanoindentation of Ti/TiN multilayer coating results in a hysteresis loop in the load-depth profiles, and this event depends on the number of cycles and the loading rates. AFM and SEM characterization of remnant imprints revealed microcraks and crack-like shear bands in nanocoatings and Zr-based metallic glasses, respectively. Based on shear-fracture driven plastic flow of the coatings, a modified cavity model is used to determine the shear stress evolution as a function of penetration depth. The finite-element simulations predicted the stress distribution beneath the indenter and are well consistent with the evolving trend of shear stress obtained from experiments.