Tribological performance of monolithic copper thin films during nanowear

• Published in: Wear 2018-01, Vol.394-395 (C), p.50-59
• Main Authors: Schultz, Bradley M., Li, Nan, Economy, David R., Sharp, Julia L., Mara, Nathan A., Kennedy, Marian S.
• Format: Article
• Language: English
• Subjects: Boxes; Contact pressure; Copper; Deformation mechanisms; Diamond films; Diamonds; Frictional wear; Hardness; Hardness testing; Loads (forces); MATERIALS SCIENCE; Mathematical models; Nanoindentation; Nanoindenters; NANOSCIENCE AND NANOTECHNOLOGY; Nanostructured materials; Nanotribology; PVD coatings; Residual stress; Sliding friction; Sliding wear; Strain hardening; Stress relaxation; Thin films; Tribology; Wear
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2017.10.005

Mathematical models suggest that the strain along the film formed by parallel passes of a nanoindentation probe in contact with the film can be either homogenous or heterogeneous, depending on contact pressure and spacing between passes. In this study, a 1µm copper thin film was worn with a cono-spherical diamond probe with normal loads ranging from 25 to 800µN and wear box edge lengths of 40, 60, and 80µm. The nanoindenter counterface was rastered across the surface to mimic dry sliding wear. To determine potential strain field changes, 10-step quasi-static indents (200–2000µN) were performed using nanoindentation inside the wear boxes created at various loads to determine if a strain field alteration could be observed in changes in hardness of the copper thin film. It was shown that there was a softening effect in the hardness for normal loads < 400µN used during nanowear compared to the as-deposited copper. Normal loads ≥ 400µN had a similar or higher hardness than the as-deposited copper. This is believed to have occurred due to a relaxation in the residual stresses created during deposition in the copper thin films at lower loads, which caused a decrease in hardness. Conversely, at the higher loads, increased deformation leads to an increase in hardness. Additionally, all of the wear boxes displayed a higher estimated strain hardening exponent than the as-deposited material. •The hardness for a deformed region increases with increasing contact pressure during deformation.•The deformed regions displayed a higher estimated strain hardening exponent than the as-deposited material.•When there is more wear overlap, the hardness of the deformed region increases.•Lower contact pressures during wear alleviate the residual stress during deposition.