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 1 µm copper thin film was worn with a cono-spherical diamond probe with normal loads ranging from 25 to 800 µN and wear box edge lengths of 40, 60, and 80 µm. The nanoindenter counterface was rastered across the surface to mimic dry sliding wear. To determine potential strain field changes, 10-step quasi-static indents (200–2000 µN) 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 < 400 µN used during nanowear compared to the as-deposited copper. Normal loads ≥ 400 µN 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.
Bibliographical noteFunding Information:
The authors would like to acknowledge support provided by the South Carolina Space Grant Consortium ( #NNX15AL49H ) to support Dr. B. Schultz during his graduate studies. This research was supported through user projects at centers affiliated with the Office of Basic Energy Sciences within the U.S. Department of Energy including the Center for Integrated Nanotechnologies ( CINT , user grant- RA2014A0002 ). Los Alamos National Laboratory, an affirmative action equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under contract DE-AC52-06NA25396 .
- PVD coatings
- Sliding wear