Wear Resistance of Cu/Ag Multilayers: A Microscopic Study
Madhavan R1, P Bellon1, R S Averback1
1Department of Materials Science and Engineering , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States.
ACS Applied Materials & Interfaces
|April 10, 2018
Summary
Microscopic wear tests on copper-silver multilayers show that decreasing layer thickness enhances wear resistance. Scratch hardness, not indentation hardness, better predicts this improved wear performance in thin films.
Area of Science:
- Materials Science
- Tribology
- Nanotechnology
Background:
- Understanding microscopic wear is crucial for designing durable materials.
- Copper-silver (Cu/Ag) multilayers offer tunable properties for various applications.
- Previous studies on bulk materials do not fully capture thin-film wear mechanisms.
Purpose of the Study:
- To investigate the microscopic sliding wear behavior of Cu/Ag multilayers.
- To correlate wear resistance with mechanical properties like hardness.
- To elucidate the subsurface microstructural evolution during wear.
Main Methods:
- Magnetron sputtering for growing Cu/Ag multilayers (2-20 nm Ag thickness) and a homogeneous film.
- Sliding wear tests using a tribo-indenter with a diamond indenter (100-400 μN load, 1-20 cycles).
- Atomic force microscopy (AFM) for wear volume measurement, nanoindentation, nanoscratch, and transmission electron microscopy (TEM) for characterization.
Main Results:
- Wear rates reached steady state within five cycles.
- Hardness increased with decreasing layer thickness, while wear rates decreased.
- Wear resistance increased disproportionately to indentation hardness, but correlated well with scratch hardness.
- TEM revealed chemical mixing and solid solution formation up to 40-50 nm depth.
- Cu/Ag interfaces in thicker multilayers significantly reduced wear rates.
Conclusions:
- Thin Cu/Ag multilayers exhibit enhanced wear resistance, superior to predictions based on indentation hardness alone.
- Scratch hardness is a more reliable indicator of wear resistance in these multilayer systems.
- Subsurface chemical mixing and interface effects play a critical role in the wear mechanisms of Cu/Ag multilayers.
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