Ultrastrong Carbon Thin Films from Diamond to Graphene under Extreme Conditions: Probing Atomic-Scale Interfacial Mechanisms to Achieve Ultralow Friction and Wear
Abstract
The goal was to gain a fundamental understanding of how to achieve low friction and wear in ultrastrong carbon-based materials. Experimentally, in situ nanotribometry method was used to enable nanoscale visualization of sliding contacts inside the TEM. These experiments are in turn modelled computationally using molecular dynamics, allowing better understanding of the atomic scale processes controlling friction and wear. The focus was on the behavior of silicon-silicon, silicon-diamond, and diamond-like-carbon (DLC)-diamond interfaces. For silicon-silicon interfaces, the nanocontacts showed a sliding-history and stress-dependent (applied normal stress) adhesion; sliding increased adhesion by more than 16 times. This is explained in terms of stress-activated covalent bond breaking that only occurs during sliding. For silicon in sliding contact with diamond, adhesion increased with applied stress and speed. This dependence is explained in terms of tip geometry changes due to atomic-scale plasticity. For DLC, wear during sliding and the evolution of adhesion forces were characterized. Wear was measured as a function of load and sliding distance. Gradual wear with sliding was observed with the wear rate increasing with the average contact stress. It neither followed the classic Archard's wear law nor recently observed behavior following transition state theory. The wear behavior over the full range of stresses is well described by multi-bond wear model that exhibits a change from Archard-like behavior at high stresses to a transition state theory description at lower stresses. Adhesion showed large scatter, which was attributed to stochastic covalent bond breaking and formation events. In summary, this work shows that understanding adhesion and wear requires careful consideration of the interplay of mechanics and chemistry at the interface.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 20, 2018
- Accession Number
- AD1060460
Entities
People
- Robert Carpick
- Yeau-Ren Jeng