Understanding the Atomic Scale Mechanisms that Control the Attainment of Ultralow Friction and Wear in Carbon-Based Materials
Final rept. 17 Jun 2014-16 Dec 2015
TRUSTEES OF PENNSYLVANIA UNIV PHILADELPHIA PA
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The wear behavior of ultrananocrystalline diamond UNCD was characterized at the nanoscale to understand the fundamental mechanisms controlling the initial stages of wear. To enable this, novel nanoscale sliding experiments were conducted in situ in a transmission electron microscope TEM. UNCD is part of a class of materials with tremendous potential for tribological applications due to their low wear and low friction behavior. However, the scientific understanding of the initial wear process is lacking, and this prevents broader application of these materials. The experiments revealed that 1 the wear follows a gradual, atomic-level removal mechanism, as opposed to fracture or plastic deformation 2 the rate of wear rate of material removal in this nanoscale, single asperity contact is orders of magnitude larger than that measured at the macroscale and 3 nevertheless, the wear follows the macroscale trend of an initially larger wear rate, followed by stabilization at a lower value. Strikingly, no amorphization during sliding was observed, in contrast with previous experimental and computational results for diamond. To better understand the contact stresses that drive the wear, a careful, long-range investigation of contact behavior was also initiated. Since adhesion is crucial in determining contact stresses, an experimental method for the nanoscale measurement of length and strength of adhesive interactions between asperities of arbitrary shape was successfully implemented.
- Atomic and Molecular Physics and Spectroscopy