Wednesday  |  Conference Center A  |  11:10 AM–11:30 AM

#13409, Nanoscale Insights on Wear of UNCD Enabled by In-situ TEM Tribometry

Nanoscale friction and wear are extremely complex processes that incorporate physical behavior from many domains. The forces and stresses involved are governed by contact mechanics, but they are influenced by adhesion behavior, which involves surface chemistry. Furthermore, the geometries are generally fractal, meaning roughness exists at every scale of interest (including atomic), which necessitates complex mathematical analyses. As a result of this complexity many questions remain in the field. In-situ experiments are uniquely capable in answering these questions by allowing visualization of processes that are generally obscured in any other experimental technique and can only be studied by simulations.

In this talk, we will discuss the visualization and quantification of wear of ultrananocrystalline diamond (UNCD) nanoscale asperities in sliding contact using in-situ transmission electron microscope (TEM) sliding experiments. Two sharp tips made of UNCD are brought into contact, enabled by a Hysitron Picoindenter TEM holder. By comparing high-resolution TEM images obtained before and after a series of sliding intervals and measuring the normal force, we quantify the evolution of the specific wear rate and visualize the morphological and crystal-structure changes as wear progresses. The image analysis is enabled by digital image correlation (DIC), which allows us to match images at different stages of the wear process and measure the removed volume between sliding intervals.

We observe a very large wear rate at the beginning of the experiments, with a dramatic and rapid drop as the asperities slid against each other for larger distances. Generation of amorphous debris is evident, providing in-situ confirmation of previous observations in both atomistic simulations and macroscale experiments. Gradual wear of grains and embedded crystallites in the amorphous debris are also observed. Our experiments suggest amorphization, gradual atomic-scale wear, and fracture all play a role in the nanoscale wear process of self-mated UNCD nanocontacts.

Rodrigo Bernal   University of Texas at Dallas
Robert Carpick   University of Pennsylvania