Solid lubrication by carbon nanotubes: Understanding transfer layer formation and sliding at a fundamental level using atomistic simulations and experimental nano analytics

• Applicants: Professor Dr. Michael Moseler; Professor Dr.-Ing. Frank Mücklich
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 407711892

• Final Report Year: 2023

Final Report Abstract

When lubrication of rolling bearings with oil or grease is not possible, solid lubrication with carbon nanotubes (CNT) is a possible alternative. To investigate the mechanisms underlying CNT lubrication of highly loaded contacts, an experimental approach is combined with molecular dynamics simulations in this project. Experimentally, CNT-coated iron plateletts and spherical aluminium oxide counterparts are used. Analysis of the friction-loaded layers indicates a phase transformation leading to layers of amorphous carbon with embedded CNT fragments as well as iron oxide and iron carbide particles. Covalent bonds to the iron surface and little transfer to the counterbody indicate sliding at the coating-sphere interface as the dominant mechanism of CNT lubrication. Atomistic simulations of CNT coatings reveal two different friction regimes: a low-load regime in which the CNTs remain intact and a high-load regime with partial damage and formation of amorphous carbon. The critical load for the transition between the regimes increases with the number of inner walls of the CNTs and the packing density. The former determines the stability of the individual CNTs, the latter the local stresses at the CNT-CNT crossings. Based on the simulation results, operation in the high load range is predicted for the experimental coatings. This is confirmed by a remarkable agreement between electron micrographs and images from atomistic simulation. Based on the results of this work, a multi-stage lubrication mechanism for CNT coatings is formulated.

Publications

• Solid Lubrication based on Carbon Nanotubes, GfT-Tagung, Sondersession SPP 2074, Göttingen, 23.09. – 25.09.2019
  T. MacLucas & A. Klemenz
  
• Solid Lubrication based on Carbon Nanotubes, GfT-Tagung, Sondersession SPP 2074, Onlineveranstaltung, 28.09. – 30.09.2020
  T. MacLucas & A. Klemenz
  
• Solid Lubrication based on Carbon Nanotubes, GfT-Tagung, Sondersession SPP 2074, Onlineveranstaltung, 27.09. – 29.09.2021
  T. MacLucas & A. Klemenz
  
• Degradation of Carbon Nanotubes Under Tribological Load, Tribochemistry Satellite Meeting, Beaune, Frankreich, 06.07. – 08.07.2022
  A. Klemenz
  
• Multiwall Carbon Nanotubes for Solid Lubrication of Highly Loaded Contacts. ACS Applied Nano Materials, 6(3), 1755-1769.
  MacLucas, Timothy; Klemenz, Andreas; Grünewald, Patrick; Presser, Volker; Mayrhofer, Leonhard; Moras, Gianpietro; Suarez, Sebastian; Dienwiebel, Martin; Mücklich, Frank & Moseler, Michael