Metastable hybridized structure transformation in amorphous carbon films during friction—A study combining experiments and MD simulation

Abstract

Amorphous carbon films have attracted substantial interest due to their exceptional mechanical and tribological properties. Previous studies revealed that the amorphous carbon films exhibited lower coefficient of friction (COF) because of the transformation in bond structure from sp3-C to sp2-C during friction processes. However, the mechanism for such a transformation during friction is not well understood. This study is conducted to get an insight into the metastable transformation in amorphous carbon film during friction by means of experiments and molecular dynamics (MD) simulation. Relevant wear tests showed that wear of the film changed from an abrasive wear mode to a mixture of abrasion and adhesive wear, resulting in a decrease in growth rate of the wear rate after the running-in stage. It is worth noting that the sp3-C atoms were increased during the running-in stage when the films contained lower sp3/sp2 ratios. However, the formed sp3-C atoms could only be short-lived and gradually transformed to sp2-C atoms with the graphitization generated on the wearing surface of the films. The radial distribution function and translational order parameter indicated that the films’ high sp3/sp2 ratio led to an increased sp2-C proportion on the wear scar after friction, which caused an increased structural ordering.

Molybdenum disulfide/carbon multilayer films achieve ultra‐low wear in vacuum

“…Previous studies have shown that under high contact stress, MoS 2 can decompose into molybdenum and sulfur atoms from a molecular dynamics perspective. Additionally, the catalytic effect of Mo atoms and stress‐induced chemical reactions can promote the transformation of amorphous carbon to an ordered graphene band structure 39,40 . In this experiment, the increasing load results in high contact stress, which accelerates the graphitization transformation to an ordered graphene band structure.…”

“…37 The G peak is located around 1610 cm À1 . 38 To obtain more information, we calculated the 39,40 In this experiment, the increasing load results in high contact stress, which accelerates the graphitization transformation to an ordered graphene band structure. This phenomenon is consistent with the Raman characterization of the transfer film's carbon characteristic peaks.…”

Adhesion and friction behaviors of a γ-Fe/diamond heterogeneous contact interface: a density functional theory study

“…With the development of computer technology and highthroughput calculations, density functional theory (DFT) simulations have been widely applied to study the adhesion and friction mechanism of the contact or sliding interface. [15][16][17] Feldbauer et al 18 investigated the adhesion and material transfer between Al and TiN contacting surfaces based on DFT theory. They observed the transfer of the material from an Al slab towards a TiN slab for the interfacial configurations, which exhibited a larger adhesion energy than the energy cost to remove layers from the Al slab.…”

Atomistic Insights into Interfacial Optimization Mechanism for Achieving Ultralow-Friction Amorphous Carbon Films under Solid–Liquid Composite Conditions

“…10−13 The relationship between the microstructure and tribological properties largely determines the application and design of a-C films. 14 The complex three-dimensional network structure of a-C films, which consists of sp 3 and sp 2 hybridization, leads to their metastable structural transformation during the sliding process, depending on factors such as the sp 2 /sp 3 ratio, 15,16 interaction with lubricating oil, 17,18 and residual stress. 19,20 These structural transformations are sensitive to the contact pressure.…”

“…The relationship between the microstructure and tribological properties largely determines the application and design of a-C films . The complex three-dimensional network structure of a-C films, which consists of sp 3 and sp 2 hybridization, leads to their metastable structural transformation during the sliding process, depending on factors such as the sp 2 /sp 3 ratio, , interaction with lubricating oil, , and residual stress. , These structural transformations are sensitive to the contact pressure. ,− Hetzner et al investigated the friction behavior of hydrogenated a-C films subjected to high contact pressures of 1–3 GPa and different counter materials. It was found that when the a-C film and a steel sheet were used as a friction pair, the film quickly failed because of adhesion and antibody steel transfer.…”