Abstract
Abrasive wear in moving mechanical systems remains a persistent concern, posing a significant risk of surface damage and component failure. This research delves into fundamental wear mechanisms at the single asperity level, providing critical atomic-scale insights essential for designing wear-resistant surfaces and coatings. The study, comprising five papers, focuses on three key aspects: (a) investigating single-asperity abrasive wear mechanisms through molecular dynamics (MD) simulations, (b) analyzing wear responses of monolayer and multilayer coatings during scratching, and (c) assessing surface roughness induced by material removal.
To begin, scratching simulations are conducted to explore abrasive wear mechanisms at the nanoscale and evaluate the applicability of empirical wear laws. The effects of adhesive strength and abrasion depth on material transfer during single-asperity abrasive processes are quantified. The results reveal a critical adhesive strength as a function of scratching depth, causing the transition from atom-by-atom to wear fragment removal. Additionally, Archard's law, originally developed for adhesive wear, and Reye's law are validated. At the nanoscale, the wear coefficient increases with adhesion strength and scratching depth before eventually reaching a constant value. This saturation corresponds to the transition from atomic attrition wear to plasticity-induced wear. This understanding reconciles discrepancies in experimental observations regarding the validity of Archard's wear relation at the nanoscale and confirms the possibility of obtaining a depth- and adhesion-independent wear coefficient when plastic deformation governs abrasive wear.
Moving forward, the study analyzes the abrasive wear performance of monolayer and multilayer coatings using the scratching model. In single-crystal Al coatings, the interplay between crystal orientation and scratching direction triggers atomic displacement along various slip systems, resulting in scratching anisotropy. For DLC coatings, plastic deformation is mediated by atom rearrangement, leading to a transition from sp$^{3}$ to sp$^{2}$ bonding configurations. Furthermore, the study investigates the influence of layering thickness on the abrasive wear response of DLC/WC multi-nanolayer coatings through systematic experiments and molecular dynamic simulations. It identifies a critical bilayer thickness associated with maximum scratch hardness and wear resistance. Simulations demonstrate that when the thickness of WC layers falls below 2 nm, the deformation mechanism shifts from interface-induced dislocation confinement to interface-induced amorphization, thereby reducing the mechanical properties of the coating.
Finally, the research quantifies the evolution of surface roughness during material removal processes such as scratching and cutting. Crystal anisotropy in single crystal Al leads to orientation-dependent scratch morphologies and roughness. Additionally, the study systematically investigates the impact of depth of cut on cutting mode and roughness evolution. The results validate the transitional depth of the Cut model as an accurate predictor of material removal mechanisms, influenced by ductile-brittle properties and cutting depth.
To begin, scratching simulations are conducted to explore abrasive wear mechanisms at the nanoscale and evaluate the applicability of empirical wear laws. The effects of adhesive strength and abrasion depth on material transfer during single-asperity abrasive processes are quantified. The results reveal a critical adhesive strength as a function of scratching depth, causing the transition from atom-by-atom to wear fragment removal. Additionally, Archard's law, originally developed for adhesive wear, and Reye's law are validated. At the nanoscale, the wear coefficient increases with adhesion strength and scratching depth before eventually reaching a constant value. This saturation corresponds to the transition from atomic attrition wear to plasticity-induced wear. This understanding reconciles discrepancies in experimental observations regarding the validity of Archard's wear relation at the nanoscale and confirms the possibility of obtaining a depth- and adhesion-independent wear coefficient when plastic deformation governs abrasive wear.
Moving forward, the study analyzes the abrasive wear performance of monolayer and multilayer coatings using the scratching model. In single-crystal Al coatings, the interplay between crystal orientation and scratching direction triggers atomic displacement along various slip systems, resulting in scratching anisotropy. For DLC coatings, plastic deformation is mediated by atom rearrangement, leading to a transition from sp$^{3}$ to sp$^{2}$ bonding configurations. Furthermore, the study investigates the influence of layering thickness on the abrasive wear response of DLC/WC multi-nanolayer coatings through systematic experiments and molecular dynamic simulations. It identifies a critical bilayer thickness associated with maximum scratch hardness and wear resistance. Simulations demonstrate that when the thickness of WC layers falls below 2 nm, the deformation mechanism shifts from interface-induced dislocation confinement to interface-induced amorphization, thereby reducing the mechanical properties of the coating.
Finally, the research quantifies the evolution of surface roughness during material removal processes such as scratching and cutting. Crystal anisotropy in single crystal Al leads to orientation-dependent scratch morphologies and roughness. Additionally, the study systematically investigates the impact of depth of cut on cutting mode and roughness evolution. The results validate the transitional depth of the Cut model as an accurate predictor of material removal mechanisms, influenced by ductile-brittle properties and cutting depth.
| Original language | English |
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| Publisher | Aarhus University |
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| Number of pages | 157 |
| Publication status | Published - Jan 2024 |