Tribological Oxidation of MoS₂-Based Solid-Lubricant Coatings: Understanding the Role of Water in Coating Degradation and Lifetime

MoS₂-based coatings are widely used as solid lubricants in applications requiring low friction, wear resistance and reliable operation under dry, vacuum or harsh conditions. However, their performance and lifetime decrease strongly in humid and oxidizing environments, where oxygen and water can promote tribochemical degradation and the formation of oxidized molybdenum species. Although these effects are well documented experimentally, the elementary reactions responsible for coating degradation at buried sliding interfaces remain poorly understood.

This project aims to clarify the microscopic role of water in MoS₂ coating oxidation: whether it directly participates in degradation, modifies O₂-driven pathways, or stabilizes OH, S–O and Mo–O intermediates. The researchers will combine large-scale AI-driven molecular dynamics with first-principles reaction-path validation. A MACE machine-learning interatomic potential for the Mo–S–O–H chemical space will be used to simulate MoS₂ coating interfaces of approximately 18,000–20,000 atoms under tribological conditions. Exploratory simulations will compare dry O₂, H₂O-only and mixed H₂O/O₂ environments, while selected elementary reactions will be reconstructed through MLIP-NEB and validated with DFT climbing-image NEB calculations. Systematic production simulations will then quantify how load, temperature, sliding velocity and molecular concentration affect coating degradation.

The project will deliver chemically validated degradation descriptors, including S–O and Mo–O bond formation, OH lifetime, molecular dissociation events, sulfur vacancy evolution and MoOₓ-like growth. These results will provide a mechanistic framework for understanding water-assisted failure of MoS₂-based solid-lubricant coatings and support the design of more durable coatings for humid, oxidizing and mechanically demanding conditions.