Microscopic deformation mechanism and failure behavior of AlN/TiN nanolamellar structure in AlTiN coatings: MD simulation and HRTEM characterization

Despite extensive investigations in the literature, a quantitative understanding of how the AlN/TiN nanolamellar structure influences mechanical properties remains a significant challenge. Using molecular dynamics modeling combined with HRTEM characterization, this study provides a quantitative framework linking nanoscale deformation mechanisms to macroscopic mechanical properties in AlTiN coatings. The investigation reveals a three-stage continuous deformation process consisting of dislocation evolution, elastic-plastic transition, and an FCC-to-HCP phase transformation with martensitic shear characteristics. Notably, two distinct crack propagation modes are identified and quantitatively analyzed, with their transition threshold determined by the Al content in the Ti-rich (Ti(Al)N) lamellae and the AlN/TiN thickness ratio. The results indicate that stress-induced phase transformation can be utilized to achieve an optimal balance between fracture toughness and strength in the material. Overall, this study establishes a quantitative interaction mechanism among the composition, structure, and properties of AlTiN coatings, providing theoretical guidance for coating design optimization and practical insights for the development and application of coatings for advanced cutting tools.