Multiscale Regulation Mechanism of Mechanical Behavior in NiTi Orthodontic Archwires with Titanium Nitride Coatings of Varying Thickness

To enhance the mechanical stability and resistance to plastic damage of Nickel-Titanium (NiTi) orthodontic archwires, this study employs numerical simulations to investigate the multiscale mechanical responses of three types of archwires with different diameters (0.014, 0.016, and 0.018 inch) coated with Titanium Nitride (TiN) of varying thicknesses (550–1550 nm) under uniaxial tension and cyclic loading. The study focuses on analyzing key parameters such as von Mises stress, elastic strain energy density, equivalent deviatoric strain, and axial displacement, and it explores the regulation mechanisms of TiN thickness variation in stiffness enhancement, stress sharing, energy storage, and deformation suppression. The results indicate that the TiN coating can enhance the overall stiffness, load-bearing capacity, and cyclic stability of the archwires; reduce plastic strain accumulation; and optimize energy distribution, among which the thickness range of 800–1300 nm yields the most balanced overall performance. When the coating thickness exceeds the critical value, the strengthening effect tends to saturate, and adverse boundary effects such as a local stress concentration may occur. In addition, archwires with smaller diameters are more sensitive to coating reinforcement, exhibiting higher performance gains. This study reveals the multiscale regulation mechanisms governing the mechanical properties of NiTi archwires as a function of TiN coating thickness, providing a theoretical basis and design guidance for their structural optimization and surface engineering.