Thickness and sp³ bond modulation of (Ti/tetrahedral amorphous carbon)_n multilayer coatings

The durability of wear-resistant tetrahedral amorphous carbon (ta-C) coatings is intimately linked to their thickness and the concentration of sp³ bonds. To enhance the lifespan of the coatings, we have prepared a multilayer coating consisting of alternating layers of Ti and ta-C, denoted as (Ti/ta-C)_n, using arc ion plating. A multi-layer structure in conjunction with stage cooling is employed to enhance the thickness and promote sp³ bonding. The results indicate that the I_D/I_G value, representing the ratio of the intensity of the D peak to that of the G peak in Raman spectroscopy, decreases from 0.85 when no stage cooling is applied to 0.35 when stage cooling is employed, suggesting an enhancement in the fraction of sp³ bonds within the coating. The obtained (Ti/ta-C)_n multilayer coating without peeling off has a maximum thickness of 1.14 μm, which is almost double that of the ta-C coating single layer coating. At the same time, the coating has a low coefficient of friction, down to 0.069, and maintains excellent friction properties with a wear rate of 3.4 × 10^–6 mm³·N⁻¹·m⁻¹. The results conclusively show that the preparation technology can enhance both thickness and sp³ bonding in ta-C coatings, significantly expanding their utility across tools, molds, and precision engineering components.