Abstract:
Friction reduction of AlTiN-based hard coatings is gaining much attention among researchers worldwide to
broaden their tribological applications. Metal/non-metal inclusions, as well as the design of a novel coating
architecture, are primarily focused on reducing friction while retaining wear resistance. This study investigates
the tribological characteristics of magnetron sputtered AlTiN coatings by incorporating amorphous carbon (a–C)
at different concentrations (5–25 at.%), as well as the compositionally graded AlTiN/a-C coatings (CGC). The
XPS and Raman spectroscopy results confirm the presence of a-C features, while XRD reveals the formation of
ceramic carbide phases in AlTiN coatings with higher carbon content and CGC coatings. The CGC AlTiN/a-C have
shown a maximum hardness of 34.3 GPa and an elastic modulus of 321 GPa due to their refined grain structure.
The CGC had the lowest friction (0.18 at 300 K and 0.37 at 673 K), as well as improved wear resistance (2.74 ×
10- 7 mm3/Nm (300 K) and 4.93 × 10- 7 mm3/Nm (673 K)). The tribolayers are found to be mainly composed of
sp2/sp3 bonded a-C features (including C=C/C─C, C─N, and C─O), which reduces the friction force significantly.
The CGC AlTiN/a-C coating has exhibited improved wear resistance behavior due to their finely grained
structure and improved mechanical properties.