Wear and Friction Behavior of TiB₂ Thin Film–Coated AISI 52100 Steels under the Lubricated Condition

Abstract

Magnetron-sputtered physical vapor deposited (PVD) thin-film TiB₂ coatings were investigated as a wear-resistant cam tappet coating that runs under the boundary lubrication regime in internal combustion engines (ICEs). AISI 52100 samples with a high negative bias were coated at RF powers of 150, 170, and 190 W. Coatings were characterized via nanoindentation, scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDX), X-ray diffraction (XRD), and Raman analysis. Friction and wear behaviors of these coatings were evaluated by tribometer tests at 25 and 50 N loads. Tests and tribochemical analysis showed that thin-film TiB₂ coatings are very effective to reduce the friction coefficient (COF) and wear rate with a hardness value of approximately 30 GPa and elastic modulus of 424 GPa. Therefore, thin-film TiB₂ has been evaluated as a good cam tappet coating for ICEs.

Keywords:

• Thin-film TiB₂ coatings
• magnetron-sputtered PVD
• RF power
• boundary lubrication regime
• cam tappet coating