Tribological Behavior of High-Velocity Oxygen Fuel-Sprayed Ni-Based Self-Lubricating Composite Coatings

In this paper, Ni-based composite coatings containing varying amounts of Ag (5, 10, and 15 wt.%) and fixed amount of MoS₂ (10 wt.%) were prepared using the high-velocity oxygen fuel (HVOF) technique. The tribological behavior of developed coatings was evaluated at four different loads (5, 10, 15, and 20 N) and fixed sliding speed of 0.3 m/s using ball-on-disk test rig at room temperature (RT) against alumina ball (counterface). Results indicated that average coefficient of friction (COF) and wear rate decreased as the load increased till 15 N, beyond which an increasing trend was observed. Among the coatings, the lowest COF (0.41) and wear rate (4.0 × 10⁻⁶ mm³/Nm) at 15 N were displayed by coating reinforced with 10 wt.% Ag. The observed wear behavior was explained on the basis of the synergistic influence of optimal binary solid lubricants (Ag and MoS₂) in order to form novel lubricious phases like Ag₂MoO₄, MoO₃, AgO, and NiMoO₄ between the contacting interfaces.