Tribological Performance of Nickel-Alloy Matrix Self-Lubricating Coatings

Nickel-alloys matrix self-lubricating composite powder (NiCrMoAl-Ag-BaF₂/CaF₂) was prepared by high-energy ball milling combined with spray dry granulation method, and a nickel-alloys matrix self-lubricating coating was prepared by plasma spraying technology. A pin-on-disk HT-1000 friction-meter was used to test the friction and wear properties at different rubbing speeds (0.2~1.0 m/s) and under different testing temperatures (25~800 ℃). The microstructures, phase compositions and wear mechanism of the coating were analyzed by scanning electron microscopy, energy dispersive spectroscopy and Raman. The results indicate that at a wide temperature range from 25 ℃ to 800 ℃, the friction coefficient of the coating firstly increased and then decreased with the increasing temperature. The friction coefficient reached the maximum value of 0.37 at 400 ℃; and then reduced to a minimum value of 0.17 at 800 ℃. The friction coefficient of the coating decreased firstly and then increased with increasing sliding speed. The lowest friction coefficient of the coating was about 0.17~0.29 at 0.8 m/s, and then increased to 0.20~0.27 at 1.0 m/s. The favorable lubricating properties of the coating could be attributed to the low shear of the soft metal Ag, and especially the synergistic lubrication effects of BaF₂/CaF₂, Ag and high-temperature products such as molybdate and chromate rendered the coating with excellent lubricity properties under temperature range of 600~800 ℃.