Effect of Loads on Tribological Behaviors of Ni₃Al Matrix Self-Lubricating Composite Coating

The micron spherical Ni₃Al based composite powder has been fabricated by high-energy ball milling combined with spray granulation. Then it was deposited on an 1Cr18Ni9Ti stainless steel by plasma spraying to form a coating, then the influences of testing temperatures (25 ℃ to 800 ℃) and loads (5 N, 10 N and 20 N) on the tribological behaviors of this coating were evaluated. SEM, EDS and Raman techniques were adopted to study the lubrication and wear mechanisms of the coating tested at different loads, by analyzing the microstructure and phase constitutes of the wear debris, wear scar of the coating and the counterface pins. The results indicated that within temperature range 25~200 ℃, the increase of load from 5 N to 10 N accelerated the precipitation of the lubricant resulting from the synergism between the frictional heat and applied load, providing a friction and wear reduction. However, with further increasing the load to 20 N in this temperature range, the coating was deformed plastically, leading to blocking effect and thus increasing the friction and wear. At temperature from 400 to 600 ℃, the oxidation process was accelerated by the friction heat caused by the increased loads, thereby decreased the friction and wear. At 800 ℃, the worn surfaces tested at all the loads were covered by a continuous and smooth oxidized glaze layer, which was rich in NiCr₂O₄, Ag₂MoO₄ and NiO. The distinction was that when the load of 20 N was applied, the local high stress destroyed the integrity of the lubricating film, thereby decreased the tribological properties.