VAPOR-PHASE LUBRICATION OF HIGH-TEMPERATURE ALLOYS

In a previous study, it was found that when a nickel-based superalloy IN750 was heated to high temperatures, a passive layer of aluminum oxi de formed on the surface, preventing vapor phase lubrication. In this study, two nickel-chrome-iron alloys and a nickel-copper alloy were st udied for high temperature lubrication to see if these alloys, which c ontained small amounts of aluminum, would exhibit similar behavior. It was found that under static conditions, all three alloys formed a lub ricious nodular coating when exposed to a vapor of aryl phosphate. Und er dynamic sliding conditions at 500-degrees-C, these alloys were succ essfully lubricated with a coefficient of friction of 0.1 and no detec table wear. In order to explain these results, a direct correlation be tween successful vapor phase lubrication and the composition of the al loys containing aluminum has been proposed. If the ratio of copper/alu minum or iron/aluminum is greater than 100 vapor phase, lubrication wi ll be successful. If the ratio is less than 10, a passive aluminum oxi de layer will prevent vapor phase lubrication. By selecting alloys wit h a high iron or copper content, vapor phase lubrication can provide e xcellent lubrication at high temperatures.