Gallium-Rich Films as Boundary Lubricants in Air and in Vacuum to 10−9mm Hg

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Abstract
The friction and wear characteristics of various materials coated with thin gallium-rich films were determined at temperatures to 1000 F in air and at room temperature in vacuum between 10−7 and 10−9 mm Hg. Evaporation rates of gallium were measured at 10−7 mm Hg and ambient temperatures to 1000 F. The friction and wear experiments were conducted with 3/16 inch radius rider hemisphere sliding on a 21/2-inch diameter disk at surface speeds of 28 to 4490 feet per minute and a load of 1000 gms. Utilizing a gallium-diffused film, boundary lubrication of 440-C stainless steel was obtained. The friction and wear obtained with the gallium-diffused films were lower in vacuum than in air. The use of relatively inert materials such as boron carbide and aluminum oxide as rider specimens reduced the corrosion problem normally encountered with gallium in all-metal systems. Gallium was not equally effective as a lubricant for all materials; it reduced friction and wear for several alloys (52100 and 440-C), other materials including a nickel base alloy were not effectively lubricated.

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