AU CR SPUTTER COATING FOR THE PROTECTION OF ALUMINA DURING SLIDING ATHIGH-TEMPERATURES/

A sputter-deposited bilayer coating of gold and chromium was investiga ted as a potential solid lubricant to protect alumina substrates in ap plications involving sliding at high temperatures. The lubricant was t ested in a Pin-on-disk tribometer with coated alumina disks sliding ag ainst uncoated alumina pins. Three test parameters-tenperature, load a nd sliding velocity-were varied over a wide range in order to determin e the performance envelope of the Au/Cr solid lubricant film. The trib o-tests were run in air al temperatures of 25 degrees to 1000 degrees C, under loads of 4.9 to 490 N and al sliding velocities from 1 to 15 ms(-1). Posttest analyses included surface profilometry, wear factor d etermination and SEM/EDS examination of worn surfaces. Compared to unl ubricated Al2O3 sliding, the use of the Au/Cr film reduced friction by 30 to 50 percent and wear by one to true orders of magnitude. Increas es in test temperature resulted in lower friction and the Au/Cr film c ontinued to provide low friction, about 0.3, even at 1000 degrees C. P in wear factors and friction were largely unaffected by increasing loa ds up to 29.4 N. Sliding velocity had essentially no effect on frictio n, however, increased velocity reduced coating life (total sliding dis tance). Based upon these research results, the Au/Cr film is a promisi ng lubricant for moderately loaded, low speed applications operating a t temperatures as high as 1000 degrees C.