The Performance of PS400 Subjected to Sliding Contact at Temperatures from 260 to 927°C

Adequate high-temperature lubrication between loaded surfaces in sliding contact can be one of the most challenging tribological problems confronting today's designers. In an attempt to provide a possible solution a test program was initiated to evaluate PS400, a recently patented, high-temperature solid lubricant coating. Made from nickel–molybdenum–aluminum, chrome oxide, silver, and barium fluoride–calcium fluoride, PS400 is a variant of the earlier coating, PS304, but is formulated for higher density, smoother surface texture, and greater dimensional stability. It was initially developed to minimize the start–stop wear in foil air bearings but is expected to perform well in other high-temperature applications where sliding friction and wear are a concern, such as variable inlet guide vanes and process control valve stems. To better define its operational capabilities, a series of tests was conducted to study the behavior of PS400 under reciprocating sliding contact at temperatures from 260 to 927°C. The tests were performed on stationary, uncoated cobalt-based superalloy bushings loaded against reciprocating PS400-coated shaft specimens in a flat-on-cylinder configuration at Hertz contact pressures from 14.1 to 20.1 MPa. For tests conducted below 927°C, friction coefficients ranged from 0.37 to 0.84 with wear factors on the order of 10−5 and 10−6 at the high temperatures but substantially increased at the lowest temperature. Data collected at 927°C were limited because the coating was found to be dimensionally unstable at this temperature.