The Evaluation of a Modified Chrome Oxide Based High Temperature Solid Lubricant Coating for Foil Gas Bearings
This paper describes the friction and wear performance of PS304, a modified chrome oxide based coating, for foil gas bearings. PS304 contains 60 wt. % NiCr binder, 20 wt. % Cr203 hardener, and 10 wt. % each Ag and BaF2ICaF2 lubricants. For evaluation, the coating is plasma spray deposited onto test journals which are slid against a superalloy partial arc foil bearing. The test load was 10 KPa (1.5 psi) and the bearings were run under start/stop cyclic conditions. The data show good wear performance of the bearing especially at temperatures above 25 °C. Bearing friction was moderate (μ ≤≈0.4) over the entire temperature range. Based upon the results obtained, the PS304 coating has promise for high temperature, oil-free turbomachinery applications. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999
Hydrodynamic air lubricated compliant surface bearing for an automotive gas turbine engine. 2: Materials and coatings
Part III of a technology program performed for the NASA Lewis Research Center for the development of hydrodynamic air lubricated journal bearings for an automotive gas turbine engine is described. Part I of the program had focused on advancing compliant surface journal bearing technology by providing design information through an experimental and analytical effort. Part II of the program has investigated and tested materials and coatings for compliant surface bearings and journals good to either 540/sup 0/C or 650/sup 0/C environment. The most promising combination (Kaman DES) was tested at 35 kPa (5 psi) loading in partial-arc bearing form. This coating combination successfully completed 2000 start-stop cycles. Some of the coating was worn under the loaded area. There was some coating left on the grain boundaries, and the remaining area was oxidized during exposure to higher temperature. This combination was further tested at 14 kPa (2 psi) loading as a complete bearing. It completed 1000 start-stop cycles. A considerable amount of loose wear debris collected at the interface and, apparently, could not easily escape. As a result, it damaged the surfaces.
The effect of counterface on the tribological performance of a high temperature solid lubricant composite from 25 to 650°C
The effect of counterface selection on the tribological performance of a Ag/BaF{sub 2}-CaF{sub 2} containing composite coating is studied. Ceramic (Al{sub 2}O{sub 3}) and metal (Inconel X-750) pins are slid against PS300 (a metal bonded chrome oxide coating with Ag and BaF{sub 2}/CaF{sub 2} lubricant additives) in a pin-on-disk tribometer at 25, 500 and 650 C. Compared to the ceramic counterface, the metal counterface generally exhibited lower friction and wear at 25 C but higher friction and wear at 650 C. Friction coefficients, for example, for the Al{sub 2}O{sub 3}/PS300 combination at 25 C were 0.64 compared to 0.23 for the Inconel/PS300 sliding couple. At 650 C the ranking was reversed. The Al{sub 2}O{sub 3}/PS300 combination gave a friction coefficient of 0.19 while the friction for the metal counterface increased slightly to about 0.3. Based upon these tribological results and other information found in the literature, it appears that the performance of each counterface/PS300 combination is affected by the ability of the solid lubricant additives to form an adequate transfer film. The effects of surface wettability and tribological compatibility are discussed in relation to the observed tribological results.