Lubricous Deposit Formed In Situ Between Wearing Surfaces at High Temperatures

In vapor phase lubrication, an organic liquid (in our studies a thioether was used) is vaporized into a flowing air stream that is directed to sliding surfaces where lubrication is needed. The organic vapor reacts at the concentrated contact sliding area generating a lubricous deposit. This deposit has been characterized as a thin polymeric film that can provide effective lubrication at temperatures greater than 400 °C.

Initial tribological studies were conducted at the NASA Lewis Research Center and Cleveland State University with a high-temperature friction and wear tribometer. A cast iron rod was loaded (a 4-kg mass was used to generate a contact pressure of 1.2 MPa) against a reciprocating, cast iron plate at 500 °C. This system was then lubricated with the vapor phase of thioether. The following results were obtained:

• The deposited film resulted in friction coefficients as low as 0.01.

• Cast iron wear was not detectable.

• The system could self-recover: when the vapor flow was stopped and the system allowed to go into failure (a friction coefficient greater than 0.3), renewal of the vapor flow reduced the friction coefficient back to 0.01.

• The amount of thioether used was 0.014 wt % in air (1.2 ml/hr of lubricant in 2000 ml/min air).

Vapor phase lubrication will not only allow operation at higher temperatures, but it will produce a net savings in weight aboard aircraft because no large oil reservoirs will be needed.

Coefficient of friction versus time for various concentrations of thioether in air. Thioether on cast iron; plate temperature, 500 °C; vapor temperature, 400 °C; load, 4 kg.