Lubrication at 750°C in a vacuum by a transfer film from self‐lubricating composites for roll/slide contact of Si 3 N 4

Roll/slide friction tests were carried out at a temperature of 750°C in a vacuum. Disc specimens were made of Si 3 N 4 with or without a sputtered MoS 2 film. A pin specimen was rubbed against one disc to supply a lubricating transfer film. With a pin made of an MoS 2 ‐based composite, the friction coefficient was around 0.3 and almost no wear of the discs was observed after 24 h of operation at a load of 50 N, a rotating speed of 0.5 m/s, and a slip ratio of 10%. Transferred patchy MoS 2 films were observed on the friction track. With a pin made of Ni‐based composite containing BN and graphite, the friction coefficient increased from 0.2 to 0.7 over a test time of about 8 h and severe disc wear was found. In an additional test using Si 3 N 4 discs with a sputtered MoS 2 film without a pin, the friction coefficient was about 0.3, and no wear of the discs was found after 24 h of operation. The appearance of the friction track was similar to that in the test using the MoS 2 ‐based composite pin. It seems that the sputtered MoS 2 film wore, but wear particles reattached on the friction path to develop an effective lubricating film. These results demonstrate the effectiveness of transfer film lubrication for long‐term operation in a high‐temperature vacuum, and the superior ability of MoS 2 to develop an effective transfer film.