Solid Lubrication of Silicon Nitride with Cesium-Based Compounds: Part I - Rolling Contact Endurance, Friction and Wear

The high temperature rolling contact endurance, friction, and wear of 16 cesium-based compounds with solid lubricating properties were investigated on silicon nitride (Si 3 N 4 ). Some were also investigated on bearing tool steels and several state-of-the-art high temperature solid lubricants were investigated for comparison. Experiments were conducted in air at temperatures up to 650°C, contact stresses up to 4.34 GPa, and a pure rolling surface speed of 1.8 m/s. Although all of the cesium-based compounds exhibited self-lubricating properties, the best overall performance was achieved with a cesium silicate reaction film formed in-situ (Cs 2 O·xSiO 2 ) and a hydrated cesium silicate bonded coating (Cs 2 O·3SiO 2 ·nH 2 O). Bonded coatings of cesium oxythiotungstate + tungsten disulfide mixture (Cs 2 WOS 3 + WS 2 ) and cesium hydroxide (CsOH) also performed well. It is hypothesized that high temperature chemical reactions between the cesium-containing compounds and the silicon nitride surface form a lubricious cesium silicate film. Presented at the 55th Annual Meeting Nashville, Tennessee May 7-11, 2000