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 ce sium-based compounds with solid lubricating properties were investigated on silicon nitride (Si3N4) Some were also investigated on bearing tool steels and several state-of-the-art high temperature solid lubricants were invest igated for comparison. Experiments were conducted in air at temperatures ri p to 650 degrees C, contact stresses lip to 4.34 GPa, and a pure rolling su rface speed of 1.8 m/s. Although all of the cesium-based compounds exhibite d self-lubricating properties, the best overall performance was achieved wi th a cesium silicate reaction film formed in-situ (Cs2O . xSiO(2)) and a hy drated cesium silicate bonded coating (Cs2O . 3SiO(2). nH(2)O). Bonded coat ings of cesium oxythiotungstate + tungsten disulfide mixture (Cs2WOS3 + WS2 ) 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.