Self-replenishing solid lubricant films on boron carbide

This study introduces a simple annealing procedure that leads to the formation of a self-replenishing solid lubricant film on bulk boron carbide (B4C) and its coatings. The procedure uses short duration annealing at 800 degrees C far 15 min. Subsequently, the specimens are cooled to room temperature and tested in a pin on disc machine. During annealing, B4C reacts with oxygen in air and forms a glasslike boron oxide (B2O3) layer an the exposed surface. Eventually, this layer reacts spontaneously with moisture in the surrounding air, thus farming a thin baric acid (H3BO3) film. The friction coefficients of 440C steel and zirconia pins against this film are 0.04-0.06. Electron microscopy and Raman spectroscopy were used to elucidate the formation and self-lubricating mechanisms of this solid boundary film on sliding B4C surfaces. (C) 1999 IoM Communications Ltd.