Tribological behavior of B4C/hBN ceramic composites coupled with grey iron under the lubrication of emulsion

With the aim of improving tribological performance of boron carbide (B4C), hexagonal boron nitride (hBN), as solid lubricants, was introduced to form a B4C based ceramic composites. In this paper, pure B4C, together with B4C/hBN ceramic composites, fabricated via hot press sintering, were coupled with grey cast iron (GI) on a pin on disk tribometer under the lubrication conditions of fully immersed emulsion and drop-feeding emulsion. We have studied the influence of hBN mass fraction on tribological behavior of ceramic-iron couple for both lubricating conditions. The morphology of friction surfaces has been observed by scanning electron microscope (SEM). The composition of tribo-chemical products has been analyzed by energy dispersive spectrometer (EDS) and Raman spectroscopy. The results show that, in a fully immersed emulsion, when sliding distance is increased, the friction coefficient of B4C coupled with GI reduces from 0.1 to 0.04, while the friction coefficient of B4C/hBN ceramic composites coupled with GI is maintained at 0.1. On the contrary, under drop-feeding emulsion, the friction coefficient of B4C/hBN ceramic composites coupled with GI reduces remarkably, whereas the friction coefficient of BNOO-GI couple remains in the range of 0.1 to 0.15. The friction coefficient of B4C/(30 wt%) hBN ceramic composites coupled with GI is 0.005 under drop-feeding emulsion, which presents superior tribological behavior.