Tribological Behavior of B₄C/hBN Ceramic Composites Sliding against Ductile Iron

Boron carbide/boron nitride (B₄C/hBN) ceramic composites, prepared by hot-pressing sintering as pin samples, were coupled with ductile iron disks (QT) in air on a pin-on-disk tribometer. The influences of mass fraction (0%, 10%, 20% and 30%) of boron nitride and normal loads (5 N, 7 N, 10 N) on tribological performance of each friction couples were investigated. The morphology features of friction surfaces were observed with scanning electron microscope and the compositions of friction surfaces and worn debris were measured by Energy dispersive spectrometer, X-ray photoelectron spectroscopy and X-ray diffraction. The results indicate that, at 5 N load, the friction coefficients of B₄C/hBN ceramic composites with 0% and 10% mass ratio of hBN (BN00, BN10) and QT couples were high up to 0.5. In contrast, when hBN contents reached 20% and 30% (BN20, BN30), the friction coefficient were reduced to 0.2. The tribological mechanism of QT-BN00 couple was mainly adhesive wear and severe plastic deformations was observed on worn QT disk. A continuous surface film was discovered on BN30 worn surface and the main tribological morphology of the coupled grey cast iron was mild micro-cuttings. With the increasing normal load (7 N, 10 N), the wear mechanism of QT-BN00 and QT-BN10 was adhesive wear with comparable friction coefficients to that at 5 N load. However, as test load increased, the film formed on BN30 worn surface was damaged, resulting in the rise of the friction coefficient. The friction coefficient increased to 0.6 at the load of 10 N, indicating that the addition of hBN had no improvement on lubrication.