Tribological Behavior of B₄C/hBN Ceramic Composites Sliding Against Gray Cast Irons Without Lubrication

Based on hot-pressing sintering, boron carbide/boron nitride (B₄C/hBN) ceramic composites were prepared as pin samples to slide against gray cast iron disks (GCI) in the air on a pin-on-disk tribometer. In the study, we investigated the influence of hBN mass fraction and test load on the tribological performance. The morphology features of friction surfaces were observed with scanning electron microscope. The compositions of friction surfaces and wear debris were analyzed by X-ray photoelectron spectroscopy and X-ray diffraction. Our results show that in the case of 5 N load, the friction coefficients of B₄C/hBN (hBN content of 0, 10 % weight ratio, named as BN00, BN10) ceramic composites coupled with GCI were reached up to 0.5. However, as hBN contents reach to 20 and 30 % (BN20, BN30), the friction coefficient was reduced to 0.2. The tribological mechanism of GCI-BN00 couple is mainly based on adhesive wear with severe plastic deformation of GCI disk. On the contrary, a continuous surface film is promoted on the worn-surface BN30. Thus, the main tribological morphology of the coupled gray cast iron shows slight micro-cuttings. With an increase in the test load, the wear mechanism of GCI-BN00 and GCI-BN10 is still adhesive wear with similar friction coefficients compared to 5 N load. However, as test load increases, the film formed on BN30 worn surface is damaged, resulting in the rise of the friction coefficient. The friction coefficient increases to 0.6 at the load of 10 N, indicating that the addition of hBN has no improvement on lubrication in this load regime.