Effects of boron nitride nanoplatelets on the tribological properties of alumina chemically bonded phosphate ceramic coatings

The tribological properties of the alumina chemically bonded phosphate ceramic coatings were improved by adding boron nitride nanoplatelets (BNNP). In this paper, the powder with BNNP was uniformly dispersed by the homogenizer, and then the coatings with different contents of BNNP were fabricated on 304 stainless steel. The phase compositions, morphology and tribological properties of coatings with different content of BNNP were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and ball-and-disc tribometer. Results show that the main phases of the coatings are Al₂O₃, AlPO₄, Zn₃(PO₄)₂ and BNNP, which indicates that the added BNNP does not participate in the coating curing reaction. The added BNNP, as the nucleating agent of the bonding phase, could fill or cover the pores. With the increasing content of BNNP, the surface quality of the coating is improved. The surface porosity of the coating with 1wt% BNNP is the lowest (4.33%), 55.27% lower than the coating without BNNP. As the content of BNNP increases, the friction coefficient and wear rate of the coatings decrease. When the content of BNNP is 1wt%, the friction coefficient reduces from 0.372 to 0.242, and the wear rate decreases from 1.512×10^–3 mm³/(N×m) to 0.494×10^–3 mm³/(N×m). The main wear mechanisms of coatings are abrasive wear and adhesive wear. These results conclude that the addition of BNNP can improve the friction and wear properties of the alumina chemically bonded phosphate ceramic coatings.