Effects of hBN content and particle size on microstructure, mechanical and tribological properties of NiCr-Cr3C2-hBN coatings

Abstract

With a stable two-dimensional layered structure at high temperatures, hexagonal boron nitride (hBN) is considered a good solid lubricant in a wide temperature range. Adding hBN lubricating phase into NiCr-Cr3C2 coatings is expected to enhance the tribological properties of coatings and improve the compatibility between friction pairs. In this study, NiCr-Cr3C2-hBN composite powders with different hBN contents (3 wt%, 6 wt%) and particle sizes (1–2 μm, 15–45 μm) were prepared using a ball milling and spray granulation method. Subsequently, low-porous (1 %–4 %) and high-hardness (800-1200 HV) composite coatings were created using supersonic plasma spraying technology. The structure, phase, and chemical composition of the powders and coatings were analyzed using SEM, EMPA, and XRD characterization techniques. The mechanical and tribological properties of the coatings were also tested. Research findings reveal that supersonic plasma spraying successfully creates wide-temperature-range wear-resistant self-lubricating coatings with the hBN phase, effectively protecting GH4169 substrates. The properties of the coatings are influenced by the concentration and particle size of hBN. When the hBN content is excessively high, the tangential cohesive strength weakens, which negatively impacts wear resistance and rate. Larger hBN particles result in a mixed distribution, while smaller particles promote a uniform dispersion. The 3 wt% hBN (1–2 μm) coating exhibits optimal performance; however, the 3 wt% hBN (15–45 μm) coating may show improvement if its cohesive strength is enhanced by increasing the wettability of hBN.