Study On Preparation And Properties Of NiCr/Cr₃C₂-BaF₂·CaF₂Self-lubricating Coating

NiCr/Cr3C2-BaF2·CaF2coating was sprayed firstly on1Cr11Ni2W2MoV steel substrate by high velocity oxy-fuel spraying(HVOF). NiCr/Cr3C2coating was also prepared for the purpose of comparison. After that, the microstructures and compositions of the two coatings were observed and detected by using OM, SEM, EDS and XRD.The results showed that some more defects were founded in the interface between the NiCr/Cr3C2-BaF2·CaF2coating and substrate. It was thought that the more defects of NiCr/Cr3C2-BaF2·CaF2coating may cause the problem mentioned above.In order to improve the bind force between NiCr/Cr3C2-BaF2·CaF2coating and substrate, NiCoCrAlYTa, and NiCr/Cr3C2coating were prepared as the interlayer by HVOF method. From the results of the tensile tests, it was found when using NiCr/Cr3C2as the interlayer, the binding strength of coating increased obviously. And the thermal vibration resistance of the twolayer coating also improved greatlyFrom tribological test of the coatings, the friction coefficient of NiCr/Cr3C2-BaF2·CaF2was smaller than NiCr/Cr3C2coating from room temperature to650℃, but the wear rate of coating was higher than NiCr/Cr3C2. The wear rate of NiCr/Cr3C2coating increased rapidly when at800℃, while NiCr/Cr3C2-BaF2·CaF2coating had better frction and wear property, the wear rate of which was only half the NiCr/Cr3C2coating, and the friction coefficient was even lower.From room temperature to800℃, the main abrasion mode of NiCr/Cr3C2-BaF2·CaF2coating was micro-cutting wear. With the temperature increased, furrows phenomenon eased. While NiCr/Cr3C2coating’s main abrasion mode transformed from micro-cutting wear to adhesive with the temperature in range of room temperature to650℃. When the temperature was up to800℃, the coating had severe plastic deformation, so the main abrasion mode was contact fatigue at this time. In the bristles-coating couple Tribo-Tester experiments at650℃, NiCr/Cr3C2-BaF2·CaF2coating performed much better than NiCr/Cr3C2coating in protecting brush bristles from oxidation.By building a boundary lubrication model, it was believed the reason why NiCr/Cr3C2-BaF2·CaF2coating could get better lubrication effect was that liquid chromate film formed at the coating surface, which caused lubrication effect like fluoride phase.