Microstructure And Tribological Properties Of Laser Clad Ni20Cr Composite Coatings

With the rapid development of aerospace technology, the traditional oils and greases cannot meet their requirements for its sealing system. It has been taken attention to obtain self-lubricating wear resistance on the surface coating currently in aerospace research.Therefore, it is significant to prepare the self-lubricating wear-resistant coating.Because of excellent wear resistance, good corrosion resistance and high temperature oxidation resistance, Ni20 Cr was chosen as the primary material. By laser cladding,Ni20 Cr, Ni20Cr+MoS2 self-lubricating coatings and Ni20Cr+Cr3C2/Mo wear resistant composite coatings were prepared on low carbon steel substrate. The composition and microstructure of the coatings were examined by optical metalloscope(OM), X-ray diffraction(XRD), scanning electron microscope(SEM), energy dispersive spectroscopy(EDS), electron back-scattered diffraction(EBSD). The wear resistances of the coatings were evaluated by the tribometer and the wear mechanism was discussed in this work.The experimental results show that, only γ phase exists in the Ni20 Cr coating. The microstructure of the Ni20 Cr self-lubricating coatings with MoS2 consist of γ and CrxSy phases. Due to the decomposition of MoS2 phase, sulfur reacted strongly with the melt Cr forming CrxSy in the molten pool. Average microhardness of the Ni20 Cr self-lubricating coatings is higher than that of Ni20 Cr coating. The friction coefficient and wear rate of the Ni20 Cr self-lubricating coatings are greatly decreased due to the CrxSy sulfide, which has excellent self-lubricating property. In all self-lubricating coatings, when the addition of MoS2 in Ni20 Cr coatings 20 wt.%, the tribology property of the coating surface is the best.The phases in Ni20Cr+Cr3C2 coating are γ and Cr3C2. While that in Ni20Cr+Mo coating isγ phase. Compared with Ni20 Cr coating, the wear resistance of Ni20Cr+Cr3C2/Mo coatings is increased at same applied loads. In all wear resistant coatings. The wear resistance of Ni20Cr+30% Cr3C2 coating is the highest in the Ni20Cr+Cr3C2/Mo coatings,which indicates that Ni20Cr+30% Cr3C2 coating has the most excellent wear resistance.