Study Of The Properties Of Ni-P Gradient Coating And Ni-P-SiC Gradient Composite Coating

Electroless Ni-P alloy plating with high hardness, corrosion and wear resistance has been used in decorating, protection of nonmetallic material and conductors such as steels, copper, plastics and ceramics.High innerstress, low bingding force, wear resistance, and single function showed in elctroless Ni-P coatings reported before can't meet the special needs of corrosion and wear parts yet.FGM developed with the requiremnt of high function can enhance the bingding strength between coating and substrate effectively and simultaneously improve corrosion and wear resistance because of the compatibility between component and structure. SiC is a kind of excellent grinding materials and special functional ceramics.Ceramics and CFCC with low density, high strength, better wear resistance, chemical stability, and steady friction coefficient showed a great application potentiality in friction materials.In this paper, low-P,middle-P, high-P, and H-M-L, L-M-H Ni-P gradient coatings were prepared on 45# steel surface by electroless plating with the design thinking of FGM. Influences of component and structure gradient changing on corrosion and wear resistances were investigated by microhardness, XRD,SEM, corrosion and wear experiments.The results showed that component and structure gradient changing in coating can relieve functional variance caused by interface abrupt between coating and substrate. The purposes of reducing friction coefficient, improving corrosion and wear resistance were realized. Comprehensive performance of H-M-L gradient coating was the best. H-M-L gradient coating showed excellent anti-corrosion function under acidic and alkaline conditions, with bingding force of 90N,lower friction coefficient(0.5966) and wear volume(1.888×10-1mm3).Ni-P-SiC composite plating and gradient composite plating were prepared by adding and co-depositing of SiC granules based on Ni-P alloy coating. The results showed that the hardness of Ni-P-SiC composite coating reached a maximum when the addition of SiC granules was 6g/L; Ni-P-SiC gradient composite coating showed high microhardness (962HV),excellent bingding strength (78N) and wear resistance (4.186×10-2mm3),but inferior corrosion resistance.