Preparation And Properties Of Ni-P Nano-composite Coatings By Electroless Plating

With the development of nano science, the composite deposition receives a new opportunity. Nano particles have particular physical and chemical characterizations because of small dimension effect, surface effect, and macroscopical quanta tunnel effect etc. The Ni-P matrix nano composites that are obtained by incorporating nano particles into Ni-P bath show superior mechanism performance, electrical catalysis performance etc and are increasingly causing more and more attention of researchers.In this paper, nano-α-Al₂O₃ and nano-SiC powders were incorporated into Ni-P alloy matrix by electroless deposition to obtain nano Ni-P/Al₂O₃ and Ni-P/SiC composite coatings. The influence of concentration of particles in bath, temperature, pH and other technique parameters on nano particles content in coatings and rate of deposition was investigated. Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) were used to figure the surface and microstructure of coatings. The wear resistance, micro-hardness and corrosion resistance of coatings before and after heat treatment were also studied. The results showed that with the increase of nano particle content in the electroless plating solution, the nano particle content in deposits increased first and then decreased, the nano-Al₂O₃ particle content in deposits can reached the maxium value in 10.1%(wt), and the nano-SiC particle content in deposits can reached the maxium value in 13.1%(wt). With the increase of nano particle content in deposits, the wear resistance, micro-hardness and corrosion resistance were developed and better than Ni-P alloy. Compared with Ni-P coatings, the hardness of Ni-P/nano-Al₂O₃ composite coating increased by 28%, while the wear loss decreased by over 20% when the nano-Al₂O₃ particle content in deposits reached 10wt.%, and the hardness of Ni-P/nano-SiC composite coating increased by 59%, while the wear loss decreased by over 23% when the nano-SiC particle content in deposits reached 13wt.%. Compared with Ni-P coatings, the corrosion resistance of Ni-P/nano-SiC composite was enhanced obviously. After 400℃heat treatment, the amorphous composite coating transforms to crystalline structure , the wear resistance and micro-hardness were increased, but corrosion resistance was decreased.