Microstructure And Property Of Nano Ni-p-al₂o₃ Electroless Plating Layer Treated By Laser Technology

With the social development,there is greatly increasing in the request on the surface performance of the key parts and components in industry,especially in petroleum,chemical engineering,machine and so on.The tranditional treatment technologies can't satisfy the request,and the development of laser technology applies a new direction for resolving this problem.In this paper,high power continuous wave(CW)CO₂ laser beam was used as the heat source with different technological parameters to process the Ni-P-Al₂O₃ electroless plating,combining the beam effect and on the basis of laser processing technic.Then Optical microscope (OM)and scanning electron microscopy(SEM)were used to observe the morphologies of coating.X-ray diffraction(XRD)and X-ray energy dispersive spectroscopy(EDS)were employed to analyze the phase transformation and element compositions of the coating.The microhardness and abrasive resistance before and after laser processing were checked respectively.Finally,electrochemical corrosion test was employed to test the electrochemical corrosion resistance of the coating. Comparing with the results after conventional heat treatment,the main researching conclusions are as follows:1 The Ni-P-Al₂O₃ coating after laser processing appears undulatory,neat and smooth,and the grains were greatly fined;the elements in the processing layer was homogeneous and the gaps and micro-cracks between the coating vanished;The nano- Al₂O₃ particles mainly dispersed in the top of the cellular crystal surface,and accelerated the nucleation as the core of heterogeneous particles.2 The microstmctures of the laser processing layer were mainly divided into three zones as follows from the surface to the inner:strip cellular crystal zone,crude columnar crystal zone and fined isometric crystal;the main phases were Ni₃P,Ni₅P₂,Fe,Ni andAl₂O₃.3 The highest hardness of the laser processing layer was 3.5 times of the substrate;the everage friction coefficient and weight loss were 5/6and 3/4 of the substrate,respectively,which showed the abrasive resistance was improved a lot.The self-corrosion potential was about 1.5V,far above of the substrate o.1V,so the electrochemical corrosion resistance was also improved.4 The strengthening mechanism of the coating after laser processing was made up of dispersion strengthening of Al₂O₃,the fined microstmcture and strengthening phase Ni₃P;the optimum condition were P=2000W, v=500mm/min,power density 10⁴W/cm².5 The hardness,abrasive resistance,electrochemical corrosion resistance all appears a optimum value with the change of laser ratio-energyλ,and the value was 22 according to the result.