Preparation And Properties Of Electroless Ni-P-β-Sic Composition Coating On Low Carbon Steel

Electroless coating is a new kind of surface treatment technology. People pay more and more attention to it because of its simple process、low energy consumption、low cost and so on. Beta-SiC has many advantages such as good finish and polishing properties、excellent creep resistance、fracture resistance、low coefficient of expansion. By adding beta-SiC into the solution, electroless composition coating with excellent comprehensive properties can be obtained which don’t only have the feature of the electroless coating but also the beta-SiC particle’s feature.In this paper, the process of electroless Ni-P plating was optimized by orthogonal test first. The effect of nickel sulfate、hypophosphite、lactic acid in solution and PH of solution were studied. The preferable solution composition and plating condition for electroless Ni-P plating are as follows:nickel sulfate25g/L、hypophosphite27g/L、lactic acid27ml/L、sodium bicarbonate20-23g/L、sodium fluoride lg/L、lead acetate lmg/L、PH5.2、temperature84±2℃. The most influential factor on the deposition rate of composite coating is PH and the most influential factor on microhardness is the concentration of nickel sulfate in solution.The microhardness of electroless plating was tested by micro hardness tester. The surface and cross-sectional micrographs of the plating were observed by optical microscope and SEM. And the chemical composition and phase transformation of electroless plating were analyzed with EDS and XRD. The result shown that a medium phosphorous coating with8.77%P on average was obtained. The surface of coating is bright and smooth and appear to be cell structure. The coating with an uniform thickness was well-bonded with the substrate.The as-plated coating is of amorphous structure. The deposition rate of is13.21μm per hour and the microhardness is528.3OHV0.05.The effect of beta-SiC concentration in solution to the properties of Ni-P-beta-SiC composite coating is studied. It is shown that particles content in the composite coating and microhardness reach the maximum when beta-SiC concentration in solution is5g/L. At this time，t h e d e p o sit io n ra te o f c o mp os it e c o a tin g is14.42μ m pe r ho u r a nd th e mic r oh a rd ne s s is578.41HV0.05. The we a r re s ist an ce o f c o mp o sit e c oa ting is b e tte r th a n ele c t ro le ss N i-P p la tin g.Th e as-p la t e d c om p o sit e c o a ting is o f a mo rp ho u s str u ctur e to o. b eta-S iC pa rtic les is w elld is trib u te d in th e c o mp o sit e c oa tin g. Th e c om p o sit e wit h a n u ni fo r m thi c kn e s s h a s a s moo t hsur face. The in ter face o f co mp o s it e coa tin g a n d s u bs tr a te is we ll-b on d e d. Th er e is n o p o re sand c rack s in th e sur fa c e o f c o mpo sit e c oa tin g. Aft er h e ta tre a t me n t， th e c o mp o sit e c oa tin gcha n ge s from amo rp h o us to cry s talli ne s ta te. In thi s p roc ess， th e mic r o ha rd ne s s a nd wea rre s ist a n ce is impr o v ed b e c a us e o f the fo rma tio n o f nic ke l p ho s p hi d e.