Composition,corrosion behaviors and formation process of trivalent chromate ultrathin passive film on electroless Ni-P coating

To control environment pollution,a new developed Cr3+ method was used to replace the traditional Cr6+ method to treat electroless Ni-P coating. And by this new method,an ultrathin chromate passive film was obtained on electroless Ni-P coating. Electrochemical test and nitric acid exposure test showed that the passivation treatment obviously improved the corrosion properties of Ni-P coating. X-ray photoelectron spectroscopy (XPS) indicated that the passive film comprised C,O,Cr,Ni,N and P,the high-resolution XPS analysis for Cr2p illustrated the Cr in passive film was in the form of Cr2O3 and Cr(OH)3. Based on the XPS result,the forming process of passive film was briefly analyzed.