Preparation Of Corrosion Resistance Pd-Ni Film And The Corrosion Resistance Research

Stainless steels usually possess good corrosion resistance in natural environments due to the passive film on the surface. However, in some industrial environments such as sulfuric acid at high temperature, severe corrosion may happen for stainless steels because the passive state is unstable or the passive film is damaged. The Pd alloy coatings showed quite good corrosion resistance in strong reducing media and effectively protected the stainless steel substrate. However, in complicated industrial environments, because the effects of flow, aggressive ions such as chloride ions, the performance of the coatings is limited and further improvement is necessary. In this paper, multilayer Pd-Ni films with better corrosion resistance were prepared, and the protection mechanism of Pd-Ni film was studied.In this research, the effects of current density on electroplated Pd-Ni film on 316L stainless steel were studied. SEM, EDS, XRD were used to character the surface morphologies and compositions of alloy films. Corrosion behaviors of Pd -Ni films were carried by weight loss> micro-hardness?adherence strength?porosity?contact angle?internal stress and electrochemical methods, such like polarization curves and EIS analysis.Corrosion resistance of Pd-Ni films is better when current density ranged from 0.8 A/dm2 to 1.5 A/dm2. When the current density is too high or too low, the corrosion resistance of Pd-Ni film decreased. At the current density of 1.5 A/dm2 the micro-hardness of the Pd-Ni coating was the highest,453.8 HV. At the current density of 1.2 A/dm2 the adherence strength was the best,4.81 MPa.By controlling the current density in the same coating bath, multi-layer Pd-Ni coatings were prepared. Compared with single layer Pd-Ni coating, the micro-hardness and internal stress are obviously improved. The adhesion strength after immersion improved from 3.25 MPa to 4.13 MPa, porosity decreased from 11.75/cm2to 2.75/cm2. The corrosion rate of multilayer Pd-Ni films in 85 ? 20% H2SO4+200 ppm Cl-+520 rpm solution decreased from 0.043 g·m-2·h-1 to 0.013 g·m-2·h-1 for single layer Pd-Ni film.On the surface of 316L stainless steel, electroplating Pd-Ni/Pd alloy film can improve the corrosion potential of stainless steel in strong reducing solution to a high value which in its passivation range zone. Results showed that the smaller area ratio?potential passivation membrane when the higher, the better corrosion resistance. Compared air oxidated passive film, in promoted passive film surface, Cr(OH)3 content increased from 5.29% to 52.75% and Fe3O4 increased from 13.04% to 30%, which make the passive film more stable and showed better corrosion resistance.