Double glow surface alloying of low carbon steel with electric brush plating Ni interlayer for improvement in corrosion resistance

The present study concerns double glow plasma alloying of low carbon steel with predeposited Ni (by electric brush plating) to enhance corrosion resistance of a single alloying layer without electric brush plating interlayer. The composition and microstructure of the alloying layer were analyzed using scanning electron microscopy and X-ray diffraction. The results indicated that the composite layer consists of single γ phase, but the single alloying layer without predeposited Ni interlayer (by brush plating) consisted of a γ matrix and several precipitates (M6C and μ phase). Owing to thermal effects during the double glow plasma alloying process, Ni could diffuse toward the substrate, which taken as a barrier layer for carbon was effective to decrease the content of carbon in the composite alloying layer and at the same time formation of interface diffusion between the brush plating layer and the substrate could improve the adhesion strength. Corrosion resistance of the composite alloying layer was investigated by an electrochemical method in 3.5% NaCl and 5% HCl solution, and 20-h immersion tests in 20% H2SO4 and 20% HCl solution. The experimental results showed that the corrosion resistance of composite layer was better than that of the single alloying layer. Thus, it was concluded that double glow plasma surface alloying of low carbon steel with electric brush plating Ni interlayer was an appropriate technique to enhance the corrosion resistance as compared with single double glow surface alloying.