PROCESS OF FORMATION OF CORROSION FILMS ON ALLOY 70Cu-30Ni IN SEAWATER
70Cu—30Ni合金海水腐蚀产物膜形成过程

The characteristics and composition changes of the corrosion films of alloy 70Cu-30Ni immersed in seawater for different times were investigated.The results show that there is a Ni-rich zone in the films, which becomes wider and higher in the degree of Ni enrichment with increasing the immersed time. The film rich in Ni serves as an anode so as to protect the matrix. For the change of the structure or composition or for inner stress making the film broken, cracks or trenches appear in the film immersed in seawater for long time.With the solution and scaling off of the outer layer,the cracks or trenches become convex lines. Because the concentration ratio Ni / Cu at the convex lines is higher than average ratio Ni/Cu in the zone between convex lines,the preferred dissolution of convex lines leads the surface of the film to smoothness.The carbon in the film increases with increasing immersion time and can be thought to be from seawater not from residual carbon films.