28
M. V. Ved’ et al.
Fig. 1.23 The Nyquist plots
for steel electrode (1),
Fe-Co-Mo (2), and Fe-Co-W
(3) alloys in a neutral
chloride-containing
environment
Fig. 1.24 The equivalent circuits of corrosion processes in a neutral chloride-containing environment: (a) steel electrode, Fe-Co-W alloy, (b) Fe-Co-Mo alloy
Fig. 1.25 Corrosion
diagrams for coatings
Co(76)-Mo(24) (1) and
Co(72.2)-Mo(24.1)-Zr(3.7)
(2) in 1 M Na 2 SO 4 (pH 3):
cathodic plots (1, 2) and
anodic plots (1 , 2 )
declines by almost an order of magnitude compared with the binary system (Table
1.5). It can be explained by an increased zirconium trend to passivity as can be
seen from the corrosion plots (Fig. 1.25) and anodic polarization dependences
(Fig. 1.26).
Also ternary alloy increases resistance to pitting corrosion as it was shown for
other corrosion-resistant materials [46, 47]. The difference in corrosion rate of CoMo and Co-Mo-Zr coatings in an alkaline environment is not as great due to the
acidic nature of passive oxides of molybdenum and zirconium.