OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 and selective dissolution of copper phases. The dissolution of copper according to reactions (3)–(6) is limited by a protective oxide film, which impedes the spread of corrosion pits over the entire surface. Therefore, the morphology of the CuAl9Mn2 alloy after CV measurements is characterized by protrusions (“flakes”) and neighboring areas free of corrosion pits (Fig. 7, c). On the contrary, in the specimen CuAl9Mn2 – 10 vol. % ER 312 an intensive corrosion damage (Fig. 7, d) of a pitting nature is observed. Numerous and deeper pits predominate, forming a network of porous structures. In our opinion, the nature of corrosion damage in the CuAl9Mn2/ER 312 composites is associated with contact and crevice corrosion. When the α-Cu and α-(Fe,Cr) phases come into contact, the Fe/Cu galvanic couples are formed, which change the kinetics of the redox reactions due to the movement of charges between dissimilar metals (Fe, Cu) with different electrochemical potentials. As a result of contact corrosion, the primary sites for pitting initiation are the α-Cu/α-(Fe,Cr) interphase boundaries due to the formation of corrosion couples (Fig. 7, e). In this case, the working surface of the CuAl9Mn2 – 10 vol. % ER 321 composite is divided into cathodic (matrix grains α-Cu) and anodic (particles α-(Fe,Cr)) areas. It is important to note that due to a spontaneous passivation of the ferrite phase (presumably by nickel and chromium oxides), its dissolution in 3.5 wt. % NaCl solution is limited, while Cu-containing phases are Fig. 7. XRD patterns and SEM images of the surface after corrosion tests of CuAl9Mn2 (а, c) and composite CuAl9Mn2 – 10% ER 321 (b, d); e – scheme of the formation of pitting damage on the composite surface due to galvanic corrosion
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