Effect of Cu on the corrosion resistance of a NiMo2B2-Dispersed Ni-based alloy

Corrosion of NiMo 2 B 2 -dispersed Ni-based alloy containing Co, Mn, Cr, Fe or Cu was examined by measuring the mass loss and the corrosion potential in 6 mass%HNO 3 aqueous solution and by metallography. The corrosion was accelerated by addition of Co or Mn while it was retarded by addition of Cr, Fe or Cu. In particular, the addition of Cu greatly improved the corrosion resistance. The corrosion proceeded by a mechanism in which the Ni-matrix phase worked as anode while the NiMo 2 B 2 phase worked as cathode. The addition of Cu shifted the corrosion potential of the Ni-matrix phase to the noble side by about 15 mV, and consequently the difference in the corrosion potential between the Ni-matrix phase and the NiMo 2 B 2 phase decreased, As a result the preferential corrosion of the Ni-matrix phase was extremely retarded.