Resistance to Forms of Corrosive Attack

In general, nickel and its alloys have an excellent resistance to corrosion. In certain conditions, of course, they may be susceptible to some forms of attack. A few of the forms of corrosion are described below in terms of the resistance or susceptibility of nickel and its alloys.

Uniform Corrosion

Nickel and its alloys are very resistant to general corrosion in a wide range of environments. Since it is a relatively noble metal, alloys with a high nickel content typically exhibit a good resistance to uniform corrosion.

Galvanic Corrosion

Since nickel is a relatively noble metal and also a fairly cathodic in the Galvanic Series compared to most other metals, it is not very susceptible to galvanic corrosion. It may however, exhibit a degree of corrosion due to galvanic action, if it is coupled with a more noble metal.

Pitting and Crevice Corrosion

Nickel is somewhat susceptible to pitting and crevice corrosion in seawater and other environments. Typically, surface impurities are the cause of pitting, since they can act as a nucleating point for corrosion. Crevice corrosion can occur, particularly in areas where there is stagnant seawater.

Intergranular Corrosion

Nickel has a good resistance to intergranular corrosion, although in certain nickel alloys with inappropriate heat treatments it may be susceptible to this particular form of corrosion. In general, a higher nickel content corresponds to a better resistance to intergranular corrosion. In environments containing sulfur, nickel alloys have an increased susceptibility to intergranular corrosion.

Stress Corrosion Cracking

Alloys that contain mostly nickel with a small amount of iron tend to be susceptible to SCC. Nickel alloys seem to have a greater resistance to SCC compared to stainless steels.

High Temperature Corrosion

Nickel and its alloys may be susceptible to oxidation, carburization, nitridation, sulfidation and halogenation at high temperatures. Certain alloying elements however, can provide augmented resistance to high temperature corrosion in environments where these contaminants are present.