Nickel Alloys

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Nickel Alloys.

Many nickel alloys have been developed specifically for their high resistance to corrosion. The alloys in this group are among the most corrosion resistant materials in many environments and some of the alloys are essentially immune to attack.

Nickel.

Nickel, as usually applied as a plating material, is resistant to corrosion in mildly corrosive environments but is not resistant to corrosion in chloride containing environments. Except in chemical processing, nickel is seldom used as a structural material.

Nickel-Copper Alloys.

The most common nickel-copper alloy is Monel 400, which is nominally 70% nickel and 30% copper. Monel 400 is highly resistant to corrosion in many environments but is not totally resistant to corrosion in seawater. It is subject to pitting attack in seawater if exposed without coupling to other metals. The incubation time for pitting in seawater is rather long and ranges from 1 to 2 years. Monel 400 is subject to metal ion concentration attack and the corrosion of this alloy is usually reduced within crevices. Monel is cathodic to most other common alloys. Monel K-500 is an age hardenable nickel-copper alloy and has higher strength than Monel 400 but has comparable corrosion characteristics.

Other Nickel Alloys.

Nickel alloys such as Inconel 625 and Hastelloy C-276 are essentially immune to corrosion in many environments. Inconel alloy 718 has high strength in the order of 150 ksi and has good resistance to corrosion in many environments and usually only exhibits small amounts of crevice corrosion attack.

A-286 is a nickel chromium- titanium-molybdenum alloy that is widely used as a high strength fastener alloy. While subject to crevice corrosion with initiation times and propagation rates similar to Type 316 stainless steel, it has been successfully used in many applications. Its practical corrosion resistance is improved due to its cathodic potential with respect to many materials and the significant improvement in its corrosion resistance when coupled to more anodic materials.