Copper Nickels

Overview

Copper nickel alloys are very corrosion resistant and thermally stable. The copper nickel alloys contain from 2 to 30% nickel depending upon the application. These alloys usually have additions of iron, chromium, niobium, and or manganese to improve the strength and corrosion resistance. They are virtually immune to stress corrosion cracking and exhibit high oxidation resistance in steam and moist air. The copper nickel alloys have moderate strength even at elevated temperatures. The higher nickel alloys are well known for their corrosion resistance in sea water and their resistance to marine biofouling. The copper nickel alloys are used in applications such as electrical and electronic products, tubes for condensers in ships and power plants, various marine products including valves, pumps, fittings and sheathing for ship hulls. The wrought alloys are designated as UNS C70100 through C72950. The cast alloys are C96200 to C96900. Cast copper nickel alloys are typically used aboard ships, on offshore platforms and in coastal power plants.

Copper nickel alloys are single phase alpha structures because nickel is completely soluble in copper. The as cast dendrites are heavily cored, they contain a composition gradient, because the alloys freeze over a wide temperature range. The as cast structures consist of alpha dendrites, that have a decreasing nickel content from the center to the edge of the dendrite. The interdendritic regions, being the last liquid to solidify, are higher in copper. Mechanical treatments break up the dendritic structure, but even repeated mechanical and thermal treatments do not homogenize the alloying elements. Segregation of the alloying elements, which starts out as coring of the dendrites, is seen as banding in the wrought microstructures. The microstructure of the wrought materials is similar to that of unalloyed copper, it consists of twinned grains of alpha copper. The banding of the alloying elements shows up as dark rows or stripes across the grains.

NOTE: The file size of the Larger and Largest View of the Micrographs are substantially larger than the thumbnail shown. The Larger View images range in size from 11K to 120K depending on the image. The Largest View images range in size from 125K to almost 500K.