Copper nickel-based alloys

Sato, S., Nagata, K. and Yamaha, T., 1977, Re-evaluation of corrosion resistance of copper-nickel based alloys to sea water. INCO Power Conference, Lousanne. 

An especially insidious type of corrosion is localized corrosion (1—3,5) which occurs at distinct sites on the surface of a metal while the remainder of the metal is either not attacked or attacked much more slowly. Localized corrosion is usually seen on metals that are passivated, ie, protected from corrosion by oxide films, and occurs as a result of the breakdown of the oxide film. Generally the oxide film breakdown requires the presence of an aggressive anion, the most common of which is chloride. Localized corrosion can cause considerable damage to a metal stmcture without the metal exhibiting any appreciable loss in weight. Localized corrosion occurs on a number of technologically important materials such as stainless steels, nickel-base alloys, aluminum, titanium, and copper (see Aluminumand ALUMINUM ALLOYS Nickel AND nickel alloys Steel and Titaniumand titanium alloys). 

Brazing is generally considered unsuitable for equipment exposed to ammonia and various ammoniacal solutions because of the aggressiveness of ammonia to copper- and nickel-base alloys, but recently an alloy based... 

For several years, additions of Be to commercial copper- and nickel-based alloys have enabled these materials to be precipitation-hardened to strengths approaching those of heat-treated steels. Yet Cu-Be alloys retain the corrosion resistance, electrical and thermal conductivities, and spark resistance of copper-based alloys. 

A large number of copper-base and nickel-base alloys (such as cupro-nickels, Monel, and aluminum brass) have been used in sea-water service with success. Special materials such as Hastelloy C, Illium, and titanium are available for extremely corrosive situations. The evidence, so far, indicates titanium to be outstanding and to rank above other commercially available metals in corrosion resistance under conditions involving high temperature, velocity, and other adverse environmental conditions. 

The enhancement of creep by anodic dissolution is well known, for copper in acetic acid153 and austenitic stainless steels and nickel-based alloys in pressurized water reactor (PWR) environments. The initial vacancy injection from the surface is followed by vacancy attraction to the inside dislocations, which promotes easier glide, climb, and crossing of microstructural barriers. This mechanism illustrates the corrosion-enhanced plasticity approach.95... 

Two special copper alloys, beryllium copper and nickel silver, although only used on a small scale, contribute valuable metal properties for special uses. Two percent beryllium added to copper gives greater fatigue resistance to the metal and confers a nonsparking (on impact) quality to tools made of this alloy, important for impact tools in flammable or explosive atmospheres. Nickel silver, a copper/nickel/zinc alloy with an appearance very like silver, is important as the strong base metal for silver-plated tableware. 

Alloys are nsnally designated by the Unified Numbering System (UNS) [7, 8], which incorporates earlier identihcation systems developed for particular alloy families such as aluminum and copper alloys. The UNS system is particnlarly useful when designating proprietary alloys snch as the nickel-based alloys. Ordinary alloy designations that are nonproprietary, snch as those of the 300-series stainless steels, are commonly used instead of the UNS nnmber. 

Aluminum, copper, and other face-centered cubic metals and alloys (such as the austenitic stainless steels and nickel-base alloys) do not become brittle at low temperatures, except if heavily cold worked. Most such alloys are exempt from impact testing for design temperatures down to -320°F (-195°C). Some types, such as Type 304, are exempt down to 25°F (-255°C). The exemption temperatures for weld metals and HAZs are usually higher than those for the parent metal. 

An example of a nickel-based alloy that is resistant to stress-corrosion cracking is inconel. Inconel is composed of 72% nickel, 14-17% chromium, 6-10% iron, and small amounts of manganese, carbon, and copper. 

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