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|60 Chapter 6 Nonferrous Metals and Alloys: Production, General Properties, and Applications
electrical conductors, the copper is refined further electrolytically to a purity of at least
99.95 % (oxygen-free electrolytic copper). A more recent technique for processing cop-
per is hydrometallurgy, a process involving both chemical and electrolytic reactions.

6.5 Nickel and Nickel Alloys

Nickel (Ni) is a silver-white metal discovered in 1751 and a major alloying element
that imparts strength, toughness, and corrosion resistance. It is used extensively in
stainless steels and in nickel-based alloys (also called superalloys). Nickel alloys are
used in high-temperature applications (such as jet engine components, rockets, and
nuclear power plants), in food-handling and chemical-processing equipment, in
coins, and in marine applications. Because nickel is magnetic, nickel alloys also are
used in electromagnetic applications, such as solenoids. The principal use of nickel as
a metal is in the electroplating of parts for their appearance and for the improvement
of their corrosion and Wear resistance. Nickel alloys have high strength and corro-
sion resistance at elevated temperatures. Alloying elements in nickel are chromium,
cobalt, and molybdenum. The behavior of nickel alloys in machining, forming, cast-
ing, and Welding can be modified by various other alloying elements.
A variety of nickel alloys, with a wide range of strengths at different tempera-
tures have been developed (Table 6.8). Although trade names are still in wide use,
nickel alloys are now identified in the UNS system with the letter N. Thus, Hastelloy
G is novv N06007. Other common trade names are:

° Monel is a nickel-copper alloy.
° Inconel is a nickel-chromium alloy with a tensile strength of up to 1400 MPa.
Hastelloy (also a nickel-chromium alloy) has good corrosion resistance and high
strength at elevated temperatures.
° Nichrome (an alloy of nickel, chromium, and iron) has high electrical resistance
and a high resistance to oxidation and is used for electrical heating elements.
° Invar and Kovar (alloys of iron and nickel) have relatively low sensitivity to tem-
perature (Section 3.6).

TABLE 6.8
Properties and Typical Applications of Selected Nickel Ailoys (All Are Trade Names)

Ultimate
Nominal tensile Yield Elongation
Type and UNS composition strength strength in 50 mm
number (%) (MPa) (MPa) (%) Typical applications
Nickel 200 (annealed) None 380-550 100-275 60-40 Chemical and food processing
industry, aerospace equipment,
electronic parts
Duranickel 301 4.4 Al, 0.6 Ti 1300 900 28 Springs, plastics extrusion equipment,
(age hardened) molds for glass, diaphragms
Monel R-405 30 Cu 525 230 35 Screw-machine products, water meter
(hot rolled) parts
Monel K-500 29 Cu, 3 Al 1050 750 30 Pump shafts, valve stems, springs
(age hardened)
Inconel 600 15 Cr, 8 Fe 640 210 48 Gas turbine parts, heat-treating
(annealed) equipment, electronic parts, nuclear
reactors
Hastelloy C-4 16 Cr, 15 Mo 785 400 54 Parts requiring high-temperature
(solution treated stability and resistance to stress-
and quenched) corrosion cracking