Nickel and its Alloys

Nickel is obtained commercially from oxide ores, arsenical ores, and ores of Copper, Manganese and Iron, at least 85 percent of all nickel production is obtained from Sulphide ores.

Pure nickel is tough silver-coloured metal, rather harder than Copper and have about the same strength, but possessing somewhat less ductility. It closely resembles Iron in several of its properties. It is malleable, weldable, and perceptibly magnetic. But unlike Iron, it is little affected by dilute acids. It is far less readily oxidisable, and deteriorates much less rapidly under atmospheric influences than Iron. For this reason, articles of Iron and Steels are frequently Nickel-plated to protect them from rusting. Nickel is much used for cooking utensils and other vessels for heating and boiling. Nickel is mixed as a constituent into a large number of ferrous and non-ferrous alloys and frequently finds application as a catalyst in important industrial processes. Nickel alloy, which are particularly useful for general industrial purposes are described below.

Monel Metal

It is an alloy of 60 percent Nickel, 38 percent Copper and a small amount of Aluminium or Manganese. It is a white, tough, and ductile metal and can be readily machined. It welds without difficulty. It can be heat-treated. It is also resistant to corrosion by most agents and has high strength at elevated temperatures.

Monel metal is used in the forms of rod, sheet, wire, and welded tubing. It is widely employed for structural and machine parts which must have a very high resistance to corrosion and high strength as steam turbine blade, impeller of centrifugal pump, etc.

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German Silver

An alloy of Copper (25 to 50 percent), Nickel (10 to 35 percent), and Zinc (25 to 35 percent) is known as German silver. Sometimes, Tin and Lead are also added. It is hard and ductile. This is usually of bright silver colour, but may also assume various other pleasing colours by adjusting the proportions of Copper, Nickel and Zinc. In addition to colour, it has good mechanical and corrosion resisting properties. It is also known as Ni-silver. German silver is used for making utensils and resistances in electrical work.

Inconel

It contains 75 to 80 percent Nickel, 10 to 15 percent Chromium and the rest is Iron. It can be used for parts that are exposed to high temperature for extended period. It is less reactive to acid than Nichrome.

Nichrome

This is an alloy of Nickel with Chromium and is used widely as resistance wire for electrical appliances.

Nimonics

A new type of Nickel alloy called Nimonics are developed, which by proper heat treatment attain excellent properties for very high temperature service as well as under intermittent heating and cooling conditions. They contain 15 to 18 percent Chromium, 15 to 18 percent Cobalt, 3.5 to 5 percent Molybdenum, 1.2 to 4 percent Titanium, 1.2 to 5 percent Aluminium, and the remainder Nickel.

Alloys for High Temperature Service

Many components in jet and rocket engines and in nuclear equipment have to withstand temperatures in excess of 1100C. This has made to develop a number of highly specialized alloys. Nickel or Cobalt forms the base metals in this range of alloys. Most of these alloys posses yield strength in excess of 70 MN/mm2 and 250 to 370 Brinnel hardness number at room temperature. The various high temperature alloys are Nimonic 80A, Inconel 713C, Hastelloy and Vittalium.

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