The history of the discovery of nickel alloys. Physical and mechanical properties.
Nickel has the property of dissolving other metals, while it does not lose its merits, giving alloys heat resistance and plasticity. Thanks to this property, a large number of nickel alloys have appeared, which have a number of advantages. Nickel forms solid solutions with other metals, which are distinguished by ferromagnetism, high corrosion resistance in gas and liquid aggressive media. Allotropic transformations are absent in alloys.
Since the end of the XIX century, nickel-copper alloys with high plasticity, valuable electrical properties and corrosion resistance have become increasingly popular. Monel-type alloys have found the widest practical application. Such alloys, along with kunialy, are distinguished among structural materials by high chemical stability in water, gas media, in strong alkalis and acids.
Ferromagnetic alloys (40−85% Ni + Fe) play an important role in engineering. These alloys belong to the class of magnetically soft materials. Among them there are alloys that are characterized by a high value of permittivity — permalloy; Constancy, qualities under changing external conditions — perminvar; High magnetic permeability and maximum magnetic saturation — permang. Such alloys are widely used in virtually all areas of technology, where high sensitivity of the working elements is required to oscillations of the magnetic field.
Alloys with 45−55% Ni are in demand in sealed contacts between glass and metal. Such alloys, doped with Co or Cu, have practically the same coefficient of linear thermal expansion with glass.
Ni + Co alloys, which have 4 or 18% nickel, belong to the group of magnetostrictive materials. Such alloys have high corrosion resistance in sea and river water. As a rule, they are widely used for the manufacture of hydroacoustic equipment.
With the advent of the twentieth century and the development of electrical engineering, a new class of nickel alloys was developed. The heat resistance of this metal in air is very high, but it can improve Cr, Si, Al. Nickel alloys with Si Al, Mn and Ni alloys with 10% Cr have a heat resistance in combination with thermoelectric properties. The most common thermocouples are chromel-alumel thermocouples, they are used in laboratory engineering and industry. Also used are thermocouples from the copel and chromel.
Ni-Cr alloys, They are also called nichromes. These alloys are heat resistant and widely used in engineering. Still, nichrome with a nickel content of about 80% is very popular. They were considered the most heat-resistant industrial alloys, but only until the appearance of chromals. To reduce the cost of nichromes began to reduce the content of nickel in them, thus, appeared ferronichromes. In ferronichromes, most of the nickel is replaced by iron. The most common composition contains 60% Ni, 15% Cr, 25% Fe .
Compared with nichrome, ferronichromes have lower operational resistance and are used at lower temperatures. It should be noted that both nichromes and ferronichromes have a very high electrical resistance of about 1.05−1.4 μΩ · mm 2 / m. Together with the chromals they are included in the most important classes of alloys, which are used to make high-temperature electric heaters. As a rule, nichromes are used which are doped with silicon, up to about 1.5%, together with metals such as rare-earth and alkaline-earth metals. The operating temperature limit of the nichrome of this type is 1200 ° C, and in some grades up to 1250 ° C. Competition of nichromes is based on heat-resistant alloys, which contain 15−30% Cr and up to 4% Al. Alloys alloyed with Si are not as heat-resistant. But from chromium-containing alloys doped with aluminum, it is much more difficult to obtain a homogeneous tape or wire for reliable operation of electric heaters. Because of this, these alloys serve mainly in the manufacture of heat-resistant parts with an acceptable operating temperature up to 1250 ° C, not subject to high mechanical stress.
During the Second World War in Britain, the production of nimonics — high-temperature Ni-Cr-Ti-Al alloys. These alloys of special strength are obtained due to chromium alloying with 2.5% titanium, and 1.2% by aluminum. These alloys are superior to nichrome and alloy steels in terms of heat resistance. Prior to this, steel was used, working up to t ° 750−800 ° C. The appearance of nimonics opened the era of aviation gas turbine engines. In a short time a large number of complex alloys were created, which are related to nimonics. These are alloys with Ti, Al, Nb, Ce, La, B, Zr. Their operating temperature reaches 1000 ° C… The complicated alloying effect on the quality of alloys adversely affects the ability of alloys to be hot-worked by pressure. It should be noted that deformable and alloyed foundry alloys have been recognized precisely because of their high heat resistance. But in this case, cast alloys are not very homogeneous structure, in connection with which there is a spread of properties. To find the optimal composition, refractory thorium oxides, zirconium and aluminum, and also other compounds were introduced into the alloys. The best was a nickel alloy with highly dispersed thorium oxides.
A very important role in engineering is played by alloyed Ni-Mn, Ni-Cr, Ni-Mo alloys. These alloys have valuable electrical properties: high electrical resistance, low value of the coefficient of thermal expansion, and paired with copper have a small value of thermo-emf. These alloys are inferior to manganin in terms of the coefficient of temperature electrical resistivity in the room temperature range, but they have 3−4 times the specific electric resistance. Such alloys are used for small-sized resistive elements where constant electrical properties are required throughout the life of the product. These elements are made of thin foil or micro-wire with a thickness of 5 to 20 μm. Ni-Cr or Ni-Mo alloys are used for manufacturing small-sized strain gauges. In such alloys there is a linear dependence of the change in electrical resistance on the value of elastic deformation.
Chemical equipment often works in aggressive media of sulfuric, and hydrochloric, and phosphoric acids of different concentrations at a temperature that is as close as possible to the boiling point. Ni-Cr-Mo, Ni-Mo alloys are known abroad as halstel and remanite. On the territory of the USSR, these alloys are known under the brands H70M28, X15N65M16B, H70M
In practice, many more nickel alloys are used, with Fe, Mo, and Cr, as well as with other elements that have the right combination of mechanical and physico-chemical properties. Thus, corrosion-resistant alloys for springs and solid alloys for dies are obtained, as well as many others. In addition to the listed alloys, nickel is part of other metals, as a component.
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