The metallurgical industry plays an important role in everyone’s life, because every day you have to deal with various metal products. And they are made of all kinds of alloys, which are obtained through smelting. At least two metals are used in the production of these materials, and special additives are used to improve properties. This article will consider several alloys of iron with nickel, their properties and applications.
About the properties of iron
Pure iron - silver gray, has ductility and ductility. Native ingots found in nature have a pronounced metallic luster and significant hardness. At the height and conductivity of the material, it easily transmits current using free electrons. The metal has medium refractoriness, softens at a temperature of +1539 degrees Celsius and loses ferromagnetic properties. This is a chemically active element. At normal temperature, it easily reacts, and when heated, these properties are enhanced. In air, it is covered with a film of oxide, which interferes with the continuation of the reaction. When exposed to a humid environment, rust appears, which no longer prevents corrosion. But, despite this, iron and its alloys are widely used.
A bit of history
Invar is an alloy of iron with nickel, which includes 36% of the dopant. It was first discovered in France in 1896 by physicist Charles Guillaume. At this time, he was working on the search for inexpensive metal for standards of measures of mass and length, which were made from a very expensive platinum-iridium alloy. Thanks to this discovery, the scientist in 1920 received the Nobel Prize in physics.
The word "invar" in translation from Latin means invariable. This means that in the alloy of iron with nickel, the coefficient of thermal expansion remains constant over a wide temperature range - from -80 to 100 degrees Celsius. This alloy has several other names: nilvar, vakodil, nilo alloy, radio metal. Invar is a trademark of Imphy Alloys Inc., a company owned by Arcelor Mittal Steel.
Alloy of iron with nickel
To improve the properties of iron, using various additives, alloys are obtained. Scientists believed that it would not be difficult to obtain an iron-nickel alloy, given the thermodynamic properties of metals. But in practice, they ran into problems. In the interaction of metals, during the production of an alloy of iron with nickel, as a result of a side oxidative process, iron passes from a divalent state to a trivalent one.
As a result, the yield of the alloy decreases and certain physical properties deteriorate. To solve this problem, amines and organic acids are added to the electrolyte, which form compounds with low solubility with ferric iron . In this regard, the elasticity of the precipitate becomes better, and for its uniform distribution, the electrolytes are mixed. The resulting alloy of iron with nickel is called Invar.
Invar alloy application
The insignificant temperature coefficient of expansion allows using it for production:
- parts of instrumentation;
- tapes and wires for geodetic works;
- bearing structures of the laser;
- parts of clock mechanisms, pendulums of chronometers;
- rolled: hot rolled bar and sheet, cold rolled tape, seamless pipes, forged bars.
To increase the strength, cold plastic deformation of the alloy of iron with nickel is performed, and then low-temperature heat treatment is performed. For greater resistance to corrosion under normal atmospheric conditions, its surface is polished and a protective layer is applied if the product is intended for use in aggressive environments. The anti-corrosion properties of Invar will also increase when about 12% chromium is added to its composition, while it maintains a constant elasticity when heated to 100 degrees.
Magnetic Alloys
These alloys are widely used in electrical engineering. Permanent magnets, transformer cores, electrical appliances, electromagnets are made from them. People have long known that iron has magnetic properties and as a result, it finds many uses.
Much later, it was discovered that the same property is inherent in nickel and some other metals. Products made from a magnetic alloy of iron and nickel also have the ability to maintain their own magnetic field when the external is already absent. Moreover, this personal field is again able to act on other magnetic bodies.
Nickel, cobalt and their alloys
Cobalt and nickel are elements of a subgroup of iron. All three elements have similar properties, but there are significant differences. Both metals have a higher density than iron, and are much harder and stronger than it. They are less active in chemical terms, are corrosion resistant. In addition, metals are valued for their high resistance to gas corrosion.
The disadvantages of cobalt and nickel are their high toxicity and significant cost relative to iron. They find their application for the external corrosion-resistant coating of products made of carbon steel and iron by electrochemical reactions. And also they are used for the manufacture of components and parts requiring enhanced strength and hardness. It should be noted the special importance of alloys of iron, nickel and cobalt, which are called Coinvar, Invar, superalloy, permalloy and malla. Their main advantage lies in their high magnetic properties. These alloys are used for the production of magnetic circuits of various electromagnetic devices.
Alloy Kovar
The mixture consists of metals with excellent mechanical properties. They are easy to process, they are easily rolled, broached, forged and stamped. And the alloy of cobalt, nickel and iron is otherwise called treachery. A well-chosen combination of chemical elements provides the material with excellent characteristics. This alloy has good thermal conductivity, a high coefficient of electrical resistivity and close to zero linear expansion in a large temperature range. The only drawback is the low corrosion resistance in a wet environment, so silver coatings are often used. Kovar is widely used in industry for the production of:
- pipes, tapes and wire;
- capacitors;
- equipment cases in instrument making;
- parts in electronics;
- enclosures in the electric vacuum industry.
The content of expensive cobalt and nickel in the alloy increases the cost of the material, but good performance and long-term operation cover the initial investment.
Alni Alloys
Alni is the group name for the iron-nickel-aluminum magnetic alloys. With an increase in the concentration of aluminum and nickel within certain limits, the residual induction decreases, and the coercive force increases. Most often, alloys are used, in which aluminum is from 11 to 18%, and nickel - 20–34%. The main properties of such alloys are electrical conductivity, thermal conductivity and ductility. All of them are characterized by good welding.
To use alloys in the
manufacture of magnets, they are alloyed with cobalt and copper. In this case, the material becomes hard and brittle and has a coarse-grained structure. Alni alloys are used as a structural material for parts of gas turbine and jet engines operating under the influence of high temperatures of more than 1000 degrees Celsius for a long time, keeping the metal without damage.
Conclusion
All metals used extensively in modern industry are alloys. For example, almost all the iron that is received in the world is used for the production of cast iron and steel. This can be explained by the fact that alloys are characterized by better properties than the metals from which they are obtained. It should be noted that alloys produced by industry have properties common to them: strength, hardness, elasticity and ductility. And iron-nickel also has magnetic properties, which are enhanced by additional alloying during production.