In the metallurgy an alloy is a mixture of two or more chemical elements, from which at least a metal is, and which a metallic character has. The alloying element can with the basic element a solid solution form (single-phase alloy) or it form itself several phases. While during single-phase alloys the characteristics are essentially determined by the chemical composition, these are affected when multi-phase alloys additionally considerably by the distribution of the phases (structures).

The alloying elements are added to the base metal in the fusionliquid condition with the intention of changing the material properties (examples hardness, corrosion resistance) in the desired way. In contrast to it the foreign matter stands. Alloying elements and base metal are called also components of an alloy. In the list of the alloying elements selbige and their effects on the respective base metals are specified.

Word origin

Originally originate from latin ligare alloy the verb and mean together - bind, connect or also combine. In 17. Century was transferred in the meantime easily modified putting acres (of same importance) to German.

Organization

Depending upon number of components in the alloy one speaks of a two, a three, a four or a multi-material alloy, whereby only those components are counted, which determine the characteristic characteristics. Since iron and steel are in the technology of special importance, alloys are divided into iron and non ferrous alloys. Further organizations arise as a result of the kind of the alloy formation, there these not only from fusing the components develop or also from special abilities of alloys.

• Natural alloys result to melt opens of elements from heat effect and for example on the inside from heavenly bodies. Since these alloys were not controlled naturally by humans, they are not subject also of them to defined compositions and characteristics.
• Ferrous alloys are divided into cast irons and steel. The distinction is based on the content of carbon. See major item iron carbide diagram.
• Non ferrous alloys (NE-alloys; Example bronze, brass, amalgam) are alloys on the basis of non-ferrous metals.
• Diffusion alloys result from the diffusion of atoms in the crystal lattice of the base metals. Particularly the first elements in the periodic system are because of the Kleinheit of their atoms opposite the base metal able to immigrate to its crystal lattices. The best example of a diffusion alloy is carburizing workpieces, in order to be able to harden it.
• Heusler alloys are not contained magnetic alloys, iron, cobalt or nickel (example Ni2MnGa, Cu2AlMn).
• Form memory alloys are metals, which return to a deformation by heat effect to the their origin form.
• Cast alloys are directly usable, while forgeable alloys are first transformed.
• One calls pseudo alloys through sinters (press together more differently, intimately blended metallic powders) the developed workpieces. With this procedure also elements can be mixed, which would not separate in the fusionliquid condition into one another. Many Wolfram-Legierungen are manufactured e.g. in such a way.

History

Copper is one of the first metals used by humans; it probably became before approximately 6000 - 10000 years by coincidence in particularly hot burning charcoal fires discovers, where it can withdraw in pure form from cupreous rocks. Also tin was early discovered, before approx. 5000 years. From the discovery of these two metals up to the production of first alloys (CuSn = bronze) from it it was then only a short way, which gave its name to a whole culture epoch (Bronzezeit). Weapons, utensils and decoration were made of bronze.

Zinkerz (zinc carbonate, a zinc salt) is for the Bronzezeit well-known and in the antique one with copper to brass (CuZn) was alloyed. Already about 3000 before Christ it was used in Babylon and Assyrien, in Palestine about 1400 - 1000 before Christ. In addition, brass was used fast an important during the minting, gladly during the decoration production.

Ferrous alloys already used in the antique one, however only from meteorites, in which frequently the alloy iron nickel (Fe-Ni) is. Since meteorites were found rare, articles from iron were accordingly valuable. The Sumerer called it "sky metal ", the Egyptians "black copper of the sky ". Smelted iron (recognition by absence of nickel) was found in Mesopotamien, Anatolien and Egypt and about 3000 to 2000 before Christ developed. It was more valuable than gold and particularly for ceremonies purposes was used. Iron offered and offers however many advantages, the most important was the larger hardness in relation to the bronze and the copper. Improvements in the production and processing let humans turn into to manufacture first weapons and then tools such as plows from iron. The Bronzezeit was replaced thereby from the Eisenzeit.

Alloy formula

In order to describe an alloy, one indicates usually the proportional proportions of its components. The alloy CuZn 37 (earlier designation brass 63) consists for example of 37% zinc and 63% copper, i.e. in 100 kg CuZn 37 are contained of 37 kg zinc and 63 kg copper.

The indication of alloy portions is among other things by the DIN 1310 composition of merge phases (gas mixture, solutions, mixed crystal); Fundamental ideas regulated.

Phase diagram (temperature-concentration diagram, phase diagram)

As alloying elements behave within an alloy, depends on several factors:

• Crystal system of base metal and alloying element
• Number and proportion of alloying elements
• Temperature.

By crystallization test series with different alloys of different composition with the thermal analysis the crystallization and/or crystal change points is noted and registered into a temperature composition diagram, whereby the temperature stands in dependence for alloy composition.

For two-component systems in the case of it particularly in regard to the crystal system three typical forms of phase diagrams resulted:

Two-component systems with complete solubility in the solid state

With complete solubility in the solid state mixed crystals form in each composition. There are two possibilities of the mixed crystal formation (MK), storage and substitution-mixed crystal-typical substitution MK Bildner is the alloys to iron chrome, iron nickel, Gold-Kupfer, gold silver and Kupfer-Nickel.Ein of important storage MK Bildner is austenite

So that an alloy in each composition can form mixed crystals with perfect solubility in the solid state, the following conditions are necessary:

1. Both metals must exhibit the same crystal system (for example cubically).
2. The grating spaces may differ around maximally about 15%.
3. The two metals must have one "certain chemical similarity ".
4. The may not be "too large ".

Also with still so large similarity of the alloying elements the crystal lattice is always distorted by the mixed crystal formation, since the different elements possess also different atomic diameters. Thus tensions develop; the gliding planes of the crystallites are obstructed to give way to deformations. The lattice distortion increases thus the hardness.

A popular example of an alloy with perfect solubility in the solid state is the two-component system cu-Ni.

The alloys (curves 2-5) solidify contrary to the base metals (curves 1.6) not at a firm temperature, but in a Haltebereich. The temperature remains thus not constant, but sinks slowly. The Haltebereiche of different compositions of an alloy however always lie between the respective solidification temperatures of their pure components.

A cause for it is "the handicap "of the crystallization in an alloy by component A (curve 1), those, if it could, at still lower temperature would solidify. Component B against it "pushes "on solidification, which would actually have had to begin already rather. This fact is also the reason for the fact that the crystals developing during the solidification change their mixing proportion and with sufficient slow cooling (thermal equilibrium) up to the end of the solidification the desired mixing proportion is only reached by diffusion.

To read off these compositions at the phase diagram leave themselves, by pulling a horizontal one by any point on the selected alloy (fig. wl) to the solidus. At the liquidus temperature TLi (beginning of the solidification) possess the first crystals thus a composition of WMLi.Auch the respective composition of the remainder melt can be determined in this way, by pulling the horizontal one through up to the liquidus for example with TM. The melt would have thus at this point the composition WSm and the mixed crystals the composition WMm.

With the help of the phase diagram can be also computed, how high with each intermediate temperature is the portion of melt and/or the portion of mixed crystals:

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