Alloy element

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Alloying elements are chemical elements that are added ( alloyed ) to a metal in order to improve its material properties in the desired way.

Types of alloy elements

Alloying elements can even be metals such as chromium , molybdenum and manganese , but also semimetals such as boron and silicon or non-metals such as. B. be carbon and nitrogen . However, their behavior within alloys is not always the same. Different elements often have a similar, but different effect on the base metal. Since alloy elements also influence each other, their changes in properties cannot simply be added up.

Technically used elements can on the one hand be an alloying element, on the other hand the base metal for an alloy itself. The list of alloying elements provides information about the positive and negative effects on the respective base metals.

Effect of alloying elements

Alloy elements have different effects on the base material. In general, as the content of elements increases, the strength and hardness increase, while the elongation at break decreases. The electrical conductivity and the thermal conductivity usually also decrease.

Solid solution strengthening is an important function . If the atoms of the alloying element are only slightly larger or smaller than those of the base metal, then they form a substitution solid solution in which places where atoms of the base metal would normally be located are occupied by atoms of the alloying element. Because of the different atom sizes, the atoms can move less against each other, which is necessary for a permanent change in shape of the material. The strength thus increases. If, however, the atoms of the alloying element are very much smaller than those of the base metal (eg., Carbon in the steel), they occupy the spaces between the atoms of the base material and form a so-called solid solution , which is also associated with an increase in strength.

Another mode of action is based on the formation of further chemical compounds, often from the group of intermetallic compounds that are partly metallic and partly non-metallic in character (e.g. electrically conductive like metals, but hard and brittle like ceramics). Many alloying elements in steel form carbides , that is, compounds with carbon (carbides). The often alloyed elements tungsten and chromium form, for example, tungsten carbide and chromium carbide . They are usually in the form of tiny, very hard particles and thus improve wear resistance. Some alloy elements can also form compounds with the base material. Among other things, iron combines with carbon to form cementite in steel and Al 2 Cu is formed in aluminum-copper alloys , which is largely responsible for the higher strength of this alloy.

Alloy elements in steel

One of the most important construction materials is steel , an alloy of iron and carbon. The properties of steel can be adapted to the respective needs in a variety of ways. In the case of alloying elements, a basic distinction must be made as to whether they are carbide, austenite or ferrite formers and for what purpose they are added to the steel. Austenite and ferrite are the two main modifications of iron.

The presence of the alloying elements in the steel is often only the prerequisite for achieving the desired properties. Usually further processing steps such as B. the heat treatment necessary. The most important alloying elements are:

Metallic alloy elements

Important non-metallic alloying elements are:

literature

  • Elvira Moeller: Handbook of construction materials: selection, properties, application . 1st edition. Carl Hanser Verlag GmbH & Co. KG, 2007, ISBN 978-3-446-40170-9 , p. 1035 .
  • Alfred Böge, Rainer Ahrberg, Klaus-Dieter Arndt, Werner Bahmann, Lutz Barfels, Jürgen Bauer, Ulrich Borutzki, Gert Böge, Wolfgang Böge, Berthold Heinrich, Arnfried Kemnitz, Peter Kurzweil, Susanna Labisch, Petra Linke, Manfred Ristau, Werner Roddeck, Johannes Sebulke, Dominik Surek , Werner Thrun, Jürgen Voss, Frank Weidermann, Wolfgang Weißbach, Heinz Wittig: Mechanical engineering manual: Fundamentals and applications of mechanical engineering . 21st edition. Springer Vieweg, 2012, ISBN 978-3-8348-2478-3 , p. 1500 .
  • Wilhelm Domke: Materials science and material testing. Cornelsen Verlag, ISBN 3-590-81220-6 .

Web links

Individual evidence

  1. ↑ Alloying elements: influence of alloys on steel. (PDF) Verlag Stahlkey, accessed on February 11, 2014 .