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Alloying allows to improve the properties of one material at the cost of changing them for the second material. As an example, the hardness of a base metal may be increased while at the same time the electrical conductivity decreases with even small additions of the second alloying component.
*'''Composite Materials'''
Composite materials are a material group whose properties are of great importance for electrical contacts that are used in switching devices for higher
Those used in electrical contacts are heterogeneous materials composed of two or more uniformly dispersed components in which the largest volume portion consists of a metal.
The properties of composite materials are determined mainly independent from each other by the properties of their individual components. Therefore it is for example possible to combine the high melting point and arc erosion resistance of tungsten with the low melting and good electrical conductivity of copper, or the high conductivity of silver with the weld resistant metalloid graphite. <xr id="fig:fig2.1Powder metallurgical manufacturing of composite materials (schematic)"/> shows the schematic manufacturing processes from powder blending to contact material. Three basic process variations are typically
applied:
*Infiltration (Press-Sinter-Infiltrate, PSI)
<figure id="fig:fig2.1Powder metallurgical manufacturing of composite materials (schematic)">[[File:Powder metallurgical manufacturing of composite materials (schematic).jpg|right|thumb|<caption>Powder-metallurgical manufacturing of composite materials (schematic) T<sub>s</sub> = Melting point of the lower melting component)</caption>]]
</figure>
Pure Gold is besides Platinum the chemically most stable of all precious metals. In its pure form it is not very suitable for use as a contact material in electromechanical devices because of its tendency to stick and cold-weld at even low contact forces. In addition it is not hard or strong enough to resist mechanical wear and exhibits high materials losses under electrical arcing loads. This limits its use in form of thin electroplated or vacuum deposited layers.
Main ArticelArticle: [[Gold Based Materials| Gold Based Materials]]
==Platinum Metal Based Materials==
The platinum group metals include the elements Pt, Pd, Rh, Ru, Ir, and Os [[Platinum_Metal_Based_Materials|Table 1]]<!--(Table 2.6)-->. For electrical contacts platinum and palladium have practical significance as base alloy materials and ruthenium and iridium are used as alloying components. Pt and Pd have similar corrosion resistance as gold but because of their catalytical properties they tend to polymerize adsorbed organic vapors on contact surfaces. During frictional movement between contact surfaces the polymerized compounds known as “brown powder” are formed which can lead to significantly increase in contact resistance. Therefore Pt and Pd are typically used as alloys and not in their pure form for electrical contact applications.
Main ArticelArticle: [[Platinum Metal Based Materials| Platinum Metal Based Materials]]
==Silver Based Materials==
Main Article: [[Silver Based Materials| Silver Based Materials]]
==Tungsten and Molybdenum Based Materials==
==Special Contact Materials (VAKURIT) for Vacuum Switches==
Main ArticelArticle: [[Special Contact Materials (VAKURIT) for Vacuum Switches| Special Contact Materials (VAKURIT) for Vacuum Switches]]
==References==
Manufacturing Equipment for Semi-Finished Materials
(Bild)
[[de:Kontaktwerkstoffe_für_die_Elektrotechnik]]
