Cermet (materials technology)

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Cermets (composed of cer amic and met al) are composite materials made of ceramic materials in a metallic matrix ( binder ). They are characterized by a particularly high hardness and wear resistance .

Cermets and hard metals

The term cermet describes all types of hard materials , especially in the Anglo-American language . This is why hard metals , in particular tungsten carbide- free hard metal cutting materials, also count among the cermets, although there are differences in the manufacturing process, in mechanical behavior and in the interactions between the composite components. Electrical conductivity is recommended as the limit to hard metals , with cermets being considered non-conductors . In addition, cermets have a higher thermal shock and oxidation resistance than cemented carbide.

Properties and composition

The ceramic components are often aluminum oxide (Al 2 O 3 ) and zirconium dioxide (ZrO 2 ), while niobium , molybdenum , titanium , cobalt , zirconium , chromium and others are possible as metallic components .

The vastly different density between the metallic and ceramic sintered components easily lead to segregation , so that stabilizing additives are necessary. The sintering process is the same as with homogeneous powders, except that the metal is compressed more than the ceramic with the same pressing force.

use

Cermets based on titanium carbide (TiC) and tantalum carbide (TaC), which are embedded in a niobium, molybdenum or, more rarely, cobalt binder phase and sometimes contain other additives such as molybdenum carbide , vanadium carbide , zirconium carbide and others as additives depending on the intended application , are used as cutting material layers, see Cermet (cutting material) . They are a complex multi-substance system with other elements such as tungsten and tantalum . The great advantage of cermets as cutting materials is their high thermal shock resistance , which is achieved by the TiC / TaC and can be up to 1800 ° C. This means that cermets can also be used with cooling lubricants . The abbreviation according to ISO 513 for TiC and TaC cermets is HT (hard metal based on titanium / tantalum carbide). Monolithic cermet cutters have not caught on due to their low bending strength .

Various material combinations are also used as conductor material or resistance layer in electronic thick-film circuits or trimming potentiometers . Furthermore, they have to be a thermocouple - protective tubes in the heat metallurgy introduced and allowed, for example, the complete automation of the Linz-Donawitz process .

Another application is in processing as armor-piercing ammunition. The cermet is the core of the bullet, which has similar operating principles as the hard core bullet . This ammunition was used for the 15 mm Mauser machine gun MG 151/15 .

See also

Footnotes

  1. ^ Wolfgang Weißbach: Material science - structures, properties, testing; P. 299; Vieweg + Teubner, Wiesbaden; 2010, ISBN 978-3-8348-0739-7 .
  2. ↑ Werner Schatt (Ed.): Powder metallurgy, sintered and composite materials. , Heidelberg: Hüthig, 1986, ISBN 3-7785-1319-2 , pp. 527-531
  3. ↑ Stephen F. Krar, Arthur Gill: Exploring Advanced Manufacturing Technologies . Industrial Press Inc., 2003, ISBN 0-8311-3150-0 ( limited preview in Google Book Search).