Changes

===2.1 Introduction===The contact parts are important components in switching devices. They have tomaintain their function from the new state until the end of the functional life of thedevices.

The requirements on contacts are rather broad. Besides typical contact propertiessuch as

they They have to exhibit physical, mechanical, and chemical properties like high electricaland thermal conductivity, high hardness, high corrosion resistance, etc . and besidesthis , should have good mechanical workability, and also be suitable for good weld andbrazing attachment to contact carriers. In addition they must be made fromenvironmentally friendly materials.

Materials suited for use as electrical contacts can be divided into the following groupsbased on their composition and metallurgical structure:

*'''Pure metals''' Within this group, silver has the greatest importance for switching devices in the higher energy technology. Other precious metals such as gold and platinum are only used in applications for the information technology in the form of thin surface layers. As a nonprecious metal, tungsten is used for some special applications such as, for example, automotive horn contacts. In some rarer cases, pure copper is used, but mainly paired to a silver-based contact material. '''Alloys''' Besides these few pure metals, a larger number of alloy materials made by melt technology are available for the use as contacts. An alloy is characterized by the fact, that its components are completely or partially soluble in each other in the solid state. Phase diagrams for multiple metal compositions show the number and type of the crystal structure as a function of the temperature and composition of the alloying components.

Besides these few pure metals a larger number They indicate the boundaries of liquid and solid phases and define the parameters of alloy materials made by meltsolidification.technology are available for Alloying allows to improve the use as contacts. An alloy is characterized by properties of one material at the factthat its components are completely or partially soluble in each other in cost of changing them for the solid statesecond material.Phase diagrams for multiple metal compositions show As an example, the number and type hardness of a base metal may be increased while at thecrystal structure as a function of same time the temperature and composition electrical conductivity decreases with even small additions of the second alloying componentscomponent.

*Composite Materialsmaterials are a material group whose properties are of great importance for electrical contacts that are used in switching devices for higherelectrical currents.

Composite materials are a material group whose properties are of greatimportance for electrical contacts that are used in switching devices for higherelectrical currents.Those used in electrical contacts are heterogeneous materials , composed of twoor more uniformly dispersed components , in which the largest volume portionconsists of a metal.The properties of composite materials are determined mainly independent fromeach other by the properties of their individual components. Therefore it is forexample possible to combine the high melting point and arc erosion resistanceof tungsten with the low melting and good electrical conductivity of copper, orthe high conductivity of silver with the weld resistant metalloid graphite.

Figure 2The properties of composite materials are determined mainly independent from each other by the properties of their individual components.1 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:Powder metallurgical manufacturing of composite materials (schematic)"/> shows the schematic manufacturing processes from powderblending to contact material. Three basic process variations are typicallyapplied:

<figure id="fig:Powder metallurgical manufacturing of composite materials (schematic)">[[File:Powder metallurgical manufacturing of composite materials (schematic).jpg|thumb|<caption>Powder-metallurgical manufacturing of composite materials (schematic) T_s = Melting point of the lower melting component)</caption>]]</figure>  During ''sintering without a liquid phase '' (left side of schematic) , the powder mix isfirst densified by pressing, then undergoes a heat treatment (sintering), andeventually is re-pressed again to further increase the density. The sinteringatmosphere depends on the material components and later application; avacuum is used for example for the low gas content material Cu/Cr. Thisprocess is used for individual contact parts and also termed press-sinterrepresssinter-repress (PSR). For materials with high silver content , the starting point atbefore pressing is most mostly a larger large block (or billet) which is then , after sintering , hotextruded into wire, rod, or strip form. The extrusion further increases the densityof these composite materials and contributes to higher arc erosion resistance.Materials such as Ag/Ni, Ag/MeO, and Ag/C are typically produced by thisprocess. ''Sintering with liquid phase'' has the advantage of shorter process times due to the accelerated diffusion and also results in near-theoretical densities of the composite material. To ensure the shape stability during the sintering process, itis however necessary to limit the volume content of the liquid phase material. As opposed to the liquid phase sintering, which has limited use for electrical contact manufacturing, the ''Infiltration process'' as shown on the right side of the schematic, has a broad practical range of applications. In this process the powder of the higher melting component, sometimes also as a powder mix with a small amount of the second material, is pressed into parts. Then, right after sintering, the porous skeleton is infiltrated with liquid metal of the second material. The fill-up process of the pores happens through capillary forces. This processreaches, after the infiltration, near-theoretical density without subsequent pressing and is widely used for Ag- and Cu-refractory contacts. For Ag/W or Ag/WC contacts, controlling the amount or excess on the bottom side of the contact of the infiltration metal Ag, results in contact tips that can be easily attached to their carriers by resistance welding. For larger Cu/W contacts, additional machining is often used to obtain the final shape of the contact component. ==Gold Based Materials== 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 material losses under electrical arcing loads. This limits its use in form of thin electroplated or vacuum deposited layers. Main Article: [[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 due to 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 a significant increase in contact resistance. Therefore Pt and Pd are typically used as alloys and are rather not used in their pure form for electrical contact applications. Main Article: [[Platinum Metal Based Materials| Platinum Metal Based Materials]] ==Silver Based Materials== Main Article: [[Silver Based Materials| Silver Based Materials]] ==Tungsten and Molybdenum Based Materials== Main Article: [[Tungsten and Molybdenum Based Materials| Tungsten and Molybdenum Based Materials]] ==Contact Materials for Vacuum Switches== The low gas content contact materials are developed for the use in vacuum switching devices.  Main Article: [[Contact Materials for Vacuum Switches| Contact Materials for Vacuum Switches]] ==References== Vinaricky, E.(Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.Springer-Verlag, Berlin, Heidelberg etc. 2002 Lindmayer, M.: Schaltgeräte-Grundlagen, Aufbau, Wirkungsweise.Springer-Verlag, Berlin, Heidelberg, New York, Tokio, 1987 Rau, G.: Metallische Verbundwerkstoffe. WerkstofftechnischeVerlagsgesellschaft, Karlsruhe 1977 Schreiner, H.: Pulvermetallurgie elektrischer Kontakte. Springer-VerlagBerlin, Göttingen, Heidelberg, 1964 Hansen. M.; Anderko, K.: Constitution of Binary Alloys. New York:Mc Graw-Hill, 1958 Shunk, F.A.: Constitution of Binary Alloy. 2 Suppl. New York; Mc Graw-Hill, 1969 Edelmetall-Taschenbuch. ( Herausgeber Degussa AG, Frankfurt a. M.),Heidelberg, Hüthig-Verlag, 1995 Rau, G.: Elektrische Kontakte-Werkstoffe und Technologie. Eigenverlag G. RauGmbH & Co., Pforzheim, 1984 Heraeus, W. C.: Werkstoffdaten. Eigenverlag W.C. Heraeus, Hanau, 1978 Linde, J.O.: Elektrische Widerstandseigenschaften der verdünnten Legierungendes Kupfers, Silbers und Goldes. Lund: Hakan Ohlsson, 1938 Engineers Relay Handbook, RSIA, 2006 Großmann, H. Saeger, K. E.; Vinaricky, E.: Gold and Gold Alloys in ElectricalEngineering. in: Gold, Progress in Chemistry, Biochemistry and Technology. JohnWiley & Sons, Chichester etc, (1999) 199-236 Gehlert, B.: Edelmetall-Legierungen für elektrische Kontakte.Metall 61 (2007) H. 6, 374-379 Aldinger, F.; Schnabl, R.: Edelmetallarme Kontakte für kleine Ströme.Metall 37 (1983) 23-29 Bischoff, A.; Aldinger, F.: Einfluss geringer Zusätze auf die mechanischenEigenschaften von Au-Ag-Pd-Legierungen. Metall 36 (1982) 752-765 Wise, E.M.: Palladium, Recovery, Properties and Uses. New York, London:Academic Press 1968 Savitskii, E.M.; Polyakova, V.P.; Tylina, M.A.: Palladium Alloys, Primary Sources.New York: Publishers 1969 Gehlert, B.: Lebensdaueruntersuchungen von Edelmetall Kontaktwerkstoff-Kombinationen für Schleifringübertrager. VDE-Fachbericht 61, (2005) 95-100 Holzapfel,C.: Verschweiß und elektrische Eigenschaften vonSchleifringübertragern. VDE-Fachbericht 67 (2011) 111-120 Schnabl, R.; Gehlert, B.: Lebensdauerprüfungen von Edelmetall-Schleifkontaktwerkstoffen für Gleichstrom Kleinmotoren.Feinwerktechnik & Messtechnik (1984) 8, 389-393

Sintering with liquid phase has the advantage Kobayashi, T.; Koibuchi, K.; Sawa, K.; Endo, K.; Hagino, H.: A Study of shorter process times due toLifetimethe accelerated diffusion of Au-plated Slip-Ring and also results in nearAgPd Brush System for Power Supply.th Proc. 24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 537-theoretical densities of the542

FigHarmsen, U. 2; Saeger K.E.1: Powder-metallurgical manufacturing of composite materials Über das Entfestigungsverhalten von Silberverschiedener Reinheiten. Metall 28 (schematic1974)T = Melting point of the lower melting component683-686

composite materialBehrens, V. To ensure ; Michal, R.; Minkenberg, J.N.; Saeger, K.E.: Abbrand undKontaktwiderstandsverhalten von Kontaktwerkstoffen auf Basis von Silber-Nickel. e.& i. 107. Jg. (1990), 2, 72-77 Behrens, V.: Silber/Nickel und Silber/Grafit- zwei Spezialisten auf dem Gebietder Kontaktwerkstoffe. Metall 61 (2007) H.6, 380-384 Rieder, W.: Silber / Metalloxyd-Werkstoffe für elektrische Kontakte,VDE - Fachbericht 42 (1991) 65-81 Harmsen,U.: Die innere Oxidation von AgCd-Legierungen unterSauerstoffdruck.Metall 25 (1991), H.2, 133-137 Muravjeva, E.M.; Povoloskaja, M.D.: Verbundwerkstoffe Silber-Zinkoxid undSilber-Zinnoxid, hergestellt durch Oxidationsglühen.Elektrotechnika 3 (1965) 37-39 Behrens, V.; Honig Th.; Kraus, A.; Michal, R.; Saeger, K.-E.; Schmidberger, R.;Staneff, Th.: Eine neue Generation von AgSnO₂ -Kontaktwerkstoffen.VDE-Fachbericht 44, (1993) 99-114 Braumann, P.; Lang, J.: Kontaktverhalten von Ag-Metalloxiden für den Bereichhoher Ströme. VDE-Fachbericht 42, (1991) 89-94 Hauner, F.; Jeannot, D.; Mc Neilly, U.; Pinard, J.: Advanced AgSnO Contact 2th Materials for High Current Contactors. Proc. 20 Int. Conf. on Electr. ContactPhenom., Stockholm 2000, 193-198 Wintz, J.-L.; Hardy, S.; Bourda, C.: Influence on the shape stability during the sintering process itElectrical Performances ofAssembly Process, Supports Materials and Production Means for AgSnO₂ .Proc.24_th Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 75-81 Behrens, V.; Honig, Th.; Kraus, A.; Michal, R.: Schalteigenschaften vonverschiedenen Silber-Zinnoxidwerkstoffen in Kfz-Relais. VDE-Fachbericht 51(1997) 51-57 Schöpf, Th.: Silber/Zinnoxid und andere Silber-Metalloxidwerkstoffe inNetzrelais. VDE-Fachbericht 51 (1997) 41-50 Schöpf, Th.; Behrens, V.; Honig, Th.; Kraus, A.: Development of Silver Zincth Oxide for General-Purpose Relays. Proc. 20 Int. Conf. on Electr. Contacts,Stockholm 2000, 187-192 Braumann, P.; Koffler, A.: Einfluss von Herstellverfahren, Metalloxidgehalt undWirkzusätzen auf das Schaltverhalten von Ag/SnO in Relais. 2VDE-Fachbericht 59, (2003) 133-142 Kempf, B.; Braumann, P.; Böhm, C.; Fischer-Bühner, J.: Silber-Zinnoxid-Werkstoffe: Herstellverfahren und Eigenschaften. Metall 61(2007) H. 6, 404-408 Lutz, O.; Behrens, V.; Finkbeiner, M.; Honig, T.; Späth, D.: Ag/CdO-Ersatz inLichtschaltern. VDE-Fachbericht 61, (2005) 165-173 Lutz, O.; Behrens, V.; Wasserbäch, W.; Franz, S.; Honig, Th.; Späth,D.; Heinrich, J.: Improved Silver/Tin Oxide Contact Materials for Automotiveth Applications. Proc.24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008,88-93 Leung, C.; Behrens, V.: A Review of Ag/SnO Contact Materials and Arc Erosion. 2th Proc.24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 82-87 Chen, Z.K.; Witter, G.J.: Comparison in Performance for Silver–Tin–IndiumOxide Materials Made by Internal Oxidation and Powder Metallurgy.th Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver, BC, Canada,(2009) 167 – 176 Roehberg, J.; Honig, Th.; Witulski, N.; Finkbeiner, M.; Behrens, V.: Performanceof Different Silver/Tin Oxide Contact Materials for Applications in Low Voltageth Circuit Breakers. Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver,BC, Canada, (2009) 187 – 194 Muetzel, T.; Braumann, P.; Niederreuther, R.: Temperature Rise Behavior ofth Ag/SnO Contact Materials for Contactor Applications. Proc. 55 IEEE Holm 2Conf. on Electrical Contacts, Vancouver, BC, Canada, (2009) 200 – 205 Lutz, O. et al.: Silber/Zinnoxid – Kontaktwerkstoffe auf Basis der InnerenOxidation fuer AC – und DC – Anwendungen.VDE Fachbericht 65 (2009) 167 – 176 Harmsen, U.; Meyer, C.L.: Mechanische Eigenschaften stranggepresster Silber-Graphit-Verbundwerkstoffe. Metall 21 (1967), 731-733 Behrens, V.: Mahle, E.; Michal, R.; Saeger, K.E.: An Advanced Silver/Graphiteth Contact Material Based on Graphite Fibre. Proc. 16 Int. Conf. on Electr.Contacts, Loghborough 1992, 185-189 Schröder, K.-H.; Schulz, E.-D.: Über den Einfluss des Herstellungsverfahrensth auf das Schaltverhalten von Kontaktwerkstoffen der Energietechnik. Proc. 7 Int.Conf. on Electr. Contacts, Paris 1974, 38-45 Mützel, T.: Niederreuther, R.: Kontaktwerkstoffe für Hochleistungsanwendungen.VDE-Bericht 67 (2011) 103-110 Lambert, C.; Cambon, G.: The Influence of Manufacturing Conditions andis however necessary to limit Metalurgical Characteristics on the volume content Electrical Behaviour of the liquid phase materialSilver-Graphiteth Contact Materials. Proc. 9 Int. Conf.on Electr. Contacts,Chicago 1978, 401-406 Vinaricky, E.: Grundsätzliche Untersuchungen zum Abbrand- undSchweißverhalten von Ag/C-Kontaktwerkstoffen. VDE-Fachbericht 47 (1995)159-169 Agte, C.; Vacek, J.: Wolfram und Molybdän. Berlin: Akademie-Verlag 1959 Keil, A.; Meyer, C.-L.: Der Einfluß des Faserverlaufes auf die elektrischeVerschleißfestigkeit von Wolfram-Kontakten. ETZ 72, (1951) 343-346 Slade, P. G.: Electric Contacts for Power Interruption. A Review. Proc. 19 Int.Conf. on Electric Contact Phenom. Nuremberg (Germany) 1998, 239-245 Slade, P. G.: Variations in Contact Resistance Resulting from Oxide Formationand Decomposition in AgW and Ag-WC-C Contacts Passing Steady Currentsfor Long Time Periods. IEEE Trans. Components, Hybrids and Manuf. Technol.CHMT-9,1 (1986) 3-16

As opposed to the liquid phase sintering which has limited use for electricalcontact manufacturingSlade, the Infiltration process as shown on the right side of theschematic has a broad practical range of applicationsP. G. In this process thepowder : Effect of the higher melting component sometimes also as a powder mix witha small amount of the second material is pressed into parts Electric Arc and after sinteringthe porous skeleton is infiltrated with liquid metal of Ambient Air on the second material. TheContactfilling up Resistance of the pores happens through capillary forces. This process reachesafter the infiltration near-theoretical density without subsequent pressing and iswidely used for Ag- Silver, Tungsten and CuSilver-refractory contactsTungsten Contacts. For Ag/W or Ag/WC contacts,controlling the amount or excess on the bottom side of the contact of theinfiltration metal Ag results in contact tips that can be easily attached to theircarriers by resistance weldingJ.Appl. For larger Cu/W contacts additional machining isoften used to obtain the final shape of the contact componentPhys.47, 8 (1976) 3438-3443

===2Lindmayer, M.; Roth, M.: Contact Resistance and Arc-Erosion of W-Ag andWC-Ag. IEEE Trans components, Hybrids and Manuf. Technol.CHMT-2 Gold Based Materials===, 1 (1979) 70-75

Pure Gold is besides Platinum the chemically most stable of all precious metalsLeung, C.-H.; Kim, H.J.In its pure form it is not very suitable for use as a contact material in electromechanical devices because : A Comparison of its tendency to stick Ag/W, Ag/WC and cold-weld at even Ag/Mo Electricallow contact forcesContacts. In addition it is not hard or strong enough to resistmechanical wear and exhibits high materials losses under electrical arcingIEEE Trans. Components, Hybrids, Manuf. Technol.,loads. This limits its use in form of thin electroplated or vacuum deposited layersVol.CHMT-7, 1 (1984) 69-75

For most electrical contact applications gold alloys are usedAllen, S.E. Depending on thealloying metal the melting is performed either under in a reducing atmosphere orin a vacuum; Streicher, E. : The choice Effect of alloying metals depends Microstructure on the intended use of theElectricalresulting contact material. The binary Au alloys with typically <10 wt% th Performance of otherprecious metals such as Pt, Pd, or Ag or non-precious metals like Ni, Co, andCu are the more commonly used ones (Table 2.2). On one hand these alloyadditions improve the mechanical strength and electrical switching propertiesbut on the other hand reduce the electrical conductivity and chemical corrosionresistance (Fig. 2.2) to varying degrees.Under the aspect of reducing the gold content ternary alloys with a gold contentof approximately 70 wt% and additions of Ag and Cu or Ag and Ni resp., forexample AuAg25Cu5 or AuAg20Cu10 are used which exhibit for manyapplications good mechanical stability while at the same time have sufficientresistance against the formation of corrosion layers (Table 2.3). Other ternaryalloys based on the AuAg system are AuAg26Ni3 and AuAg25Pt6. These alloysare mechanically similar to the AuAgCu alloys but have significantly higheroxidation resistance at elevated temperatures (Table 2.4)WC-C Contact Materials.Caused by higher gold prices over the past years the development of alloys withfurther reduced gold content had a high priorityProc. The starting point has been theAuPd system which has continuous solubility of the two components44 IEEE Holm Conf. Besidesthe binary alloy of AuPd40 and the ternary one AuPd35Ag9 other multiplecomponent alloys were developed. These alloys typically have < 50 wt% Au andoften can be solution hardened in order to obtain even higher hardness andtensile strength. They are mostly used in sliding contact applications.Gold alloys are used in the form of welded wire or profile (also called weldtapes),segments, contact rivets, and stampings produced from clad stripmaterials. The selection of the bonding process is based on the cost for thejoining process, and most importantly on the economical aspect of using theleast possible amount of the expensive precious metal componentElectr.Besides being used as switching contacts in relays and pushbuttonsContacts, goldalloys are also applied in the design of connectors as well as sliding contacts forpotentiometers, sensorsArlington, slip ringsVA, and brushes in miniature DC motorsUSA (Table 2.51998)., 276-285

Table 2Haufe, W.; Reichel, W.; Schreiner H.3: Mechanical Properties of Gold and GoldAbbrand verschiedener W/Cu-Sinter-Tränkwerkstoffe an Luft bei hohen Strömen. Z. Metallkd. 63 (1972) 651-Alloys654

Table 2Althaus, B.; Vinaricky, E.1: Commonly Used Grades of GoldDas Abbrandverhalten verschieden hergestellterWolfram-Kupfer-Verbundwerkstoffe im Hochstromlichtbogen.Metall 22 (1968) 697-701

Table 2Gessinger, G.H.; Melton, K.N.2: Physical Properties Burn-off Behaviour of Gold and GoldWCu Contact Materials in anElectric Arc. Powder Metall. Int. 9 (1977) 67-Alloys72

FigMagnusson, M. 2.2:Abbrandverhalten und Rißbildung bei WCu-TränkwerkstoffenInfluence of 1unterschiedlicher Wolframteilchengröße. ETZ-10 atomic% of differentalloying metals on the electrical resistivity of goldA 98 (according to J. O. Linde1977)681-683

FigHeitzinger, F. 2; Kippenberg, H.; Saeger, K.E.; Schröder, K.H.3:Contact Materials forPhase diagramof goldplatinumVacuum Switching Devices. Proc. XVth ISDEIV, Darmstadt 1992, 273-278

FigGrill, R. 2; Müller, F.4:Verbundwerkstoffe auf Wolframbasis fürPhase diagramof goldHochspannungsschaltgeräte. Metall 61 (2007) H. 6, 390-silver393

FigSlade, P. 2: G.5:The Vacuum Interrupter- Theory; Design; and Application. CRCPhase diagramof gold-copperPress, Boca Raton, FL (USA), 2008

FigFrey, P. 2; Klink, N.; Saeger, K.E.6: Phase diagram of goldUntersuchungen zum Abreißstromverhalten vonKontaktwerkstoffen für Vakuumschütze. Metall 38 (1984) 647-nickel651

FigFrey, P. 2; Klink, N.; Michal, R.; Saeger, K.E.7: Phase diagram Metallurgical Aspects of goldContactMaterials for Vacuum Switching Devices. IEEE Trans. Plasma Sc. 17, (1989) 743-cobalt740

FigSlade, P. 2.8:Advances in Material Development for High Power Vacuum InterrupterStrain hardeningth Contacts. Proc.16 Int. Conf. on Electr. Contact Phenom.,of Au by cold workingLoughborough 1992,1-10

FigBehrens, V. 2; Honig, Th.; Kraus, A.; Allen, S.9:Softening Comparison of Au after annealingDifferent Contactth Materials for 0Low Voltage Vacuum Applications. Proc.19 Int. Conf. on Electr.5 hrs after 80%cold workingContact Phenom., Nuremberg 1998, 247-251

FigRolle, S. 2; Lietz, A.; Amft, D.; Hauner, F.10:CuCr Contact Material for Low VoltageStrain hardening ofth Vacuum Contactors. Proc. 20 int. Conf. on Electr. Contact. Phenom. StockholmAuPt10 by cold working2000, 179-186

FigKippenberg, H. 2: CrCu as a Contact Material for Vacuum Interrupters.11:Strain hardeningof AuAg20 by cold workingth Proc.13 Int. Conf. on Electr. Contact Phenom. Lausanne 1986, 140-144

FigHauner, F. 2; Müller, R.; Tiefel, R.12:CuCr für Vakuumschaltgeräte-Strain hardening ofHerstellungsverfahren, Eigenschaften und Anwendung.AuAg30 by cold workingMetall 61 (2007) H. 6, 385-389

Fig. 2.14[[de:Softeningof AuNi5 after annealingfor 0.5 hrs after 80%cold workingKontaktwerkstoffe_für_die_Elektrotechnik]]