loads. This limits its use in form of thin electroplated or vacuum deposited layers.
For most electrical contact applications gold alloys are used. Depending on thealloying metal the melting is performed either under in a reducing atmosphere orin a vacuum. The choice of alloying metals depends on the intended use of theresulting contact material. The binary Au alloys with typically <10 wt% 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)''. Caused by higher gold prices over the past years the development of alloys withfurther reduced gold content had a high priority. The starting point has been theAuPd system which has continuous solubility of the two components. 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 component. Besides being used as switching contacts in relays and pushbuttons, goldalloys are also applied in the design of connectors as well as sliding contacts forpotentiometers, sensors, slip rings, and brushes in miniature DC motors''(Table 2.5)''. Table 2.3: Mechanical Properties of Gold and Gold-Alloys Table 2.1: Commonly Used Grades of Gold Table 2.2: Physical Properties of Gold and Gold-Alloys Fig. 2.2:Influence of 1-10 atomic% of differentalloying metals on the electrical resistivity of gold(according to J. O. Linde) Fig. 2.3:Phase diagramof goldplatinum Fig. 2.4:Phase diagramof gold-silver Fig. 2.5:Phase diagramof gold-copper Fig. 2.6: Phase diagram of gold-nickel Fig. 2.7: Phase diagram of gold-cobalt Fig. 2.8:Strain hardeningof Au by cold working Fig. 2.9:Softening of Au after annealingfor 0.5 hrs after 80%cold working Fig. 2.10:Strain hardening ofAuPt10 by cold working Fig. 2.11:Strain hardeningof AuAg20 by cold working Fig. 2.12:Strain hardening ofAuAg30 by cold working Fig. 2.13:Strain hardening of AuNi5by cold working Fig. 2.14:Softeningof AuNi5 after annealingfor 0.5 hrs after 80%cold working Fig. 2.15:Strain hardeningof AuCo5 by cold working Fig. 2.16:Precipitation hardening ofAuCo5 at 400°C hardeningtemperature Fig. 2.17:Strain hardeningof AuAg25Pt6 by cold working Fig. 2.18:Strain hardeningof AuAg26Ni3 by cold working Fig. 2.19:Softeningof AuAg26Ni3 afterannealing for 0.5 hrsafter 80% coldworking Fig. 2.20:Strain hardening ofAuAg25Cu5by cold working Fig. 2.21:Strain hardening ofAuAg20Cu10by cold working Fig. 2.22:Softeningof AuAg20Cu10 afterannealing for 0.5 hrsafter 80% cold working Fig. 2.23:Strain hardening ofAuCu14Pt9Ag4by cold working Fig. 2.24:Precipitationhardening ofAuCu14Pt9Ag4at differenthardeningtemperaturesafter 50%cold working Table 2.4: Contact and Switching Properties of Gold and Gold Alloys Table 2.5Main Articel: Application Examples and Forms of [[Gold and Based Materials| Gold AlloysBased Materials]]
==Platinum Metal Based Materials==
