Influence of Core/Shell Nanoparticles on the Fretting Behavior of Gold Coated Electrical Contacts

Abstract A protective coating is usually applied in electrical contacts to prevent corrosion and fretting corrosion and to extend the lifetime of electrical contacts. A gold coating is recommended for applications functioning under very severe operation conditions, such as highly corrosive environments, or where a stable current should be reliably guaranteed even at very low voltage. However, the high price of gold material limits the use of gold coatings. Thus, a method to reduce gold consumption, for example to lower the required gold coating thickness without decreasing the lifetime and performance of the gold coating is of great interest. In this paper, a method to fabricate a novel gold coating co-deposited with nanoparticles with a core/shell structure, i.e. Ag (shell) @ Al 2 O 3 (core), is introduced. The influence of the nanoparticle concentration in the electrolyte and the agitation of the galvanic bath on the lifetime of the nanoparticles co-deposited gold coating is investigated. By co-depositing the Ag @ Al 2 O 3 nanoparticles, the microhardness of the gold coating is increased by around 30% compared to the pure gold coating; however, there is no significant difference in the microhardness among the co-deposited coatings fabricated with the different Ag @ Al 2 O 3 nanoparticle concentration in the electrolyte. The lifetime is also significantly prolonged by nanoparticle co-deposition. A favored nanoparticle concentration in the electrolyte is determined with regard to the topic of lifetime. The gold coatings made of the favored nanoparticle concentration in the electrolyte show a 2.2-fold of the average lifetime of the pure gold coating in the wear and fretting corrosion test. When considering the best lifetime of the nanoparticle co-deposited coating, the value is 4.3-fold of the lifetime of the pure gold coating. By employing a higher bath agitation in the electroplating process, a smoother nanoparticles co-deposited gold coating with fewer pores and finer grains is produced, which improves the average lifetime of the coatings to 3.7-fold of the co-deposited coatings produced under a lower bath agitation, while the standard deviation of the lifetime of the coatings in the wear and fretting corrosion test is decreased. Moreover, the mechanism of lifetime enhancement is discussed.