Applications and Analysis of Palladium Vapor Deposited on Stainless Steel for High Temperature Electrical Contacts

Using electron beam evaporation, Pd thin films of 300 nm thickness have been deposited on 301 stainless steel for high temperature electrical contact studies. The structure and composition of the films were studied in detail using x-ray diffraction (XRD), scanning electron microscopy (SEM), elec­tron probe microanalysis (EPMA), and x-ray photoelectron spec­troscopy (XPS) with sputter depth profiling. The contact prop­erties, such as contact resistance, fretting wear resistance, and thermal stability have been measured. The contact resistance re­mains low after heat-aging in air for 168 h at 150 and 200°C, but increases significantly after heat-aging at 340° C. This increase in contact resistance is caused by the formation of about a 27 nm (1 μ in.) thick PdO. In contrast, the thickness of the PdO is too thin to cause measurable contact resistance increases after heat-aging at 150 and 200°C. The fretting wear resistance of Pd coated 301 stainless steel is better than that of electroplated Sn of several thousand nm thickness. Thus, vapor deposited Pd coatings on 301 stainless steel may replace electroplated Sn for electrical contact applications at elevated temperatures.