Physical Vapor Deposition of Nanocrystalline Composites of Ag-Ni for Electrical Contacts in Automotive Industries

Using vapor deposition as a tool, novel coating structures have been developed for low friction coefficient, fretting wear resistant and high temperature stable electrical contacts. Thin films of Ag-Ni nanocrystalline composites between 100 ­and 500-nm thick were deposited by electron beam evaporation onto sputter-cleaned 301 stainless steel substrates. 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 Auger depth pro­filing. The contact properties, such as contact resistance, fric­tion coefficient, fretting wear resistance, and thermal stability of these coatings have been measured. Both the Ag and Ag81Ni19 composite coatings about 500-nm thick passed the 1,000,000 cy­cle fretting wear test. These coatings also showed good high temperature stability during heat-aging at 150 ºC in air, espe­cially the Ag81Ni19 composite coating. This study shows that vapor deposition is a powerful technique which can be used to discover new coating compositions and structures for electrical contact applications.