Vacuum heated electroless nickel plated contacts

Electroless nickel plating has been tried on steel or brass substrates. By selected conditions of heat treatment in a high vacuum environment the plating can produce chromium equivalent hardness without the effluents of the hard chromium plating process. The resulting surfaces were examined and characterized under an optical and a scanning electron microscope. X-ray diffraction analysis was also performed to investigate recrystallization effects. The fabricated contact materials were also tested under corrosion conditions and linear polarization measurements were performed. To exploit possible utilization of produced coatings as electrical contact or connector materials, semispherical nickel plated steel joints were tested under the simultaneous application of mechanical fretting and a low-voltage electrical load. Their contact resistance was monitored during 20,000 cycle tests. The results show that after a 2-min heat treatment under 800°C in a high vacuum environment, the plating acquires a crystalline structure with microhardness exceeding 1100 HV and a very good adhesion to the substrate material, without deteriorating its corrosion wear properties. In addition they exhibit a low and stable electrical contact resistance when operating in adverse environments i.e. fretting conditions or corrosive atmosphere.