The effects of graphite additions on the performance of silver-nickel contacts

Silver-nickel 90/10 contacts with 0, 0.5, and 1.0 wt.% graphite additions were evaluated for their electrical switching performance. Powder metallurgically produced sample contacts were subjected to static gap tests, 200-A weld tests, and endurance tests at 100 A, 240 VAC in relays. In the fixed arc energy weld tests the addition of graphite to silver-nickel 90/10 reduced the maximum weld strengths. In the endurance tests, material loss due to arc erosion was less for 0.5% graphite addition than for the 1% graphite addition. This was a result of the increase in arc energy with the addition of graphite under the test conditions. Microstructural changes observed in the arc-affected surface layers included the oxidation and comminution of the nickel, the presence of porosity, and the formation of masses of nickel much larger than the initial particles. The amount of the graphite addition influenced the extent to which these transformations occurred