The effect 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 AC, in a commercial relay. The addition of graphite to silver-nickel 90/10 reduced the maximum weld strengths with increasing graphite content for fixed arc energy. Material loss due to arc erosion is less for 0.5% graphite addition than for the 1% C addition. This seemed to be a result of the greater arc intensity with increased graphite percentage. The formation of large nickel articles and the oxidation of nickel are the microstructural changes observed near the contact surfaces as a result of the arcing. The graphite addition influenced the extent to which these transformations had occurred.<
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