Practical failure analysis

, Volume 2, Issue 2, pp 41–49 | Cite as

Analysis of high contact resistance in silver impregnated graphite (SIG) contacts

  • B. Vamsi Krishna
  • R. K. Sidhu
Peer Reviewed Articles


Silver impregnated graphite (SIG) contacts are used in high safety applications of railway signaling, traffic signaling, and numerous other applications due to high silver content that eliminates the risk of welding in the presence of graphite. High contact resistance (>200 mΩ) was observed in SIG contacts in a railway signaling operation after a few thousand operations of the relay. The high contact resistance was discovered to be a result of loose dust/foreign particles residing between the two contacts. Silver had been preferentially removed from the contacting surfaces during switching operations by an abrading effect of the dust/foreign particles, leaving only graphite on the contact area. Wear was accentuated by the presence of porosity and low hardness of the contacts, leading to improper interaction between the mating surfaces.


SIG contact materials contact resistance failure analysis contamination 


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Copyright information

© ASM International - The Materials Information Society 2002

Authors and Affiliations

  • B. Vamsi Krishna
    • 1
  • R. K. Sidhu
    • 1
  1. 1.Materials Science & Technology Division, Thapar Centre for Industrial Research and DevelopmentThapar Technology CampusPunjabIndia

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