Third-body formation by selective transfer in a NiCr/AgPd electrical contact. Consequences on wear and remediation by a barrel tumble finishin

摘要

The work addresses a particular case of interaction between adhesive and abrasive wear in the electrical contact field, characterized by a selective adhesive transfer layer. The system studied is composed of a resistive element (NiCr thin layer) and a contactor (AgPd), forming an angular position sensor lubricated with a standard silicone oil/PTFE grease. The angular position/electrical resistance relationship is disturbed by wear of the NiCr surfaces, enhanced by the formation on the AgPd contactor of a third body enriched in Ni. From a practical point of view, it has been found that this detrimental Ni-selective transfer formation can be controlled by inserting tumble finishing with lamellar alumina powder as the last step of NiCr track manufacturing. Acting like a solid lubricant, alumina clusters of 1-5 mu m in size adhere to NiCr surface giving rise to a delay or cancel of Ni adhesion on the contactor which lead to a significant improvement of electrical behavior of the position sensor.