STUDY OF METAL TRANSFER IN ELECTRICAL CONTACTS BY RADIOACTIVE TRACER METHOD.

The mechanism of metal adhesion and transfer between contacting metals was examined under the condition that the surface film was broken down electrically. Measurements were made on the amount of metal transfer, adhesion force and contact resistance with the crossed-rod contact configuration. The amount of metal transfer was measured by the gamma -counting of transferred **1**9**8Au and **6**4Cu activated by thermal neutron irradiation. Under a 10 g contact load, the amount of metal transfer of Au ranged from 5 multiplied by 10** minus **1**0 to 2 multiplied by 10** minus **5g with increase in current from 0. 1 to 380 A and that of Cu ranged from 2 multiplied by 10** minus **1**1 to 7 multiplied by 10** minus **8g. The contact voltage was estimated from contact resistance and current. The softening voltages of Au and Cu were 50 and 75 A, respectively. The melting voltage of Au was 300 A and that of Cu was not attained with the current up to 380 A. Below the softening voltage, the metal transfer of Au was the same as that above the softening voltage and that of Cu was very small. The surface film influences metal adhesion and transfer. Above the softening voltage, the surface film was broken down completely and the metal transfer increased with contact current irrespective of Au or Cu. The adhesion forces of Au and Cu above the softening voltage coincided satisfactorily with their tensile strengths multiplied by the real contact area. The temperature rise of the contact surfaces due to the Joule heat was estimated from the Vickers hardness at high temperature and contact resistance. Reasonable results were obtained and the self-diffusion caused by this temperature rise was estimated to be small enough compared with metal transfer.