Welding Characteristics of Ag-W Contacts Under High-Current Conditions

The welding characteristics of Ag-W (65 weight percent W) have been evaluated In a weld-test apparatus at 1000 A, 2000 A, and 3000 A. Two experiments are discussed: a) comparison of the welding characteristics of two different samples of Ag-W contacts and b) changes In the surface structure of the Ag-W contacts and the effect of these changes on the contacts' welding characteristics. It is shown that, in new contacts, the Ag content at the surface Is relatively high (about 5O percent by volume). As the contacts continue to operate at these high currents the Ag Is gradually ejected from both the contact surface and also from the contact's subsurface. This leaves a brittle W-rich surface on top of a weak porous W matrix. The Ag-W contacts are shown to exhibit n higher probability of welding and they also form stronger welds during the first few operations of the weld-test apparatus than they do Inter In the experiments. Indeed, any difference between contact samples is shown to occur during the first 50 operations of the weld-test apparatus.