A contact material used in electrical devices such as relays and magnetic switches, and circuit breakers is often made from an Ag including additives for improving its contact qualities, namely, wear resistance, welding resistance, and contact resistance.
A typical additive to the Ag, for example, is metal oxide. In particular, an Ag-CdO contact material has low contact resistance, good welding resistance, and good wear resistance; however, it is environmentally unsafe since it contains Cd, a highly toxic metal. Another example for metal oxide added to the Ag is SnO.sub.2. An Ag-SnO.sub.2 contact material has excellent welding resistance and good wear resistance, but the contact material has, unfortunately, high contact resistance.
Instead of these metal oxides, it has been proposed to add W (tungsten) to the Ag. As a result, an Ag-W contact material has excellent welding resistance, but the contact material has, unfortunately, poor wear resistance and high contact resistance. Moreover, it has been known that the addition of Ni to the Ag improves electrical conductivity of an Ag base contact material and working ability, in processing a contact material into contact wires or rivets, thereof. Yet, only a problem is that an Ag-Ni contact material has poor welding resistance compared with those of the Ag-metal oxide contact materials. Therefore, in order to improve the welding resistance of the Ag-Ni contact material, various additives have been added to the Ag-Ni contact material individually or as a combination of the additives.
These additives are disclosed in the following publication listed below.