2007 Volume 25 Issue 1 Pages 45-50
To improve the quality of a joint composed of metallic micro-structural parts, a novel resistance brazing method called the "two-step resistance brazing method" has been developed. The target application of the two-step resistance brazing is the fabrications of medical devices and micro-machines. In this method, resistance brazing is completed in two steps. The first step is performed with relatively low electric energy input so that the uniformity of the surface contact condition between two parts can be improved due to local melting and subsequent solidification, and so that the optimal energizing condition for the second step of resistance brazing can be determined through the electric current data acquired during the first step. The second step is performed with the determined electric energy input so that brazing filler metal between two parts can be melted adequately.
To prove the efficacy of the two-step resistance brazing method for joining metallic micro-structural parts, type 304 stainless steel wire with a diameter of 100μm was butt-joint brazed with gold and copper brazing filler metal plated individually on each surface of the base metals. The plated filler metals were alloyed due to the Joule's heat, resulting in the formation of an interlayer between the base metals. All the brazed joints which fractured in the base metals but not in the joined region during tension testing had an interlayer of gold-rich alloy including dispersed dendrites, and consequently the tensile strengths ranged from 624 to 707 MPa. The high strength of the brazed joints is caused by the less deterioration of the base metals during the two-step resistance brazing.