Effects of Gap Width and Surface Finish on Braze Flow and Strength in Sinter Brazing

Sinter brazing is a widely-used process in the powdered metal industry whereby two parts are metallically bonded together using a filler metal during sintering. This project studied the sinter-braze strength vs. gap width and surface roughness (as a function of density). The project tested braze joints made with SB-107 braze paste, and FC-0208 transverse rupture strength (TRS) bars of varying densities (6.7, 6.9, and 7.1 g/cc) and various gap widths (0.001”, 0.003” and 0.005” [0.0254 mm, 0.762 mm, and 0.127 mm]). The highest braze strength achieved was 8988 lbf [39.98 KN], which occurred when using a 0.003” [0.762 mm] gap width with a 6.9 g/cc base metal, while the next highest strength was 8139 lbf [36.20 KN], which occurred when using a 0.001” [0.0254 mm] gap with a 7.1 g/cc base metal. These results are explained by considering the capillary force of pores in the powdered metal compacts, surface capillary caused by surface roughness of the compacts, and the parallel plate capillary force caused by the gap set in the joint.