Research on vacuum brazing of W-Cu composite to stainless steel with Cu-Mn-Co brazing metal

This thesis is a discussion on obtaining a vacuum brazing joint of W-Cu alloy and 18-8 stainless steel with Cu-Mn-Co filler metal under the process parameter of a brazing temperature of 1060 degrees C and holding time of 1 h. Four-point bending strength was tested at room temperature. Microstructure, microhardness, and element distribution near the interface of the brazed seam were observed via micro sclerometer, scanning electron microscope (SEM), and energy disperse spectroscopy (EDS) methods. Finally, analysis of the existence for phase composition near the interface was conducted using X-ray diffraction. Corresponding to a four-point bend strength of 780 MPa, there was a plain-interface, dense microstructure without obvious microdefects that formed. Microhardness values increased near the interface of the brazed joint and decreased gradually to the center of the brazed seam. Element distribution indicated that elements (Cu, Mn, Co) from the filler metal diffused into the interface or even substrates, and Fe and Cu element, together with a little of W element, from the substrates dissolved into the brazed seam region. Fracture morphology of the W-Cu/18-8 steel joint was identified as a mixed feature of fracture type. Moreover, the brazing seam contained mainly a Cu-rich phase, W0.4Cu0.6, alpha-Fe, and simple substance of W, together with a little of Co0.7Fe0.3.