Investigation of the microstructure and properties of W75-Cu/W55-Cu brazed joint with Cu-Mn-Co filler metal

Abstract W75-Cu and W55-Cu alloys were brazed with a Cu-based filler metal under the process parameters of a brazing temperature of 1060°C and a holding time of 30 min in a vacuum furnace with a vacuum level >6×10 ^-3 Pa. The microstructure, element distribution, phase constituents, four-point bending strength, and fracture morphology of the brazed joint were studied with a series of standard methods. The results indicated that the main microstructure of the brazing seam region was a Cu-based solid solution of Mn and Co dissolved in the Cu phase. The element Cu and a little element W from two sides of the base metals transited into the brazing seam region, and the elements Cu, Mn, and Co contained in the brazing filler metal diffused into the interface or even substrates. The main phases that existed in the brazed joint were Cu-rich phase Cu(Mn,Co), simple substance of W, simple substance of Cu, and trace amounts of Cu _0.4 W _0.6 . The four-point bending strength was about 950 MPa, and fracture occurred at the interface near the W75-Cu alloy side. The fracture morphology of the W75-Cu/W55-Cu brazed joint was identified as mixed ductile-brittle.