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WC flexible cloth was fabricated by rolling WC powder that was pre-mixed with a nano-scale binder. BNi-2 braze alloy was used to braze the WC flexible cloth to a workpiece surface in a vacuum to form a compact composite coating. The composite coatings with different percentages of WC (wt.%, 30 %, 50 % and 80 %) have been successfully brazed onto Q345 steel substrate. Microscopic morphology and interfacial structure were characterized in terms of porosity, segregation and the distribution of WC particles. The bonding strength between the coating and the substrate was evaluated by shear test. The results showed that the segregation of WC particles appeared in all three coatings. With the increase of WC content in the coating, the segregation phenomenon was gradually reduced, and the WC particles were more closed. Furthermore, the thickness of the coating and matrix reaction layer was narrower, and more holes were found in the coating. Fracture of the 30 % and 50 % WC coatings was mainly plastic fracture, and the fracture of the 80 % WC coating was mainly brittle fracture accompanied by local plastic fracture. The maximum bonding strength of the coating to the substrate was determined to be 302 MPa.

W–Cu composite and Fe-based powder alloy were brazed with filler metals of Ag–Cu and Cu–Mn–Co alloys in a vacuum furnace. Both of filler metals can join W–Cu composite with Fe-based powder alloy directly in the experiment process. Microstructure, distribution of elements and fracture morphology were observed and analyzed using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) methods, and phase composition of bonding area was analyzed by X-ray diffraction (XRD). The obtained results indicated that the smooth faying surface and dense microstructure of brazed joint were formed and the primary microstructure of brazing seam were, respectively, Ag(Cu) solid solution and Cu(Mn) solid solution, which ensured forming the stable connection of brazed joint. The bending strength of Ag-based and Cu-based brazed joint can, respectively, reach to 317 and 704 MPa, where fracture showed a typical ductile fracture characteristic. The fracture of Cu-based brazed joint located at brazing seam area, and the fracture of Ag-based brazed joint occurred in Fe-based powder alloy side.

Abstract: Tungsten-copper (W-Cu) composite and 1Cr18Ni9 stainless steel were brazed with Ag-28wt%Cu brazing filler metal in a vacuum furnace, via controlling brazing temperature 855–865 °C and holding time 30 min. Microstructure, microhardness, four-point bend strength, element distribution and phase constituents near interface of the brazed joint, were investigated by a series of standard technique. Results indicated that Ag-Cu eutectic phase near W-Cu composite side and the bulk phase near 1Cr18Ni9 steel side were formed in the brazing seam region. Microhardness of the eutectic phase was low, while that of the bulk copper-rich phase was high. Four-point bend strength was as high as 576 MPa, and the fracture occurred at interface near 1Cr18Ni9 steel side. On the brazed interface, Cu and a little W element were transited from W-Cu composite into the brazing seam region, as same as Fe from 1Cr18Ni9 steel. Ag contained in the brazing filler metal was diffused into the W-Cu composite. Element concentration of Ag was high at interface of both two base metals, which was helpful to promote the metallurgical reaction. Phase constituents of the brazed joint were Cu(Ag, Fe), Ag(Cu) and a little of Ag0.7Fe0.3 and FeCu4, formed in the metallurgy of Fe from 1Cr18Ni9 steel and the Ag-Cu brazing filler metal.

Si3N4 ceramics and 304 stainless steelwere joined by the Cu/Ag-Cu/Ti laminated fillermetal. Interfacialmicrostructure of brazed joint and effect of brazing temperature and thickness of Cu foil on mechanical properties were studied in this paper. Research results showed that the interfacial microstructure of the brazed joint might be 304 stainless steel/TiFe2/Ag-Cu eutectic + Cu(s,s)/Cu(s,s)/Cu(s,s) + Ag-Cu eutectic/Cu3Ti + TiN/Si3N4 ceramics. With the increasing of the brazing temperature, four-point bending strength of the brazed joint initially increased, then decreased. The bending strength reached the maximum value of 53MPa at 1153K when the thickness of Cu foil was 500 µm. The bending strength reached the maximum value of 57MPa with 1mmthickness Cu interlayer under the brazing temperature of 1153 K. [ABSTRACT FROM AUTHOR]