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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.

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. [ABSTRACT FROM AUTHOR]

The present paper concentrates on the factors inducing cracking near the Cu/Al vacuum brazing interface using Al-Si brazing alloy. Various analysis and test methods were adopted to analyse the cause of the cracking. Experiment results indicated that two intermetallic compounds layers -- δ phase and θ phase -- were formed near the interface of Cu and brazing seam region. The microhardness of both the two intermetallic compounds phases reached 720 and 510 HM respectively. The brazing seam region consisted mainly of θ phase and α-Al (Cu) solid solution. Si presence had led to obvious zone liquation in the brazing seam region. Stress concentration appeared on the margin and edge region of the joint. The crack initiated on the θ phase layer, and then extended towards the brazing seam region and δ phase layer. The separation in the d phase had an obviously brittle fracture surface. [ABSTRACT FROM AUTHOR]

Dissimilar metals of copper (T2) and aluminium (1035) were brazed by vacuum brazing technology. Microstructure and phase constitution for the Cu/Al vacuum brazing were studied by means of metallography, electron probe microanalyser and X-ray diffraction. Experiment results indicated that an obvious transition layer of copper based solution was formed near the interface of copper and braze metal. The brazing seam zone mainly consists of various solid solutions between many elements and a few intermetallic compounds which are hard and brittle. This is favourable to the enhancing of service performance of the Cu/Al brazed joint. Process parameters of vacuum brazing are: brazing temperature T=425°C, vacuum level=10-3 Pa, holding time t=15 min. [ABSTRACT FROM AUTHOR]