Effect of the structural state of the brazing alloy on the physical-mechanical properties of brazed joints

In recent years, many applications used as brazing alloys amorphous and microcrystalline (AM) alloys, produced by the methods of rapid (10-10K/sec) solidification of the melt on a spinning drum-cooler. The authors of Ref. 1-4 described composition, certain properties and special features of application of AM-alloys brazing alloys for high-temperature brazing. However, no comparative investigations of the properties of brazed joints, produced using AM and conventional crystalline brazing alloys have been carried out. The aim of this work is the examination of the properties of brazed joints, produced using brazing alloys of the same composition in different initial structural conditions. The investigations were carried out on different brazed joints in copper, steel and also dissimilar materials. The main characteristics of the brazing alloys, brazing conditions and brazed materials are presented in Table 1. The results of preliminary investigations show that the properties of the brazed joints strongly depend on the type of brazing alloy used (powder, paste, rolled strip, etc). In order to eliminate the effect of the given factor, the brazing alloys in the crystalline conditions were used in the form of sheets with the thickness equal to the thickness of AM-strips (40-50 um). For this purpose, sheets of brazing alloy with a thickness of 200-250 um were cut by the electrospark method from crystalline ingots of the alloys, and produced by 6-8 fold remelting of the charge in MIFI-9 furnace in argon. The required thickness (40-50 urn) was obtained by grounding and etching the sheets. Thus, the strips (sheets) of the brazing alloys in different structural conditions were characterised by the same mass and thickness. The brazing of the specimens in the conditions, presented in Table 1, was carried out in a vacuum with a residual pressure not lower than 10~ Pa in SShV-type furnaces. The properties of the brazed joints were investigated by metallographic and x-ray spectrum microanalysis and mechanical tests. The experimental results show that when using the brazing alloys in different initial structural conditions it is possible to produce brazed joints with greatly differing microstructure and distribution of the elements in the brazing zone. In the brazed joints, produced using AM-brazing alloys, there was a small number of intermetallic compounds and other brittle phases as a result of extensive diffusion of the alloying component of the brazing alloys (P, B, Si) into the parent metal. As an example, Fig. 1 shows the microstructure of the brazed joints BrKhTsrBrKhTsr, produced using CTEMET 1101 brazing alloy in the amorphous and crystalline conditions. The distribution of the elements in the brazing zone was investigated using a WDX-3PC spectrometer (Microspec). The distribution of phosphorus in the cross-section of the brazed joints of the given type is presented in