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Abstract

This paper discusses issues related to optimising the technological parameters of the process of brazing gold in a vacuum furnace. An investigation of the brazing process was carried out for materials used in constructing components for aircraft engine fuel systems. The vacuum brazed material was AMS 5510 stainless steel (in the form of plates and pipes). AMS 4787 (BAu-4) was used as the brazing filler. In particular, the influence of the method of preparing the surface on solder spreading and the thickness of the diffusion zone were analysed. The best spreading of solder was obtained for nickel plated surfaces. When the sample surface was more rough or scratched, the effect of the spreading of solder was limited and the diffusion process of the solder into the base material became dominant. Moreover, the influence of the brazing temperature on microstructure changes and on interdiffusion of the AMS 5510 stainless steel/BAu-4 solder system was determined. It was observed that an increase in the brazing temperature modifies the morphology of the formed joint by forming a massive and rounded phase. Furthermore, an increase in the brazing temperature enhances the exchange of components.
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Abstract

Brazing of two dissimilar structural materials; Zircaloy-4 and SS-316L was performed at 900oC under high vacuum conditions. The metallic glass ribbons (Zr55Cu30Al10Ni2Fe3-at. %) of 30 µm thickness, were used as an interlayer. The bonded region was characterized by scanning electron microscope (SEM), energy dispersive spectroscope (EDS) and microhardness testing. The metallurgical bond formation was due to compositional changes in the molten interlayer and later on its subsequent solidification. Assessment of the bonded zone (BZ) revealed three distinct regions (Region-I, Region-II and Region-III). Diffusion transformation was observed in Region-I and Region-III which were interface with base alloys SS-316L and Zircaloy-4 respectively. However, Region-II at the middle of the BZ was composed of isothermally and athermally solidified portions. The highest values of Microhardness were observed in Region-III which was due to the presence of hard phases. Moreover, a crack parallel to BZ was observed in Region-III and was attributed to differential contraction of base alloys during cooling. Maximum shear stress acting on the BZ was calculated and correlated to the brittle phase cracking.
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Abstract

The article summarizes the theoretical knowledge from the field of brazing of graphitic cast iron, especially by means of conventional flame brazing using a filler metal based on CuZn (CuZn40SnSi – brass alloy). The experimental part of the thesis presents the results of performance assessment of brazed joints on other than CuZn basis using silicone (CuSi3Mn1) or aluminium bronze (CuAl10Fe). TIG electrical arc was used as a source of heat to melt these filler materials. The results show satisfactory brazed joints with a CuAl10Fe filler metal, while pre-heating is not necessary, which favours this method greatly while repairing sizeable castings. The technological procedure recommends the use of AC current with an increased frequency and a modified balance between positive and negative electric arc polarity to focus the heat on a filler metal without melting the base material. The suitability of the joint is evaluated on the basis of visual inspection, mechanic and metallographic testing.
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