Papers by Keyword: Vacuum Brazing

Abstract: In this study, one novel WC/Ni flexible cloth coatings were prepared to enhance the abrasion and erosion resistances and meanwhile to accommodate the complicated component surfaces. Neither precipitation of WC particle nor pores or cracks were detected in the coating. The scarification extent of WC particle decreased with the increase in the WC content. With the abrasion mechanism of three body abrasive wear, the WC/Ni coating with 59.8 wt.% WC (WC/Ni-59.8 wt.%) showed the best abrasion resistance with the wear rate of 0.3% of 304 stainless steel. At 30° of impact angle, the WC/Ni-59.8 wt. % exhibited a superior erosion resistance to that of WC coating developed by high velocity oxygen fuel (HVOF). The application potential of WC/Ni flexible cloth coating for the commercial components was testified by developing the coating on a ball valve disc.

Abstract: Process parameters play a crucial role in the final characteristics and properties of every product. The current work focuses mainly on improving the vacuum furnace brazing process for tungsten carbide reinforced Ni-based alloy (NiCrBSi) metallic composite coatings, by establishing the best set of parameters adapted to this specific chemical composition. In order to determine the optimum parameters, a fine adjustment of a typical vacuum brazing process was performed. The melting interval of the filler metal was identified by means of Differential Thermal Analysis. Morphology, microstructure and metallurgical bond of the cladding to the substrate material were investigated by Scanning Electron Microscopy and Light Microscopy combined with a Porosity Analysis Software. The process optimization resolved the initial problem of fractures and crack initiation, making possible to achieve high quality hardfacing coatings with a low degree of porosity (approximately 1 %).

Abstract: The Sirius Project is an initiative of the Brazilian Synchrotron Light Laboratory - LNLS (CNPEM - MCTI), for the design, construction and operation of a new synchrotron radiation source 3rd generation, with high brightness and energy of the electrons of 3.0 GeV. Among many other components there will be built 80 ceramic cameras embedded in special magnets, whose function is to act to correct the orbit of the electron beam in the storage ring. The ceramic chamber is crucial for this application because this material is transparent to the magnetic field generated in the electro magnet and thus acts directly on the electron beam. The difficulty of these constructive components lies in the fact that, the ceramic components must be attached to metal components will join vacuum chambers that make up the ring, and then must present excellent mechanical and vacuum tight. The process of chemical bonding between the ceramic and metal components is performed by brazing in high vacuum. After brazing, a film is deposited of copper with 7 micrometers thickness. The objective of this paper is to describe the process of film deposition and brazing of copper and the excellent results obtained in the production, mechanical characterization, microstructural and tightness.

Abstract: Cu-Cr-Zr-Ti alloy is being used widely in aerospace engines, due to its synergetic combination of high strength and thermal conductivity. Brazing is the preferred process being adopted to realize intricate shapes and complex dimensions. In the present work, Cu-Cr-Zr-Ti alloy was brazed using Cu-Mn-Ni-Sn-Fe base brazing foil. This braze foil exhibits liquidus temperature of ~980°C. Brazing experiments were carried out at 1030°C under high vacuum condition. The effect of varying load (0.5-2 kg) has been studied in the current experiment. Microstructural study of the parent materials and joints were carried out using optical microscope (OM). Lap shear testing (1T configuration) of the brazed joints was evaluated to obtain shear strength values. Also, micro-hardness traverse has been carried out across the brazed joint. Applied load plays a significant role in obtaining defect free braze joint.

Abstract: This paper explains the technique of vacuum brazing for joining Molybdenum and Kovar. Joining of Molybdenum and Kovar is difficult because of difference in their mechanical properties and Melting Points. Kovar is an alloy of Fe, Ni , Co (composition : Ni 29% , Co 17% , rest Iron) . Molybdenum is a refractory material and its joint with Kovar is used for high temperature applications. Various parameters affecting the vacuum brazing process , vacuum furnace and factors affecting joint strength are discussed.Vacuum brazing of Molybdenum and Kovar samples was carried out inside vacuum brazing furnace using Copper a filler material. Vacuum level of furnace hot zone was maintained better than 10^-6 mbar. The joint-strength was evaluated in Universal testing machine with the help of fixtures as per AWS C 3.2 Standard for testing strength of brazed joints. Ram tensile test was conducted. Factors affecting the joint strength of brazed joints like external compressive weight, diffusion of filler material into the parent materials, surface roughness of parent materials, surface flatness have been discussed. Joint strength of 75 MPa is obtained. Failure was found at the brazed joint interface.

Abstract: This work aims at brazing 70 vol.% SiCp/Al composites using Al-15Cu-8.5Si-4Ni-1.5Mg alloy powder as filler metal. The microstructures and shear strengths of the joints made with 70 vol. % SiCp/Al composites at different brazing temperature and different holding time were examined. It is found that the brazing temperature has an apparent effect on the quality of the joints. The sample brazed at 580 °C, with the holding time of 90 min demonstrates the best metallurgical bonding. The joint mainly contains α-phase, flake-like eutectic silicon, small amounts of primary silicon and bright white θ (Al₂Cu) phase. The maximum shear strength of the brazed joint is 49.7MPa, and the fracture surface shows the characteristic of brittle fracture.

Abstract: In order to improve the poor wettability of SiC_p/Al composites, surface modification by copper brush plating and an active Al-base solder containing Cu, Mg and Sn were investigated in this paper. After vacuum brazing, a good soldered joint with high shearing strength of 145.6MPa was succesfully frabricated at 580°C, holding time of 30min. The microstructure of soldered joints was studied by SEM and EDS. The results show that the Cu-plating , as a bridge, could obviously enhance the reaction between the molten solder and composites, the fractography revealed the fracture occurs within the composite, indicating a good adhesion between the solder alloy and the SiC_p/Al composites.

Abstract: Fast-developing such advanced industries as aviation, automotive and power-generation are increasing demand for new engineering materials which could resists such extreme operation conditions as high operating temperature, considerable stresses or operation in fume-affected environment. Highly desirable properties of such materials should include high hardness and strength, corrosion resistance (also when exposed to aggressive fumes) but also, first of all, low density. However such materials also requirements engineering methods to ensure obtain of good sound joints. Results in growing interest in modern engineering materials characterised by increasingly better operational parameters combined with a necessity to obtain joints of such materials representing good operation properties create important research and technological problems of today. These issues include also titanium joints or joints of titanium alloys based on intermetallic compounds. Brazing is one of the basic and sometimes even the only available welding method used for joining the aforesaid materials in production of various systems, heat exchangers and, in case of titanium alloys based on intermetallic compounds, turbine elements and space shuttle plating etc. This article presents the basic physical and chemical properties as well as the brazability of alloys based on intermetallic compounds. The work also describes the principle and mechanisms of diffusion-brazed joint formation as well as reveals the results of metallographic and strength tests involving diffusion-welded joints of TiAl48Cr2Nb2 casting alloy based on TiAl (γ) phase with the use of sandwich-type layers of silver-copper-titanium based filler metal (Ag-63%; Cu-35,5%; Ti-2%). Structural examination was performed by means of light microscopy. Furthermore, the article reveals the results of shear strength tests involving the aforementioned joints. Obtained mechanical test results of TiAl48Cr2Nb2 joints brazed with usage of three/different filler metal alloys ware compared.

Abstract: Aluminum metal matrix composites (Al-MMCs) are new promising materials for aviation, aerospace and automotive industries. However, due to the poor weldability they have very limited applications. In this paper, the authors present the welding achievements of Al-MMCs developed by their scientific research team in recent years. Laser welding, liquid phase impact diffusion welding and vacuum brazing were utilized. Based on analysis of microstructure, good joints can be achieved by using these welding methods.

Abstract: In this study, vacuum brazing of diamond grit was performed using an Ni-10Sn-28Cr alloy in order to examine the interfacial behaviors. In order to study the wettability between diamond grit and the brazing alloy, a graphite was used instead of diamond grit. The contact angle of Ni-10Sn-28Cr alloy and graphite decreased with increasing holding time and temperature. The shear strength between graphite and Ni-10Sn-28Cr filler alloy showed the best value of 29.8 MPa at 1100°C brazing temperature. It was shown that the shear strength was decreased significantly due to the increase of the thickness of brittle reaction layer and interface residual stress, as the brazing temperature increased up to 1200°C. In regards to the thermal stability evaluation of diamond grits, the graphitization of diamond grit was observed to occur at 1300°C brazing temperature after 60 minutes. Beyond 1100°C brazing temperature, diamond grit exhibited ideal setting in the brazing filler alloy, whereas process diamond grit was observed to be fully embedded in the brazing alloy and damaged at 1200°C temperature. The results of interface analysis of the diamond grit joints brazed by the brazing alloy showed that the chromium carbides played an important role in high strength bonding and as the brazing temperature increased, existing angular chromium carbide transformed into acicular chromium carbide.