Papers by Keyword: Brazing

Abstract: The research followed the development of deep joint brazing joints with economic efficient materials between the reinforcement, made from sintered wolfram carbide, and the support, drill bit made from low alloy steel with chromium, from the earthmoving equipment. The brazing procedure selected is heating until the semi-products of the addition materials reach melting temperature, with oxyacetylene flame slightly carburized. The pressure of reducing manufacturing costs for drill bits highlighted the need to replace brazing alloys Ag156 according to SR EN ISO 17672 with coated rods type VIAg140R, which are less expensive and successively deposit two layers in one melt, one buffer layer and a filler layer. The buffer layer has a high moistening capacity of sintered wolfram carbides; it contains Ag156 that comes from the coat of the covered rods, in which it participates with up to 10%. The filler layer of the brazed joint is made out of Ag140. The global chemical composition of the deposited metal with VIAg140R complies with prescriptions SR EN ISO 17672 for Ag140. Metallographic analysis and sclerometric tries of specific area of the brazed joints did not highlight any embrittlement imperfections, which lead to the possibility of suggesting the new technology for brazing and extending it to a large number of similar joints

Abstract: The purpose of this investigation is concentrated on brazing Inconel 600 (IN-600) using pure Cu and Cu-6Sn (wt%) filler foils in order to replace the current plate heat exchanger made by austenitic stainless steel. Both Cu and Cu-6Sn brazed joints consist of interfacial chromium carbides in the Cu/Ni-rich matrix. The application of Cu-6Sn filler foil to braze IN-600 alloy demonstrates average shear strengths of above 300 MPa, which is much better than those of Cu brazed ones (217 ~ 290 MPa). Ductile dimple fracture is observed from all fractographs of Cu-6Sn brazed joints after shear tests. Because the brazing temperature of Cu-6Sn filler is lower than pure Cu, dissolution of IN-600 substrate into the brazed joint is significantly decreased. Isothermal solidification of Cu-6Sn brazed joint becomes less prominent than that of Cu brazed one. Better Cu-6Sn brazed joint is obtained due to less isothermal solidification defects in the joint. The Cu-6Sn filler foil shows great potential in brazing the IN-600 plate heat exchanger for industrial application.

Abstract: The purpose of this investigation is focused on brazing Inconel 600 alloy using the nickel-based VZ-2150 filler foil for advanced plate heat exchanger application. Based on SEM microstructural observations and WDS chemical analysis results, both the amount and shape of precipitates in the brazed joint are changed with brazing parameters. With increasing the brazing temperature and/or time results in depletion of the boron from the joint into the grain boundary of base metal. The amount of boride in the joint is greatly decreased, and continuous grain boundary boride will dominate the entire brazed joint. However, the continuous grain boundary boride cannot be completely eliminated by increasing the brazing temperature and/or time.

Abstract: Solid-liquid interactions in metal-ceramic systems are extremely important in high temperature brazing processes. These interfacial phenomena are reviewed here, from both the thermodynamic and microstructural viewpoints. At high temperature, the wetting characteristics and the adhesion properties of the joints are strongly related to the high atomic mobility of the different phases, giving rise to different phenomena, ranging from the dissolution of the ceramic in the liquid phase, reactions, formation of new phases and reprecipitation at the solid-liquid interface. The role phase diagrams in guiding the choice of the filler alloys composition and to optimize the brazing procedures is emphasized. In particular, it is shown that the computation of new diagrams and the critical use of the existing ones is essential to understand how to suppress the substrate dissolution and to interpret the evolution of the system. Experimental data are presented and discussed concerning the interactions between liquid metals with early-transition-metal diborides (TiB₂, ZrB₂, HfB₂) as a typical example involving the joining of Ultra-High Temperature Ceramics (UHTCs). Overall, these studies represent the basic step linking the chemical and structural information to the design of industrial processes involving a liquid phase at high temperature, such as the production of metal-ceramic joints or composite materials to be used in highly demanding applications.

Abstract: This paper investigated the effect of Si addition on intergranular corrosion susceptibility for brazed Al–Mn–Cu alloy. Water-quenched samples have no intergranular corrosion (IGC) susceptibility, however, slowly cooled samples have IGC susceptibility. This implies that IGC susceptibility was caused by precipitation during cooling. In addition, IGC susceptibility depends on Si content. Low Si additive alloy has high IGC susceptibility. This is because the Mn/Cu depleted zone is formed near the grain boundary due to preferential precipitation of Mn-bearing compound and CuAl₂ on the grain boundary. Conversely, optimum Si addition inhibits IGC due to the absence of preferential precipitation on the grain boundary. The excess Si alloy has high IGC susceptibility as the Si depleted zone is formed around the grain boundary due to the preferential precipitation of coarse Si particles on the grain boundary.

Abstract: The work formulates a particular problem on redistribution of an active element from brazing alloy into brazed materials with due account for thermodiffusion effect. The analysis of the solution has demonstrated that thermodiffusion can facilitate the acceleration of mass transfer from brazing alloy into brazed materials and cause the accumulation of components in the vicinity of contact boundaries.

Abstract: The productivity of large scale process manufacturing, of mill cutters for removing the asphalt, is significantly influenced by the deep joint brazing process, by wolfram cable stiffeners sintered in supports made of low alloy steel with chromium. Unanimously accepted solutions of brazing in oven with controlled conditions or in CIF, requires brazing material in shape of pastille having well defined properties of deoxidiser of basic materials, of lifting and complete filling through capillarity of brazing joint and of assurance a good resistance to thermo-mechanical fatigue. The experiments made in CIF with economical materials type Ag140+Ag156+Cu-Sn-Si, in couple with boron-fluorine flows, have underlined a good behaviour to brazing and complete joints filling characteristics. These materials can easily be done by powder technology. The shape and position of the inductor, corroborate with heating-cooling parameters of the brazing assembly, ensure a good resistance to thermal shock of stiffeners made of sintered carbides. Metallographic analysis and hardness tests have revealed structures with defects like: decarburization, oxidizing corrosion and white spot, in the limit allowed by the product norms.

Abstract: The Al-based amorphous ribbons were prepared by the copper roller melt spinning method, and then the laser brazing was carried out between aluminum alloy and aluminum alloy. Subsequently, the Micro Vickers Hardness Tester, Metallographic Microscope, Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were used to characterize the hardness, morphology, micro structure and composition distribution of the welded joints respectively, so as to analyze the structural characteristic, performance characteristic and binding effect of the matrix metal joints. The results indicate that the prepared Al-based amorphous ribbon is of amorphous structure, the soldering point between aluminum alloy and aluminum alloy is well-connected and the joint’s hardness is identical to that of the base metal. The connection between the metal sheets can be achieved by using Al-based amorphous ribbon as solder, which could provide concrete references for the development and application of amorphous brazing in various fields.

Abstract: Brazing is extensively used in liquid rocket engines for realizing various subsystems. In the case of cryogenic engines, brazing operation is done to realize the gas generator. Gas Generator is one of the major systems of cryogenic engine. It generates and supplies hot gases required for running turbine of main turbo pump. This uses liquid oxygen and gaseous hydrogen as propellant combination. Combustion chamber of Gas Generator is of double walled construction with the cylindrical outer shell of transition class ICSS-0716-301 austenitic-martensitic stainless steel and inner shell of ICSS-1218 321, aTi stabilized austenitic stainless steel material brazed together with Fe-Ni-Mn type braze alloy at a temperature of 1180°C. This temperature can cause the grain growth and related issues to the base material. Thus the present work focuses on the effect of the brazing/thermal cycle on mechanical properties and microstructure of the base materials in post braze condition. The results obtained on metallurgical/mechanical behavior of the material showed the different grain growth patterns in inner and outer shell materials. This helped in understanding the effect of brazing condition on the changes in mechanical properties of base materials.

Abstract: The temperature and concentration dependences of kinematic viscosity of alloys of Cu-Ag system with Ag content to 99 mass % in liquid state have been studied. It has been found that heating above certain critical temperatures leads to transform the melt to equilibrium state. The kinematic viscosity of the Cu-Ag melts are extremely depend from silver content in the alloy. The new regime of amorphous ribbon production is selected. Proposed regime leads to increasing of microhardness and weld strength on 10 % and corrosion resistivity on 15 %.