Papers by Keyword: Brazing

Abstract: The phases formed in the wide-gap region brazed with Ni-14Cr-10Co-3.5Al-2.5Ta-2.8B filler metal powder in IN738 superalloy were investigated by electron backscatter diffraction (EBSD). The wide-gap brazing process was carried out in a vacuum of 2×10-5 torr at 1503 K. The region brazed with filler metal powders had a microstructure consisting of two kinds of eutectic colonies, one is Ni solid solution-CrB eutectic and the other is Ni solid solution-Ni3B eutectic. EBSD pattern analysis revealed that the CrB phase had orthorhombic structure with lattice parameters of a=0.297, b=0.786 and c=0.293 nm, and the Ni3B phase had orthorhombic structure with lattice parameters of a=0.439, b=0.522 and c=0.662 nm. The cuboidal-shaped phase precipitated in the Ni solid solution was found to be the γ' (Ni3Al) phase, which had cubic structure with lattice parameter of a=0.357 nm.

Abstract: A new segmented grinding wheel of the brazed monolayer diamond was developed with a defined grains pattern on the wheel surface. Results of grinding zirconia using brazed segmented diamond wheel were presented. The experiment results showed that the grinding forces ratio becomes higher with the increasing of the specific material removal rate and the specific energy falls with the increasing of the maximum undeformed chip thickness during grinding zirconia process. In this investigation, brazed diamond wheels with defined distribution patterns was conditioned by touch-dressing method so that grit tips get micro-conditioned and allow the underlying grits to participate and consequently improve the quality of finish. All the ground surfaces of zirconia were generated by the combined removal modes of brittle and ductile.

Abstract: Plenty of studies on wear mechanism of diamond grains show that the specific failure form of single diamond grit has a close relationship with its load. Monolayer diamond grinding wheels and samples for shearing test are prepared by a high frequency induction brazing technique in this paper. The normal abrasion mechanism of diamond grains has been found through the comparison between the single grain tangential load during grinding and the shearing failure-load of the single grit of the test samples. The result shows that the dynamic strength of diamond grains is relative to the static strength after being brazed. Most of the grains are micro-broken during grinding, and only a few of them are pulled-out or broken-off.

Abstract: This research introduces a review on the advanced fracture mechanics theory called (MN – rp – σθ) theory, and includes the history, the formulation, the predictions, the uses and applications in the different engineering fields.

Abstract: Currently there is an increasing demand for composites and joints composed of hard materials, such as ceramics, superabrasives or metal-carbides, and metals. Wear pads, welded or brazed machining tools or composites employed for grinding tools are typical fields of application. All those various materials solutions have in common that there are interfaces between materials that typically have a covalent or ionic bonding and metals. Consequently, wetting and bonding problems arise. The paper presents different examples and discusses them with emphasize on the corresponding interfacial interactions. Furthermore measures are analysed that can be taken to influence the intensity and strength of the interfacial bonding between the materials to be joined.

Abstract: High purity alumina/stainless steel joints were produced via activated molybdenummanganese (Mo-Mn) route using 72Ag-28Cu solder. Microstructures of the metallized ceramic and joint sections were observed by scanning electron microscopy. Joint strength was tested by shear-loading method. Some process factors were characterized and analyzed, which include temperature, holding time and heating and cooling rate in ceramic metallization process. The effects of Ni plating and succedent annealing were also investigated. Experimental results show that, migration of glassy phases is the main mechanism of the ceramic metallization. Glass migration direction is from metallizing layer to ceramic side. In the ranges of temperature and holding time of metallization, joint strength firstly increases and then falls with temperature raising and time extending. More fully sintered metallizing layer can be obtained while the temperature increases from 1200oC to 1500oC, and the time prolongs from 30min to 60min. Over-sintering of the metallizing layer will take place with metallizing temperature of 1600 oC and overlong holding time of 70min, which reduces the joint strength. The slower heating and cooling rate, and the annealing after Ni plating both help enhance the seal strength, due to relieving or eliminating interlayer residual thermal stress. However, too slow heating and cooling rate, such as 5 oC /min, is equivalent to overlong holding time and finally also decline the strength. A thin Ni coating helps solder wet metallizing surface, and stops solder erode metallizing layer.

Abstract: A Cu brazing sheet has been developed using a Cu-P composite plating method. A Cu-P composite plating layer, which contains 7mass%P, was formed on a Cu plate with a copper sulfate solution including P particles. The melting start temperature of the Cu-P composite layer was determined to be approximately 765°C. Microstructure and joint strength of a brazed joint with the Cu-P composite layer were investigated and compared with those of the joint with a conventional Cu-7P filler foil. As the results of the study, it was clarified that the Cu-P composite layer developed is feasible to use as a brazing material for Cu and Cu alloys.

Abstract: The brazed plate-fin structure is the key component of a compact plate-fin heat exchanger (PFHE). The thermal deformation and residual stresses induced by vacuum brazing may bring negative effects on the quality and the life of the plate-fin structure. Thus it is important to optimize the brazing parameters in order to minimize such effects. This paper presents a three-dimensional finite element analysis for determining the thermal deformation and residual stresses of a three layers of stainless steel plate-fin structure fabricated by nickel-based brazing. The feature of thermal deformation and residual stresses distribution are discussed. The effects of three major factors including brazing temperature, clamping pressure and filler metal on the thermal deformation and residual stresses are investigated respectively.

Abstract: Aircraft engine components are assemblies of several parts that are manufactured using various processes: deep drawing and machining, among others. Deep drawing cannot control accurately wall thicknesses and is performed in numerous steps. Machining parts from solids is less and less cost effective as prices for raw materials increase. Hence, the use of near net shape manufacturing methods is becoming more appealing. An alternative forming process is here investigated: flowforming, process well adapted to axisymmetric parts. The amount of forming steps, welding and machining could be significantly reduced, reducing lead-times and manufacturing costs. Examples are presented for the forming of selected parts (gas generator cases, fan cases and diverter ducts), together with their metallurgical and mechanical properties. Flowforming, however, can only generate shells with some hollow details: most flanges, bosses, stiffeners or weld lips cannot be obtained. Hence, methods of adding material are explored.

Abstract: In this work, the effect of mischmetal (48wt%Ce–27wt%La–14wt%Nd–6wt%Pr) additions on the microstructural characteristics of an Cu-7wt%P brazing filler metal (BCuP-2) were investigated. The volume fraction of primary Cu was considerably increased with increasing mischmetal addition in the BCuP-2. Also, the eutectic structure was changed from lamella to fibrous morphology and the pseudo-eutectic phase (Cu3P) was formed around the primary Cu with the mischmetal addition above 0.03wt%. Compound containing a small amount of mischmetal was formed in the primary Cu phase and this compound acts as the nucleation sites of primary Cu. The fraction of primary Cu was increased by about 1-2wt% due to the mischmetal rich phase. The mischmetal rich phase also formed in the pseudo-eutectic phase and this enhanced the formation of pseudo-eutectic phase. The addition of mischmetal changes the eutectic phase lamella to fibrous by suppressing both the solid-liquid interfacial energy and the surface energy of the solid. The mischmetal additions showed a very strong influence on the nucleation process of primary Cu and the subsequent formation of Cu3P phase as well as the eutectic structure change.