Papers by Keyword: Diffusion Bonding (DB)

Abstract: The solid-state diffusion bonding processes were successfully carried out to join new Ni-Cr-W superalloys at different temperatures (850°C-950°C), under pressures of 20MPa and holding 45min in a vacuum furnace by taking Cu foil as interlayer. The influence of bonding temperature on the microstructural evolution and the diffusion behavior across the joints was investigated in details. Results indicate that the Ni-Cu solid solutions in the interface lead to a sound bonding interface without any void or impurity. As the temperature increases, the reaction layers become thicker due to the decrease of M23C6 precipitation in the grain boundaries and the rise of atoms diffusion capability. Furthermore, hardness measuremental result also reveals that the increased thickness of reaction layers cannot improve the microhardness of bonding interfaces apparently.

Abstract: Ti/Cu-8Ag/S20C composite were processed by High Press Torsioning(HPT) and the effect of post-HPT heat treatment on the interfacial reaction products and the mechanical performance were studied. Intremetallic compound layer with the thickness of 11 μm was observed at the interface between Ti and Cu-8Ag for the clad heat-treated at 600°Cfor 24hrs. On the other hand, no intermetallic compounds were observed at the Cu-8Ag/S20C interface. No cracks were observed to be emanated from the corner of the indentation mark on the intremetallic compound layer at the Ti/Cu-8Ag interface, suggesting those intermetallic compounds is not so brittle. The stress-strain curves exhibited two steps in as-HPTed clad samples and those heat-treated at 600°C for 24hrs. The careful examination of the fractured plates revealed that S20C plate fractured first and then Ti and Cu-8Ag layers fractured together, suggesting the bonding strength between two layers is fairly high in the presence of intermetallic layer between Ti and Cu-8Ag layers

Abstract: The paper describes a finite element method in 2D and 3D to simulate the super plastic forming of a demonstrator jet engine fan blade made from Titanium alloy sheet. The fan blade is an assembly of three sheets in which a single inner (core) sheet is diffusion bonded to the two outer (skin) sheets at prescribed zones, which is then super-plastically formed to a desired fan profile. In the model, the diffusion bonded zones between the core and skin sheets are simulated using tied interfaces. The thickness of each skin sheet is not uniform and significant change in thickness can occur over a short distance as well as gradually over the entire skin sheet. The thickness of the core sheet which is smaller than the thickness of each skin sheet remains uniform. The paper describes the design for a scaled-down demonstrator fan blade and model build process. Selected results and evaluations of finite element simulations are presented and discussed.

Abstract: Titanium is difficult to fabricate into complex aircraft configurations. There is several elevated temperature forming techniques that are available to produce titanium components for aircraft, two of which will be discussed here: Superplastic Forming (SPF) and hot forming. SPF is used when complex shapes are required, for example, tight radii, and uses a tool that contains the required configuration and seals around the periphery so inert gas pressure can be used to form the material. Since SPF is a process where the material is stretched, the part is not a uniform thickness when completed. A variation of the process combines SPF with diffusion bonding (SPF/DB) of two or more pieces of titanium together to produce integrally stiffened structure containing very few fasteners. The hot forming process uses matched metal tools, offset by the thickness of the starting material, are used to form the part contour at elevated temperature. The required part geometry usually contains no sharp features that have to be formed. Since the material is free to move as the die is closed, the part is fairly uniform in thickness when completed.

Abstract: Principles of fabrication of ultrafine grained bulk and sheet materials for superplastic deformation by the methods of multiple isothermal forging and warm rolling are formulated. New data on superplastic behaviour of commercial alloys, on diffusion bonding of similar and dissimilar materials, and superplastic forming of titanium alloys are presented. The recent application of the diffusion bonding and superplastic forming technology for the production of hollow blades is demonstrated.

Abstract: Plastic deformation of magnesium alloy is limited because of its HCP structure. Though the grain refined magnesium alloy exhibits superplastic deformation at elevated temperature, the strength decreases due to induced cavitation. This study focusses on developing the random texture of magnesium alloy and causes relatively high plastic deformation even at room temperature. Random texture is produced through newly proposed accumulative diffusion bonding process using commercial AZ91 magnesium alloy sheets. Tensile and V-bending tests reveal that the enhanced ductility of the produced magnesium alloy sheet.

Abstract: In most super-plastic forming (SPF) investigations the focus is usually on the material aspects. In this paper the authors develop a model to improve the heat management of SPF. The model presented improved process possibilities. The improved design involves selective application of heat to the material. Final product shape can easily be controlled by accurate temperature control of the work piece. Numerical simulation has been carried out on various components including a ‘top hat shape‘ and a heat exchanger part. Simulation comparisons are made between selective heating and conventional processing, where all of the formed material is at the same temperature, and greater process efficiency of the selective heating approach is demonstrated.

Abstract: In this paper, we proposed a new superplastic forming and diffusion bonding (SPF/DB) structure and processed validation between traditional SPF/DB four sheets structure and the new structure at the coincidence boundary conditions by FEM method. The calculation results show that the new structure can decreases the maximum stress at the joining part by 82% and decreases the maximum displacement at the aerofoil tip by 51% at the cost of the mass increases less than 20%. It induces that the new structure presents better stiffness and greater load carrying capacity than traditional ones, therefore, it could be used in titanium main load-carrying structure especially the structure which has the assembling and lose weight requirement very effectively.

Abstract: Diffusion bonding between the Cu-10%Fe and Al6061 alloys were successfully achieved at various temperatures (450-525°C) in the argon atmosphere. The bonding interface regions were analyzed using scanning electron microscopy and energy dispersive spectrometry and XRD. The presence of Fe particles in Cu was found to have an influence on the kinetics of intermetallic compound layer formation. Cu-Fe/Al 6061 exhibited the slower growth rate of intermetallic layers than Cu/Al 6061 after diffusion bonding. The movement of Cu-Fe/Cu9Al4 interface into Cu-Fe substrate appears to be hindered by the presence of populated Fe-containing particles and filaments. In addition to Cu9Al4, CuAl and CuAl2 intermetallic layers, Al7Cu2Fe and unreacted Fe were observed to be present in the intermetallic layers. The intermetallic layers which are close to Cu such as Cu9Al4 and CuAl were observed to be harder in Cu-10%Fe/Al 6061 than in Cu/Al 6061, suggesting Fe and its intermetallics have some strengthening effect on Cu9Al4 and CuAl.

Abstract: This paper describes joining of bulk MS (mild steel) plates using a domestic microwave oven at a frequency of 2.45 GHz and a power of 900 W. Microwave Hybrid Heating (MHH) is used for joining of MS plate by placing an interlayer of Ni powder of average thickness of about 0.3 mm between two interfacing surfaces. Characterization of the joints has been carried out using X ray diffraction (XRD), SEM (Scanning Electron Microscope), and Vickers micro indentation. The back scattered electron (BSE) image shows complete melting of powder particle yielding diffusion bonding between interfacing powder particles and MS plates The average micro hardness of the joints observed to be 420 ± 30 Hv which is significantly higher than the substrate hardness of 230 ± 10 Hv. The results obtained after performing tensile test show that the joints have an average strength of 250 MPa with a percentage elongation of 6 percent