Materials Science Forum Vols. 551-552

Abstract: Everything in the universe is a result of their own evolution, in consequence all advanced structural materials are physical objects spatially extended in a permanently cosmic connection with the advanced structural universe. In this context, the nature expansion rate of the universe (ξ u) was obtained in a similar way of super plastic flow in terms of the rate reaction theory, with the strong temperature dependence of strain rate as follow: exp 70( / sec)/ 2.26854593 . 18 1 0 − − = =         −         = = km Mpc s kT c Q H P P P u λ ξ Where, QP = the Planck activation energy of the system at the Planck scale (QP = 1.221x1028eV), λP = Planck length (λP = 1.62x10-35m), c = the speed of light (c = 299 792 458 m/s), (c/λP) = the overall frequency factor, k = the Boltzmann constant (k = 8.617x10-5eV/K), TP = the Planck temperature (TP = 1.010285625x1030K) and H0 = the Hubble constant. On the basis of this mathematical expression and their combination with the Orowan equation, it was obtained the mathematical model to predict the activation energy (Q) that is necessary to the glide cellular dislocations during deformation of the super plastic advanced structural materials. Consequently, in this work the application of this mathematical model for super plastic flow in advanced structural materials and the concept of cellular dislocation are reviewed in order to integrate in a general form the unified interpretation of Hubble flow, plastic flow and super plastic flow [1-3].

Abstract: In this paper uniaxial tensile tests were carried out at temperature range of 650~810°C and initial strain rate range of 10-4~10-1s-1 to evaluate the superplasticity of as-casting aluminum-bronze QAl10-3-1.5 alloy. The superplastic forming technology (SPF) was adopted to produce solid-bearing cages made of aluminum-bronze QAl10-3-1.5 alloy. The results demonstrate that as-casting QAl10-3-1.5 copper alloy shows good superplasticity without prior-treatment. The maximum elongation of 545% is obtained at 790°C and initial strain rate of 1.0×10-2 s-1, while the maximum flow stress is only 12.4MPa. By using superplastic extrusion technology solid-bearing cages used in railway vehicles were obtained. As-extruded cages have good surface quality and the dimensional accuracy satisfies the design standards. Using this technology the production efficiency is greatly enhanced and the manufacturing cost is reduced, especially the expensive copper alloys are saved.

Abstract: The superplasticity of cast copper alloys used for solid cages is studied by tests of tension and compression in this paper. The results show that cast copper alloys exhibited superplasticity without any pretreatment. Cast aluminum bronze is of superplasticity at the temperatures between 750~800°C with the initial strain rate 1×10-2s-1, the elongation being over 260%. Under the condition of superplasticity compression with the strain rate (1.136~9.091)x10-4s-1 at temperatures between 600~650°C, the cast lead brass presents the superplasticity effect with the maximum flow stress under 2MPa.

Abstract: The Superplastically Formed and Diffusion Bonded (SPF/DB) titanium structure in production today for Boeing products, not including engines, are all diffusion bonded using matched metal tooling and are all fabricated using the common 6Al-4V alloy. The matched metal tooling concept presents a challenge in obtaining high quality bonds over large areas where direct tool pressure is being used to place the titanium sheets into contact with each other. This is due to tolerance build-up in the tools and in the titanium sheets that are used to fabricate the components. Also, because the parts are partially formed before bonding begins, material has been pulled away from the bonding area and the thickness in that location is now less than what the tool was designed for which makes achieving a good quality bond even more challenging. Boeing Commercial Airplanes (BCA) is currently advancing the state of the SPF/DB process in several ways. One of these advances is using a different approach for diffusion bonding. The process includes using stop-off between the sheets and diffusion bonding the pack first and then superplastically forming the stiffening features. This generates a component that is very well bonded in the required locations. However, this process also has its challenges. One of these involves how to apply the stop-off material in the proper location using the most cost effective process. Historically, the application method has been silk screening. A new method has been developed for applying the stop-off that eliminates the need for several pieces of equipment that are required for the silk screening process as well as the associated floor space. Another advancement has been in the development of a different titanium alloy for use in SPF/DB structure.

Abstract: Superplastic forming (SPF) is well known in aircraft production of Titanium and Aluminium parts. The process technology is commercially interesting for small quantities. The advantage of low upfront cost for the tooling is quickly lost however in conjunction with the longer cycle times of forming under purest SPF conditions. At given production rates typical for the aircraft industry the technology has an economical advantage over conventional, ambient temperature sheet metal forming processes. Compared to established processes the break-even point is at about 400 to 4000 parts/year, depending on the metal alloy and the geometry. Transfer to high volume production as afforded by automotive production of niche products calls for a modified forming process and an optimisation of the production flow. One alternative for a modified process is called “Hot Gas Pressure Forming” (HGPF). This process is very comparable to SPF, but the applied strain rates are much higher than recommended for SPF. HGPF can be applied in combination with a pre-forming operation done by cold or hot forming. The production line which has to be created to establish a constant production flow of outerbody parts like doors, inner and outer, fenders, bonnet and trunklid, inner and outer and roof for a project with an annual production quantity of ~30 to 40 000 cars has been engineered on the basis of the material’s forming behaviour studies, process investigations, cost analysis studies, etc. The elements of the production line like presses, interstockers, transportation , etc have been defined and placed with the help of a production simulation tool to get the best efficiency combined with suitable flexibility.

Abstract: This paper presents a diffusion bonding technology at vacuum using a high-boiling liquid protection, diethylene glycol dimethyl ether (C6H19O3). After washing in alcohol, the specimens were immersed in diethylene glycol dimethyl ether. Before heating, the vacuum chamber was vacuumized to about 10-1Pa. Then chamber was heated to about 80°C, and held for 20 minute to evaporate the liquid protection in order to make the clean bonding surfaces contact. Metallographic observations of the interface by optical microscope were carried out. The experimental results show that the protections have successfully protected the bonding surfaces from re-oxidation prior to bonding. The metallographs show that the vacancies at the bonding interface bonding at 560°C for 2 hours are obvious and the materials at the interfaces of specimens bonded under the pressure of 5 MPa at 535°C for 2 hours were well joined.

Abstract: Over the last 40 years there have been many papers published showing superplastic properties of metallic materials. However there has been no standardized test available to assess and compare material, and researchers and companies in the field have devised a number of different methods to show superplastic properties. The value of these properties can vary dependent on the test method used. ASTM International (formerly The American Society for Testing and Materials ) has developed a standardized test method for superplastic properties. The standard is intended for all to use as a common platform for testing, evaluating and publishing superplastic properties to a uniform format, useful for both academia and industry. The paper outlines the main points of the standard, including:- The coupon geometry and the method of clamping the coupon in the grips. The furnace and test machine requirements. The testing conditions and the method of pulling the coupon. The analysis of the load and extension data from the test, and the standard presentation of superplastic properties. The basic superplastic properties of stress versus strain for any particular constant strain rate. The method to determine ‘m’, using a step method at a particular strain. Some data is presented showing how the properties of fine grain Ti-6Al-4V titanium alloy are derived and presented using the standard.

Abstract: During a superplastic cycle and part loading/unloading operations, a superplastic tool withstands thermal cycles which affect its life-time, the superplastic cycle time and hence the productivity of the press. A thermal simulation of the tool behavior in superplastic conditions helps to understand which actions could reduce the effects of heat-shields opening/closing and of part loading/unloading on the cooling of the tool and on the heating of the part. Temperature measurements in transitory conditions and in steady-state have been collected on a tool of large dimensions in superplastic conditions of production. The paper will present the correlation between actual measures and simulation in steady state, in slow transitory conditions and in fast transitory conditions.

Abstract: Different geometries of tensile test specimens have been analyzed to get information about the variability of the measured physical quantities during tensile tests in superplastic conditions. A commercial aluminium alloy (AA5083) sheet has been used for the experimentation. The influences of main geometrical parameters on the elongation to failure, the measured stress and other test responses have been investigated using a universal testing machine and a split furnace. A numerical model has been used to better understand deformation phenomena involved in tensile tests.

Abstract: Forming Limit Diagrams (FLD’s) for AA5083 aluminum sheet were established under both Superplastic Forming (SPF) and Quick Plastic Forming (QPF) conditions. SPF conditions consisted of a strain rate of 0.0001/s at 500°C, while QPF conditions consisted of a strain rate of 0.01/s at 450°C. The forming limit diagrams were generated using uniaxial tension, biaxial bulge, and plane strain bulge testing. Forming limits were defined using two criteria: (1) macroscopic fracture and (2) greater than 2% cavitation. Very little difference was observed between the plane strain limits in the SPF and QPF conditions indicating comparable formability between the two processes with a commercial grade AA5083 material.