Materials Science Forum Vols. 838-839

Abstract: The influence of High-Pressure Torsion (HPT) on texture and superplasticity in an Al-7075 was studied using X-ray diffraction and tensile testing. The alloy was processed by HPT at room temperature under a pressure of 6.0 GPA up to a maximum of 20 turns. The pole figures were measured at mid-radius of the disks after 1, 5, 10 and 20 turns. The results show the presence of a typical torsion texture during HPT, in particular, the C{001}<110> component was found to develop preferentially. With increasing deformation, the A {111}<110> and the C components are reinforced after 5 turns and the texture tends to be random with the presence of a fibre texture near the center. Moreover, the fraction of C components tends to gradually decrease and a fairly isotropic microtexture is apparent after 20 turns. Tensile testing showed the development of excellent superplastic properties in this alloy with elongations up to ~700% when testing at a temperature of 623 K.

Abstract: Method for tensile testing of superplastic materials had been standardized as ISO 20032: 2007, which is based on JIS, Japanese Industrial Standard, H 7501 and H 7505. These standards specify the test specimens of S-and R-types. Recently, the working group organized by Osaka Science and Technology Center, Japan, proposed a revised version of ISO 20032 with several corrections. After systematic review and voting at ISO/TC (Mechanical Testing of Metals) 164/SC2 (Ductility Testing), the second edition of ISO 20032 was published in 2013. Now, a working group has been set for proposing a revised version of JIS corresponding to ISO 20032: 2013. This paper reports the constitution process of these ISO and JIS standards.

Abstract: A heat assisted superplastic dieless drawing process that requires no dies or tools is applied to the drawing of a Zn-22Al and β titanium superplastic alloy for not only circular but also noncircular microtubes such as square, rectangular and noncircular multi core tubes having square inner and rectangular outer cross sections. As a result, the tendency has been to increase the limiting reduction in area with increasing strain rate sensitivity index m value. We successfully fabricate Zn-22Al alloy, AZ31 magnesium, β titanium circular microtubes with outer diameter of 191μm, 890μm and 180μm, respectively. Furthermore, a noncircular micro tube, which has inner square tubes with a 335μm side, and an outer rectangular tube of 533×923μm were fabricated successfully. During the dieless drawing process, the geometrical similarity law in cross section which the tube is drawn while maintaining its initial shape can be satisfied. The smooth surface can be obtained in case of superplastic dieless drawing process without contact situation with dies and tools. Consequently, it is found that the superplastic dieless drawing is effective for the fabrication of circular and noncircular multicore microtubes.

Abstract: Much work has been carried out in understanding the mechanics of superplasticity (SP). Some of the present challenges in SP forming revolve around the use of lower forming temperatures and faster strain rates, which may involve pushing the process boundaries to incorporate “superplastic-like” forming – perhaps also in materials with non-optimized microstructures. For process optimization there is a requirement to be able to model both within the SP and superplastic-like processing window in an integrated way. From a mechanics point of view the presence of high rate sensitivity is often seen as the key factor in controlling SP response. However, changes in phase distribution and grain morphology, or the accumulation of damage (cavitation) may compromise this assumption. The paper will examine the range of validity of some SP constitutive models and how they may be adapted to take into account processing routes that may incorporate superplastic-like and more conventional SP deformation modes.

Abstract: Ultra-fine grained (UFG) and nanostructured metallic materials obtained via severe plastic deformation typically show very high mechanical strength but low tensile ductility, which dramatically limits their practical utility. Significant efforts were made to improve uniaxial tensile ductility of ultra-fine grained and nanostructured metallic materials. The developed strategies can be divided into two main groups. (1) The ‘mechanical’ strategies employ the mechanical characteristics of these materials, such as their work hardening ability and/or strain rate sensitivity. These mechanical characteristics can be varied via changing testing parameters, such as temperature and/or strain rate. (2) The ‘microstructural’ strategies are based on idea of intelligent microstructural design to suppress necking at early stages of plastic deformation thus improving ductility. However, not much attention was paid to the fact, that in metallforming operations, metallic materials are not deformed uniaxially, but have to undergo deformation under complex strain paths. This work aims to demonstrate that despite UFG metallic materials have low tensile ductility, they can show enhanced formability during plastic deformation in complex stress state (such as formability under biaxial stretch, which is sufficient for metalforming operations.

Abstract: A new high-temperature lead-free solder joint which withstands up to 300°C utilizing superplasticity in the Al-Zn eutectoid alloy has been developed to realize SiC power semiconductor devices. The new solid state joining process consists of interfacial cleaning of joints utilizing superplasticity of the Al-Zn-eutectoid alloy at 250°C followed by diffusion bonding between 350 and 390°C. The bonding strength of the new joints exhibits almost the same value at the temperature range from RT to 300°C, above which it decreases slightly with increasing temperature. It is also found that the bonding strength of the new joints is 8 times as high as those of a high-temperature Pb-5wt%Sn-1.5wt%Ag solder and the Al-Zn eutectoid alloy solder without utilizing superplasticity at 250°C. The Al-Zn eutectoid alloy solder joint has shown high reliability in the temperature cycle testing between 50°C and 300°C up to 300 cycles.

Abstract: With its experience in the SPF simulation and tool manufacturing, Aurock completes its offer in the titanium SPF field with the part forming and brings a global support from the conception up to the manufacturing. Aurock proposes tool design, forming strategy and simulation, rapid tool manufacturing made of refractory castable reinforced with metallic fibre and now titanium superplastic forming. To improve its offer, Aurock started from a blank page and developed a specific SPF press to test and assess new heating solutions. One major innovation permits to reduce the heating time using a direct sheet heating. The process becomes anisothermal. This approach avoid time to heat up to 900°C large toolings. The completed offer for titanium SPF parts and successful results on the heating solutions are presented.

Abstract: Superplastic forming (SPF) commonly requires industrial presses with an integrated large furnace able to uniformly heat the tools and the blank. In this work the feasibility to form via SPF an automotive component using a different heating approach was investigated. The heat is localized only where it is really needed embedding electric heating elements directly in the forming tools. Preliminary numerical simulations of the heating phase were aimed at calculating the electrical power and at choosing a suitable positioning of the heating elements. Further forming simulations were run to calculate the pressure profile. SPF experiments were finally conducted and sound components were obtained saving energy costs and using a common industrial press with lower investment costs.

Abstract: Worldwide there is a trend to use diffusion bonding for more and more applications, for example for large scale micro channel heat exchangers and heat sinks. For large scaled parts there is only a limited range of systems commercially available today. One most important criterion for large scale diffusion bonding is a homogeneous load distribution. To achieve this, different concepts can be used, e.g. multiple supports around pressing plates or using very thick pressing plates. In the presentation an overview of bonded examples, made of different materials, is given as well as a detailed description of the used diffusion bonding systems. In addition, the methods for characterization of the systems and bonded parts are included as well.

Abstract: The combination of FSW and SPF processing is one of most attractive fabrication method for the larger structures and integrate substructure to reduce the part count of aircraft assemblies and costs. One purpose of the SPF technology development is to decrease the forming temperature and increase the forming rate, then reduce cost and enhance the efficiency. Maybe FSW could supply another way to achieve this besides reduce the grain size by traditional rolling process. The purpose of this study is to indicate some new results of the superplasticity of weld nugget for the Ti-6Al-4V alloy. It is found that the temperature has no much effects on the superplastic tensile elongation of the weld nugget, and deformation rate has the contrary effects on the superplasticity to the traditional results, the elongation will be higher with the higher deformation rate. The mechanism will be discussed with the analysis of the microstructure by SEM. The tensile properties was tested after SPF process with a 60% strain.