Papers by Keyword: Cryogenic Temperature

Abstract: Aluminum materials are popular materials for research in terms of lightweight construction. How cryogenic forming can be used to increase material utilization in terms of resource efficiency is one of the areas being investigated. Subject of this study are numerical and experimental investigations regarding the formability of the aluminum alloy AA6014-T4 with macro-structured deep drawing tools at cryogenic temperatures. The macro-structure of the deep drawing dies significantly reduces the heat flux between the dies and the blank due to the reduced contact area. For this reason, active cooling or heating of the dies is not required. The process of heat conduction between the tool and the blank, as well as the deep drawing process, is calculated using the FE-method and compared with the experimental investigations. In addition, the induced residual stresses are determined using the hole-drilling method and compared with the computational solution. The presented examination shows an improved deep drawing ratio of the aluminum alloy AA6014-T4 at cryogenic blank temperature without active tool cooling. Additionally, the influence of the blank temperature on the forming regarding the residual stresses in the cups is analyzed and discussed.

Abstract: Since Fe-based amorphous alloys are widely used in magnetic separators, sensors and other fields, it is of practical significance to carry out research on amorphous strips used in this field.The effects of annealing temperature on the soft magnetic properties of Fe_70.43Nb_10.77Si_15.77Cu_2.34B_0.69 amorphous nanostrips with 25 μm and 28 μm thickness prepared by the single roll cold method were investigated at 20 and 300K.Five specimens were annealed at472.12K, 672.12K, 772.12K, 822.12Kand 872.12K, respectively, and their microstructure and magnetic properties were tested viametallographic microscopy, X-ray diffraction, and vibrating specimen magnetometer. At cryogenic temperatureof 20K, specimens annealed at 672,12K exhibited the best magnetic properties, including the coercive forceof8.1265A/m, saturation magnetic induction intensity of1.4351T,and its residual value of 0.2462T. The comparative analysis of experimental results obtained strongly indicates that the soft magnetic properties of the amorphous alloy are significantly improved by the particular annealing treatment.

Abstract: The structure and misorientations of grain boundaries of ultrafine-grained nickel subjected to rolling and forging at liquid nitrogen temperature are studied. It is shown that as a result of rolling in UFG nickel obtained by the ECAP the forming of a band fragmented structure with the formation of special twin boundaries Σ3 is observed. An increase in the strain rate (forging) leads to the appearance of localized deformation bands in which the formation of new small grains is observed through dynamic recrystallization. The development of recrystallization results in increase up to 7% in UFG nickel the fraction of special twin boundaries Σ3 which are similar in nature to annealing twins.

Abstract: This study presents manufacturing cryogenic tanks for aerospace applications. Since most high strength aerospace alloys like titanium alloys and Al-Li alloys exhibit low formability due to low ductility and work hardening, superplastic forming technology is applied to manufacture hemispherical shapes. Superplasticity is the ability of materials to deform plastically to show very large amount of strains. Advantages of superplastic forming technology include its design flexibility, low tooling cost and short leading time to produce. In this study, various manufacturing processes, like superplastic forming, diffusion bonding, laser beam welding and friction stir welding, are applied to manufacture titanium and aluminum cryogenic tanks. Using these technologies in manufacturing process makes the aerospace components lighter and stiffer, with efficient energy and cost saving.

Abstract: By using the material of reinforced polyurethane (RPU) foam, the common bulkhead is devised for cryogenic tanks in this paper. Properties of RPU foam are obtained through experiments. Based on the properties, the structure is designed with the integration of special features including lightweight, easy to manufacture, load bearing and thermal insulation. Based on numerical simulation, thermal analysis, stability and thermal mechanical coupling behavior of the structure are analysed. The results show that the common bulkhead not only satisfies the heat insulation requirements of cryogenic tanks for liquid hydrogen and oxygen, but also keeps stability.

Abstract: Experiments show that high purity titanium (HP-Ti) samples have been successfully processed by equal channel angular pressing (ECAP) using a 120 degree die and a relatively slow ram speed at cryogenic temperature when the HP-Ti rods were trapped with 6061 Al alloy tubes. Optical microscopy (OM) and transmission electron microscopy (TEM) were utilized to investigate the deformed microstructure of the material. Typical microstructures of shear bands and deformation twinning were found in the deformed microstructure of ECAPed HP-Ti. Furthermore, the SAED pattern analysis of the twinning structures revealed that the deformation twinning occurred on {112} planes. Keywords: High purity titanium; ECAP; TEM; Deformation twinning; Cryogenic temperature.

Abstract: Ti-5Al-2.5Sn alloy is widely used in aerospace applications due to its high specific strength, low coefficient of thermal expansion and good corrosion resistance. Presence of interstitial elements in the alloy has some significant effects on its properties. However the high notch toughness and cryogenic ductility attracts the usage of Ti-5Al-2.5Sn for usage at cryogenic temperatures even at 20K. For hydrogen embrittlement studies and for investigating notch sensitivity of Ti-5Al-2.5Sn alloy, the notched and smooth specimens from ELI grade of Ti-5Al-2.5Sn alloy were subjected to LH₂ exposure and tensile test at 20K (-253°C) and at 77K (-196°C). The tensile properties obtained from different specimens were compared and analyzed. Also the notch to smooth tensile strength ratio (NSR) were compared and analysed. The obtained NSR was above unity which confirms the low notch brittleness. The tensile strength values between LH₂ exposed and unexposed specimen at 20K and 77K were compared and it revealed greater compatibility of Ti-5Al-2.5Sn-ELI with liquid hydrogen environment.

Abstract: Austenitic stainless steels are extensively used as structural materials for various aerospace systems. Nitrogen containing stainless steels have special role due to their austenite stabilization tendency down to subzero temperatures, improved strength and resistance to sensitization. Primary processing of nitrogen containing cryogenic grade stainless steel 202 has been carried out through two different melting routes viz. (1). conventional melt route of electric arc furnace (EAF) melting followed by vacuum oxygen decarburization (VOD) & vacuum degassing (VD) and other one through (2). vacuum induction melting (VIM) followed by ESR. Chemical analysis and macrostructure analysis was carried out on the samples drawn from these billets. Homogenization and thermomechanical processing parameters were selected and the same were followed for the ingots made through both the melt routes. Mechanical properties evaluation (including tensile properties at subzero temperature of 77K) and micro structure characterization of the products realised from all the two melt routes were carried out. It is observed that, both the melt routes could result in achieving the required aerospace quality of alloy with respect to the chemical composition, metallurgical and mechanical properties. This paper confirms that any of the melt routes studied herein can be adopted according to availability of the facilities. The process development and characterization of the steels processed by conventional EAF+ VD & VOD and VIM+ESR melt routes is presented in this paper.

Abstract: Ti-6Al-4V alloy is widely used in Aerospace applications owing to its high specific strength, low coefficient of thermal expansion and good corrosion resistance. Presence of interstitial elements in the alloy has some significant effects on its properties. However the poor notch toughness and cryogenic ductility restricts the usage of Ti-6Al-4V for temperatures lower than 77 K (-196 °C). The Extra Lower Interstitial grade alloy was developed in order to improve the notch toughness and cryogenic ductility of the Ti-6Al-4V alloy. In this refined grade, the interstitials, Oxygen and Carbon are controlled to a maximum limit of 0.12% and 0.08% respectively as compared to a maximum of 0.2% and 0.1% of standard Ti-6Al-4V alloy. In this study, the ELI grade of Ti-6Al-4V rods from three different manufacturing sources were subjected to tensile test at liquid hydrogen temperature at 20 K (-253 oC). The tensile properties obtained are compared and analyzed. The obtained ductility at 20 K is observed to have close relation with the chemical composition and interstitial content and compared with the Ti5Al2.5Sn-ELI which is ideally suitable for low temperatures upto 20 K, owing to its single phase HCP structure. A correlation has been made between the ductile properties and microstructure. By close control of chemical composition and mechanical working, Ti6Al4V-ELI can be used for temperatures lower than 77 K (-196 oC), which is otherwise is forbidden. This paper details the test data obtained from three different compositions of Ti6Al4V-ELI at 20 K, which enables the usage of this material for temperatures lower than 77 K (-196 °C) upto 20 K.

Abstract: The aim of this study consists in comparing effects of temperature on various Silicon Carbide power devices. Static and dynamic electrical characteristics have been measured for temperatures from 80K to 525K.