Authors: Chang Liang Li, Hua Ding, Yong Qing Zhao, Lian Zhou
Abstract: Superplastic forming provides a good way for Ti alloys which are usually difficult to
be deformed. Ti75 alloy with a nominal composition of Ti-3Al-2Mo-2Zr is a newly developed corrosion resistant alloy, with a middle strength and high toughness. In the present paper, superplastic behavior of the alloy was investigated, the microstructural evolution in superplastic deformation was observed and the superplastic deformation mechanisms were analyzed. The results showed that the strain rate sensitivity, m, of the Ti75 alloy was larger than 0.3 and the strain was over 2.0 without surface cracking at 800°C and 5×10-4s-1 in compressive testing.
During the first stage of superplastic deformation, a phase grains became equiaxed, fine and homogeneous due to the recrystallization in a phase and diffusion in b phase. Newly formed equiaxed a grains then could slide and rotate, exhibiting superplastic features. The stress concentration caused by grain sliding of a grains could be released by slip and diffusion in b phase between the a phase grains, which acted as accommodation mechanisms.
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Abstract: Equal Channel Angular Extrusion (ECAE) has become a very popular tool for studying the evolution of microstructure and properties under severe plastic deformation. It is believed that the stress-strain characteristics are uniform in a cross-section of the billet and this uniformity of the stress-strain distribution ensures the uniformity of microstructure and mechanical properties in ECAE processed billet. However, some experimental data such as the fracture of the extruded billet, which is initiated at the inner surface of the sample, has caused doubts about uniformity of stress-strain distribution. This non-uniformity has been proved recently by Finite Element Simulation.
In this paper the studies of the positive role of the applied back-pressure during ECAE are reviewed and the influence of a back-pressure on the uniformity of the stress-strain distribution, strain localisation, die corner filing, and the prevention of fracture is shown. The effect of back-pressure on grain refinement and improvement in mechanical properties is emphasized. The paper summarises our results from over seven years of work using a unique machine for ECAE with computer-controlled back-pressure and velocity of the backward punch.
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Authors: Sabbah Ataya, Marcus Korthäuer, Essam El Magd
Abstract: Copper reinforced by tungsten particles has high potential applications in the fields of
electronics and electric contacts where high strength accompanied with good electrical conductivity is
required. The effects of different scaling parameters (deformed volume, tungsten volume fraction and
the tungsten particle size) affect the force needed for the machining of the W/Cu particle reinforced
composites.
W/Cu composites with different weight percentages of tungsten (80, 70 and 60 wt.%) were tested
under compression loading. Different sizes of the compression specimens were tested; the specimen
diameter DS was varied to be 1, 2, 4, 6 and 8 mm. The effect of the tungsten particle size was varied to
be 10 and 30-m. The compression tests were done at strain rates of 0.1s-1. The experiments were
carried out within a temperature range from 20 °C to 800°C. The mechanically tested specimens were
metallographically investigated to determine the degree of deformation of the tungsten particles in
different specimen geometries.
A clear dependence of the flow stress on the volume of the deformed specimens and the tungsten
volume fraction was found. This size effects were more obvious with increase of the tungsten volume
fraction at lower temperatures. The metallographic investigation was helped to understand the
observed size effect of the composites in relation to the volume fraction and the specimen size
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Authors: Xiao Yu Zhong, Guang Jie Huang, Fang Fang He, Qing Liu
Abstract: Uni-axial tensile plastic deformation behavior of rolled magnesium alloy AZ31B under the temperature range from room temperature(RT) to 250°C with strain rates between 10-3 and 10-1s-1 has been systematically investigated. Microstructure evolution and texture were determined using optical microscopy (OM) and electron back-scattered diffraction (EBSD) techniques, respectively. Our results indicated that the strength and elongation-to-fracture were more sensitive to strain rates at elevated temperature rather than that at room temperature; dynamic recrystallization (DRX) and relaxation of stress at elevated temperature resulted in dramatic change of mechanical properties. Compared with strain rate, the temperature played a more important role in ductility of AZ31B Mg alloy sheet.
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Authors: Xu Dong Zhou, Xiang Ru Liu
Abstract: The researches of non-oriented silicon steel are mainly focused on the effect of main processing parameters on the microstructure and magnetic properties, but there have been few studied about its flow stress until now. In this paper, the non-oriented silicon steel 50A1300 of hot forming is studied by thermal-mechanical simulation method. The hot deformation behavior of the steel is explored and the flow stress model of the steel is established based on the creep mechanism. The model has good accuracy and is feasible.
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