Papers by Keyword: Compressive Deformation

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Authors: Qing Wei Jiang, Lin Xiao, Xiao Wu Li
Abstract: The temperature-dependent deformation and damage behaviors of ultrafine-grained (UFG) Cu and Ti produced by equal channel angular pressing (ECAP) were investigated and compared. It was found that ECAPed materials with different crystalline structures, e.g. the present fcc Cu and hcp Ti, exhibited significantly distinctive high-temperature deformation and damage characteristics. As the testing temperature is below recrystallization, small- and large-scale cracks or voids formed along the shear bands (SBs) on the surface of UFG Cu, whereas only a few fine shear lines and some non-propagation voids appeared on the surface of UFG Ti. As the temperature is above recrystallization, some small cracks (or voids) formed along grain boundaries and slip deformation took place in many coarsened grains, while only extrusions and intrusions instead of obvious cracks or voids are observable for UFG Ti. The corresponding microstructual changes after compressive deformation, e.g. grain coarsening, were also examined and confirmed by TEM observations.
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Authors: A. Kumao, N. Nakamura, H. Endoh, Y. Okamoto, Mayumi Suzuki
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Authors: Yao Wang, Qing Wei Jiang, Ying Wu, Xiao Wu Li
Abstract: The individual or joint effects of annealing and equal channel angular pressing (ECAP) treatments on the high-temperature compressive deformation and damage behavior of cast LY12 Al alloys were studied. The compressive deformation behavior and surface deformation and damage characteristics of differently treated LY12 Al alloy samples were examined at temperatures ranging from 25°C to 400°C. It is found that the LY12 Al alloy exhibits different compressive mechanical behavior depending on different treatments, and the compressive deformation and damage characteristics of LY12 Al alloys with different microstructural states are closely related with the testing temperature. As compared to other samples (e.g. as-cast, annealed, as-cast+2ECAPed), the sample annealed at 450°C for 3h followed by ECAPed for 2 passages (i.e. annealed+2ECAPed) shows a better high-temperature deformation stability.
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Authors: Wei Min Gan, Ming Yi Zheng, S.B. Li, Kun Wu
Abstract: Compressive deformation behaviors of extruded SiCw/AZ91 were investigated in Gleeble-1500 thermal simulator at temperatures from 743 K to 783 K and strain rates from 6.4×10-2 s-1 to 1.0×101s-1. Results showed that high strain rate sensitivity (~0.5) occurred during compression; deformation activation energy normalized by threshold stress was higher than the lattice self-diffusion activation energy of magnesium. Dynamic recovery (DRV) and dynamic recrystallization (DRX) took place during compression, which refined the grains. The increase of deformation energy was attributed to non-basal planes slip and climbing of dislocations and also the presence of liquid phase.
827
Authors: Ming Yi Zheng, S.W. Xu, Wei Min Gan, Kun Wu, Shigeharu Kamado, Yo Kojima, Heinz Günter Brokmeier
Abstract: An ultrafine-grained (UFG) Mg-5.0wt%Zn-0.9wt%Y-0.2wt%Zr magnesium alloy with a grain size of about 0.8 µm was produced by subjecting the extruded alloy to equal channel angular pressing (ECAP) for 8 passes at 473 K. Compressive testing was performed on the ECAPed alloy in a temperature range from 423 K to 523 K and under strain rates from 1.67×10-3 to 1.67×10-1 s-1. The ultrafine grains of the ECAPed alloy were stable during compression because of the presence of the dispersion of a fine quasicrystal I-phase and of precipitates in the alloy, which restricted grain growth. The activation energy for the compression at the temperature range from 423 K to 523 K is close to the value for grain boundary diffusion in magnesium, indicating that the compressive deformation is mainly controlled by grain-boundary sliding.
287
Authors: Shou Jiang Qu, Jie Cai Han, Song He Meng
Abstract: The compressive properties characterized as a function of the true stress-strain response of the ferritic oxide dispersion strengthened (ODS) alloys, fabricated by mechanical alloying, were examined at strain rates ranging from 0.01 to 0.5s-1. Based on the differential scanning calorimeter (DSC) analysis, the solidus temperature of the ferritic ODS alloys is 1446oC. Therefore, the compressive temperatures were chosen to be from 1050oC to 1300oC. Transmission electron microscopy (TEM) observation is indicative of the homogeneous distribution of the nano-yttria particles with the granularity of 100~200nm, which may exert a strong pinning effect on subgrains. The results indicate that flow stress of the ferritic ODS alloys enhances with decreasing compressive temperature and increasing strain rate. Investigation of the strain rate sensitivity exponent and apparent activation energy of the ferritic ODS alloys has been carried out in detail.
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Authors: S.B. Li, Wei Min Gan, Ming Yi Zheng, Kun Wu
Abstract: Compressive behaviors of SiCw/AZ91composite and AZ91 alloy were investigated at temperatures from 423 K to 723 K and strain rates from 0.002 s-1 to 0.25 s-1. Microstructure evolutions after compressed at 623 K and 0.01 s-1 were observed by SEM and TEM. Results showed that compressive flow stress decreased with the increase of temperature; whiskers were broken and redistributed to the direction normal to the compression direction. At the initial stage of compression, dislocation sliding is the mainly deformation mode for the composite, while for AZ91 alloy, twining was the dominant mechanism.
783
Authors: Philippe Burger, Richard Duclos, Jacques Crampon
567
Authors: Chun Yan Wang, Kun Wu, Ming Yi Zheng
Abstract: The high temperature compressive tests of squeeze casting ZK60 magnesium alloy with temperatures of 573-723K and strain rate in the range of 0.001-1s-1 were performed on Gleeble-1500D thermal simulator testing machine. Optical microscopy was performed to elaborate on the dynamic recrystallization (DRX) grain growth. TEM findings indicate that mechanical twinning, dislocation slip, and dynamic recrystallization are the materials typical deformation features. Variations of flow behavior with deformation temperature as well as strain rate were analyzed. Analysis of the flow behavior and microstructure observations indicated that flow localization was observed at lower temperature and higher strain rates, which should be avoided during mechanical processing. Dynamic recrystallization occurred at higher temperature and moderate strain rates, which improved the ductility of the material. The optimum hot working conditions for ZK60 alloy were suggested.
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