Bulk nanocrystalline steel sample was obtained in laboratory through refining of austenite grains and controlled rolling. Transmission electron microscopy micrographs show that some textures are evolved in the process...Bulk nanocrystalline steel sample was obtained in laboratory through refining of austenite grains and controlled rolling. Transmission electron microscopy micrographs show that some textures are evolved in the process of the treatment and two typical carbides are classified according to their size and location. The tensile strength of the nanocrystalline sample is obviously lower than conventional consideration, and scanning electron microscopy observation shows that the existence of the first type of carbide is considered as the main reason for the failure.展开更多
A series of rare earth bulks with the ultrafine nanocrystalline structure were prepared by applying an 'oxygen-free'(an environmental oxygen concentration less than 0.5 ppm) in-situ synthesis system,where the ...A series of rare earth bulks with the ultrafine nanocrystalline structure were prepared by applying an 'oxygen-free'(an environmental oxygen concentration less than 0.5 ppm) in-situ synthesis system,where the inert-gas condensation was combined with the spark plasma sintering technology into an entirely closed system.The thermal and mechanical properties of the prepared ultrafine nanocrystalline bulks were characterized and compared with those of the raw polycrystalline bulks.It was found that the specific ...展开更多
We perform the high-pressure energy dispersive x-ray diffraction experiments of nickel nanoparticle chain using a synchrotron source under quasi-hydrostatic compression up to 44.7GPa. There is no phase transition over...We perform the high-pressure energy dispersive x-ray diffraction experiments of nickel nanoparticle chain using a synchrotron source under quasi-hydrostatic compression up to 44.7GPa. There is no phase transition over the pressure range. The bulk modulus Ko, the first pressure derivative of bulk modulus K＇0 and the volume Vo are calculated from the pressure-volume data using the Birch-Murnaghan equation of state. A decrease of compressibility is observed, in agreement with the Hall-Perch effect.展开更多
This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduc...This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction （XRD）, respectively. Our results show that the average grain size of samples decreases from about 830 nm to 127 nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.展开更多
基金supported by the NationalNatural Science Foundation of China (No. 50527402)
文摘Bulk nanocrystalline steel sample was obtained in laboratory through refining of austenite grains and controlled rolling. Transmission electron microscopy micrographs show that some textures are evolved in the process of the treatment and two typical carbides are classified according to their size and location. The tensile strength of the nanocrystalline sample is obviously lower than conventional consideration, and scanning electron microscopy observation shows that the existence of the first type of carbide is considered as the main reason for the failure.
基金supported by the National Natural Science Foundation of China (50871001)the Program for New Century Excellent Talents in University (NCET 2006-06-0182)the Doctorate Foundation of Chinese Ministry of Education (20070005010)
文摘A series of rare earth bulks with the ultrafine nanocrystalline structure were prepared by applying an 'oxygen-free'(an environmental oxygen concentration less than 0.5 ppm) in-situ synthesis system,where the inert-gas condensation was combined with the spark plasma sintering technology into an entirely closed system.The thermal and mechanical properties of the prepared ultrafine nanocrystalline bulks were characterized and compared with those of the raw polycrystalline bulks.It was found that the specific ...
文摘We perform the high-pressure energy dispersive x-ray diffraction experiments of nickel nanoparticle chain using a synchrotron source under quasi-hydrostatic compression up to 44.7GPa. There is no phase transition over the pressure range. The bulk modulus Ko, the first pressure derivative of bulk modulus K＇0 and the volume Vo are calculated from the pressure-volume data using the Birch-Murnaghan equation of state. A decrease of compressibility is observed, in agreement with the Hall-Perch effect.
基金supported by the National Natural Science Foundation of China (Grant No 50572067)
文摘This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction （XRD）, respectively. Our results show that the average grain size of samples decreases from about 830 nm to 127 nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.
