分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-26
摘要： Solution annealed type 316L austenitic stainless steels were irradiated using 2 MeV Fe ions at room temperature. The implanted fluences were 2012 ions/cm2 and 1013 ions/cm2, respectively. Variable mono-energetic positron beam was performed to characterize the evolution of microstructure and irradiation induced defects. Results show that large amount of vacancy defects formed after heavy ion irradiation. In which, some of mono-vacancies might migrate to form small-sized clusters at room temperature. After irradiation, implanted Fe atoms mainly be interstitials atoms, but some Fe atoms might recombine with vacancies due to their high mobility, which could decrease the defect concentration, effectively.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-26
摘要： An element analysis method, coincidence Doppler broadening spectroscopy of slow positron annihilation, was employed to detect helium in ion irradiated Fe9Cr alloys. Spectra with higher peak to background ratio were recorded using a two-HPGe-detector coincidence measuring system. It means that information in the high-momentum area of the spectra can be used to identify helium in metals. This identification is not entirely dependent on the helium concentration in the specimens, but is related to the structure and microscopic arrangement of atoms surrounding the positron annihilation site. The results of Doppler broadening spectroscopy and transmission electron microscopy show that vacancies and dislocations were formed in ion irradiated specimens. Thermal helium desorption spectrometry was performed to obtain the types of He traps.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-26
摘要： Here, we investigated the irradiation defect in reduced activation ferritic/martensitic steels by slow positron beam. Three ion-irradiation experiments were carried out: (i) He2+ irradiation, (ii) H+ irradiation and (iii) He2+ irradiation followed by H+ irradiation, at temperature 450 oC. The presents of vacancy defects, represented by ∆SHe+H parameter, induced by sequential irradiations was larger than the sum of defects, ∆SHe parameter + ∆SH parameter, caused by single He ions and single H ions. The synergistic effect of He and H was confirmed clearly from the perspective of positron annihilation spectroscopy.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-24
Eryang Lu
Xingzhong Cao
Shuoxue Jin
Chunxiong Zhang
Peng Zhang
Liping Guo
Te Zhu
Yihao Gong
Baoyi Wang
摘要： In order to study the microstructural evolution of the He+ irradiated FeCrNi model alloy, 140 keV He+ ions were implanted into the specimen with the fluence of 1015 ions/cm2 at room temperature. Positron Annihilation Spectroscopy was used to characterize the evolution of micro defects during isochronal annealing between 423 K and 873 K. The decrease of the S parameter between 573 K and 623 K has been associated to the annihilation of vacancy clusters, which were not trapped by helium atom. While the decline of the S parameter between 773 K and 823 K in the damage region might be caused by the dissociation of HenVm clusters. The dissociated vacancy clusters were unstable and annihilated rapidly, which decreases the concentration of vacancy defects.
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