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1. chinaXiv:201708.00302 [pdf]

Electronic origin of strain effects on solute stabilities in iron

Subjects: Materials Science >> Metals and Alloys

Nonuniform strain fields might induce the segregation of alloying solutes and ultimately lead to the mechanical performance degradation of body-centered-cubic (bcc) Fe based steels serving in extreme environments, which is worthy of investigation. In this paper, two typical volume conserving strains, shear strain (SS) and normal strain (NS), are proposed to investigate the strain effects on solute stabilities in bcc iron by first-principles calculations. For solutes in each transition metal group, the calculated substitution energy change due to SS exhibits a linear dependence on the valence d radius of the solutes, and the slope decreases in an exponential manner as a function of the absolute difference between the Watson’s electronegativity of iron and the averaged value of each transition metal group. This regularity is attributed to the Pauli repulsion between the solutes and the nearest neighboring Fe ions modulated by the hybridization of valence d bands and concluded to be originated from the characteristics of valence d bonding between the transition-metal solutes and Fe ions under SS. For main-group and post transition-metal solutes, the considerable drop of substitution energy change due to NS is concluded to be originated from the low-energy side shift of the widened valence s and p bands of the solutes. Our results indicate that the stabilities of substitutional solutes in iron under volume-conserving strain directly correlate with the intrinsic properties of the alloying elements, such as the valence d radius and occupancy, having or not having valence s and p bands.

submitted time 2017-08-23 Hits12902Downloads1401 Comment 0

2. chinaXiv:201708.00285 [pdf]

The behaviors of helium atoms in tantalum, rhenium and osmium

Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We present systematic first-principles studies of occupancy, diffusion, and segregation of He atoms, as well as underlying evolution mechanism of He clusters in Ta, Re and Os precipitates to help to understand the effect of alloying solutes on He retention and bubble formation. It is found that single He atom prefers tetrahedral (T) site in Ta and basal octahedral (BO) site in Re and Os. Single He atom prefers the diffusion path from one T site to the closest T site in Ta, and the diffusion path from one BO site to the next BO site passing an octahedral site along $\langle$0001$\rangle$ direction in Re and Os. The diffusion of single He atom in Ta, Re and Os is relatively difficult than that in W. He atoms are energetically favorable to segregate at interstitial sites forming He$_{n}$ clusters in Ta, Re and Os, and form close-packed He monolayer structure between (110) planes in Ta. The binding strength of He$_{n}$ cluster in Ta, Re and Os is relatively small than that in W (W>Os>Re>Ta). Compared with interstitial sites, He atoms are more energetically favorable to aggregate in vacancy cluster forming VacmHen. The binding strength order of VacmHen cluster in the systems obeys W>Os>Re>Ta. We thus expect that the presence of Ta and Re may contribute to reduce He retention and bubble formation in W.

submitted time 2017-08-23 Hits1102Downloads668 Comment 0

3. chinaXiv:201704.00080 [pdf]

Synergistic Optimization of Thermoelectric Performance in P-Type Bi0.48Sb1.52Te3/Graphene Composite

Xie, DW; Xu, JT; Liu, GQ; Liu, Z; Shao, HZ; Tan, XJ; Jiang, J; Jiang, HC
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We report the synergistic optimization of the thermoelectric properties in p-type Bi0.48Sb1.52Te3 by the additional graphene. Highly dense Bi0.48Sb1.52Te3 + graphene (x wt%, x = 0, 0.05, 0.1 and 0.15) composites have been synthesized by zone-melting follo

submitted time 2017-04-06 Hits1018Downloads541 Comment 0

4. chinaXiv:201703.00583 [pdf]

Detection of helium in irradiated Fe9Cr alloys by coincidence Doppler broadening of slow positron annihilation

Xingzhong Cao; Te Zhu; Shuoxue Jin; Peng Kuang; Peng Zhang; Eryang Lu; Yihao Gong; Liping Guo; Baoyi Wang
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

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.

submitted time 2017-03-26 Hits2172Downloads1239 Comment 0

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