依赖环境的氢化钛相稳定性:第一性原理预测

在充分考虑所有可能的H原子构型的条件下,构建各种TiH_(x)(x=1-2)相结构,并基于第一性原理能量学,计算评估各相的形成能力及其力学和热力学稳定性,进而构建稳定和亚稳TiH_(x)的相稳定性图。结果显示,很多稳定和亚稳TiH_(x)相具有非常接近的形成能,可能同时共存。这些相的相对稳定性强烈依赖于环境温度(T)和氢分压(p(H_(2)))。在整个感兴趣的T和p(H_(2))范围内,只可能存在γ-TiH和γ-TiH_(2)2种稳定相,以及ε-TiH、γ-TiH_(1.5)、ε-TiH_(1.75)、δ-TiH_(1.75)和ε-TiH_(2)5种亚稳相。这些亚稳相均满足力学稳定性,且在热力学上具有不断吸收或释放H,向平衡相γ-TiH_(2)或γ-TiH发生转化的趋势。

Effects of helium irradiation dose and temperature on the damage evolution of Ti3SiC2 ceramic

The effects of 400 keV helium ion irradiation dose and temperature on the microstructure of the Ti3SiC2 ceramic were systematically investigated by grazing incidence x-ray diffraction, scanning electron microscopy, and transmission electron microscopy.The helium irradiation experiments were performed at both room temperature(RT) and 500℃ with a fluence up to 2.0 × 1017 He+/cm2 that resulted in a maximum damage of 9.6 displacements per atom.Our results demonstrate that He irradiations produce a large number of nanometer defects in Ti3SiC2 lattice and then cause the dissociation of Ti3SiC2 to TiC nano-grains with the increasing He fluence.Irradiation induced cell volume swelling of Ti3SiC2 at RT is slightly higher than that at 500℃, suggesting that Ti3SiC2 is more suitable for use in a high temperature environment.The temperature dependence of cell parameter evolution and the aggregation of He bubbles in Ti3SiC2 are different from those in Ti3AlC2.The formation of defects and He bubbles at the projected depth would induce the degradation of mechanical performance.

Description of a new Pratylenchus species from China(Tylenchida,Pratylenchidae)

Pratylenchus ekrami from maize(Zea mays)roots in Shenyang and luffa(Luffa cylindrica)roots in Dalian,China,are described in this paper.Nematodes from the two areas were identified consistently,and were characterized by a heavy cephalic sclerotization,extending posteriorly up to two body annuli,stylet 11−13μm long,elongating conoid tail,and becoming thinner from vulva.Males were not found.Pratylenchus ekrami is close to Pratylenchus vulnus,but the most critical characteristics between the two species were the number of lip annuli,stylet size,and shape of stylet knobs.This species is the first reported in China.

Description of a new Pratylenchus species from China(Tylenchida, Pratylenchidae)

Pratylenchus ekrami from maize （Zea mays） roots in Shenyang and luffa （Luffa cylindrica） roots in Dalian, China, are described in this paper. Nematodes from the two areas were identified consistently, and were characterized by a heavy cephalic sclerotization, extending posteriorly up to two body annuli, stylet 11-13 p.m long, elongating conoid tail, and becoming thinner from vulva. Males were not found. Pratylenchus ekrami is close to Pratylenchus vulnus, but the most critical characteristics between the two species were the number of lip annuli, stylet size, and shape of stylet knobs. This species is the first reported in China.

Microstructure and hardening effect of pure tungsten and ZrO2 strengthened tungsten under carbon ion irradiation at 700℃

Microstructure evolution and hardening effect of pure tungsten and W-1.5%ZrO_(2) alloy under carbon ion irradiation are investigated by using transmission electron microscopy and nano-indentation.Carbon ion irradiation is performed at 700℃ with irradiation damages ranging from 0.25 dpa to 2.0 dpa.The results show that the irradiation defect clusters are mainly in the form of dislocation loop.The size and density of dislocation loops increase with irradiation damages intensifying.The W-1.5%ZrO_(2) alloy has a smaller dislocation loop size than that of pure tungsten.It is proposed that the phase boundaries have the ability to absorb and annihilate defects and the addition of ZrO_(2) phase improves the sink strength for irradiation defects.It is confirmed that the W-1.5% ZrO_(2) alloy shows a smaller change in hardness than the pure tungsten after being irradiated.From the above results,we conclude that the addition of ZrO_(2) into tungsten can significantly reduce the accumulation of irradiated defects and improve the irradiation resistance behaviors of the tungsten materials.

Analytical Bond-order Potential for hcp-Y

The lattice parameters, elastic constants, cohesive energy, structural energy differences, as well as the properties of point defects and planar defects of hexagonal closepacked yttrium （hcpY） have been studied with ab initio density functional theory for constructing an ex tensive database. Based on an analytical bondorder poial scheme, empirical manybody interatomic potential for hcpY has been developed. The model is fitted to some properties of Y, e.g., the lattice parameters, elastic constants, bulk modulus, cohesive energy, vacancy formation energy, and the structural energy differences. The present potential has ability to reproduce defect properties including the selfinterstitial atoms formation energies, vacancy formation energy, divacancy binding energy, as well as the bulk properties and the thermal dynamic properties.

Preliminary assessment of high-entropy alloys for tritium storage

Tritium is the key fuel in nuclear fusion reactors.With the development of the international thermonuclear experimental reactor(ITER)project,the annual requirement of tritium has increased up to several kilograms.The candidate materials for tritium storage have many shortcomings such as insufficient kinetic performance,disproportionation effect,poor oxidation resistance,and poor helium(He)retaining ability.Therefore,it is urgent to develop a novel material system which satisfies all the requirements of tritium storage materials.High-entropy alloys(HEAs)have a unique structure of severe lattice distortion and have attracted much attention as hydrogen storage materials due to their high storing capacity and great hydrogenation performance.The distorted lattice helps to provide more interstitial sites for accommodating H atoms and enhance the He retaining ability by slowing down the He diffusion in the HEA lattice.In this work,the current research status of tritium storage materials,including the background and the basic criterion of tritium storage materials,as well as the disadvantages of the current materials,has been reviewed.Moreover,the theoretical and experimental studies of HEAs,focusing on the hydrogenation properties and the defect evolution in the distorted lattice,have been summarized.The HEAs may have great potential as tritium storage materials due to their potential hydrogenation performance and He retaining ability.Finally,the existing challenges and future development directions are also proposed.