NiAl中空位的回复行为

用正电子湮没技术研究了金属间化合物ＮｉＡｌ的淬火缺陷和电子辐照缺陷的回复行为。发现高温淬火试样在２８０℃左右和５００℃左右有两个明显的回复阶段。进一步采用嵌入原子法类型的势函数．角分子动力学方法对ＮｉＡｌ中的单、双空位进行了计算机模拟研究．计算了空位三种迁移机制的激活能。结果表明，空位六步跳跃循环运动是能量上有利的迁移机制。实验和计算结果的对照表明：低温回复是由于Ａｌ空位的退火，而高温回复对应于Ｎｉ空位的退火．并且ＮｉＡｌ有序合金中的扩散主要是由于空位的运动而引起的。     

应用正电子湮没技术定量估算高纯铁形变的位错密度和空位浓度

采用慢拉伸与多普勒展宽相结合．研究了单一试样以５×１０－５／ｓ的应变速率拉伸时，高纯铁形变作品５００Ｋ回复前后Ｓ参数随形变量的变化［Ｓ（ε）曲线］。实验结果表明．回复前的Ｓ（ε）曲线包含位错和空位的贡献．回复后仅食位错的贡献。对于同一形变量的样品．５００Ｋ回复后Ｓ参数下降．形变量越大下降量越大．对应空位贡献也越大：根据两态捕获模型计算可得：高纯铁拉伸变形产生空位和位错．空位浓度和位错密度均随形变量的增加而增加．空位浓度ＣＶ的数量级为１０１７－１０１９ｃｍ－３．位错密度ρｄ的数量级为１０９－１０１１ｃｍ－２．     

TiAl金属间化合物的淬火缺陷研究

采用自电子寿命谱技术研究了ＴｉＡｌ以下Ｔｉ３Ａｌ金属间化合物的淬火缺陷及其回复行为，结果表明，充分退火ＴｉＡｌ试样中有一定数量的晶界存在的ＴｉＡｌ合金高温淬火过程中在产生大量空位的同时也产生了一定数量的空位团和空位－杂质原子复合体等二次缺陷，在３００－６００℃的温度范围内，由于这些复合缺陷的分解和迁移，使空位团进一步聚集长大。     

晶体本征空位的填充分数极限：填充方钴矿

本文用密度泛函方法研究了不同杂质在cosb3晶格的本征空位处的掺杂极限或填充分数极限（FFL）。FFL不仅取决于杂质和主原子的相互作用，也取决于杂质原子和一种主原子形成的第二相。预测了Ca、Sr、Ba、La、Ce和Yb原子在CoSb3中的FFL，与报道的实验数据吻合得很好。本文还讨论了杂质原子的FFL与价态和电负性的相关性。     

极性晶体极轴方向负性单空位及空间电子密度分布规律的正电子湮没测试方法研究

本文从理论上研究了极性晶体极轴方向负性单空位及空间电子密度分布规律,并探讨用正电子湮没测试负性单空位及空间电子密度分布的方法。     

金属中空位及空位团的正电子寿命谱

本文从理论上讨论了金属中正电子湮没寿命和金属的空位、空位团的体积的关系,利用密度泛函和交换关联能的局域密度近似,系统地计算了一系列金属中不同空位团的正电子寿命值。可以看出,正电子湮没技术是研究金属微观缺陷结构的有力手段。     

反应堆压力容器钢中溶质元素空位型扩散机理研究

辐照或热老化导致元素偏析和沉淀析出是反应堆压力容器(reactor pressure vessel,RPV)钢性能退化的主要影响因素,点缺陷与合金/杂质元素结合与扩散是引起元素偏析和沉淀析出的主要原因。本文利用分子动力学方法研究了反应堆压力容器钢中几种主要合金/杂质元素(Cu、Ni、Mn、P)的空位型扩散机理。研究了空位与合金/杂质元素的结合性能;基于多频模型计算了合金/杂质元素的空位风参数和扩散系数。通过计算发现,Cu、P与第1近邻、第2近邻空位均具有较大的结合能,Ni与第2近邻空位具有较大的结合能;溶质元素的空位风均随着温度的升高而增大,表明在高温下合金/杂质元素均倾向通过与空位互换位置而扩散。     

钨中空位及其团簇的能量学和动力学性质参数

在总结前人钨中空位及其团簇的能量学和动力学行为的研究成果基础上，采用第一性原理方法系统计算了钨中空位及其团簇的结合能和扩散能垒。研究发现，交换关联泛函PW91和PBE较PBEsol、AM05和LDA更适合用于计算钨空位的能量学性质。基于第一性原理计算结果对文献中单空位形成能、双空位作用性质等争议性问题进行了讨论，并对钨经验势进行了评估。研究结果表明，钨中孤立单空位间总是相互排斥，而空位团簇（V_n>3）对单空位具有很强的吸引作用，其结合能随着所含空位个数增多呈现波动性增大的趋势。空位团簇稳定结构可通过最小化Wigner-Seitz表面积来确定，其结合能与V_n与V_n-1之间的Wigner-Seitz面积之差呈正比。     

一种计算正电子在金属单空位中寿命的简单方法

在Manninen等人的理论计算的基础上,根据无逃逸模型(即正电子被单空位捕获后一般不能逃逸)提出了一种计算正电子在金属单空位中寿命的简单方法。 我们注意到Manninen的理论计算值和实验值偏离较大,认为产生这种偏离的主要原因是他们把均匀电子气中的Brandt公式运用到非均匀电子气中。考虑到正电子的湮没率λ(其倒数为寿命τ)应直接从λ=∫|ψ+(r)|~2n(r)γ(n)dr计算。式中,ψ(r)为正电子波函数,n(r)为电子密度,γ(n)为增强因子。按照无逃逸捕获模型及湮没率和单空位中电子密度的具体形式关系不大的看法,我们对Manninen利用HKS法计算所得的单空位中的正电子波函数作了球Bassel近似,对电子密度作了抛物线近似,同时取增强因子γ(n)≈γ((0)),其中n(0)为r=0处的电子密度。对于简单金属,我们得到如下公式     

不同相结构Cu－Zn合金脱锌腐蚀的正电子寿命研究

测量了α、β、γ、ε四种单相Ｃｕ－Ｚｎ合金脱锌腐蚀前后的正电子寿命谱．发现脱锌腐蚀速率与材料腐蚀过程中产生的非平衡空位的体积百分比有正变关系．进而时Ｃｕ－Ｚｎ合金脱锌腐蚀的微观机理进行了讨论。     

Dynamic structural response of LMFBR head closures to hypothetical core disruptive accidents

Presented here is an investigation of the dynamic structural response of the primary vessel's head closure to a hypothetical core disruptive accident (HCDA). Two head-closure designs were considered: the first represents a loop-type design and the second represents a pool-type design. Using representative configurations of liquid metal fast breeder reactors (LMFBR), independent models were used (1) to derive loading pressure histories and (2) to study the structural response of the head closures. Results for loading pressures, displacement histories, deformed profiles, stress magnitudes and plastically deformed regions are presented.     

纯铝中氢致缺陷的正电子湮没和透射电镜研究

用正电子湮没技术和透射电镜研究了退火和变形纯铝中的氢致缺陷。光学显微镜和透射电镜观察结果表明充氢可以在退火铝中引入气泡、位错等．纯度较低的样品比较容易形成氢致缺陷．说明铝中杂质是氢致缺陷的成核中心。正电子湮没结果表明．随着充氮量的增加．退火铝的平均正电子寿命无显著变化．变形铝的平均正电子湮没寿命有所缩短：这一结果从实验上证实了充入铝中的氢以质子形式填充于缺陷中。屏蔽了缺陷对正电子的吸引或使缺陷内的正电子寿命下降．从而降低了正电子寿命方法对缺陷的敏感性．     

A mechanism for the ease of slip in UO2+x

The microstructure of plastically deformed hyperstoichiometric uranium dioxide crystals has been reexamined by transmission electron microscopy. Although the U₄O₉ phase is present with its usual superlattice structure, dislocations which thread interfaces between it and the adjacent UO₂ phase exhibit uniform contrast, (i.e., no separation into superdislocations is resolved). Dislocations lying totally within the UO₂ phase are decorated by “shadows” of gray contrast, which can be removed by heating in the microscope atmosphere. These have been identified as “atmospheres” of U₄O₉. A geometrical argument, based on the coordinates of anion interstitials published by Willis, is used to explain how these “atmospheres” might account for the observed incidence of extensive cross-slip in plastically deforming UO_2+x.     

Trapping and re-trapping of mobile particles by uniformly distributed non-saturable traps

The trapping and re-trapping of mobile particles by uniformly distributed non-saturable traps in solids have been calculated by solving the steady-state diffusion equation for mobile particles deposited in a thin layer just beneath the surface.As an extension of earlier work on the trapping of mobile particles, in more detail the probability for re-trapping of earlier trapped mobile particles after release from the traps has been calculated. The consequences of trapping and especially of re-trapping as described here have been discussed in view of the application of this theory to Thermal Helium Desorption Spectrometry (THDS) on defects in plastically deformed metals.     

Metallographic studies of fatigue in 20% cold-worked zircaloy-2 containing zirconium hydride

The fatigue behaviour of unhydrided and hydrided 20% cold-worked zircaloy-2 reactor pressure-vessel tubing has been studied for fluctuating tension at room-temperature and 300 °C and for reversed torsion at room-temperature. At room-temperature, high concentrations of zirconium hydride markedly reduce the critical crack length. This effect is attributed to a lowering of the fracture toughness, since hydrides fracture in the path of crack propagation and promote matrix cleavage. At 300 °C, hydride particles constrained by the matrix are plastically deformed without fracturing; the toughness is probably unaffected by the presence of hydride.     

Acoustic emission caused by reversed plastic deformation in polycrystalline graphite

The reversed plastic deformation in polycrystalline graphite grade IG-11 during unloading has been verified using the acoustic emission technique. The change in root mean square (RMS) voltage for continuous acoustic emission was detected as IG-11 graphite was plastically deformed. In Pyroid graphite, the RMS voltage for continuous acoustic emission was unchanged around zero level as long as the graphite was elastically deformed. The shape of plastic strain rate-total strain curve in IG-11 graphite was relatively in good agreement with that of RMS voltage-total strain curve under loading. The cause of continuous acoustic emission was attributed to the plastic deformation for IG-11 graphite. The reversed plastic deformation was shown by using acoustic emission technique during unloading in compressive and tensile tests as we expected. The mechanism of the reversed plastic deformation can be explained using the bicrystal model of polycrystalline graphite. Upon reimposing load, the Kaiser effect is not observed in polycrystalline graphite, which resulted from the reversed plastic deformation.     

Positron annihilation studies on alpha-irradiated and deformed niobium

Positron lifetime and annihilation lineshape measurements have been made to study the defect kinetics and He-vacancy interactions in alpha-irradiated Nb. A comparative study on plastically deformed Nb has also been performed. The isochronal annealing results are discussed with a brief review of previous investigations. Dislocation/vacancy loops annealing occurs above 700°C. Positron trapping rate at He-vacancy clusters is seen to increase with the addition of He atoms to the clusters. Results favour the idea of He-bubble growth by an addition of He atoms or vacancies at intermediate temperatures (350–750°C) and by bubble migration and coalescence at high temperatures (800–900 ° C). Annealing out of He-bubbles/He-vacancy complexes is seen above 900°C.     

强流脉冲电子束轰击对单晶Si表面形貌的影响

用强流脉冲电子束技术对两种取向的单晶Si片进行了表面轰击,对电子束诱发的表面形貌进行了分析.实验结果表明,当能量密度～3 J/cm2时,轰击表面开始形成大量的熔坑.能量密度～4 J/cm2时,表面开始出现微裂纹,微裂纹的形态与单晶Si的晶体取向密切相关;强流脉冲电子束轰击能够诱发表层强烈的塑性变形,[111]取向单晶Si表面出现剪切带结构,而[001]取向单晶Si表面变形结构则以微条带为主;此外,变形区域内还出现大量<100 nm的微孔洞形貌,这些微孔洞的形成为制备表面多孔材料提供了可能.     

Deformed microstructures of two-phase Zr-2.5Nb alloy: Effects of the second phase hardness

Two types, A and B, of Zr-2.5Nb samples were subjected to compression tests. Both samples consisted of similar microstructure - hexagonal closed packed (hcp) α phase (the primary phase) and grain boundary bcc (body centered cubic) β phase. However, the hardness of the β phase differed between the samples - respectively being hard (sample A) and soft (sample B) relative to the primary phase. This difference was caused by the presence of fine ω precipitates. The relative hardness of β phase determined almost all aspects of deformed microstructure developments. In sample A, the primary phase had higher lattice strain and in-grain misorientation developments. In sample B, on the other hand, the softer β phase was clearly linked to more deformation twinning and associated grain size refinement and ‘texturing’ of the hcp α phase.     

Influence of oxygen on the production and recovery of defects in low-temperature deformed zirconium

The production and elimination of defects in high-purity zirconium and in oxygen doped zirconium (750 and 1100 × 10⁻⁶ at.), deformed by torsion at 4.2 K, were investigated by using electrical resistivity measurements. In all types of samples, the resistivity produced by cold-work increases linearly with shear strain. The rate of increase in resistivity is more important in oxygen doped zirconium than in the pure metal (it is multiplied by a factor of about 2.5). This increase in resistivity increment was attributed to an effect of oxygen on the deformation mechanisms. An important fraction of the excess of resistivity produced by deformation in the Zr-O dilute alloys anneals at about 35 K. The amplitude of this recovery stage increases with oxygen content and might be due to the elimination of the supplementary defects induced by oxygen atoms. Several small recovery stages were observed up to room temperature in pure zirconium and the addition of oxygen appears to have little effect on them.