含扭转晶界位错Al金属拉伸强度第一性原理预测

本文基于密度泛函理论第一原理方法,从影响力学性能本质的电子结构计算上,对含Σ 5{001}扭转晶界位错Al金属拉伸强度进行了预测,发现其理论拉伸强度达到8.73 GPa,临界应变为 24%.拉伸强度低于文献报道(Phys. Rev. B 75, 174101 (2007))的倾斜晶界位错Al金属的理论拉伸强度9.5 GPa,但其临界应变却远大于倾斜晶界的16%.本研究结果表明,通过工艺参数控制,改变缺陷形态,可极大地改变其力学性能.进一步地,从电子结构层次上, 分析了含晶界位错Al金属拉伸断裂行为的实质,通过分析电荷密度分布、键长变化等,发现其断裂处发生在晶界处;理论计算结果将对Al金属结构设计及力学性能改善具有重要的指导作用.     

Characterization of dislocation structures in copper single crystals using electron channelling contrast technique in SEM

The dislocation structures induced by low‐plastic‐strain‐amplitude cyclic deformation of [111] multiple‐slip‐oriented Cu single crystals were investigated using electron channelling contrast (ECC) technique in scanning electron microscopy (SEM). At a low plastic strain amplitude γ_pl of 8.8 × 10^–5, the saturated dislocation structure is mainly composed of labyrinth‐like vein structure (or irregular labyrinths), and the cyclic hardening behavior at such a low γ_pl is interpreted as being the result of dislocation multiplication by a Frank‐Read mechanism. As γ_pl increases to 4.0 × 10^–4, the unsaturated dislocation structure exhibits two kinds of distinctive configurations, i.e., dislocation walls and misoriented cells. Interestingly, these misoriented dislocation cells are strictly aligned along the primary slip plane (111), constituting a unique persistent slip band (PSB) structure. Here, these cells are thus called PSB cells. In addition, there is a locally distinctive region comprising some cells having a recrystallization‐like feature in the whole structure of PSB cells. The formation of the structure of PSB cells is discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relative thermoluminescence effects of alpha‐ and beta‐ radiation

Abstract

A study has been made of the relative thermoluminescence response to α- and β-radiation of six phosphors (two types of natural fluorite, CaF₂: Mn, CaF₂: Tb, CaSO₄: Mn and quartz) using samples which are thin compared to the range of the α-particles. The α- and β-radiations induce the same glow peaks, but at low doses (<100 rads) the TL response per rad of α-radiation (3.7 MeV) is less than that per rad of β-radiation in all the glow peaks studied. The α-efficiency ranges from 53 per cent for CaF₂: Mn to 2 per cent for quartz (110°C peak) at 3.7 MeV and decreases with decreasing α-particle energy. At higher doses (10⁶?10⁷ rads) the TL responses to α- and β-radiation become equal within 15 per cent; most of the glow peaks are in or near saturation at these doses. The higher the β-dose at which a peak saturates, the higher is the α-efficiency (at low doses) of that peak. The results support the interpretation that the α-efficiency is low because the phosphor is near or in saturation in the localized region near the α-path. This interpretation is given quantitative support by a theoretical calculation of the localized energy-density.     

Maximum size of bubbles during nucleate boiling in an electric field

By taking account of the electric field effects on the shape of bubbles. Fritz's analysis on maximum bubble volume during boiling was extended to the boiling process in the presence of a uniform electric field. It was found that the maximum bubble volume decreases with increase in electric field strength and the dielectric constant of the boiling liquid. The decrease of bubble departure size with increase in electric field strength was confirmed by experimental observations.     

DSC evaluations in quenched and in cold-rolled Cu-20 at.% Mn alloys

Calorimetric energy measurements associated with the different peaks involved during the linear heating of Cu-20 at.% Mn were performed employing cold-rolled and quenched materials. Unlike the situation in the quenched alloy in which disperse-short-range order (DSRO) is developed, in the deformed alloy such a process is inhibited by the segregation of solute atoms to partial dislocations. This conclusion was drawn by determining the dislocation density in the deformed alloy on the basis of expressions governing the energy release which accompanies the pinning process. After the computed value for the dislocation density had been employed to evaluate the energy evolved during recrystallization, it is verified that this energy does not differ much from the experimentally measured value. The above interpretation of the behaviour exhibited by this alloy is also supported by kinetics and solute balance analyses. After tensile tests performed in the deformed alloy subjected to a low thermal heat treatment at 423 K for 30 min, an increase in 0.2 offset YS (yield stress) of 25 and 21% in UTS (ultimate tensile strength) was achieved, if compared with those values corresponding to the deformed alloy without heat treatment. However, the as quenched alloy subsequently heat treated at 560 K for 30 min exhibits an increase of 10% in 0.2% offset YS, and a very small increment in UTS with respect to the solely quenched alloy condition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal conditions of growth and the necking evolution of Si,GaSb AND GaAs

The configuration of thermal gradient is illustrated for various types of crucible rotation, which is important for the creation of dislocations, which decreases along the grown axis of crystal. A new mechanism for dislocation elimination during the growth is proposed to explain this phenomenon, which provides a good agreement with the experimental results. The concentration of etch pits rapidly decreased from the beginning to the end of the crystals and the dislocation densities in the middle portion of all investigated crystals were found less than 102 cm^-2. The shallow vertical temperature gradients and virtually flat solidification interface prevented thermal stress from their building up in the crystals. As a result, the dislocation formation had random distribution. Using good necking procedures and choosing an appropriately oriented starting crystal with the shoulder angle <38.94° (assuming growth in <111> direction) it is possible to produce almost dislocation-free crystals without resorting to additional doping normally employed to reduce dislocation formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seven basic regimes of steady crystal growth in two dimensions

Using a Markov rate-process model, exact expressions are found for the steady growth rate of an edge of a two-dimensional crystal in terms of the numberM of particles along the edge, the height difference (or number of permanent steps)K along the edge, the nucleation rate , and the speed + of movement of steps. The familiar growth regimes can be identified with asymptotic regimes for the parametersK, (v/)^1/2, andM. From a mathematical viewpoint, there are seven basic regimes, of which the known physical regimes are special cases.     

EDTA和KCl双掺杂下KDP溶液的稳定性研究

研究了EDTA与KCl不同掺杂浓度和不同过饱和比下KDP溶液的成核过程,测定了不同条件下KDP过饱和溶液的诱导期;根据经典成核理论计算了成核热、动力学参数,并分析了溶液稳定性随掺杂浓度的变化情况。利用化学腐蚀法对KDP晶体(100)面进行了腐蚀,得到了清晰的位错蚀坑,并使用光学显微镜观察了(100)面位错蚀坑的分布特点。结果表明,当过饱和度为4%、掺杂浓度为0.01 mol%EDTA和1 mol%KCl时,不仅KDP过饱和溶液的稳定性比较高,而且位错蚀坑的分布比较均匀、密度小,适合高质量的KDP晶体生长。     

钢铁材料中形变诱导相变超细化机理研究

通过计算机编程建立奥氏体相中12[1 1 0]刃位错、奥氏体相中非形变区和形变区奥氏体/铁 素体相界模型.用实空间的连分数方法计算了非形变区和形变区奥氏体/铁素体相界界面能， 计算了碳、氮及微合金元素在完整晶体及位错区引起的环境敏感镶嵌能，进而讨论形变过程 中铁素体形核的难易程度，碳、氮及合金元素在位错区的偏聚及析出与铁素体细化的关系. 计算结果表明：α-Fe易于在高密度位错区（形变带、亚晶界、晶界）形核，在奥氏体形变 过程中，就会大大提高α-Fe形核率，细化铁素体晶粒；碳、氮和微合金元素易于单独或共 同 关键词： 奥氏体/铁素体相界 刃位错 形变 晶粒细化