Mobility of interstitial clusters in alpha-zirconium

Clusters of self-interstitial atoms (SIAs) formed in displacement cascades in metals irradiated with energetic particles play an important role in microstructure evolution under irradiation. They have been studied in the fcc and bcc metals by atomic-scale computer simulation, and in this article, we present the results of a similar study in a hexagonal close-packed (hcp) crystal. Static and dynamic properties of clusters of up to 30 SIAs were studied using a many-body Finnis-Sinclair type interatomic potential for Zr. The results show a qualitative similarity of some properties of clusters to those for cubic metals. In particular, all clusters larger than four SIAs exhibit fast thermally activated one-dimensional (1-D) glide, which is in a <1120> direction in the hcp lattice. Due to the structure of the hcp lattice, this mechanism leads to two-dimensional mass transport in basal planes. Some clusters exhibit behavior peculiar to the hcp structure, for they can migrate two-dimensionally (2-D) in the basal plane. The jump frequency, activation energy, and correlation factors of clusters have been estimated, and comparisons drawn between the behavior of SIA clusters in different structures. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Processing map for hot working of alpha-zirconium

The hot deformation characteristics of alpha-zirconium in the temperature range of 650 °C to 850 °C and in the strain-rate range of 10_-3 to 10² s^-1 are studied with the help of a power dissipation map developed on the basis of the Dynamic Materials Model.[7,8,9] The processing map describes the variation of the efficiency of power dissipation (η =2m/m + 1) calculated on the basis of the strain-rate sensitivity parameter (m), which partitions power dissipation between thermal and microstructural means. The processing map reveals a domain of dynamic recrystallization in the range of 730 °C to 850 °C and 10⁻² to 1⁻¹ with its peak efficiency of 40 pct at 800 °C and 0.1 s^-1 which may be considered as optimum hot-working parameters. The characteristics of dynamic recrystallization are similar to those of static recrystallization regarding the sigmoidal variation of grain size (or hardness) with temperature, although the dynamic recrystallization temperature is much higher. When deformed at 650 °C and 10^-3 s^-1 texture-induced dynamic recovery occurred, while at strain rates higher than 1 s^-1, alpha-zirconium exhibits microstructural instabilities in the form of localized shear bands which are to be avoided in processing. Formerly Divisional Head, Physical Metallurgy Division, Bhabha Atomic Research Centre.     

Fatigue life and twinning in alpha-zirconium

Two grades of polycrystalline α-Zr containing ~0.003 and ~0.0775 wt pct O have been fatigued in tension-compression about a zero mean load at a frequency of 100 cps at room-temperature. A combined metallographic and microbeam X-ray pole-loci analysis has revealed the presence of {10•12}, {11−21}, and {11•22} twins and {1O−10} slip. In grains completely enclosed by surrounding material fatigue damage has been found in association with 11•21 twins and very occasionally with {11−22} twins but not with 10•12 twins. A further quantitative interpretation has shown that there is a critical resolved shear stress for {11−21} twinning of ~0.5 kg mm⁻² in zirconium containing 0.003 wt pct O. During observations confined to internal grains it was found that increasing grain size and decreasing oxygen content favored the formation of fatigue damage in association with these {11−21} twins. In external grains the fatigue damage was mainly in the form of edge cracks emanating from the specimen surface. The most appropriate criterion for the formation of damage in {11−2l} twin-matrix interfaces appears to be the attainment of a critical resolved shear stress in the {11−21} twinning plane in the (11−26) twinning direction. Formerly with the Department of Physical Metallurgy and Science of Materials, The University, Birmingham, England     

Anisotropy of point defect diffusion in alpha-zirconium

Two types of intrinsic defect, i.e., vacancy and self-interstitial atom (SIA), are formed in metals during irradiation with energetic particles. The evolution of defect population leads to significant changes in microstructure and causes a number of radiation-induced property changes. Some phenomena, such as radiation growth of anisotropic materials, are due to anisotropy in the atomic mass transport by point defects. Detailed information on atomic-scale mechanisms is, therefore, necessary to understand such phenomena. In this article, we present results of a computer simulation study of mass transport via point defects in alpha-zirconium. The matrix of self-diffusion coefficients and activation energies for vacancy and SIA defects have been obtained, and different methods of treatment of diffusion have been tested. Molecular dynamics (MD) shows that vacancy diffusion is approximately isotropic in the temperature range studied (1050 to 1650 K), although some preference for basalplane diffusion was observed at the lower end of the range. The mechanism of interstitial diffusion changes from one-dimensional (1-D) in a 〈11 0〉 direction at low temperature (<300 K) to two-dimensional (2-D) in the basal plane and, then, three-dimensional (3-D) at higher temperatures. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Anisotropy of point defect diffusion in alpha-zirconium

Two types of intrinsic defect, i.e., vacancy and self-interstitial atom (SIA), are formed in metals during irradiation with energetic particles. The evolution of defect population leads to significant changes in microstructure and causes a number of radiation-induced property changes. Some phenomena, such as radiation growth of anisotropic materials, are due to anisotropy in the atomic mass transport by point defects. Detailed information on atomic-scale mechanisms is, therefore, necessary to understand such phenomena. In this article, we present results of a computer simulation study of mass transport via point defects in alpha-zirconium. The matrix of self-diffusion coefficients and activation energies for vacancy and SIA defects have been obtained, and different methods of treatment of diffusion have been tested. Molecular dynamics (MD) shows that vacancy diffusion is approximately isotropic in the temperature range studied (1050 to 1650 K), although some preference for basal-plane diffusion was observed at the lower end of the range. The mechanism of interstitial diffusion changes from one-dimensional (1-D) in a direction at low temperature (<300 K) to two-dimensional (2-D) in the basal plane and, then, three-dimensional (3-D) at higher temperatures. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Mobility of blast-furnace slag

Equipment for determining the mobility of blast-furnace slag in furnace operation has been developed and tested. On the basis of research at the casting doors of the blast-furnace shop, the MgO and Al₂O₃ content corresponding to high slag mobility is established. The dependence of the slag mobility on the hotmetal temperature, the basicity of the slag, and the MgO and Al₂O₃ content in the slag is determined.     

Mobility of martensitic interfaces

Using a dislocation model of interfacial structure, kinetic theories of dislocation motion are adapted to predict the mobility of martensitic interfaces. Defining generalized driving forces and activation parameters, analytical models are developed which describe the kinetics of motion controlled by various types of obstacle interactions. The behaviors of martensitic interfaces and slip dislocations in identical microstructures are compared. For a lattice-invariant shear by slip, the martensitic interface behaves similarly to a collection of glide dislocations. The interface/obstacle interaction is much weaker if the martensite is internally twinned, giving a higher relative mobility.     

Mobility health assessment

Somatosensory evoked potentials at the cortical and spinal levels were dynamically studied in patients with vertebral column and spinal cord injuries before and after radical reparative surgery. The study showed that quantitative determination of the time course of changes occurring was highly effective in neurological disorders. Most significant were changes in the latent periods and amplitude of the peaks N11, N13, N20, P23 in the activation of n. medianus and N21, N28, P37, N45 in the bilateral stimulation of n. tibialis posterior. There was a correlation of neurophysiological and clinical manifestations in 50-60% of cases. Thus, the neurophysiological studies quantitatively verify the efficiency of surgical treatment for vertebral column and spinal cord injuries.     

Lymphocytic interstitial pneumonitis and nonspecific interstitial pneumonitis

Aggregation of host platelets by circulating tumor cells is believed to play an important role in the metastatic process. Because thrombomodulin (TM) is one of the major mediators of the activation of the anticoagulant protein C by thrombin, we examined 136 primary tumor tissues and 45 metastatic lymph node tissues of lung squamous cell carcinomas for TM expression using immunohistochemical methods. The number of tumors with positive TM staining was less in metastatic tumors (44%) than in primary tumors (74%) (P < 0.01). Of various clinicopathological factors, better differentiation and lower N stage were significantly associated with TM expression. A loss of TM expression was associated with a shortened survival in 113 patients who underwent complete resection of the lung tumor (P < 0.01). In this group, TM expression and tumor-node-metastasis staging were independent significant determinants for survival, determined using Cox's multivariate survival analysis. Since TM is apparently associated with tumor progression and differentiation, this correlation may serve as a prognostic indicator in squamous cell carcinoma of the lung.     

Intestinocystoplasty in treatment of interstitial cystitis

Nine cases of interstitial cystitis treated by intestinocystoplasty are reviewed. The longest follow-up is seventy-eight months. Two patients have since died of unrelated causes. The results reveal seven symptomatic cures and two failures. Long-term renal and vesical function have been well maintained.     

移动通信网络环境下的用户运动模式挖掘

为解决移动用户运动规律获取问题,提出了一种在移动通信网络(GSM)环境下,从用户低层基站位置信息中提取出运动模式的方法.针对基站连接的振荡、重叠等问题,该方法对原始基站位置数据进行分段、窗口化、分组和聚类处理,并将原始基站位置数据表示为聚类序列.采用关联规则挖掘算法从聚类序列中提取出用户运动模式.最后,基于真实基站位置数据,通过运动路径划分实验、位置数据聚类实验和运动模式挖掘实验对系统的有效性进行了评测,并给出了系统参数设置的建议.