Computational thermodynamic model for the Mg−Al−Y system

The ternary Mg−Al−Y system was thermodynamically modeled based on the optimization of the binary subsystems Mg−Al, Mg−Y, and Al−Y using the CALPHAD approach. Mg−Al data was taken from the COST507 database, whereas the other two binary systems were reoptimized in this work. The liquid phase was described by a Redlich-Kister polynomial model, and the intermediate solid solutions were described by a sublattice model. Ternary interaction parameters were introduced to enable the best representation of the experimental data while considering the occurrence of the ternary compound Al₄MgY. The constructed database is used to calculate and predict thermodynamic properties, binary phase diagrams of Al−Y and Mg−Y, and liquidus projections of the ternary Mg−Al−Y. The calculated phase diagrams and the thermodynamic properties are in good agreement with the corresponding experimental data from the literature. Sixteen ternary four-phase-equilibria invariant points were predicted in the Mg−Al−Y system: seven ternary eutectic points, eight ternary quasi peritectic points, and one ternary peritectic point. Further, fifteen three-phase-equilibria in variant points were determined: eight saddle points and seven binary eutectic points.     

Thermodynamic evaluation and optimization of the Ca−Si system

All available phase equilibria and thermodynamic data for the Ca−Si system were collected and critically evaluated. In a first step, the thermodynamic properties of Ca(g) were obtained from experimental vapor pressure data over pure Ca. The new vapor pressure of calcium over pure solid and liquid was used as a new reference to model the thermodynamic properties of the intermediate stoichiometric Ca−Si compounds together with other thermodynamic and phase diagram data found in the literature (liquidus temperatures, heat capacities, pressures of Ca, and heats of reaction). Optimization was performed to obtain the parameters of one set of model equations for the different solid and liquid phases to best reproduce all the experimental data simultaneously. In this way, the data are rendered self-consistent, discrepancies among the data are identified, and extrapolations and interpolations can be performed. For the liquid phase, the Modified Quasichemical Model in the Pair Approximation for short-range ordering was used.     

Thermodynamic reassessment of the Cd−Zn system

The Cd−Zn system has been thermodynamically reassessed with the CALPHAD method by combining more recent experimental data, in particular the activities of zinc in the liquid phase. A good agreement is obtained between the calculated and experimental thermodynamic parameters as well asphase boundaries.     

Effect of ball milling conditions on the microstructure and the transformation behavior of Ti−Ni and Ti−Ni−Cu shape memory alloy powders

Ti−50Ni and Ti−40Ni−10Cu (at.%) shape memory alloy poweders have been fabricated by the ball milling method. Their alloying behaviour and transformation behaviour were investigated by means of optical microscopy, electron microscopy, X-ray diffractometry and differential scanning calorimetry. As-milled Ti−Ni powders fabricated with a milling time of less than 20 hrs were a mixture of pure elemental Ti and Ni, and therefore we were unable to obtain alloy powders because the combustion reaction between Ti and Ni occurred during heat treatment. Since those fabricated with a milling time of more than 20 hrs were a mixture of Ti-rich and Ni-rich Ti−Ni solid solution, it was possible to obtain alloy powders without a combustion reaction during heat treatment. Clear exothermic and endothermic peaks appeared in the cooling and heating curves, respectively, in DSC curves of 20 hr and 30 hr milled Ti−Ni powders. On the other hand, in DSC curves of 1 hr, 10 hrs, 50 hrs and 100 hrs, the thermal peaks were almost discernible. The optimum ball milling time for fabricating Ti−Ni alloy powders was 30 hrs. Ti−40Ni−10Cu alloy powders were fabricated successfully by the optimum ball milling conditions deduced from Ti−50Ni alloy powders.     

Surface active and thermodynamic properties of some surfactants derived from locally linear and heavy alkyl benzene in relation to corrosion inhibition efficiency

Linear and heavy alkyl benzene (HAB) were sulfonated with fuming sulfuric acid (oleum) and the sulfonated products were esterified with tri and poly ethanolamine (d = 4 and 6). The prepared three esters from each series were quaternized with n‐butyl bromide. The resulted six quaternized ester of linear and HAB sulfonate were named as (L1Q, L2Q, L3Q, H1Q, H2Q, and H3Q). The surface and thermodynamic properties of these compounds have been investigated. From the data obtained, it was found that surface tension and surface active properties for the HAB derivatives were better than which obtained from linear alkyl benzene (LAB) derivatives. From the results obtained from the surface activity, the best performance compound from each group was selected to study the corrosion inhibition efficiency of them relative to the surface activity. The obtained results show that the LAB derivative L3Q exhibited inhibition efficiency (93.1%) at 1000 ppm but H3Q exhibited (97%) at 600 ppm. The diversity of the resulted data obtained was discussed in the light of chemical structure of the alkyl benzene sulfonate.     

Numerical modeling of general cracks from the viewpoint of eddy current simulations

This study discusses numerical modeling of fatigue and stress corrosion cracking in eddy current simulations. Ten fatigue crack specimens and another 10 stress corrosion crack specimens are prepared for this purpose. The specimens are made of type 316 stainless steel and measure 10 mm in thickness for a general evaluation of the model. Eddy current inspections of the specimens are performed using a differential type plus point probe; the specimens then undergo destructive tests to confirm the true profiles of the cracks. Subsequent numerical simulations are conducted to evaluate the equivalent conductivity and width of the cracks. The simulations demonstrate that a fatigue crack can be modeled as a non-conductive region, and it is not necessary to know exactly how wide the opening of a fatigue crack is. They also revealed, in contrast, that stress corrosion cracking needs to be modeled as a conductive region with a certain width.     

从制度设计看美国大学终身教职制的理念基础

终身教职制是20世纪初美国大学确立的教师任用制度,时至今日,它仍然是美国大学主要的教师任用制度。从制度设计的角度可以分析出终身教职制的三个理念基础,即对学术自由的捍卫、对职业安全的保障、对优秀人才的选拔。从制度设计看美国终身教职制的理念基础或许对我国正在进行的大学教师人事制度改革有一定的启发意义。