Phase diagrams and mechanical properties of TiC-SiC solid solutions from first-principles

First-principles calculations were carried out in order to investigate the stability and properties of the random Ti_1-xSi_xC solid solutions (alloys) with both the B1 and B3 structures. Lattice parameter, total energy, formation energy, phonon spectra, and elastic properties were studied as functions of composition. The phase diagram, in particular, binodal and spinodal curves were calculated. It was established that at 0 K the B1 alloys are energetically favorable at 0 ≤ x < 0.5, while the B3 alloys are favorable at 0.5 ≤ x ≤ 1.0. It was found that the contribution to the Gibbs free energy coming from the lattice vibrations strongly reduces the critical temperature of stabilization of the solid solutions. Calculated elastic moduli, Debye temperature, and Vickers hardness do not point to any strength enhancement of the alloys compared to TiC and SiC. Analysis of the spatial distribution of the Young and shear moduli shows that the B3 alloys exhibit much more spatial anisotropy of the elastic moduli than the B1 alloys.     

Limitations of a regular associated solution approximation in describing the thermodynamic behaviour of complex liquid alloys

The validity of the regular associated solution (RAS) model for describing the thermodynamic properties of complex liquid alloys has been analysed by applying it to the Cu-In system. The presence of Cu₃In as the associated species in equilibrium with the free atoms in the liquid state was assumed. Liquid copper-indium alloys exhibit a very complex thermodynamic behaviour where the deviations from ideality of activities and integral enthalpy of mixing vary from positive to strongly negative and the properties are strongly temperature dependent. It is seen that a regular solution type interaction among species is insufficient to model the thermodynamic properties of liquid Cu-In alloys and the temperature dependence of interaction energies among the species has to be taken into account. A modified associated solution model incorporating volume effects and temperature dependence of interaction energies could successfully describe the thermodynamic properties of liquid Cu-In alloys.     

Theoretical investigation of the interaction of oxygen with pure and K-doped NiTi shape memory surface alloys

Density functional based theories and experiments agree well on the value of the heat of formation of TiO₂ on NiTi surfaces. However, experimental studies of polycrystalline NiTi surfaces tend to indicate that Ti atoms are always abundantly available at the surface. This theoretical study indicates that whether Ti atoms are dominantly available at the surface depends on the surface index. On NiTi(001) in the B2 phase, the surface can be Ti or Ni terminated, with equal probability, while on NiTi(110) in the B2 phase and NiTi(010) in the B19? phase, Ti atoms are favored to be present at the surface.     

Predicting the density of molten alloys using computational thermodynamics

The density of a molten alloy can be calculated from the quotient of its molar mass divided by its molar volume. The molar volume of a molten alloy, however, often deviates from the average of the molar volumes of its constituents. The deviation is caused mainly by the affinity (or lack of it) between dissimilar atoms, which can be quantified by the enthalpy of mixing. Up to now, the link between the enthalpy of mixing and the volume change has been determined empirically through the regression of experimental measurements of alloy densities. In the present study, the derivative of molar volume with respect to enthalpy was deduced and the molar volumes of molten alloys were computed entirely based on the properties of pure elements and the enthalpy of mixing of the alloys. The very slight increase in the packing density due to the size difference of different atoms was also considered. The effect of cluster formation due to short range ordering was also addressed. Over six hundred data points were used in validations. Excellent agreements were achieved between the calculated values and the experimental measurements.     

Activity measurement of the constituents in molten Fe–B and Fe–B–C alloys

The distribution ratios of Fe and B between molten Fe–B alloy and molten Ag were measured at temperatures between 1573 and 1923 K. Also, distribution ratios of Fe and B between molten Fe–B–C_satd. alloys and molten Ag were measured at 1873 K. It was found that the excess Gibbs free energy of mixing in molten Fe–B and Fe–B–C alloys can be expressed by utilizing the Redlich–Kister polynomial. The activity curves of the elements in molten Fe–B alloy and Fe–B–C alloy were estimated.     

Magnetic behavior of Fe sites in Fe–Mo–Al alloys: The role of the first neighborhood

We analyse the influence of the nearest neighborhood on the magnetic behaviour at Fe sites in bcc-based Fe–Al, Fe–Mo and Fe–Al–Mo alloys. Theoretical ab initio calculations were performed in the framework of the Density Functional Theory using the Full Potential—Linear Augmented Plane Wave method as embodied in the WIEN97 code. The analysis is made through local magnetic moments considering the distribution of the first coordination shell of the Fe atoms. We find that the magnetic moment is nearly independent of the composition in the Fe–Mo binary. Although the magnetic behaviour of Fe–Al alloys is a very complex and controversial subject, our results clearly show that an increase in the number of Al nearest neighbours leads to a decrease or even to the suppression of the local moment at Fe sites. On the other hand, the ternary bcc-based Fe–Mo–Al alloys present no correlation between magnetism and the composition of the nearest neighbor shell. The results are discussed in connection with their implications for the thermodynamic modelling of magnetism in the CALPHAD approach.     

四苯并卟啉/酞菁结构及其内氢反应迁移理论研究

采用B3LYP/6-31G**法在Gaussian03程序下,优化四苯并卟啉/酞菁的结构和能量,并寻找与内氢迁移反应相关的过渡态构型.计算结果表明,中心空穴缩小、共轭效应的增强都有利于内氢迁移,但中心空穴的影响要大很多.     

Experimental investigation and thermodynamic assessment of the Al-Co-Ni system

The Al-Co-Ni system is essential to both Co- and Ni-based superalloys. In this study phase relationships among A1, L1₂ and B2 at 800 °C have been investigated by using equilibrated alloys. Four samples were prepared and annealed at 800 °C for 14 days. SEM-EDXS and XRD were used to analyze the annealed samples. The results indicated that two-phase L1₂+B2 and three-phase A1+L1₂+B2 regions exit.A thermodynamic reassessment of the entire Al-Co-Ni system has been made according to the CALPHAD method. Compared to the previous assessments, more recent experimental results have been considered. In the Al-Co binary system, the phase named Y-Co₄Al₁₃ has been added on the basis of the available literature. The order-disorder model has been adopted to describe the A1/L1₂ and A2/B2 phase relations, respectively. Three ternary compounds in the Al-rich region have been introduced. Three-sublattice model has been selected to describe the τ₁ phase with a considerable solubility extension. Thermodynamic interaction parameters have been optimized, considering the available experimental data. In this work several diagrams were calculated, which can fit experimental results in the whole composition range. A satisfactory agreement was obtained. As a result phase equilibria in the interested ferromagnetic shape memory alloys are calculated.     

Experimental investigation of phase equilibria in the Al–Cr–Fe system

The literature of the ternary Al–Cr–Fe system was evaluated and major open questions were identified. Transition temperatures between α-Fe,Al (A2) – FeAl (B2) and FeAl (B2) – Fe₃Al (D0₃) as well as solidus/liquidus temperatures in the Cr-rich corner were determined. The results from thermal analysis show a substantial decrease of the A2/B2 transition temperature with increasing Cr content at constant x(Al). Furthermore, a partial solidus and liquidus projection below 50 at.-% Al were created. Several partial isothermal sections have been studied with equilibrated alloys and diffusion couples. Therefore, complementary methods were used such as thermal analysis, electron microscopy, chemical analysis, X-ray powder diffraction and electron probe microanalysis. Equilibration experiments have been performed at 973 K, 1173 K, 1315 K, 1373 K and 1423 K and two partial isothermal sections at the two lowest temperatures were constructed indicating a solubility of 22 at.-% iron in the AlCr₂ phase at 973 K.     

Phase diagrams and elastic properties of the Fe-Cr-Al alloys: A first-principles based study

The phase diagrams and elastic properties of the Fe-Cr-Al alloys in full-temperature and all-compositional ranges are calculated. By combining first-principles calculations and cluster variation method, binary and ternary phase diagrams are obtained. A new ternary ordered phase B32 which is different from ternary extension of binary phases appears in the ternary section around temperature of 600 K. The binary FeAl phases show an extremely high solubility for Cr, while the binary CrAl phase solid solution has a low solubility for Fe. By combining first-principles calculations and cluster expansion method, the bulk modulus, shear modulus and Poisson's ratio are calculated. The shear modulus and Poisson's ratio show a strong ordering dependency, while the ordering dependency in bulk modulus is weak. Disordered Fe-Cr alloys with a little Al solvent shows ductile property, the Al-rich corner has brittle property.     

多溴苊化合物的分子结构和热力学性质

多溴苊是一类潜在的有机污染物。本文采用密度泛函理论在B3LYP/6-311G**水平上优化35个多溴苊化合物的分子几何结构,并获得它们在理想气态的一些热力学性质的数值,研究这些性质与取代的溴原子数目和位置的关系,根据各异构体的标准生成Gibbs自由能的相对大小,求得它们的热力学稳定性顺序。计算结果表明:在大部分多溴苊分子中,除4个氢原子外的其他原子在同一平面上。多溴苊最稳定及最不稳定异构体的ΔfH及ΔfG,都随Br原子数目增加而逐渐增加。溴原子数目相同的多溴苊异构体的ΔfH和ΔfG与溴原子的取代位置有很大的关系,其相对稳定性主要由分子内的处在不同六元环上的邻近Br...Br核排斥作用决定。所有多溴苊化合物在热力学上都比其母体化合物苊相对较难形成。     

Fe_3Al中合金元素的占位及对H原子的影响(英文)

利用第一原理反演原子间相互作用势，计算了多种合金元素在Ｆｅ３Ａｌ中的占位分布，与实验结果吻合很好，同时计算结果表明，Ｃｒ的加入可以降低Ｆｅ３Ａｌ表面对Ｈ原子的吸附能力，从而降低Ｈ原子在表面的偏聚。     

大规模并行原子模拟在钛合金界面行为研究中的应用

界面对钛合金的力学性能有至关重要的影响。界面行为的原子模拟涉及的原子数目庞大,必须借助大规模并行计算。本研究组开发了大规模并行分子动力学程序,并将其应用于钛合金中不同种类界面行为的模拟研究。本文以钛铝金属间化合物中的孪晶界和 α 钛中的特殊大角晶界为例,介绍研究组在钛合金晶界行为的计算模拟方面的近期研究成果。所模拟的体系尺寸达到微米级,所需 CPU 核数几十至几百不等。研究发现,钛铝模拟晶胞沿伪孪晶方向剪切变形时,等静压力下可产生 L1₁ 结构的伪孪晶形核长大,而等静张力下剪切可产生真孪晶的形核长大,提出钛铝中一种新的孪晶长大机制。在 α 钛中,特定取向的两个晶粒所形成的晶界与位错发生相互作用,裂纹形核依赖于加载外力的取向而发生在晶界处或硬取向晶粒内,从而可能导致疲劳断裂行为与加载取向相关。这些结果有助于理解钛合金的塑性变形行为,并为更高尺度的模拟研究提供了原子尺度细节。     

羧酸膦酸型化合物的阻垢缓蚀性能的量子化学研究

运用密度泛函(DFT)理论,在B3LYP／6—31G*水平下,系统研究了2-膦酸基丁烷-1,2,4-三羧酸(PBTCA)、1,2,2-三膦酸基丁烷-4-羧酸(TPBCA)、3,3-二膦酸基戊烷-1,5-二羧酸(DPPDCA)这3种羧酸膦酸型阻垢缓蚀剂的分子结构与阻垢缓蚀性能之间的构效关系。结果表明,3种膦酸分子中的羧基和膦酸基中氧原子的负电荷较多,氧原子与垢晶体中的钙离子产生静电,这些氧原子对间距与方解石晶体生长面上的钙离子对间距匹配,产生晶格畸变,阻止垢体生长。计算得到3种分子的缓蚀能力为PBTCA>DPPDCA>TPBCA,并且得到羧基中的O原子、膦酸基中的O原子对缓蚀能力贡献较大。     

芳基咪唑啉类化合物胰岛素分泌生物活性的QSAR研究

采用密度泛函理论(DFT)的B3LYP/6-311G+(d,p)方法,对芳基咪唑啉类化合物的几何构型进行全优化,将一系列量子化学参数用于结构与胰岛素分泌生物活性的定量研究中。利用SPSS16.0软件进行相关性分析,结果表明,分子的偶极矩,分子的总能量,碳原子C(2)、C(3)、C(9)上的Mulliken电荷,以及N1-C2、C2-C3的键长均对其生物活性Log(Ins)有明显影响。本文最终选取2个最为相关的量子化学参数,偶极矩μ和C(3)原子上Mulliken电荷Q_3,建立了满意的QSAR模型(Log(Ins)=0.894+0.067μ+0.297 Q_3,N=12,R~2=0.856)。     

Ab-initio calculations of the formation energies of BCC-based superlattices in the Fe---Al system

First-principles calculations of the total energies of A2 iron and aluminum, B2 (FeAl), B32 (FeAl) and D0₃ (Fe₃Al and FeAl₃) compounds were performed in the frame of density functional theory (DFT) using the Full Potential - Linear Augmented Plane Wave method (FP-LAPW). These results have been used to obtain formation energies of the respective ground states. The calculated formation energies of the D0₃ (Fe₃Al) and B2 (FeAl) compounds show excellent agreement with available calorimetric data on standard enthalpies of formation of Fe---Al alloys up to 50 at.% aluminum. As the Fe---Al system has a controversial magnetic behavior when described by ab-initio methods in the DFT, this agreement is remarkable.     

Thermodynamic modeling of selected ternary systems containing Y and CALPHAD simulation of CoNiCrAlY metallic coatings

Metallic coatings can improve the high temperature resistance of superalloys serving in the gas turbines. In general they are Al–Co–Cr–Ni alloys with small Y additions to improve oxide scale adherence.In order to complete the construction of a thermodynamic database for coatings, thermodynamic assessments of four ternary systems have been performed by means of the CALPHAD method, namely Al–Co–Y, Al–Ni–Y, Al–Cr–Y and Co–Ni–Y. All of the experimental phase diagrams and thermodynamic data available in the literature were critically reviewed. The liquid, fcc, bcc and hcp phases were modeled as substitutional solutions. The order-disorder model has been adopted to describe the A1/L1₂ and A2/B2 phase relations. A series of ternary compounds have been modeled during the present work according to the crystal structure or composition. As a result a satisfactory agreement was obtained between our calculations and the experimental data used in the assessment.Finally, interaction parameters calculated in this work have been merged in the thermodynamic database for the simulation of Al–Co–Cr–Ni–Y alloys. This has been validated by comparing our calculations with experimental data regarding selected Ni-based and Co-based alloy coatings.     

简易数字温度仪的设计

介绍了一款简易数字温度仪的设计。列出温度传感器DS18B20的基本特性。由于DS18B20具有直接输出数字信号、单总线接口、成本低等优点，将其应用在由单片机AT89C2051为核心的家庭环境监测系统中作为测温探头。给出了相应的硬件接口电路、软件流程及主要程序代码。并针对DS18B20对时序要求十分严格的特点给出了详细的介绍．