Fe－Al合金有序无序相变的电子理论研究SCIEI

利用余氏理论长程有序相的键能公式，并根据计算的键结构和键能，分析了Ｆｅ－Ａｌ合金中的有序无序相变机理。     

碳化钒有序-无序相变的热力学研究

本文分析了碳化钒由无序相转变为有序相转变的热力学问题,建立了基于碳化钒中不同类型键相互作用与熵值和自由能的函数关系,求解了碳化钒由无序相转变为有序相转变后碳原子和空位的有序度,结合粉末的DSC的测定曲线和XRD衍射分析表明:在T=1 515 K时,碳化钒粉末存在有序-无序相变,其具有一阶相变特征,有序度将由0.23突变为0。     

氮化硼对熔融石英析晶行为的影响

从析晶角度出发,研究添加氮化硼对石英陶瓷析晶行为的影响及其抑制析晶的原理。研究表明:添加3.0%(质量分数,下同)氮化硼的熔融石英样品经1200℃热处理后能保持较好非晶态,不析出方石英。分析其原理,可发现氮化硼的加入,促进了新的键合反应,改变了Si-O空间网络,该过程增大了键的重排阻力,有效地阻碍Si-O键排列由无序态向有序态的转变过程,从而实现抑制析晶的目的。     

纯γ-Mn的电子、基态属性和磁有序结构

采用第一原理方法，基于ultrasoft赝势，密度函数理论，从原子层面对纯γ－Mn的顺磁，铁磁和反铁磁性状态下的电子、基态属性，相稳定和磁有序结构进行了研究，通过自旋极化分析讨论了纯γ－Mn这3种磁性状态的结构稳定性，发现在基态时，反铁磁性状态的γ－Mn结构最稳定，且Mn原子处于高自旋状态，其理论磁通量为2．41ua/atom，这与实验结果吻合，通过局部状态密度（DOS），分析了它们的键和磁有序特性，发现主要是位于Fermi态附近的3d轨道电子对磁性起决定性的作用，其向上自旋和向下自旋的主峰分别处于Fermi能下面的键区和Fermi能上面的反键区，通过比较这3种磁性状态可知，反铁磁的γ－Mn存在显著的磁体积效果。     

我国钛容器易发生塑性开裂的原因和对策

根据固体与分子经验电子理论，对Ｗ２Ｃ相的价电子结构进行了定量分析，通过键距差方法计算了Ｗ２Ｃ晶体中各键上的共价电子数。结果表明，近似平行于ｃ轴最近邻的Ｗ－Ｃ原子键最强，其共价电子数ｎＡ＝０．６９９２５，键能ＥＡ＝１４１．２ｋＪ／ｍｏｌ；近似平行于ｃ轴的Ｗ－Ｗ原子间结合力次之，其共价电子数ｎＧ＝０．２０８３４，键能ＥＧ＝４６．２４ｋＪ／ｍｏｌ；位于（０００１）面上的Ｗ－Ｗ原子键也较强，该键上共价电子     

Fe2B相价电子结构及其本质脆性

根据固体与分子经济电子理论对Ｆｅ２Ｂ相的价电子结构进行了定量分析，通过键距差（Ｂｏｎｄ Ｌｅｎｇｔｈ Ｄｉｆｆｅｒｅｎｃｅ）方法计算了Ｆｅ２Ｂ晶体配位团各键上的共价电子数，结果表明，沿（２２０位向分布的Ｆｅ－Ｆｅ原子键最强，其共价电子数ｎＡ＝０．３８５２，键能ＥＡ－１５．７３７２ｋＪ／ｍｏｌ；沿（００２）位向分布的Ｂ０Ｂ原子键较弱，其共价电子数ｎＤ＝０．１３９２，键能ＥＤ＝４．５０５２ｋＪ／ｍｏｌ     

WSi2的价电子结构及其性能研究

根据固体与分子经验电子理论，通过键距差（BLD）方法，计算了金属间化合物WSi2的价电子结构和理论结合能。结果表明，WSi2理论结合能为1859．5kJ／mol，与实验值吻合。WSi2晶体中，沿〈331〉位向分布的W—Si键的键能最大，EA=33．397kJ／mol，且有32个等同键数，是晶体熔化时必须破坏的主干键络，因而WSi2具有高熔点。WSi2晶体中含有较高密度的晶格电子，使WSi2具有良好的导电性。WSi2晶体中键络分布不均匀性是导致晶体脆性的主要原因。     

矿物的解理性质及表面能：各向异性的表面断裂因素

利用Materials Studio软件计算研究几种属于立方、四方、六方或单斜晶系等不同晶系的典型硫化矿、氧化矿和含氧酸盐矿物的表面断裂键性质,分析这些矿物的解理特性,并建立表面断裂键密度与表面能的关系。结果表明：表面断裂键性质可以用来预测大部分矿物的解理特性,预测结果与文献报道一致。对于某种矿物,表面断裂键的密度与表面能成正比,决定系数R^2皆大于0.8,表明表面断裂键的密度大小是决定表面能的关键因素。同时,表面断裂键的数目可用来预测矿物表面的稳定性及表面原子的反应活性。     

一种基于点压技术的新型晶圆键合方法

金金热压键合法在半导体制造领域中应用广泛，为了进一步改进该键合方法，首次提出了一种基于点压技术的新型晶圆键合方法，并研究了工艺温度、压强以及时间对点压键合法单点键合面积的影响. 通过超声扫描显微镜图像，着重比较了传统金金热压键合法与点压键合法的键合面积比. 对点压键合法的可选择键合性进行了讨论. 结果表明，点压键合法工艺步骤简单，工艺稳定性较好，且具有一定的可选择键合特性，在半导体制造领域中将具有广泛的应用前景.     

MoSi2和WSi2的价电子结构及性能分析

根据固体与分子经验电子理论，对MoSi2和wSi2的价电子结构进行了定量的分析，通过键距差方法计算了MoSi2和WSi2晶体中各键上的共价电子数．结果表明：在MoSi2和WSi2晶体中，沿（331）位向分布的Mo-Si和W-Si原子键最强，这些键上的共价电子数和键能分别影响化合物的硬度和熔点．晶体中晶格电子数影响其导电性和塑性，MoSi2晶体中含有较高密度的晶格电子，因此MoSi2的导电性和塑性比WSi2好．并从键络分布的不均匀性解释了MoSi2和WSi2脆性产生的原因．     

Electronic structure of Au-Cu alloys

By studying the correlativity between energy, volume and electronic structure of characteristic crystals and bound conditions of OA theory, the potential energy function, atomic volume interactive function and electronic structure of Au-Cu alloys have been determined. Then following the general Vegard‘s law in characteristic theory, the electronic structure and properties of disordered continue solid solution and three ordered alloys with the maximum ordering degree are calculated. It is found that the non-bonding electrons and near-free electrons in outer shell will transform to covalent electrons during alloying. By analyzing the variation of electronic structure and cohesion of ordering and disordered alloys, the transformation of order-disorder transition Au-Cu alloy has been studied.     

EFFECTS OF INTERSTITIAL IMPURITIES ON PHASE TRANSFORMATION OF Ti-Al ALLOYS

１ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｔｉｔａｎｉｕｍａｌｕｍｉｎｉｄｅｃｏｍｐｏｕｎｄｓｈａｖｅｒｅｃｅｉｖｅｄｃｏｎｓｉｄｅｒａｂｌｅａｔｅｎｔｉｏｎｒｅｃｅｎｔｌｙａｓｃａｎｄｉｄａｔｅｍａｔｅｒｉａｌｓｆｏｒｒｅｌａｔｉｖｅｌｙｈｉｇｈｔｅｍ...     

Influence of Aluminum Content in g-TiAl with L10 Structure during Ordering Processes

Based on EAM (embedded atom method) interatomic potential, the effect of aluminum content on the type of order-disorder transformation (ODT) and the structure properties (lattice constants, volume, c/a ratio and configuration energy) during ordering processes was investigated for g-TiAl based alloys. Results show that for the alloys with lower than 50%Al (all composition is in atom number fraction), the ODT is the first order transition, and the second order transition for the alloys with equal or higher than 50% Al. The increase of aluminum content results in the critical temperature increasing. The aluminum content has a very little effect on the lattice constants, the volume and the c/a ratio, but has a significant effect on the configuration energy. A metastable disordered state was found for the alloys with less than 50%Al.     

Valence bond structure of Ta-W alloys

The valence bond structure of substitutional BCC based Ta-W alloys is studied using characteristic crystal(CC)theory.This theory is based on cluster statistics of random alloys.By studying the correlativity between energy and volume of the CC in Ta-W alloys,the valence bond structure of CC is determined by the energy and shape method.Then,following additive law of CC,the valence bond structure of Ta-W alloys is calculated.It is found that the outer shell valence electronic distribution of Ta-W alloys shows ...     

Effect of Plasma Spraying Process on Microstructure and Microhardness of Titanium Alloy Substrate

High-temperature titanium alloys are considered as good candidate materials for many aerospace applications. In order to increase the usable temperatures and oxidation resistance of titanium alloys, plasma spraying thermal barrier coatings (TBCs) on the titanium alloys is considered as an effective method. The effect of plasma spraying process on microstructure and microhardness of the titanium alloy (Ti-6.6Al-3.61Mo-1.69Zr-0.28Si in wt.%) was investigated by scanning electron microscope, energy dispersion analytical X-ray spectroscopy (EDAX) and microhardness test. The results show that the microstructure of the titanium alloy inside the substrate keeps unchanged after plasma spraying, and no interaction and atomic diffusion happen evidently at the bond coat/substrate interface. However there exists a thin layer of plastic deformation zone in the substrate beneath the bond coat/substrate interface after plasma spraying. The residual stresses are induced inside the titanium alloy due to the thermal expansion mismatch and the temperature gradient inside the substrate during plasma spraying, and lead to generating microcracks in the surface beneath the bond coat/substrate interface and the increase of microhardness in the substrate.     

Calculation of thermodynamic quantities of metals and alloys by the statistical moment method

The thermodynamic properties of metals and alloys are studied using the moment method in the statistical dynamics, which allows us to take into account the anharmonicity of thermal lattice vibrations and size mismatch of constituent atoms, going beyond the quasi-harmonic approximation. Within the fourth-order moment approximation, the free energy and equilibrium lattice spacing of the binary alloys are given explicitly in terms of the effective pair potentials and the second- and fourth-order vibrational constants. The long-range order (LRO) parameter η and order-disorder transition temperatures (ODTs) T_c of binary alloys are obtained by solving the explicit transcendental equations. The numerical calculations of thermodynamic quantities for Cu₃Au and β-CuZn alloys show that the inclusion of the anharmonicity of lattice vibration plays an essentially important role in determining the phase stabilities of metals and alloys.     

Calculation of thermodynamic quantities of metals and alloys by the statistical moment method

The thermodynamic properties of metals and alloys are studied using the moment method in the statistical dynamics, which allows us to take into account the anharmonicity of thermal lattice vibrations and size mismatch of constituent atoms, going beyond the quasi-harmonic approximation. Within the fourth-order moment approximation, the free energy and equilibrium lattice spacing of the binary alloys are given explicitly in terms of the effective pair potentials and the second- and fourth-order vibrational constants. The long-range order (LRO) parameter η and order-disorder transition temperatures (ODTs) T_c of binary alloys are obtained by solving the explicit transcendental equations. The numerical calculations of thermodynamic quantities for Cu₃Au and β-CuZn alloys show that the inclusion of the anharmonicity of lattice vibration plays an essentially important role in determining the phase stabilities of metals and alloys.     

Influence of the order-disorder transition on the magnetic properties of Fe75Al25-xSix alloys

The influence of the different crystal structures and the variation of the lattice parameter on the evolution of the magnetism in the order-disorder transition produced by crushing and mechanical milling in the intermetallic Fe₇₅Al_25-xSi_x alloys (x = 7.5, 12.5, 17.5, 25) has been systematically studied by means of XRD measurements, Mössbauer spectroscopy and magnetic measurements. The results indicate that with the addition of Si to binary Fe₇₅Al₂₅ alloy the mechanical deformation needed to disorder the alloys increases. At the same time the variation of the lattice parameter due to the disorder is reduced as Si is added. The magnetic measurements indicate that there is a complex behaviour in ternary alloys with an opposite influence of Si and Al during the order-disorder transition. However, when the transition is fulfilled there is a linear relationship between structural and magnetic parameters.     

Influence of alloy composition and thermal history on carbide precipitation in γ-based TiAl alloys

Carbide precipitation in TiAl alloys with different alloying element additions and thermal history was investigated by transmission electron microscopy and high energy X-ray diffraction. The results reveal that Nb addition in TiAl alloys does not increase the carbon solubility in the γ matrix significantly. With increasing carbon concentration in the alloys, a splitting of the P-type carbides takes place earlier in the course of ageing at 800 °C and the formation of H-type carbides is promoted. For a nearly single γ phase alloy Ti51Al5Nb0.5C, H-type carbides are the thermodynamically stable phase. However, with decreasing Al concentration, P-type carbides become thermodynamically stable at low carbon concentration (below 1%) in Ti45Al and Ti45Al5Nb alloys. It is feasible to achieve high thermodynamical stability of the P-type carbides in TiAl alloys through controlling alloying elements.     

Microstructure and mechanical behaviour of Nb–Al–V alloys with 10–25 at.% Al and 20–40 at.% V—I: microstructural observations

The microstructures of three Nb–Al–V alloys with nominal compositions Nb–10Al–20V, Nb–15Al–20V and Nb–25Al–40V (in at.%) have been investigated. It is shown that the alloys each exhibit an A2 or B2 matrix and often contain A15 and/or σ phase precipitates depending on thermal history. Both the A15 and σ phase precipitates exhibit two different well-defined orientation relationships and for the former these correspond to minimisation of elastic strain energy. ALCHEMI data from the B2 phase indicate that this is more stable for higher Al concentrations, and this is consistent with measurements of A2/B2 order-disorder transformation temperatures. In the alloy Nb–15Al–20V, the precipitation of the A15 phase in a supersaturated B2 matrix is preceded by the separation of the B2 phase into Al-rich domains in an Al-lean matrix.