L12-Al3Li金属间化合物点缺陷浓度的第一原理计算

运用第一原理平面波赝势方法计算L12-Al3Li金属间化合物点缺陷的形成焓,并结合Wagner–Schottky模型,研究L12-Al3Li金属间化合物在523、673、823和1 000 K时点缺陷浓度与成分之间的关系。结果表明:在这4个温度下,L12-Al3Li金属间化合物中Al空位浓度最小,Li空位浓度次之,Al反位和Li反位的缺陷浓度较大。Al反位和Li反位缺陷浓度在理想金属间化合物Al3Li化学计量比成分处基本相同,不过两种反位的缺陷浓度随着合金成分相对于化学计量比成分的偏离而变化显著,在富Al端Al反位缺陷浓度较大,在富Li端Li反位缺陷浓度较大。运用Arrhenius方程计算点缺陷的有效形成焓,结果显示Al反位和Li反位的有效形成焓较小且基本相同,Li空位次之,Al空位最大。     

D0_(19)-Ti_3Al中点缺陷浓度与相互作用的第一性原理研究

采用Wagner-Schottky点缺陷热力学模型和第一性原理平面波赝势方法,计算研究了D019-Ti3Al金属间化合物中空位和反位2种类型点缺陷的形成焓、平衡浓度及相互作用。结果表明,这些缺陷的平衡浓度均随温度升高而增大,反位缺陷浓度均高于空位缺陷,Ti原子空位的浓度高于Al原子空位。在理想化学计量比成分下,Ti原子反位与Al原子反位缺陷浓度基本相当;在略偏离计量比的富Ti成分端,Ti原子的反位缺陷浓度高于Al原子;在富Al成分端则情形相反。计算结果表明,3种点缺陷对(Al_(Ti)-Ti_(Al)、Ti_(Al)-Ti_(Al)、V_(Al)-Al_(Ti))在基体中具有较强的聚集趋势,而其它类型的点缺陷对则有向基体扩散的趋势。     

L1_2-Co_3X(X=Ti,Ta,Al,W,V)点缺陷结构的理论计算

运用第一性原理赝势平面波方法,研究了L1_2-Co_3X(X=Ti,Ta,Al,W,V)金属间化合物的基本物性及其点缺陷结构的几何、能态与电子结构。通过对相应合金中两种组元原子的空位和反位点缺陷结构形成热与结合能的计算与比较,分析了L1_2-Co_3X(X=Ti,Ta,Al,W,V)金属间化合物中点缺陷结构的种类与存在形式。结果表明,L1_2-Co_3X(X=Ti,Ta,Al,W,V)金属间化合物的点缺陷结构与L1_2-Ni_3Al合金保持一致,主要是Co原子晶格以及X原子晶格上出现反位缺陷。基于晶体总电子态密度结构信息的分析,很好地验证了上述计算结果。     

金属间化合物L1_0-TiAl点缺陷浓度的第一原理

采用第一原理平面波赝势方法,结合Wagner-Schottky缺陷热力学模型,研究金属间化合物L10-TiAl中各种空位和反位点缺陷的形成焓、热力学平衡浓度及其相互作用等。结果表明:这些缺陷的热力学平衡浓度均随温度的升高而增大,其中反位缺陷浓度均高于空位缺陷浓度,Ti空位浓度高于Al空位浓度。在理想化学计量比成分下,Ti反位缺陷的浓度与Al反位缺陷的基本相当;在略偏离计量比的富Ti成分端,Ti反位缺陷的浓度高于Al反位缺陷的;在富Al成分端则相反。不同点缺陷之间均普遍存在相互排斥性,难以聚集,将倾向于向基体中分散和扩散。     

Al3Li相反位缺陷演化的微观相场模拟

基于离散格点形式的微扩散方程(Langevin方程),模拟了Al3Li相反位缺陷随时间的演化特征及随组元浓度、温度的变化规律.结果表明,Al3Li相中主要以Al原子占据Li位形成的反位缺陷AlLi为主,同时存在少量的Li原子占据Al位形成的反位缺陷LiAl,2种反位缺陷浓度均随温度的升高而上升,且AlLi远大于LiAl上升速率;随Li浓度的增加,AlLi浓度缓慢降低,LiAl浓度略有上升,但仍远远小于AlLi浓度;浓度变化对反位缺陷的影响远不及温度对其影响大.     

铝合金细化相Al3(Zr,Sc)的能量和弹性性质的第一性原理研究

微合金化是强化铝合金的重要手段,Sc作为铝合金有效的细化剂而引起广泛关注。实验研究表明,在铝基体中同时添加Zr和Sc,在铝基质中形成Al3(Zr,Sc)细化相,可以实现更好的晶粒细化。本文基于密度泛函理论的第一性原理方法,系统地研究了不同Sc/Zr配比下形成的Al3(Zr,Sc)细化相的能量和弹性性质。结果表明,当Sc/Zr不高于1/3时,Al3(Zr,Sc)相具有较大的形成焓绝对值,细化相将优先于Al3(Zr,Sc)相析出。同时,Sc元素的加入有利于界面的形成,提高界面的结合强度和润湿效果,但高于1/3的Sc/Zr比对界面性能的提高并无积极作用。并且,Zr的加入可以有效提高细化相的弹性性能,并削弱Al3Sc的弹性各向异性特征。此理论研究指出,微合金化Zr和Sc的共同添加时Sc/Zr不高于1/3时,可以保证细化效果并大大降低合金的成本。     

点缺陷对B2-CoSc化合物物性影响的第一性原理研究

利用第一性原理的Castep软件,对B2型金属间化合物Co Sc的16种点缺陷的热力学参数、电子结构和弹性常数进行计算,分析16种点缺陷存在的类型及对化合物力学性能的影响。结果表明:Co单空位形成热和结合能分别是-6.78 e V和-0.43 e V,Co单空位化合物最容易形成、稳定性最好;其次是Co单反位化合物,形成热和结合能分别是-6.152 e V和2.504 e V。从而得出16种点缺陷最稳定存在形式是Co空位和Co反位;存在的组态是Co单空位、Co双空位、Co三空位和Co双反位。由电子态密度图中的费米能级和赝能隙也定性判断出,Co空位和反位缺陷化合物比Sc空位和反位缺陷化合物稳定。计算6种点缺陷的泊松比?可知,Co三空位的化合物金属键最强、塑性最好。与完整的Co Sc金属间化合物塑性相比,有空位缺陷的金属间化合物塑性得到提高。     

Al-Li-Mg(Ti)合金形成焓的EAM研究

采用普适分析型的嵌入原子模型,通过拟合纯元素的晶格常数、空位形成能、结合能和体积弹性模量等,确定了Al、Li、Mg和Ti 4个元素的嵌入原子模型参数.不同元素之间的相互作用势的参数由拟合实验或第一原理计算结果确定.用确定的嵌入原子模型分别计算了由Al,Li、Mg和Ti元素构成的二元系以及三元系中的有序合金化合物的形成焓,计算结果与已有的实验结果和第一原理计算结果符合得比较好.     

Sc、Zr和Er微合金化Al-5Mg填充合金的焊接热裂敏感性

采用鱼骨状试样裂纹试验、SEM和DSC等分析方法研究Sc、Zr和Er的复合添加对新型Al-5.6Mg-1.0Zn-0.6Mn基填充合金焊接热裂敏感性的影响。结果表明:Sc、Zr和Er(含Ti)参与形核核心Al3(Sc,X)的生成,Er(Ti)元素在晶界处形成富Er相,这对试验合金焊道熔池区域的晶粒度和晶间相富集状态影响显著;优化的Sc、Zr和Er成分配比能获得优异的晶粒细化效果,并抑制含Er相对晶界结合的恶化作用,使合金获得较高的焊接热裂抗力;焊接热裂敏感性降低的机理为合金偏析程度的降低、凝固终了温度的相对提高、细小晶粒的转动滑移和细晶晶界应力的分散。     

钪对铝锂合金时效硬化行为的影响

通过对190℃时效不同时间的含钪和不含钪Al—Li合金维氏硬度测量和合金中强化相析出行为的透射电镜观察,研究了钪对铝锂合金时效硬化行为的影响。结果表明,钪可以加快铝锂合金的时效硬化速度,使合金达到峰值时效的时间明显缩短;钪明显抑制了铝锂合金中δ’(Al3Li)相的长大速度,促进了S’(Al2CuMg)的析出,还可形成Al3Sc、Al,Li／Al3Sc和Al3Li／Al3(Sc,Zr)等新的析出相,这些都对铝锂合金的时效硬化行为产生影响。     

Comparison of geometries and electronic structures of polyacetylene,polyborole, polycyclopentadiene,polypyrrole, polyfuran,polysilole, polyphosphole,polythiophene, polyselenophene and polytellurophene

Geometries of monomers through hexamers of cylopentadiene, pyrrole, furan, silole, phosphole, thiophene, selenophene and tellurophene, and monomers through nonamers of borole were optimized employing density functional theory with a slightly modified B3P86 hybrid functional. Bandgaps and bandwidths were obtained by extrapolating the appropriate energy levels of trimers through hexamers (hexamers through nonamers for borole) to infinity. Bandgaps increase with increasing π-donor strengths of the heteroatom. In general, second period heteroatoms lead to larger bandgaps than their higher period analogs. Polyborole is predicted to have a very small or no energy gap between the occupied and the unoccupied π-levels. Due to its electron deficient nature polyborole differs significantly from the other polymers. It has a quinoid structure and a large electron affinity. The bandgaps of heterocycles with weak donors (CH₂, SiH₂ and PH) are close to that of polyacetylene. For polyphosphole this is due to the pyramidal geometry at the phosphorous which prevents interaction of the phosphorus lone pair with the π-system. The bandgap of polypyrrole is the largest of all polymers studied. This can be attributed to the large π-donor strength of nitrogen. Polythiophene has the third largest bandgap. The valence bandwidths differ considerably for the various polymers since the avoided crossing between the flat HOMO — 1 band and the wide HOMO band occurs at different positions. The widths of the wide HOMO bands are similar for all systems studied. All of the polymers studied have strongly delecalized π-systems.     

Acid-base behavior of cryptand 1, 4, 7, 10, 13, 16, 21, 24-octaaza-bicycio[8, 8, 8] hexacosan-3, 8, 12, 17, 20, 25-hexone and complex formation

The bicyclic cryptand 1,4, 7, 10, 13, 16, 21, 24-octaaza-bigcyclo [8, 8, 8] hexacosan-3, 8, 12, 17, 20, 25-hexone (COBH) bearing diaminoethane groups along the eight-atom bridges was synthesized. The structure consists of discrete neutral macrobicyclic units; the two cycles share the two tertiary amine nitrogen atoms, which exhibit an endo-endo conformation. Three identical branches formed by 1, 2-diaminoethane link the two tertiary amine groups. The protonation reactions ofcryptand (COBH) and its complex formation with copper (Ⅱ) were investigated by potentiometry in water and in a DMSO/water (80: 20 in mass ratio) mixture as solvents. The cryptand acts as a bis-base through its two Nbridgehead and exhibits a strong cooperativity that favors the first protonation and makes the second one difficult (pK 5.0 ). An inward rotation of the amide groups to form hydrogen bonds accounts for this cooperativity. The interaction of COBH with copper (Ⅱ) leads to several binuclear complex proton contents.     

Acid-base behavior of cryptand 1, 4, 7, 10, 13, 16, 21, 24-octaaza-bicyclo [8, 8, 8] hexacosan-3, 8, 12, 17, 20, 25-hexone and complex formation

The bicyclic cryptand I, 4, 7, 10, 13, 16, 21,24-octaaza-bigcyclo [8, 8, 8] hexacosan-3, 8, 12, 17, 20, 25-hex-one (COBH) bearing diaminoethane groups along the eight-atom bridges was synthesized. The structure consists of discrete neutral macrobicyclic units; the two cycles share the two tertiary amine nitrogen atoms, which exhibit an endo-endo conformation. Three identical branches formed by I, 2-diaminoethane link the two tertiary amine groups. The protonation reactions ofcryptand (COBH) and its complex formation with copper (II) were investigated by potentiometry in water and in a DMSO/water (80: 20 in mass ratio) mixture as solvents. The cryptand acts as a bis-base through its two Nbridgehead and exhibits a strong cooperativity that favors the first protonation and makes the second one difficult (ΔpK≈5.0 ). An inward rotation of the amide groups to form hydrogen bonds accounts for this cooperativity. The interaction of COBH with copper (II) leads to several binuclear complex proton contents.     

Supplemental Literature Review of Binary Phase Diagrams: Cs-In, Cs-K, Cs-Rb, Eu-In, Ho-Mn, K-Rb, Li-Mg, Mg-Nd, Mg-Zn, Mn-Sm, O-Sb, and Si-Sr

Recent literature on Cs-In, Cs-K, Cs-Rb, Eu-In, Ho-Mn, K-Rb, Li-Mg, Mg-Nd, Mg-Zn, Mn-Sm, O-Sb, and Si-Sr phase diagrams is reviewed in this article in order to update the 1990 compilation Binary Alloy Phase Diagrams, 2nd edition, by T.B. Massalski, et al. For some systems reaction tables and crystal structure data have been included, as well. Diagrams have been checked for consistency with rules for phase diagram construction and modified when necessary. In addition, diagrams needing more work have been identified.