【作者】 陈律；

【导师】 彭平； 湛建平；

【作者基本信息】 湖南大学 ， 材料物理与化学， 2009， 硕士

【摘要】 采用第一原理的CASTEP软件,对B2型金属间化合物（RuAl、YAg、YCu、YIn、YRh）点缺陷结构及其力学性能与Re、Ru合金化对Ni/Ni₃Al相界电子结构影响进行了第一原理研究。第一原理的CASTEP软件是一种基于量子力学的专门为固体材料科学研究所设计的程序包,采用密度泛函理论（DFT）赝势平面波方法,能够很好地探索半导体、陶瓷、金属、矿物质和硅酸盐等材料的晶体和表面性能,典型的应用包括研究材料的表面化学、结构性质、能带结构、态密度和光学性能。RuAl、YAg、YCu、YIn、YRh与NiAl同为B2型金属间化合物,然而在实验中却发现RuAl、YAg、YCu、YIn、YRh合金的室温塑性远远要比NiAl合金好。本文通过对不同点缺陷结构形成热与形成能的计算与比较,分析和预测了RuAl、YAg、YCu、YIn、YRh合金中点缺陷结构的种类与存在形式。结果表明:RuAl金属间化合物的点缺陷主要是Ru空位和Al反位,在富Ru合金中主要为Ru反位,在富Al合金中则主要是Al反位。B2-YX （X= Cu, Rh ,Ag, In）合金点缺陷结构主要是X子晶格上的空位与Y子晶格上的反位,在富Y的YX金属间化合物中主要为X空位,在富X的YX金属间化合物中则主要是X反位。进一步通过对RuAl、YAg、YCu、YIn、YRh与NiAl不同点缺陷结构Cauchy压力参数C₁₂-C₄₄和G/B0值的比较,发现点缺陷对RuAl塑性的降低程度比NiAl低,因而含有点缺陷的实际合金的室温塑性RuAl比NiAl好;相反点缺陷能明显提高YAg、YCu、YIn、YRh金属间化合物的室温塑性,推测这很可能是含有点缺陷的实际YAg、YCu、YIn、YRh多晶材料比无缺陷理想单晶和NiAl多晶材料表现出更好室温塑性的原因之一。本文第二部分研究了Ru、Re单独合金化前后γ-Ni/γ′-Ni₃Al相界的电子与能态结构。断裂功计算结果显示:Ru置换Ni/Ni₃Al相界区域中的Ni或Al原子,都可明显提高Ni/Ni₃Al相界的断裂强度,尤其置换γ-Ni/γ′-Ni₃Al相界界面层的Al原子时,对相界的强化效果最好;Re置换γ-Ni相区中的Ni均可提高Ni/Ni₃Al相界的断裂强度;进一步研究了Re与Ru复合合金化前后γ-Ni/γ′-Ni₃Al相界的电子与能态结构。断裂功计算结果显示: Re与Ru在相界区的复合合金化,当Re与Ru分别占据共格（002）γ/γ′原子层邻近（001）γ原子层上的Ni原子位与（001）γ′原子层上的Al原子位时,γ-Ni/γ′-Ni₃Al相界的断裂强度可进一步提高,若其中的Ru置换γ′-Ni₃Al相区内层Al,则复合合金化Ni/Ni₃Al相界的断裂强度不仅没有提高,反而比Ru单独合金化时Ni/Ni₃Al相界的断裂强度还低。电子态密度与电子密度分布图的分析表明:Re与Ru合金化对γ-Ni/γ′-Ni₃Al相界断裂强度的影响可归因于Re和Ru与其最近邻Ni原子间强烈的电子相互作用引起的相界区域层间原子成键相互作用的改变。更多还原

【Abstract】 Using CASTEP code based on first-principles, the point defective constructions and its mechanics property of B2 type intermetallic compound（eg: RuAl、YAg、YCu、YIn、YRh） , the energetics and electronic structure of Ni/Ni₃Al interface with Ru or Re or Ru and Re addition have been calculated. CASTEP is a state of the art quantum mechanics based program designed specifically for solid state materials science. CASTEP employs the Density Functional Theory （DFT） plane-wave pseudopotential method which allows you to perform first-principles quantum mechanics calculations that explore the properties of crystals and surfaces in materials such as semiconductors, ceramics, metals, minerals and zeolites. Typical applications involve studies of surface chemistry, structural properties, band structure, density of states and optical properties.The B2 type intermetallic compound, for example: RuAl、YAg、YCu、YIn and YRh alloy, exhibit excellent room temperature toughness in conventionality experiment. But other B2 type intermetallic compound, for example: NiAl alloy, is not. Based on the calculation and comparison on the heat of formation and the energy of formation of several point defective structures, the type and the geometrical configuration of point defects in B2 type intermetallic compound（RuAl、YAg、YCu、YIn andYRh） are analyzed and forecasted in the first part of this paper. Results show that the major point defects in B2-RuAl intermetallic compound are vacancy defect or anti-site defect in the Ru sublattice, i.e., Ru vacancy and Al anti-site. In rich-Ru alloy it is mainly Ru anti-site defect, whereas in rich-Al alloy it is mostly Al anti-site defect. The major point defects in B2-YX （X=Cu, Rh, Ag, In） intermetallic compound are the vacancy defect in the X sublattice or the anti-site defect in the Y sublattice, i.e., X vacancy defect in rich-Y intermetallic compound and X anti-site defect in rich-X intermetallic compound. In addition, the comparison of Cauchy pressre parameter （C12-C44） and the G/B0 values of ideal B2-YX （X= Cu, Rh, Ag, In）、NiAl and RuAl crystals with their point defective structures reveals: （1）decreasing degree of C12-C44 caused by point defect in RuAl is lower than that in NiAl, which is responsible for that RuAl metallic compound with point defects has a better ductility than NiAl metallic compound with point defects at room temperature; （2） point defects are beneficial for improving the ductility of B2-YX intermetallic compound. Which maybe is responsible for the outstanding ductility of B2-YX （X= Cu, Rh, Ag, In） intermetallic compound at room temperature compared with ideal B2-YX crystals and the B2-NiAl multicrystal.The energetics and electronic structure of Ni/Ni₃Al interface with Re or Ru addition have been calculated based on first principles plane-wave pseudopotential method in the second part of this paper. The calculation of Griffith rupture work W demonstrated: （1） either the substitution of Re atom for Ni atom inγ-Ni block are profitable to improve the rupture strength of the Ni/Ni₃Al interface; （2）either the substitution of Ru atom for Ni atom or Al atom in Ni/Ni₃Al interface are profitable to improve the rupture strength of the interface too, And the best is the substitution of Ru for Al atom at the coherent Ni/Ni₃Al interfacial layer among these substitutions. For the multiple addition of Re and Ru, a obvious strengthening effect on the Ni/Ni₃Al interface compared with that of the Re or Ru addition can be seen when Re and Ru atoms occupy respectively at Ni and Al sites at （001） atomic layers adjacent to the coherent （002） interfacial atomic layer. Whereas, when Ru atom locates at Al site inγ′-Ni₃Al block and far away from the coherent （002） interfacial layer, it is found the multiple addition of Re and Ru does not further elevate the rupture strengths of Ni/Ni₃Al interface but makes them decrease to a lower value than the Ni/Ni₃Al interface with Ru addition. The analysis of electron densities of states （DOS） and the distributions of valence electron densities of Ni/Ni₃Al interface before and after alloying reveals that the alloying effect of Re and Ru on the rupture strength ofγ-Ni/γ′-Ni₃Al interface is attributed to the change of the interlayer bonding in the interfacial region induced by the stronger electronic interactions within first nearest neighbor （FNN） Re-Ni and Ru-Ni atoms compared with FNN Ni-Ni and Ni-Al.更多还原