第一性原理研究点缺陷对B2结构NiAl合金性能的影响（英文）

采用基于密度泛函理论的第一性原理计算分析了含点缺陷结构NiAl晶胞的形成热、形成能、点缺陷平衡浓度、力学性能、电子结构等。将NiAl与其他B2结构的金属间化合物进行对比,发现NiAl拥有更好的塑性和成键强度。根据形成热、形成能和点缺陷平衡浓度的计算结果,发现Ni反位和空位缺陷是NiAl晶胞结构中主要的点缺陷。通过Pugh(G/B_0)和Cauchy(C_(12)–C_(44))准则预测出Ni空位和反位缺陷、Al反位缺陷能够提升NiAl合金的脆性,其中Ni空位缺陷作用最明显;而Al空位缺陷能够改善NiAl合金的塑性,但在NiAl合金中的浓度很低。态密度计算结果发现NiAl合金具有良好的导电性能,Ni空位缺陷、Al空位和反位缺陷能够提升NiAl合金的稳定性。     

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。     

B2-RuAl点缺陷结构的第一原理计算

采用第一原理赝势平面波方法,计算了B2-RuAl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金属间化合物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.这些点缺陷主要以Ru-Ru双空位和Al-Al双反位的组态结构形式出现,并且双空位以Ru-Ru为第一近邻时其点缺陷结构最稳定,而双反位则是以Al-Al为第三近邻时稳定性最高.进一步通过对NiAl和RuAl不同点缺陷结构Cauchy压力的比较,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.     

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。     

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。     

微观相场法研究高铝Ni75AlxV25-x中Ni3Al反位缺陷

采用微观相场法研究高Al浓度Ni75Akv25-x合金析出相Ni3Al的反位缺陷随Al浓度增高的变化规律.选取在1150 K温度下时效从8 at%Al至20 at%Al的共14个合金作为研究对象.研究结果显示:此类型合金主要反位缺陷类型是VAl、NiAl;随Al浓度增高,反位缺陷AlNi增高:而Ni Al、VAl、VNi 3种反位缺陷变化与Al浓度和Ni3V析出与否相关,Al浓度稍低时,有Ni3v相析出,Al浓度增高反位缺陷Ni Al降低,VHi升高,VAl没变化;Al浓度稍高时,无Ni3V相析出,Al浓度增高反位缺陷NiAl稍有降低,VNi、VAl明显降低.     

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。     

金属间化合物Ni3Al点缺陷的理论计算

本文建立起Ll_2型金属间化合物点缺陷的平衡方程,计算了Ni_3Al中反位置缺陷、空位的浓度分布并通过考察点缺陷的温度效应,在理论上澄清了对Ni_3Al中“组分点缺陷”性质的认识     

基于马儿可夫链B2-NiAl反位缺陷的模型推导与计算

基于马儿可夫链理论和Bragg-Williams型方程,建立了描述反位缺陷占位几率的基本方程和转移几率;推导出了平衡时空位与反位缺陷浓度的表达式。利用所建模型结合第一性原理平面波赝势法系统研究了NiAl中各种点缺陷,从定量计算和电子结构角度论证了平衡状态下,在Ni:Al=1附近,Ni和Al原子的占位服从Fermi-Dirac统计,并且当温度从800增加到1300K时,NiAl几率比AlNi几率大106～109倍,反位缺陷以NiAl为主。VNi浓度比AlNi浓度大105～107倍、而NiAl浓度比VAl浓度大106～1010倍。对于同一原子而言,NiAl比VNi稳定,AlNi比VAl稳定。     

基于Miedema模型Al3X(Sc, Er, Zr, Li)点缺陷形成焓的计算

运用Miedema模型研究了Al3X(Sc,Er,Zr,Li)金属间化合物的形成焓,并结合点缺陷形成理论计算了Al3X空位和反位缺陷的形成焓。结果表明Al-Sc和Al-Er系形成焓较为接近,说明Sc和Er在Al中性质相近。Al-X(Sc,Er,Li)二元化合物中X原子的空位形成焓高于Al原子的空位形成焓,表明Al-X系二元化合物更易形成Al空位。Al3Er反位缺陷形成焓最大,Al3Zr和Al3Sc居中,Al3Li最小。Al3Sc、Al3Er和Al3Zr易于出现空位和反位两类缺陷共存的情形,而Al3Li反位缺陷形成焓明显小于空位形成焓,因而更易形成反位缺陷。     

ATOMISTIC SIMULATION OF POINT DEFECTS IN NiAl ALLOY

ＡＴＯＭＩＳＴＩＣＳＩＭＵＬＡＴＩＯＮＯＦＰＯＩＮＴＤＥＦＥＣＴＳＩＮＮｉＡｌＡＬＬＯＹ①ＬｉｕＺｈｅｎｙｕｎ，ＬｉｎＤｏｎｇｌｉａｎｇ，ＣｈｅｎＤａＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅ，ＳｈａｎｇｈａｉＪｉａｏＴｏｎｇＵｎｉｖｅ...     

Point defect concentrations of L1_2-Al_3X(Sc,Zr,Er)

The point defect concentrations of Ll_2-Al_3 X(Sc,Zr,Er) were systematically investigated using the firstprinciple calculations with thermodynamics approach.The results show that the constitutional point defects of offstoichiometric Ll_2-Al_3 X(Sc,Zr,Er) prefer to occur in X sublattice,that is X anti-site in X-rich alloy and X vacancy in Al-rich alloy,respectively.And A1 anti-site also has a high density in Al-rich Ll_2-Al_3 X(Sc,Er).It is found that the point defect concentrations of stoichiometric Ll_2-Al_3 X(Sc,Zr) follow in the sequence as: A1 vacancies(V_(A1)) X vacancies(V_X) X anti-sites(X_(Al)) A1 antisites(Al_X).The point defect concentration of stoichiometric Al_3 Er is similar to that of L12-A13 X(Sc,Zr).The result suggests that the A1 vacancy(V_(A1)) is a dominant point defect in L12-A13 X(Sc,Zr,Er).A simple parameter Hv_x-Hv_(Al) can be used for a rough estimation of the point defect concentrations in Ll_2-Al_3 X structure.Some rules of point defect concentrations for L1_2-Al_3 X(Sc,Zr,Er) are also revealed.     

空位缺陷对单层MoS_2电子结构的影响

为了研究单层Mo S2中的空位缺陷形成及其对电子结构的影响,基于密度泛函理论框架下的第一性原理,采用平面波赝势方法分别计算了单层Mo S2中Mo空位和S空位的形成能、空位附近的晶格畸变、Mo S2层中的电子分布以及态密度(DOS)和能带结构。计算结果显示,2种空位缺陷都具有点缺陷特征,其附近的电子分布呈现出明显的局域化特点,且S空位比Mo空位更容易形成。通过与本征态Mo S2电子结构的对比分析,发现2种空位缺陷的存在对单层Mo S2的电子结构、尤其是对导带高能量区域的能态密度会产生十分明显的影响,这些影响可能与空位缺陷引入的缺陷能级有关。     

Site occupancies,point defect concentrations,and solid solution hardening in B2 (Ni,Fe)Al

A novel approach was used to characterize the site occupancies and point defect concentrations in the B2-ordered (Ni,Fe)Al single phase field over a wide range of composition and temperature. This approach combined atom location by channeling enhanced microanalysis (ALCHEMI) determinations of atomic site occupancies and vacancy concentration measurements. The triple defect structure was observed across the entire phase field. Qualitative thermodynamic predictions such as that Fe anti-site are more stable than Ni anti-sites were confirmed. However, in some portions of the phase field it was found that Ni anti-site concentrations were higher than expected from simplistic thermodynamic predictions of site preference. Such predictions are clearly inadequate if a quantitative determination of site occupancies is desired. The importance of this type of characterization in interpreting solid solution hardening (SSH) in ordered compounds was illustrated by considering three portions of the (Ni,Fe)Al phase field. In all three cases the solute atoms did not directly harden, but affected the hardness by altering the concentrations of other point defects.     

Point Defect Concentrations and Interactions in D0(19)-Ti3Al from First- Principles CalculationsEI北大核心CSCD

The intermetallics D0(19)-Ti3Al has low specific density and high thermal resistance for both bulk and coating applications in engineering area. The point defects such as thermal vacancy, compostion vacancy and antisite defect have great influence on the properties of D0(19)-Ti3Al, but are usally neglected. According to available research data from both theory and experiment, it is commonly considered that the thermal vacancies in D0(19)-Ti3Al provide paths for atomic migration and diffusion, the antisite defects play an important role in the disordering of D0(19)-Ti3Al, and the interaction between composition vacancy and antisite defect may have important influence on atomic diffusion and dislocation movement. So it is necessary to explore the mechanism of interaction between composition vacancy and antisite defect for more accurate understanding of the atomic diffusion, dislocation movement and plastic deform in D0(19)-Ti3Al. In this work, the formation enthalpy, equilibrium concentration, and binding energy of composition vacancy and antisite defect in D0(19)-Ti3Al intermetallics were calculated by using both the Wagner-Schottky model of point defect thermodynamics and the plane wave pseudopotential method in first-principles. Results suggest that, in the whole composition range of interest, the point defect concentrations increase with the increase of temperature. In particular, the concentrations of antisite defects are higher than those of vacancies, and the vacancy concentration of Ti is higher than that of Al. At the stoichiometric composition, the concentrations of antisite defects of Ti and Al are very close. At the Ti-rich side of component, the antisite defect of Ti dominates in concentration, while at the Al-rich side, that of Al dominates in concentration. For the calculated results of 3 types of point defect pairs, AlTi-TiAl, TiAl-TiAl and VAl-AlTi, they may have the strong trend to aggregate, while others may show the tend to diffuse into the matrix.     

Microscopic phase-field modeling of atomic anti-site behaviors in precipitation progress of Ni3(AlFe)

The effects of temperature on atomic anti-site behaviors in L12-Ni3(AlFe) phases were studied using microscopic phase-field dynamic model in precipitation progress of Ni75Al20Fe5 alloy.The results show that with the increase of temperature,the formation of NiAl and AlNi anti-sites is much easier in Ni3(AlFe),and Ni and Al anti-site atoms show clearly stronger temperature-dependent than Fe anti-site atoms.The evolution progress of anti-site atoms is completed at the initial growth stage of L12-Ni3(AlFe) phases.The site occupation probabilities of Ni atoms on the sublattice A(NiNi,face centers sites of FCC),and Al and Fe atoms on the sublattice B(AlAl and FeAl,corners sites of FCC) all present the degressive tendency with the temperature increasing.Fe atoms mainly prefer to occupy the Al sublattice at the whole temperature range.     

The native point defects in C14 Mg2Ca Laves phase: A first-principles study

The native point defects in C14 Mg₂Ca Laves phase are studied from the first-principles density functional theory calculations within GGA approximation. The defect formation energies indicate that anti-site defects are energetically favored over vacancies. Under Mg-rich and even general Ca-rich condition, defect Mg_Ca of Mg anti-site on Ca sublattice is favorable owing to the lowest formation energy. The Ca_Mg2 defect of Ca anti-site on Mg2 sublattice is also likely dominant only under extreme Ca-rich environment. The present results could explain reasonably the asymmetric off-stoichiometry of Mg₂Ca. The effective point defect concentrations of Mg₂Ca as a function of composition and temperature at experimental range are also calculated from a canonical statistical model, and the derived results show a linear relationship between the logarithm of defect concentration and T⁻¹. Geometrical factor is further studied, and it is found that atomic size possesses an obvious influence on the structure of point defect in Mg₂Ca. The electronic feature is further studied to reveal underlying mechanism for formation of point defects.     

Influence of chemical composition and alloying elements on microdefects and electron density in Ni—Al alloys

1　ＩＮＴＲＯＤＵＣＴＩＯＮＬｌ2 Ｎｉ3ＡｌａｎｄＢ2 ＮｉＡｌａｒｅｉｍｐｏｒｔａｎｔｉｎｔｅｒｍｅｔａｌ ｌｉｃｃｏｍｐｏｕｎｄｓｉｎＮｉＡｌａｌｌｏｙｓ .ＡＮｉ3Ａｌａｌｌｏｙｈａｓｒｅｌａ ｔｉｖｅｌｙｈｉｇｈｓｔｒｅｎｇｔｈａｎｄｐｒｅｓｅｎｔｓｒｅ