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。     

B2-YX（X=Cu，Rh，Ag，In）点缺陷结构及其基本物性的理论计算

采用第一原理赝势平面波方法，计算了B2-YX（X=Cu，Rh，Ag，In）金属间化合物的基本物性。通过对不同点缺陷结构形成热和形成能的计算与比较，分析和预测了B2-YX金属间化合物中点缺陷结构的种类与存在形式。结果表明：B2-YX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。通过对B2-YX金属间化合物完整晶体与点缺陷结构Cauchy压力参数C12．C44和G／B。值的比较，发现点缺陷能明显提高B2-YX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B2-YX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。     

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。     

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。     

V掺杂Ni3Al点缺陷结构及合金化效应的第一性原理研究

基于密度泛函理论的第一性原理平面波赝势方法研究了V掺杂Ni3Al合金的电子结构和点缺陷结构.通过计算与实验结果对比选择了适合Ni3Al合金计算的近似方法,计算了含有各个缺陷的晶胞的晶格常数,形成热和结合能,点缺陷的形成能和平衡浓度,态密度和电荷密度.计算结果表明:Ni3Al合金中反位缺陷较空位缺陷易形成,NiAl是Ni3Al合金中最主要的反位缺陷,Al位最易形成缺陷,在1400 K时,空位缺陷的浓度远远低于反位缺陷的浓度.V加入Ni3Al合金体系中能提高合金的稳定性.     

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。     

硼在RuAl金属间化合物中的强化和韧化作用

评述了硼(B)在RuAl金属间化合物中的强化和韧化作用.含αRu+ RuAl共晶组织的亚共晶Ru-Al合金具有优良的高温性能和室温韧性.B是RuAl金属间化合物的强化和韧化元素,当Ru53Al47合金中加入0.5at％B时,最大压缩真应变由0.17增加到0.34,最大压缩真应力由1.3GPa增加到3.0GPa.B在Ru...     

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。     

高温结构金属间化合物及其强韧化机理

综述了自1988年以来中国科学院高温合金和金属间化合物研究组(郭建亭研究组)在高温结构金属间化合物NiAl及其合金、Ni3Al及其合金、FeAl和Fe3Al及其合金、TiAl合金以及金属间化合物环境脆性方面的主要研究成果:NiAl合金超塑性的发现及其机理研究;稀土元素改善NiAl合金的室温塑性和高温抗氧化性能;NiAl合金的韧脆转变行为及其机理;纳米晶NiAl合金及其复合材料的强韧化;内生颗粒增强NiAl基复合材料及强韧化机制;NiAl合金良好的耐高温摩擦磨损性能及自润滑机理的发现;NiAl中合金元素的作用与JJ-3合金的发展;在国际上首先发现适量Zr可韧化无硼Ni3Al合金;为使Ni3Al强韧化硼含量应加至溶解度附近;FeAl合金反常屈服峰的发现及其机理研究;微量Mg可明显改善FeAl和Fe3Al合金的室温塑性;TiAl-W-Si合金的组织、相转变和界面精细结构;金属间化合物的环境脆性实质是氢致脆性;在国际上首先用第一原理方法(DVM)研究了L12型CO3Ti的环境脆性.     

ATOMISTIC SIMULATION OF POINT DEFECTS IN NiAl ALLOY

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Defect structures and ternary lattice site preference of the B2 phase in the Al–Ni–Ru system

The energies for stoichiometric and defected binary and ternary B2 phases in the Al–Ni–Ru ternary system were calculated from first-principles. The dominant compositions-conserving constitutional defect structures for NiAl and RuAl have been determined as (Al, Ni)(Ni, Va) and (Ru, Al, Va)(Al), respectively. It was observed that Ru prefers the Ni-sublattice in NiAl, while Ni has a very strong preference for the Ru-sublattice in RuAl. Furthermore, the results indicate that a miscibility gap is likely to be stable at low temperatures in the NiAl–RuAl pseudobinary system.     

High-temperature stability of nano-grained B2-structured RuAl-based intermetallics by mechanical alloying

A series of nano-grained B2-structured RuAl-based intermetallics and corresponding composites are synthesized by mechanical alloying. These RuAl-based materials include stoichiometric RuAl, B2-structured ternary (Ru,Ni)Al and (Ru,Ir)Al, eutectic RuAl–Ru and particle reinforced RuAl–ZrO₂ composite. The accumulation of impurities, mainly Fe, in grain boundaries and the structural evolution during grain growth are found to be the controlling factors for the grain growth stagnation in nano-grained B2-structured binary RuAl and ternary (Ru,Ni)Al and (Ru,Ir)Al intermetallics. Ternary alloying element forming iso-structured pseudo-binary compounds, eutectic in situ and ceramic particle reinforced composites are explored to be the effective routes to enhance the stability of single-phase RuAl. The thermal stability of microstructure in various RuAl-based materials are found to decrease in a sequence from pseudo-binary RuAl–IrAl, RuAl–NiAl, eutectic RuAl–Ru composites, ceramic particle reinforced RuAl–ZrO₂ composites to binary stoichiometric RuAl.     

Bonding characteristics of micro-alloyed B2 NiAl in relation to site occupancies and phase stability

A recently developed mean-field model has been combined with first principles calculations of binding energy to investigate the site occupancies of micro-alloying elements and vacancies in NiAl as well as the stability of the micro-alloyed B2 phase with respect to disordering and second-phase formation. The theoretical results suggest that the transition metal elements in the same row of the periodic table increasingly tend to the Ni sublattice with increasing atomic number. Micro-alloying addition tends to decrease the vacancy concentration of NiAl alloys. Alloying with X that substitutes for Ni is predicted to have the sides of its solubility lobe parallel to the Ni–X side of the isotherm, but parallel to the Al–X side if X substitutes for Al. Micro-alloying was shown to raise the ordering temperature of the B2 phase over the corresponding binary alloy, in contrast with the effect of vacancies. Alloying effects on ordering temperature and the formation of point defects appear independent of the site substitution behaviour, and are less significant for 3d than for 4d and 5d transition metal elements.     

Modelling of defects and amorphisation by ball milling of γ-TiAl

The formation and site preference energies and volume changes of single and pair of defects of ternary alloying elements in γ-TiAl intermetallic compound were studied by the density functional theory. Slight tendency to clusterization of antisite defects has been found. This may lead to disorder in the system. The V and Cr atoms prefer to reside in the Ti sublattice. The formation energy for Cr–Cr, Cr–V and V–V nearest neighbour pairs are in the 1.3–2 eV range. The Al antisite in Ti sublattice requires much less energy than the Ti antisite in Al sublattice. The amorphisation process of TiAl alloy was studied by means of high energy ball milling of Ti and Al elemental powders, which produces amorphous structure after 40 h. The amorphous states were studied by the DFT calculations of many random atomic configurations and the results were compared with the NiAl compound. Possible explanation for the amorphisation of the TiAl compound is presented.     

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.     

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.     

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

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Effects of Ni vacancy,Ni antisite,Cr and Pt on the third-order elastic constants and mechanical properties of NiAl

Effects of Ni vacancy, Ni antisite in Al sublattice, Cr in Al sublattice, Pt in Ni sublattice on the second-order elastic constants (SOECs) and third-order elastic constants (TOECs) of the B2 NiAl have been investigated using the first-principles methods. Lattice constant and the SOECs of NiAl are in good agreement with the previous results. The brittle/ductile transition map based on Pugh ratio G/B and Cauchy pressure P_c shows that Ni antisite, Cr, Pt and pressure can improve the ductility of NiAl, respectively. Ni vacancy and lower pressure can enhance the Vickers hardness H_v of NiAl. The density of states (DOS) and the charge density difference are also used to analysis the effects of vacancy, Ni antisite, Cr and Pt on the mechanical properties of NiAl, and the results are in consistent with the transition map.