V-5Cr-5Ti合金弹性和力学性质的第一性原理研究

V-5Cr-5Ti合金作为核聚变堆第一包层的主要候选结构材料之一,但对其力学性质的理论研究相对较少.采用随机固溶体模型,利用第一性原理方法计算出V-5Cr-5Ti合金的弹性常数、体模量、剪切模量、杨氏模量、泊松比和柯西压力等,并与计算出的纯钒的相关数值进行对比,结果表明V-5Cr-5Ti合金具有良好的塑性和强度,但其塑性要略低于纯钒的.并对加入氧原子后的V-5Cr-5Ti合金进行了相关计算,通过对比计算结果发现,由于氧原子的加入,使V-5Cr-5Ti合金的塑性和强度都出现了不同程度的降低.最后对V-5Cr-5Ti合金和纯钒的理论强度进行了计算,并绘制出两者的应力-应变关系图,通过对比再次验证了上面的结论.     

基于第一性原理计算Rh含量对Ir-Rh合金力学性能的影响

采用密度泛函理论的第一性原理平面波赝势方法,基于虚拟晶体势函数近似,通过计算Ir-xRh(x=0,5,10,20,30,40,50,60,70,80,90,100)合金的弹性常数、体积模量、剪切模量、杨氏模量、泊松比等力学常数、电荷密度和能态密度,研究Rh含量对Ir-Rh合金力学性能的影响通过实验对计算结果加以验证,证明将虚晶近似法运用在Ir-Rh合金力学性能的计算中是合理的研究结果表明,Ir-Rh合金的强度和硬度随Rh含量的升高迅速增大,在Ir-10 Rh处达到最大值后快速下降到Ir-40 Rh处后先缓慢上升再缓慢下降.Rh的添加会引起材料脆化,其脆性大小随着Rh含量的升高先增大后减小,在Ir-50 Rh处达到最大值.另外,计算了纯Ir,Ir-10 Rh,Ir-50 Rh,纯Rh的电荷密度、Ir和Rh的差分电荷密度以及能态密度,结果表明在铱铑合金中存在一种"伪共价键",从而导致其力学性质的异常.     

金属元素掺杂对TiAl合金力学性能的影响

利用基于密度泛函理论的第一性原理方法研究了金属元素X (X分别表示V, Nb, Ta, Cr, Mo和W)掺杂对TiAl合金性能的影响. 研究发现, 掺杂可以有效减小合金的各向异性, 增强Ti-Al 原子间的相互作用, 同时增强金属键性, 减弱共价键性, 有利于塑性变形. 在相同的压力下, 不同的掺杂浓度和掺杂元素对体积的影响不同. 通过计算不同掺杂体系的弹性常数、体弹模量和剪切模量可知: 当掺杂浓度为6.25%时, 相对于V, Nb和Ta, Cr, Mo和W掺杂能较好地改善TiAl金属间化合物的韧性; 当掺杂浓度为12.5%时, 相对其他掺杂元素Mo的韧化作用最强. 从Mo掺杂后TiAl体系的分波态密度和电荷密度图, 发现Mo和Ti 原子发生强烈的s-s, p-p, d-d电子相互作用, 有效地束缚了合金中Ti和Al原子的迁移, 有助于提高合金的稳定性和强度.     

铟钇金属间化合物力学性能的第一性原理计算

本文基于密度泛函理论的平面波超软赝势方法,对铟钇(In-Y)金属间化合物的力学结构稳定性、弹性性质和热力学性能进行了研究.通过结构优化得到了In_3Y、InY、InY_2三种金属间化合物的晶格常数,发现与实验值比较吻合.弹性常数的计算结果表明In-Y金属间化合物的结构是稳定的,由弹性常数推算出In_3Y、InY、InY_2三种合金的体积模量、杨氏模量、剪切模量、泊松比和各向异性等力学性质,发现InY_2合金的体积模量、杨氏模量、剪切模量要比其它两种的值大,其抗形变能力更强.本文还预测了In-Y金属间化合物的热力学性质,如德拜温度、热导率,通过第一性原理计算得到的In-Y金属间化合物的力学和热力学性质为In-Y合金材料的实际应用和材料设计提供了参考.     

一种获得剪切模量压强二阶偏导数G″P的方法

从晶格材料的电子结构理论出发,推导了一个计算剪切模量G的压强二阶偏导数G″_{P的方法.针对93钨合金材料计算得到G″P=-0.033GPa^{-1,把这一结果 用于Birch-Murnaghan有限应变理论的计算,并与G″P=0的计算结果进行了比较 .结果表明,G″P=0的计算结果明显高于G″P≠0的计算结果,在压 强较高时,二者结果相差较大.因此,在高压下,必须考虑G″P关键词： 剪切模量 压强二阶偏导数 钨合金 物态方程 有限应变理论}}     

Pt25Rh/TaC界面特性的第一性原理研究

铂铑(PtRh)合金具有优良的高温力学性能,是目前最具潜力的航天发动机推力器喷管材料之一.研究表明,进一步提升PtRh合金的高温性能,能有效延长航天飞行器的服役寿命.本研究利用第一性原理、Materials Studio软件,研究了Ta C热障涂层与Pt25Rh高温合金的界面特性和结合机制.结果表明,Ta C的热膨胀系数与Pt25Rh较为接近,比同类热障涂层具有更优的界面匹配性和结合力,既可作为单独的防护层使用,也可作为粘结层使用.此外,由于Ta-C,Pt-C和Rh-C键的电荷转移能力均强于Ta-Pt和Ta-Rh键,Ta C与Pt25Rh合金的最稳定结合位置为孔位的Pt25Rh (111)/Ta C (111)_C,其界面粘附功为6.202 J/m².本研究可为PtRh合金的热防护提供借鉴.     

基于剪切模量和热分析数据研究Zr_(50–x)Cu_(34)Ag_8Al_8Pd_x(x=0,2)非晶合金缺陷浓度演化

非晶合金具有独特物理和力学性能,如何建立非晶合金微观结构非均匀性与物理/力学性能之间的关联是非晶固体的重要研究课题之一.微合金化是调控非晶合金微观结构有效手段之一.本研究以玻璃形成能力优异的Zr_(50–x)Cu_(34)Ag_8Al_8Pd_x(x=0, 2)非晶合金为模型合金,借助差示扫描量热仪和电磁声转换设备,研究非晶合金铸态、弛豫态和结晶态热流和剪切模量随温度的演化规律,以及物理时效(低于玻璃转变温度)过程剪切模量的变化随时间演化规律.基于自间隙原子理论,利用热流曲线表征非晶合金在相同热历史剪切模量热效应.通过分析铸态和弛豫态自间隙缺陷浓度和激活能谱,发现结构弛豫导致自间隙缺陷浓度减小,诱导剪切模量随温度演化偏离软化过程,并伴随体系放热.与此同时,研究发现添加微量Pd元素可抑制模型合金体系原子迁移,增加特征弛豫时间.本研究从非晶合金模量热效应角度进一步理解非晶合金微观结构非均匀性.     

Kossel技术中比率方法的改进

本文对Kossel比率方法进行了改进,同时得到一种Kossel定向方法。它能适用于通常用的比率方法不能分析的许多Kossel花样。并且用它分析了Fe-0.76wt％V-0.08wt％N稀合金的随意定向的Kossel花样,其点阵参数精度达5×10^-5?。 关键词：     

铜基大块非晶合金添加微量元素对腐蚀行为的影响机理研究

通过分子动力学方法模拟了Cu-Al合金液相,然后模拟降温过程得到Cu-Al非晶合金.通过计算机编程建立了Cu-Al-M非晶基体、Cu-Al-M非晶表面及吸附O原子Cu-Al-M非晶表面原子结构模型.利用实空间连分数方法,研究了添加微量合金元素Zr,Nb,Ta,V,Y,Sc对Cu基大块非晶合金的腐蚀行为的影响机理.研究发现合金元素Zr,Nb,Ta,V,Sc不向清洁Cu基非晶表面偏聚,但除Y外向有氧吸附的表面偏聚,说明有氧吸附后Cu基非晶表面偏聚发生逆转.键级积分计算表明Zr,Nb,Ta,V,Y,Sc元素均增大与氧之间的结合力,易形成氧化膜,提高Cu基大块非晶的耐蚀性.稀土Y提高Cu基大块非晶的耐蚀性可能是由于它向合金与氧化膜界面偏聚并提高了合金与氧化膜的结合力.     

W-Cu合金力学性能的第一性原理计算

采用基于密度泛函理论的第一性原理分析方法的CASTEP软件,计算了W-Cu_x(x=6.25,12.5,18.75,25,31.25,37.5,43.75,50)合金的晶格参数、体模量、剪切模量、杨氏模量等力学常数,还计算了焓变值、能带结构、电子态密度和电荷布局,研究Cu不同含量对W-Cu合金力学性能的影响.结果表明：Cu的添加会增加W基体触头材料的可塑性,韧性大小随着Cu含量的升高而增加,在掺杂比例为43.75%时达到最大值,韧性增加使得产生微裂纹的概率减小;另外还计算了W-Cu合金的态密度、能带结构和电荷布局,结果表明随着Cu含量的增加,共价性降低,金属性增强,便于加工成型.     

Elasticity,anelasticity, and microplasticity of directionally crystallized aluminum-germanium alloys

The structure, Young’s modulus defect, and internal friction in aluminum-germanium alloys have been studied under conditions of longitudinal elastic vibrations with a strain amplitude in the range of 10^?6?3 × 10^?4 at frequencies about 100 kHz. The ribbon-shaped samples of the alloys with the germanium content from 35 to 64 wt % have been produced by drawing from the melt by the Stepanov method at a rate of 0.1 mm/s. It has been shown that the dependences of the Young’s modulus defect, logarithmic decrement, and vibration stress amplitude on the germanium content in the alloy at a constant strain amplitude have an extremum at 53 wt % Ge. This composition corresponds to the eutectic composition. The dependences of the Young’s modulus defect, the decrement, and vibration stress amplitude at a constant microstrain amplitude have been explained by the vibrational displacements of dislocations, which depend on the alloy structure.     

Thermal stability and high-temperature shape memory characteristics of Ti–20Zr–10Ta alloy

The microstructure, martensite transformation behavior, thermal stability and shape memory behavior of Ti–20Zr– 10Ta high temperature shape memory alloy were investigated. The Ti–20Zr–10Ta alloy exhibited a reversible transformation with the high martensite transformation temperature of 500oC and good thermal stability. The alloy displayed the elongation of 15% and a maximum recovery stain of 5.5% with 8% pre-strain.     

Structural and phase transformations in ferromanganese alloys during deformation under pressure

Using optical metallographic, TEM, Mössbauer spectroscopy, and X-ray analysis the structural and phase transformations in Fe-(3–55) wt % Mn alloys during shear deformation under pressure were investigated. It is established that a large deformation under high pressure causes the formation of a nanocrystalline structure with grain sizes of 40–60 nm. Nanostructure increases the hysteresis of inverse (hcp-fcc) transformation and stabilizes the (hcp) ? phase in alloys containing more than 40 wt % Mn, up to normal conditions. The Fe-3 wt % Mn alloy after shear under pressure treatment became nanostructured, retaining the original bcc phase state.     

Effects of micro-additions on structures and properties of rapidly solidified Sn-10% Sb alloy

Structure, electrical resistivity, hardness, internal friction and elastic modulus of Sn-10% Sb and Sn₈₉Sb₁₀M₁ (M₁ = Ag, Cu, Zn and Pb) alloys have been investigated. No obvious change on the electrical resistivity value was found at 293 °K of a Sn-10% Sb alloy by adding Zn and Cu, but extreme changes occurred after adding Ag and Pb. The elastic modulus, internal friction, hardness and thermal diffusivity values are greatly affected by adding the micro-additions to a Sn-10% Sb rapidly solidified alloy. It is also interesting to note that Ledbetter's theoretical values of μ/E are in good agreement with the experimental results. The rapidly solidified alloys Sn₉₀Sb₁₀ and Sn₈₉Sb₁₀Ag₁ have good properties as toxic-free lead solder alloys for high-temperature applications and good mechanical properties such as under the hood in the automobile and avionics systems. Also, the rapidly solidified alloys Sn₈₉Sb₁₀Zn₁, Sn₈₉Sb₁₀Cu₁ and Sn₈₉Sb₁₀Pb₁ have good properties as bearing materials.     

ESCA studies of Ni-Cr alloys

ESCA examination on Ni-Cr alloys has shown that a thin passive film was formed after 24 h immersion in 0.1 M NaCl. The film contained only chromium oxide in the form of Cr₂O₃. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate of the alloys. Both Ni-10 wt. % Cr and Ni-20 wt. % Cr alloys showed a slightly higher corrosion rate than the Ni-40 wt. % Cr alloy.The present ESCA study of the Ni-Cr system is part of our programme which involves an examination of the four binary alloy systems Fe-Si, Cr-Co, Ni-Cr, and Mo-Ni [1]. The aim is to correlate the structure and composition of the passive films formed in 0.1 M NaCl to the corrosion behaviour in the same solution.     

Pressure-dependence of mechanical and thermodynamic properties of Al3Zr in Al–Li alloys from first-principles calculations

The pressure-dependence of mechanical, electronic and thermodynamic properties of metastable (L1₂ type) and stable (D0₂₃ type) Al₃Zr precipitations in Al–Li alloys were investigated by employing the first-principle calculations. The calculated equilibrium parameters are in good agreement with experimental and previous calculation results available. Elastic properties including bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and universal anisotropic index are determined by Voigt–Reuss–Hill approximation. It is found that for both phases, external pressure can improve the mechanical stability, ductility and plasticity. The electronic structures are determined to reveal the bonding characteristics of both phases. In addition, both phonon method and Gibbs program have been proposed to predict thermodynamic properties of two phases. All of these results can help to have a better understanding of the physical and chemical properties of Al₃Zr precipitations in Al–Li alloy. And can offer theoretical guidance for the weight lighting, energy conservation and emissions reduction in the design of new aluminium alloys.     

Synthesis of copper alloys with extended solid solubility and nano Al2O3 dispersion by mechanical alloying and equal channel angular pressing

Cu–4.5 wt % Cr and Cu–4.5 wt % Cr–3 wt % Ag alloys, with and without nanocrystalline Al₂O₃ dispersions (particle size <10 nm), were synthesized by mechanical alloying/milling and consolidated by equal-channel angular pressing (ECAP) at ambient temperature. Microstructural characterization and phase analysis by X-ray diffraction, as well as scanning and transmission electron microscopy, provided evidence for the formation of a Cu-rich extended solid solution with nanometric (<30 nm) crystallite size after 25 h of milling, with uniformly dispersed alumina nanoparticles embedded in it. Consolidation of Cu–4.5 wt % Cr–3 wt % Ag alloy with 10 wt % nanocrystalline Al₂O₃ by eight ECAP passes was shown to result in a composite with an exceptionally large hardness of 390 VHN and enhanced wear resistance. The electrical conductivity of the pellets of the latter alloy without Al₂O₃ is about 30% IACS (international annealing copper standard), whereas pellets with 5 or 10 wt % Al₂O₃ dispersion exhibit a conductivity of about 20–25% IACS. Thus, the present room temperature synthesis and consolidation route appear to offer a promising avenue for developing high-strength, wear/erosion-resistant Cu-based electrical contacts with nano-ceramic dispersion.     

HAADF imaging of the omega (ω) phase in a gum metal-related alloy

Nanosized precipitates have been observed in a Nb-lean gum metal-related alloy, Ti–20.0Nb–0.6Ta–1.7Zr–1.1O?at.% (Ti–31.9Nb–2.0Ta–2.7Zr–0.3O?wt.%) using probe-corrected high-resolution scanning transmission electron microscopy with a high-angle annular dark-field detector (HAADF). This characterization yields three distinct atomic motifs and STEM multislice simulations are semi-quantitatively used to verify that each motif can be attributed to the widely observed “athermal” omega phase. However, the presence of chemical ordering cannot be unambiguously ruled out in this system. Data presented here, demonstrate the complexity of interpreting HAADF images of multiphase, multicomponent alloys when complementary experimental data are unavailable.     

The structural,elastic,and electronic properties of Zr_x Nb_(1-x)C alloys from first principle calculations

The structural,elastic,electronic,and thermodynamic properties of Zr x Nb1-x C alloys are investigated using the first principles method based on the density functional theory.The results show that the structural properties of Zr x Nb1-x C alloys vary continuously with the increase of Zr composition.The alloy possesses both the highest shear modulus(215 GPa)and a higher bulk modulus(294 GPa),with a Zr composition of 0.21.Meanwhile,the Zr0.21Nb0.79C alloy shows metallic conductivity based on the analysis of the density of states.In addition,the thermodynamic stability of the designed alloys is estimated using the calculated enthalpy of mixing.