Nb-Si-N 纳米复合薄膜中的界面力学性能研究

基于密度泛函理论的第一性原理方法,研究了Nb-Si-N纳米复合薄膜间隙型界面结构和置换型界面结构的力学性能。采用第一性原理方法计算了不同应变下的系统能量,通过分析得到其力学常数。计算出间隙型界面和置换型界面结构的体积模量分别为233.595 GPa和280.204 GPa,剪切模量分别为70.716 GPa和125.677 GPa,杨氏模量分别为192.702 GPa和327.994 GPa。这表明Nb-Si-N纳米复合薄膜置换型界面结构的抗剪切形变与抗压缩形变都优于间隙型界面结构。杨氏模量各向异性分析显示,两种界面结构各方向弹性较为一致,NbN各方向弹性差别较大。     

Theoretical prediction of effective elastic constants for new intermetallic compound porous material

Based on microstructure analysis of the new Ti-Al intermetallic compound porous material, a micromechanics model of heterogeneous Plateau porous structure was established and calculation formulas of elastic constants (including effective elastic modulus, effective shear elastic modulus and effective Poisson ratio) were derived by the energy method for this porous material. Calculation results show that both the effective elastic modulus and effective shear elastic modulus increase with the increase of the relative density while the effective Poisson ratio decreases. Compared with the currently-existing hexagonal honeycomb model and micromechanics model of composite materials, the micromechanics model of heterogeneous Plateau porous structure in this study is more suitable for characterizing the medium-density porous material and more accurate for predicting the effective elastic constants of the medium-density porous material. Moreover, the obtained explicit expressions of the effective elastic constants in term of the relative density rather than the microstructural parameters for the uniform and regular Plateau porous structure are more convenient to engineering application.     

Effects of cell irregularity on the elastic properties of open-cell foams

Foams are more and more widely used because of their high mechanical properties relative to their low density. Most available mechanical models are based on idealised unit-cell structures. A significant disadvantage of the unit-cell modelling approach is that it does not account for the natural variations in microstructure that are typical for most foam structures. Our objective has been to investigate how the cell irregularity affects the elastic properties of open-cell foams. We generated periodic, three-dimensional (3D), random samples with different degrees of irregularity, and used finite element analysis (FEA) to determine the effective elastic properties. The geometrical properties were investigated for 3D random open-cell foams and related to the elastic properties. The results indicate that the more irregular the foams, the larger will be their effective Young's modulus and shear modulus at constant overall relative density. On the other hand, the bulk modulus reduces with increasing degree of cell irregularity, while the Poisson's ratio is largely independent.     

第一性原理计算Mo含量及压力对CrZrNbTiMox难熔高熵合金性能的影响

利用基于密度泛函理论的第一性原理方法研究Mo含量和压力对CrZrNbTiMo_x难熔高熵合金相结构、弹性常数和弹性模量的影响。计算了CrZrNbTiMo_x难熔高熵合金的混合焓(ΔH_mix)、混合熵(ΔS_mix)、原子半径差(δ)、价电子浓度(VEC)以及参数Ω。结果表明,CrZrNbTiMo_x难熔高熵合金主要以单一的BCC无序固溶体结构为主。随着Mo含量的增加,合金的晶格畸变不断减小,但力学性能稳定且始终以金属键结合。Mo的添加对合金的抗体积变形能力提升较大、对抗切应变能力及刚度影响较小,合金表现为韧性材料。在0～25 GPa压力作用下,CrZrNbTiMo_0.6合金表现出优异的相稳定性和力学稳定性,体弹性模量(B)增幅较小,剪切弹性模量(G)、杨氏模量(E)变化较小;泊松比μ及G/B计算结果表明合金为韧性材料。     

Velocities of elastic waves and the elasticity moduli of nickel-base superalloys and of the 60N21 alloy

Measurements of velocities of elastic waves have been performed in polycrystalline samples of an intermetallic compound Ni₃Al, this intermetallic compound alloyed with niobium or cobalt, superalloys ZhS36 and VKNA-4U, and the 60N21 alloy. Elasticity moduli have been calculated, namely, Young’s modulus, shear modulus, bulk modulus, and the Poisson ratio. The results obtained are compared with those calculated from the tensor of the elasticity moduli obtained for single crystals. The calculations have been performed in the Voigt and Reuss approximations.     

First-principle study on the physical properties of ultra-incompressible ReB2

The elastic and physical characteristics of ReB₂ crystal have been predicted through a method of density functional theory within the generalized gradient approximation (GGA). Five independent elastic constants are C₁₁=662 GPa, C₁₂=150 GPa, C₁₃=146 GPa, C₃₃=1090 GPa and C₄₄=263 GPa. The bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (γ) and the ratio of linear compressibility coefficient along the a- and c-axis crystal direction (Ka/Kc) are 356 GPa, 305 GPa, 711 GPa, 0.167 and 1.758, respectively. In addition, the dependence of bulk modulus (B) on temperature (T) and pressure (p) as well as the coefficient of thermal expansion (α_L) at various temperatures are evaluated and discussed. The coefficient of thermal expansion is consistent with the famous Gruneisen's law when the temperature is less than 1500K. Our results agree well with the other experimental results.     

基于第一性原理的CrCuFeNiTi高熵合金涂层的相及稳定性分析

采用等离子弧在45钢基体上熔覆了CrCuFeNiTi高熵合金涂层,经X射线衍射分析涂层中的物相有BCC、FCC和Fe₂Ti相,并对BCC、FCC和Fe₂Ti相进行了成分测试,采用CASTEP中的虚拟晶体近似方法建立了BCC、FCC和Fe₂Ti相的晶体结构模型,基于第一性原理计算了涂层中BCC、FCC和Fe₂Ti相的晶格常数,并与涂层中BCC、FCC和Fe₂Ti相的X射线测试结果进行了比较,另外计算了BCC和FCC相的弹性常数C_ij、体积模量B、剪切模量G、杨氏模量E和泊松比ν。结果表明,涂层中BCC和FCC相以及Fe₂Ti的晶格常数计算值与试验值的误差为0.43%~3.05%,BCC、FCC和Fe₂Ti相的生成热均为负值且BCC和FCC相的弹性常数C₁₁、C₁₂和C₄₄满足立方结构高熵合金的力学稳定性限制条件,可知BCC、FCC和Fe₂Ti相是稳定的。另外由C₁₂-C₄₄>0,G/B<0.57,ν>0.26可知BCC和FCC相以金属键结合且呈现韧性的特征。     

Pd3-xRhxV合金的结构和弹性性能的第一性原理计算

利用第一性原理对Pd3-xRhxV合金的2种结构（L12和D022）的相对稳定性、电子特性以及弹性性能等方面进行研究。计算结果表明：随着铑含量的增加,L12和D022型结构的合金晶胞体积均减小,晶胞有一定程度的压缩。与Pd3V相比,加入铑元素,有利于Pd3-xRhxV合金的2种结构的稳定,并且合金结构趋于从D022型转化为更加稳定的L12型。对合金电子结构（态密度）的计算和分析说明,随着铑的加入,在费米能级以下铑和钒的杂化作用越来越明显,进一步影响L12和D022结构的稳定性。还对Pd3-xRhxV合金的L12和D022结构的弹性常数,如体积模量（B）、剪切模量（G）、弹性模量（E）和泊松比（ν）等随着铑加入的变化规律进行计算和讨论。     

多晶金属弹性性能的布里渊散射研究

针对不透明样品的多晶金属铝、铜和铁的表面布里渊散射谱进行了测量.通过谱线解读获得了瑞利波和纵波的速度,并进而计算了三种金属的弹性常数,结果与文献中的数值吻合较好,证实了对不透明样品尤其是金属样品谱图解读的正确性.同时发现,对这三种弹性常数依次增大的金属,它们的表面布里渊散射峰强度依次减小,说明弹性性能是影响金属表面晶格振幅的重要因素之一.该方法和结果对于利用布里渊散射技术进行金属表面或薄膜的弹力学性能研究具有一定的参考价值.     

铁氮化合物稳定性和弹性性能的第一性原理研究

目的计算分析ζ-Fe_2N和ε-Fe_3N两种铁氮化合物的结构稳定性和弹性性能。方法采用第一性原理模拟计算方法。结果两种物相的理论晶格常数与实验值吻合较好,且两者的形成能均为负值。通过两种物相的单晶弹性常数获取了相应的多晶弹性性能,所计算体模量(B)、剪切模量(G)和杨氏模量(E)均高于实验值。ε-Fe_3N多晶弹性性能的计算值与实验值存在一定的比例关系,约为1.3∶1,这个比例也适用于γ'-Fe_4N的体模量。两种物相的B/G比值分别为2.63和2.16。结论ζ-Fe_2N和ε-Fe_3N具有一定的热力学稳定性。两者的剪切模量和杨氏模量接近或优于钢,且具有一定的塑性。两种物相的弹性各向异性与它们的晶体结构密切相关。