力学性能二级人员资格鉴定取证复习题(之二)

一 选择题11 铸铁件适宜的硬度测试方法是( ).A.HRC B.HB C.HV12 淬火钢适宜的硬度测试方法是( ).A.HRC B.HB C.HV13 K_(IC)是( )指标.A.强度B.塑性C.韧性14 冲击载荷下的σ_s比静拉伸下的( ).A.高B.低C.相等15 疲劳断口放射区表示了疲劳裂纹的( ).A.源区B.扩展区C.最高断裂区16 拉伸断口的剪切唇表征材料最后断裂前发生了( ).     

Fe-C-Cr-Si(Ni、W)合金中的C-Me偏聚对贝氏体相变的影响

本文利用余瑞璜的固体与分子经验电子理论计算了3gCrSi、9Crsi、12CrNi3、18Cr_2Ni_4W钢奥氏体的价电子结构。从扩散与偏聚两方面讨论了原子状态-原子键力、结构、形态与性能之间的关系。并提出三个观点。 1.Fe—C—Cr—Si(Ni、W)合金奥氏体中存在着C—Me偏聚。偏聚力的大小可用C—Me共价键上的共用电子对数表示,偏聚的动力来源于C—Me间的价电子结构; 2.C—Me偏聚对相变有阻力。这种阻力和相变驱动力交互作用可改变贝氏体的典型结构和形态; 3.C—Me偏聚导致的奥氏体陈留分割细化了原奥氏体晶粒,使后生成相的有效尺寸减小;奥氏体呈角状、叉状增加了裂纹扩展的路径,这是上述合金贝氏体韧性较好的原因之一。     

金属中电子的施受交换键合

原子间相互交替施受或互换价电子是金属键合的基本模式。金属 Na 中某 A 原子可施舍或接受一个3s 电子,与其相邻的 B 原子则可接受或施舍一个3s 电子,使 A、B 原子核周围均获得封闭的电子组态。Hg 原子的电子外壳层己具有稳定的封闭状态,金属 Hg 中的相邻原子不能相互施受电子,只能互换电子。金属中的任何一个原子与其等同相邻的每一个原子有交替施受互换电子的同等机会。原属 A 原子的电子通过 A、B 原子间的施受交换过程可传递给 B 原子,再通过 B、C 原子间的施受交换过程又可转移给 C 原子,所以金属中的任何一个价电子并不始终处在定域化的束缚状态中。在外加电压的作用下可使无方向性的施受交换电子过程变成有方向性,即形成电流。价电子在原子表层中时的能量低于在晶格空隙中时的能量,在原子表层中出现的机率大于在晶格空隙中出现的机率,传导电子是沿着原子表层自一个原子越过原子面之间的间隙势垒进入另一个原子的表层的。     

稳定性同位素

同位素是在同一元素中原子序数相同而质量数不同的各种原子。同位素的化学性质相同,物理性质和质量数相异。同位素分放射性的(如~(14)C)和稳定性的(如~(13)C)两类。稳定性同位素在某些方面优于放射性同位素,如对孕妇、孩子和需重复测定等方面的应用就不宜用放射性同位素。质量数为14的氮元素天然丰度最大的为~(14)N,但稳定性同位素质量数为15的~(15)N天然丰度仅为0.365％。~(13)C与~(18)O的天然丰度分别为1.1％与0.2％。     

高温超导体研究新发现-MgB2

今年一月,日本科学家Nagawatsu等人发现了二硼化镁超导体,引起国内外的普遍关注.这是一种机关报的简单二元金属间化合物超导体(每个晶胞只有三个原子),超志转达变温度Tc高达39K,几乎是Nb3Ge(a15型金属间化合物超志体中Tc最高,23.2K)和YP2B2C(金属间硼碳化合)的两倍.     

Ni2 MnGa合金的价电子结构研究

用“固体与分子经验电子理论”研究了Ni2MnGa合金的价电子结构，研究结果表明，在Ni2MnGa中，Ni的杂化状态为A'种杂化第2阶；Mn的杂化状态为B种杂化第9阶，Ga为A种第9阶杂化。Ni的原子磁矩计算值为3.8666μB十分接近。最强的共价键是Ni-Mn键，其上的共价电子对数为0．577，其次为Ni-Ga键，其价电子对数为0．542，其它键上的共价电子对数小于0．2。     

微小型轴向内沟槽铜管缩径缺陷实验研究

二分模旋转模锻工艺是微小型轴向内沟槽铜管(AIGCT)的重要缩径工艺.本文通过实验探讨了两种不同截面尺寸类型(分别记作Ⅰ和Ⅱ)和三种不同的材料属性状态(分别记作:A、B和C)下沟槽管缩径缺陷和缩径进给速率的关系.实验结果表明,A状态Ⅰ型管的伸长率最高可达到20%以上,并随着进给速率的增加而减小;当进给速率超过21mm/s时,在A状态Ⅰ型管的成形区将会产生飞边;当进给速率超过13mm/s时,在A状态Ⅱ型管的成形区将产生凹陷.进给速率超过4mm/s和13mm/s时,将分别会在B状态Ⅰ型管和Ⅱ型管的未成形区产生扭曲.由于存在严重的扭曲和压溃,C状态内沟槽铜管不适合用二分模的方式进行缩径.     

稀土元素对FeCrMoCB系合金玻璃形成能力的影响

近年来,随着铁基大块非晶合金尺度不断取得新的突破,无磁非晶钢的开发和研究受到日益广泛的关注。然而,FeCrMoCB系非晶钢的玻璃形成能力很弱,仅能形成直径为1.5mm的大块非晶合金。采用铜模真空吸铸法,探讨Y、Pr、Gd、Tb等稀土元素对Fe48Cr15Mo14C15B6M2(M=RE)系合金玻璃形成能力的影响,实验结果表明,用2%(原子分数)的稀土元素Y、Pr、Gd、Tb分别替换Fe50Cr15Mo14C15B6中的Fe,能制备出一系列Fe48Cr15Mo14C15B6M2(M=RE)系非晶棒。Fe48Cr15Mo14C15B6M2(M=Pr,Y,Gd,Tb)非晶棒的最大直径依次可达3、8、12和12mm。     

原子转移自由基聚合制备PMMA/POSS杂化材料

以八(γ-氯丙基)倍半硅氧烷(OCP-POSS)为引发剂,通过原子转移自由基聚合(ATRP)制备了PMMA/OCP-POSS有机/无机杂化材料.采用GPC、DSC和TGA对杂化材料的结构与性能进行了表征.结果表明,在DMF、异丙醇、甲苯等3种不同溶剂中均可合成分子量分布较窄的PMMA杂化材料.以DMF为溶剂,所得PMMA/OCP-POSS杂化材料的分子量分布系数可达到1.18.与分子量相当的线形PMMA相比,含OCP-POSS的PMMA杂化材料具有更高的玻璃化转变温度和热稳定性.     

非晶软磁合金Co_(65)Fe_4Ni_2Si_(15)B_(14)的纳米晶化动力学研究

采用差示扫描量热分析(DSC)和X射线衍射技术(XRD)研究了非晶态合金Co_(65)Fe_4Ni_2Si_(15)B_(14)的非等温晶化动力学.结果表明,初始晶化的晶化峰值温度T_p与升温速率β呈线性关系:T_p=11.49lnβ+795.43.采用Kissinger和Doyle-Ozawa方法计算了表观晶化激活能E_a,分别为471.68kJ/mol和461.50kJ/mol.进一步研究发现,该非晶合金的晶化为多阶段的连续形核直至饱和的过程;当进入稳定晶化阶段时,剩余非晶的局域晶化激活能逐渐下降,非晶基体的热稳定性降低,这是由B原子的高温扩散导致的.同时,局域Avrami指数n(α)也反映了不同晶化阶段的形核长大机制.     

Magnetism in oxidized graphenes with hydroxyl groups

The magnetic properties of three oxidized graphene structures with hydroxyl groups (cases A, B and C) have been investigated through spin-polarized density functional theory. The results reveal that in a graphene hexagonal ring structure, chemical bond formation by two non-neighbored hydroxyl-bonded carbon atoms with one carbon atom between (case B) can cause unpaired spins to produce a magnetic moment of 1.2 μ(B), while chemical bond formation by two neighbored hydroxyl-bonded carbon atoms (case A) or non-neighbored hydroxyl-bonded carbon atoms with two carbon atoms between (case C) cannot generate unpaired spins for nonmagnetic states. These magnetic oxidized graphenes have great promise for new spintronics. This work provides fundamentals to controllably synthesize or/and oxidized graphene with hydroxyl groups at specific carbon positions for magnetic properties.     

Study of Vacancies and Pd Atom Decoration on the Electronic Properties of Bilayer Graphene

We have investigated the scenario of graphene when irradiated with high energetic protons and subsequently decorated with Pd atoms on one of the layers. Theoretical analyses were performed on graphene 2L (two layers) with vacancies (carbon 3 and 13) (sample A), graphene 2L with vacancies and the two carbon atoms intercalated in between the two carbon layers (sample B), graphene 2L with the vacancies intercalated and subsequently with two Pd atoms on one of the layers, the top layer (called surface) (sample C), and, last but not least, graphene 2L with vacancies intercalated and decorated with six Pd atoms on the surface (sample D). For the four cases enunciated, energy bands were performed which provided information about the semi-metallic behavior, showing more semi-metallic character for the first case, while less metallic behavior occurs for the second and third one. Moreover, sample D showed a mini gap (between the conduction and valence bands) of the order of 0.02 eV and manifest semiconductor behavior. Total and projected density of states were performed in order to provide information about the contributions from each selected atom to the total DOS in the vicinity of the Fermi level in order to analyze the effect on the electronic behavior. Pd d orbitals contribute with ∼6% to the total DOS, while graphene (carbon atoms) p orbitals contribute with ∼5%. Furthermore, a strong hybridization is manifest between these two multiple degenerate orbitals.     

Ab initio study of the electronic and optical properties of sillimanite (Al2SiO5) crystal

Ab initio calculations based on the density functional theory (DFT) are used to investigate the electronic and optical properties of sillimanite. The geometrical parameters of the unit cell, which contain 32 atoms, have been fully optimized and are in good agreement with the experimental data. The electronic structure shows that sillimanite has an indirect band gap of 5.18 eV. The complex dielectric function and optical constants, such as extinction coefficient, refractive index, reflectivity and energy-loss spectrum, are calculated. The optical properties of sillimanite are discussed based on the band structure calculations. It is shown that the O-2p states and Al-3s, Si-3s states play the major role in optical transitions as initial and final states, respectively.     

Effect of Al, Si, B, and C Impurities on the Electronic Structure and Bonding of Zirconium Nitride

The electronic structure and bonding configuration of cubic (B1 type) ZrN-based substitutional solid solutions containing Al, Si, B, or C atoms on the Zr and/or N sites were investigated using self-consistent linearized muffin-tin-orbital calculations in the atomic-sphere approximation. The total and partial densities of states, cohesion energy of the solid solutions, and charge states of the constituent atoms were evaluated. Interatomic interactions were analyzed using the semiempirical tight-binding method. The results were used to discuss the possible mechanisms of formation of ternary ZrN-based solid solutions and compare their chemical stability.     

On the crystal chemistry of NaP zeolites

Multiphase samples containing a series of well-crystallized gismondine-type NaP zeolites, unit cell content Na_xAl_xSi_16−xO₃₂ ·yH₂O with 3 ⩽ x ⩽ 8, were prepared at 90–95°C or 150°C from aluminosilicate glasses and aqueous sodium hydroxide. Powder X-ray diffraction using a Guinier-Hägg camera and energy dispersive X-ray microanalysis performed in a scanning electron microscope revealed three NaP phases with increasing silicon content, i.e., low-silica P (8–10 Si atoms per unit cell), orthorhombic medium-silica P (10–12 Si/cell), and tetragonal high-silica P (12–13 Si/cell). NaP1 (pseudocubic lattice geometry) probably represents an end-member low-silica P with 10 Si/cell, whereas NaP2 (pseudotetragonal lattice geometry) is identical to medium-silica P.     

Interaction of carbon,boron and sulphur in superalloys

The interaction of carbon, boron and sulphur atoms was studied through observation of the amount, shape and distribution of carbides, borides and sulphides at grain boundary surfaces in superalloys by means of transmission electron microscopy.

Carbon, boron and sulphur atoms segregate towards grain boundaries and can form compounds there. The increases in tendency to segregate are arranged in the order C, Band S, and the B (or S) may force the C (or B) atoms out of grain boundaries. When B (or S) content was not high, with the C (or B) content being increased, the amount and size of borides (or sulphides) were decreased while the amount and size of carbides (or borides) increased gradually. It is shown that the C (or B) atoms, which segregate towards grain boundaries, can slow down the diffusion speed of the B (or S) atoms at the grain boundaries. The temperature of M₃B₄ precipitation was lower than that for M₂₃B₆ at grain boundaries in the superalloy. It is shown that the interaction of C and B atoms may depend on ageing temperature.     

Unified theory of effects of segregated interstitials on grain boundary cohesion

Abstract

The ideas of the electron theory of chemisorption are applied to the behaviour of H, B, C, N, and 0 atoms segregated on and in iron. The general theory can be divided naturally into two branches depending on whether the valence levels of the embedded atoms ‘float’ at the Fermi level, as in the case of B, C, and N; or ‘sink’ to a level below the bottom of the d band, as with Hand O. In the former, the valence states take on the cationic role when they hybridise with nearby d states and a predominantly covalent bond is formed, which increases grain boundary cohesion. In the latter, the atoms form screened negative ions, with little covalent interaction, and thereby decrease cohesion, so promoting intergranular brittleness.

MST/1267     

Epitaxial matching of small metallic nanoclusters in large-misfit systems

The deposition at low energies of Cu and Au nanoclusters, respectively, on Au(0 0 1) and Cu(0 0 1) substrates is studied by constant-temperature molecular-dynamics simulations. Initially, clusters had icosahedral or Wulff shapes and their number of atoms ranged between 13 and 1289. The deposition energy and the temperature were, respectively, 17 meV/atom and 300 K. Atomic interactions are mimicked by a many-body potential based on the tight-binding model. A different behaviour of the clusters has been found as a function of the number of atoms and of the material. Below 100 atoms, Cu clusters align all their {2 0 0} planes with the substrate but do not achieve epitaxy since either their lattice structure becomes bcc or stacking faults arise. On the contrary, Au clusters with similar number of atoms grow epitaxially but hardly change the distances parallel and perpendicular to the interface in their unit cell. Cu clusters, for their part, fit the parallel distances to the Au lattice parameter. For larger clusters, in general, the alignment or epitaxy is not complete even in the cases of more favourable landing.     

Thermal decomposition of a gaseous multiprotein complex studied by blackbody infrared radiative dissociation. Investigating the origin of the asymmetric dissociation behavior

The blackbody infrared radiative dissociation technique was used to study the thermal decomposition of the gaseous B5 pentamer of the Shiga-like toxin I and its complexes with the Pk trisaccharide and a decavalent Pk-based oligosaccharide ligand (STARFISH, S). Dissociation of the protonated pentamer, (B5 + nH)n+ triple bond B5n+ where n = 11-14, proceeds almost exclusively by the loss of a single subunit (B) with a disproportionately large fraction (30-50%) of the parent ion charge. The degree of charge enrichment of the leaving subunit increases with increasing parent ion charge state. For n = 12-14, a distribution of product ion charge states is observed. The yields of the complementary pairs of product ions are sensitive to the reaction temperature, with higher temperatures favoring greater charge enrichment of the leaving subunit for +13 and +14, and the opposite effect for +12. These results indicate that some of the protons are rapidly exchanged between subunits in the gas phase. Dissociation of B5(14+) x S proceeds exclusively by the loss of one subunit, although the ligand increases the stability of the complex and also reduces the degree of charge enrichment in the ejected monomer. For B5(12+)(Pk)1-3, the loss of neutral Pk competes with loss of a subunit at low temperatures. Linear Arrhenius plots were obtained from the temperature-dependent dissociation rate constants measured for the loss of B from B5n+ and B514+ x S. The magnitude of the Arrhenius parameters is highly dependent on the charge state of the pentamer: Ea = 35 kcal/mol and A = 1,019 s(-1) (+14), 46 kcal/mol and 1,023 S(-1) (+13), 50 kcal/mol and 1026 s(-1) (+12), and 80 kcal/mol and 10(39) (+11). The Ea and A for B5(14+) x S are 59 kcal/mol and 10(30) s(-1), respectively. The reaction pathways leading to greater charge enrichment of the subunit lost from the B5(14+) and B5(13+) ions correspond to higher energy processes, however, these pathways are kinetically preferred at higher temperatures due to their large A factors. A simple electrostatic model, whereby charge enrichment leads to Coulombic repulsion-induced denaturation of the subunits and disruption of the intersubunit interactions, provides an explanation for the magnitude of the Arrhenius parameters and the origin of the asymmetric dissociation behavior of the complexes.     

On atoms charge states in RBa2Cu3Ox high-temperature superconductors

The distribution of charge states of all atoms in the unit cell of RBa₂Cu₃O_x; x=6,7 (R = Yb, Er, Ho, Y, Gd, Eu, Sm, Nd, Pr) is determined on the basis of comparison of the theoretical calculated electric field gradient tensor and existing experimental data. The variation of the charge states of the atoms as a function of the ionic radius is analyzed.