Phase composition and magnetic properties of phases in Sm2(Fe1 ? x ? yMnxSiy)17 alloys (with 0 ≤ x ≤ 0.1 and 0 ≤ y ≤ 0.3)

The phase composition of the Sm₂(Fe_{1 − x − y} Mn _x Si _y )₁₇ alloys (0 ≤ x ≤ 0.1 and 0 ≤ y ≤ 0.3) annealed at 1273 K has been studied. The simultaneous alloying of the alloys with manganese and silicon has been found to change their phase composition. At T < 1473 K, the Th₂Zn₁₇-type structure of the Sm₂(Fe,Mn,Si)₁₇ compound transforms into the Th₂Ni₁₇-type structure, which exists only in the presence of all these four elements. At x ≥ 0.05 and y = 0.2, the Sm(Fe,Mn,Si)₁₂ and SmMn₂Si₂ compounds are formed, and the Mn and Si concentrations in Sm₂(Fe,Mn,Si)₁₇ decrease. As a result, we failed to realize the Sm₂(Fe,Mn,Si)₁₇ compound with the uniaxial magnetic anisotropy in these alloys. Manganese additions slightly decrease the Curie temperature T _C of the Sm₂(Fe_{1 − x} Mn _x )₁₇ compound. The additional alloying with silicon is accompanied by an increase in the Curie temperature of the Sm₂(Fe,Mn,Si)₁₇ compound; however, the T _C magnitude was found to be lower than that for manganese-free compounds with the same silicon concentration. Manganese additions also decrease the Curie temperature of the Sm(Fe,Mn,Si)₁₂ phase. The substitution of manganese for iron in the Sm₂Fe₁₇ compound substantially decreases the magnetization; additional alloying with silicon further decreases the magnetization, although the decrease is less abrupt.     

挤压态Mg–1.8Zn–0.5Zr–xGd(0≤x≤2.5%)生物镁合金微观组织演化及降解机理

目的 提高Mg–0.5Zr–1.8Zn–xGd(x=0、0.5%、1.0%、1.5%、2.0%、2.5%)生物镁合金在模拟体液中的耐腐蚀性能。方法 先对Mg–0.5Zr–1.8Zn–xGd合金进行固溶处理,然后利用反向挤压技术对其进行组织细化处理,采用OM、SEM、EDS、EBSD和TEM分析了挤压后Mg–0.5Zr–1.8Zn–xGd合金的晶粒形貌、织构特征、相组成和表面腐蚀形貌。利用电化学工作站和静态腐蚀测试了挤压后合金的耐腐蚀性能。利用XPS对Mg–0.5Zr–1.8Zn–xGd合金腐蚀前、后的表面元素及其化学状态进行表征。结果 挤压温度和挤压比分别为360 ℃和7.7时,合金都发生了较为完全的动态再结晶。随Gd含量的增加,晶粒尺寸逐渐减小,耐腐蚀性能先增强后减弱。当Gd质量分数为1.5%时,合金具有较好的耐腐蚀性能,其静态腐蚀速率约为0.447 mm/a;Gd质量分数为1.5%时,合金中析出了少量的纳米级圆棒状(Mg,Zn)3Gd相颗粒和纳米级椭圆球状Mg2Zn11相颗粒,且随着Gd含量的增加,合金中第二相颗粒的数量及体积分数逐渐增大。Mg–0.5Zr–1.8Zn–1.5Gd合金在SBF中浸泡120 h内,随浸泡时间的增加,腐蚀过程分3个阶段,首先合金表面Mg(OH)2腐蚀产物的生成及增厚导致腐蚀速率在腐蚀初期快速降低,随后致密的Mg(OH)2、(Ca,Mg)3(PO4)2和Ca10(PO4)6(OH)2腐蚀产物的生成及增厚导致腐蚀速率缓慢降低,最后腐蚀产物的生成与溶解达到动态平衡导致腐蚀速率逐渐趋于稳定。结论 挤压变形能够显著细化Mg–0.5Zr–1.8Zn–xGd合金的晶粒,均匀化和弥散化析出相分布,有效改善镁合金在模拟体液中的耐腐蚀性能。     

Anisotropy of transport properties of layered superconductors Nd2? xCexCuO4 + δ and Ca2 ? xSrxRuO4

Temperature dependences of resistivity ρ _ab (T) and ρ _c (T) of single-crystal films Nd_{2 − x} Ce _x CuO_{4 + δ} (x = 0.12, 0.15, 0.17, 0.20) with orientations (001) and and single crystals Ca_{2 − x} Sr _x RuO₄ (0 ≤ x ≤ 2.0) have been investigated. It has been established that in the optimally annealed single crystal of Nd_{2 − x} Ce _x CuO_{4 + δ} (δ ≃ 0) and in single-crystal Ca_{2 − x} Sr _x RuO₄ the mechanisms of conduction differ in the orthogonal directions; namely, the conduction is metallic in the plane ab (dρ _ab /dT >0) and nonmetallic in the direction c (dρ _c /dT < 0). These layered quasi-two-dimensional systems are Anderson conductors with a strongly anisotropic localization radius (R _loc ^ab ≫ R _loc ^c ). It has been found that an increase in the oxygen content in the Nd_{2 − x} Ce _x CuO_{4 + δ} system and an increase in the calcium content in Ca_{2 − x} Sr _x RuO₄ lead to a decrease in the coefficient of the resistivity anisotropy. Thus, in these quasi-two-dimensional systems there occurs an Anderson transition caused by disorder. Original Russian Text ? A.I. Ponomarev, T.B. Charikova, G.I. Kharus, N.G. Shelushinina, A.O. Tashlykov, A.V. Tkach, A.A. Ivanov, 2007, published in Fizika Metallov i Metallovedenie, 2007, Vol. 104, No. 1, pp. 72–85.     

Phase stability among the α(A1), β(A2), and γ(D83) phases in the Cu-Al-X system

The phase equilibria among the α(A1), β(A2), and γ(D8₃) phases in the Cu-Al-X systems (X: Ti, V, Mn, Fe, Co, Ni, Zn, Sn, and Sb) at 700 and 800 °C were investigated, and the effects of these alloying elements on the phase boundaries, homogeneous solid solution ranges, and tie-lines among the α, β, and γ phases were accurately determined by the diffusion couple method. The phase stabilities among α, β, and γ phases are discussed in terms of the partition coefficient. In addition, a modified Guillet’s method, which is used to estimate the effect of alloying elements on microstructure, is proposed by taking into account the change of equivalent coefficient with the phase fraction, and applied to predict the effect of alloying elements on the microstructure of the Cu-Al base alloy.     

内生型(Ti0.474Zr0.34Cu0.06Be0.126)100 - x Fe x (x=0, 2)金属玻璃基复合材料的动态力学行为

为了解内生β-Ti相的Zr/Ti基金属玻璃复合材料的动态力学性能和热力学稳定性,采用力学弛豫谱研究了(Ti_0.474Zr_0.34- Cu_0.06Be_0.126)_100-xFe_x（x=0,2）金属玻璃复合材料。通过引入Fe元素,提高了β-Ti相的稳定性。此外,还发现了一个异常的内耗峰,这是由于在亚稳的β-Ti相中析出ω-Ti所引起的。在玻璃化转变温度T_g以下,由于相变和非晶基体部分结晶的耦合效应,2种金属玻璃复合材料的储能模量均表现出异常过冲行为。所得结果为更好地理解内生亚稳β-Ti型金属玻璃复合材料的复杂动态力学弛豫行为提供了借鉴。     

Phase transition of Ni55-xCoxMn20Ga25(8.5≤x≤11.0) alloys with different compositions and magnetic fields

Studies on Co-doped Ni-Mn-Ga ferromagnetic shape memory alloys(FSMAs) have been quite active topics in recent years.Unlike previous reports where the amount of Co doping was generally less than 8 at%,in this work Ni_55-xCo_xMn₂₀Ga₂₅(8.5 相似文献   

Effect of alloying by gadolinium on the magnetic properties of irradiation-amorphized oxides of the Y3 ? xGdxFe5O12 system

Magnetometry and X-ray diffraction have been used to study the structural state and magnetic properties of the system of oxides with an iron garnet structure, Y_{3 − x} Gd _x Fe₅O₁₂ (x = 0, 0.75, 1.5), in the course of amorphization via irradiation by fast neutrons. It has been established that the partial replacement of diamagnetic yttrium ions by paramagnetic gadolinium dramatically changes the behavior of the magnetic moment of the garnets during their gradual amorphization. The magnetic moment of the yttrium iron garnet decreases significantly with increasing fluence, whereas the magnetic moments of gadolinium-alloyed garnets, on the contrary, increase noticeably along with the simultaneous increase in the compensation temperatures of the sublattice magnetizations. The observed differences in the radiation behavior of the garnets are explained by the different behavior of the iron and gadolinium sublattices under irradiation. It is shown that the irradiation to a fluence of 3 × 10²⁰ cm⁻² leads to a complete amorphization of all samples investigated. It has been established that the amorphous samples were in a spin-glass state.     

Effect of lithium content on electrochemical property of Li1+x(Mn0.6Ni0.2Co0.2)1-xO2 (0≤x≤0.3) composite cathode materials for rechargeable lithium-ion batteries

In order to confirm the optimal Li content of Li-rich Mn-based cathode materials (a fixed mole ratio of Mn to Ni to Co is 0.6:0.2:0.2), Li_1+x(Mn_0.6Ni_0.2Co_0.2)_1-xO₂ (x=0, 0.1, 0.2, 0.3) composites were obtained, which had a typical layered structure with and C2/m space group observed from X-ray powder diffraction (XRD). Electron microscopy micrograph (SEM) reveals that the particle sizes in the range of 0.4-1.1 μm increase with an increase of x value. Li_1.2(Mn_0.6Ni_0.2Co_0.2)_0.8O₂ sample delivers a larger initial discharge capacity of 275.7 mA·h/g at the current density of 20 mA/g in the potential range of 2.0–4.8 V, while Li_1.1(Mn_0.6Ni_0.2Co_0.2)_0.9O₂ shows a better cycle performance with a capacity retention of 93.8% at 0.2C after 50 cycles, showing better reaction kinetics of lithium ion insertion and extraction.     

Finishing of optical moulds to λ/20 by automated corrective polishing

Tungsten carbide is widely used to make replication moulds for small aspheric and freeform optics, like camera lenses. Since aspheric generation by grinding generally fails to reach ultra-precision criteria, a time efficient method for finishing moulds is needed. Using a 7-axis CNC polishing machine, an on-machine tool forming technique and compensation software were developed to correctively polish a plano WC surface of diameter 25 mm from a form error above λ to below λ/20 (29 nm P-V) in under 1 h, while reducing roughness to 1.0 nm Ra. This automatic method and tooling are applicable to aspheric and freeform moulds.     

双相Mg-Li合金的 α→β 相变及热加工性能研究

在温度为250-400℃、应变速率为0.1-10 s^-1条件下进行了热压缩试验,研究了双相Mg-Li合金的热加工性能、显微组织演变和相组成。建立了整合加工和α-Mg相含量的最佳热加工窗口。结果表明,所建立的Arrhenius本构模型能够准确预测软化过程中的应力流动行为。通过对合金显微组织的观察,发现动态回复(DRV)、动态再结晶(DRX)和α-Mg相变是主要的软化机制。α-Mg相以球化和α-Mg相内析出的形式转变为β-Li相,尤其是在300℃以上相变现象显著。同时,DRX行为容易在β-Li相中发生,而在α-Mg相中会被抑制。基于动态材料模型和微观结构分析,获得最佳加工窗口：温度300-350℃/0.1-1 s^-1和温度250℃/0.1 s^-1。     

γ/α 2 相界面对TiAl合金超音速微粒轰击影响的分子动力学模拟

为探究γ/α₂相界面对TiAl合金在轰击过程中的变形机制和轰击后力学性能的影响,通过分子动力学来模拟超音速微粒轰击双相TiAl合金的过程。结果表明：γ/α₂不同厚度比模型的冲击变形机制不同,变形主要集中在γ相和界面处。随着γ相厚度的减小,与相界面接触的位错首先被界面处的失配位错网络吸收,然后在相界面处成核,最终穿过相界面进入α₂相。冲击过程中产生的位错以Shockley位错为主,试样中形成了不完全层错四面体。冲击之后分别使用单轴拉伸模拟和纳米压痕模拟,测定了试样的强度和表面硬度。拉伸过程中相变、孪晶和层错是不同厚度比试样的主要变形机制。与其他试样相比,厚度比为1:3的双相TiAl合金在冲击后具有最高的屈服强度、硬度和弹性模量。     

Electrical properties of dense and nanocrystalline Sm3+-doped Ce1?xSmxO2?δ (0.05 ≤ x ≤ 0.3) electrolytes for IT-SOFCs

Sm³⁺-doped Ce_1−xSm_xO_2−δ (0.05 ≤ x ≤ 0.3) nano-sized powders for solid electrolytes were synthesized by a solution combustion method, using aspartic acid as a combustion fuel. The calcined Ce_1−xSm_xO_2−δ powders were a ceria-based single phase with a cubic fluorite structure. The nano-sized Ce_1−xSmxO_2−δ powders provided a high density, ultra-fine grain size, and high electrical conductivity even at a low sintering temperature of 1400 °C. The grain size and relative density of the Ce_1−xSm_xO_2−δ pellets ranged from 329 nm to 496 nm and from 91.9 % to 99.2 %, respectively. The grain size and density of the Ce_1−xSm_xO_2−δ pellets decreased with an increase of Sm³⁺ content. The electrical conductivity of the Ce_1−xSmxO_2−δ increased with an increase of Sm³⁺ content up to x = 0.25 and then decreased with higher Sm³⁺ content. The maximal electrical conductivity (0.105 Scm⁻¹) was obtained with Ce_0.75Sm_0.25O_2−δ at 800 °C.     

Modeling and simulation of grain growth in Si3N4-II. The α–β transformation

The anisotropic Ostwald ripening model has been developed for completely faceted crystals. This model has been applied to the simulation of grain growth in β-Si₃N₄ with a highly anisotropic rod-like grain shape developed in the liquid phase. The reduction of aspect ratio after the phase transformation observed by previous studies is proved to be a consequence of the anisotropic Ostwald ripening. This model predicts a growth exponent n=3 for totally interfacial reaction controlled kinetics, and higher values when the diffusion constant approaches the interfacial reaction constants. This would explain the puzzling results reported by previous works that growth exponents n=3 or higher have been observed in the grain growth of faceted crystals. While the length distribution becomes wider with time, the reduced radius distribution approaches the shape that is known as the asymptotic distribution function derived from the LSW theory.     

基于三态组织的近 α 钛合金近 β 锻+固溶时效工艺参数匹配

基于正交试验结果,对近β锻+固溶时效工艺参数进行了显著性分析,并详细讨论了工艺参数对TA15钛合金显微组织的影响及合理的工艺参数,以获得性能优异的三态组织。结果表明：变形温度、固溶温度和固溶时间是3个最为重要的工艺参数,分别对等轴α_p相的体积分数和直径、片层α_s相的体积分数及片层α_s相的厚度影响最大。较合理的TA15钛合金处理工艺参数为970 ℃/0.1 s^-1/60%变形程度/水淬+930 ℃/1.5 h/空冷+550 ℃/5 h/空冷。     

基于内聚力模型的 γ-TiAl合金中 γ/γ 界面裂纹扩展的多尺度模型

通过建立多尺度模型预测γ-TiAl合金中裂纹的扩展行为。利用分子动力学（MD）建立了真孪晶（TT）γ/γ界面模型,得到了界面内聚力区域（CZM）的本构参数;采用Voronoi方法生成了多晶γ-TiAl合金介观模型,将CZM本构参数耦合到该模型中,得到了对应的不含缺陷、含钝裂纹和钝裂纹+中心空洞缺陷的临界应力断裂云图,利用几何相似性平均了多晶模型和整体裂纹拉伸关系曲线并分析了γ-TiAl合金的损伤机理;根据连续介质假说建立了宏观有限元模型（FEM）,通过对紧凑拉伸试样模拟给出了力-位移曲线并得到了材料的断裂韧性。最后,将宏观有限元模拟得到的裂纹扩展行为与实验结果进行比较,验证了该模型的有效性。结果表明：在晶粒数比例相同的情况下,缺陷对整个近γ结构的强度有着显著的敏感性,同时该多尺度方法可以有效地连接不同尺度并预测裂纹的扩展。     

Microstructure and electrical properties of Ti-modified (Na0.5K0.5)(TixNb1?x)O3 lead-free piezoelectric ceramics

Ti-Modified (Na_0.5K_0.5)(Ti _x Nb_1−x )O₃ (NKNT) piezoelectric ceramics were fabricated by double-layer buried powder process at 1020°C for 2 h. The microstructures, and piezoelectric and dielectric properties of the lead-free NKNT ceramics were investigated. X-ray diffraction results indicated that Ti⁴⁺ had diffused into the (Na_0.5K_0.5)NbO₃ lattices to form a solid solution with a perovskite structure. The introducing of Ti into the (Na_0.5K_0.5)NbO₃ solid solution effectively reduced the sintering temperature and densified the microstructure with a decreased grain size. The highest relative density reached more than 90%. The highest piezoelectric dielectric coefficient d ₃₃ and planar mode electromechanical coupling coefficient k _p were 110 pC/N and 19.5%, which were obtained in the NKNT ceramic with 1 mol% Ti. The piezoelectric properties of the NKNT ceramics were enhanced by aging in air for a period of time owing to the compensation of oxygen vacancies.     

Graphene micro-substrate-induced π gap expansion in MgB2

The lattice effect induced by tensile strain on the superconductivity of graphene–MgB₂ composites was studied systematically to deduce the electron–phonon coupling (EPC) and the multiple superconducting gap behavior. Compared with nano-carbon doped MgB₂, graphene–MgB₂ composites show larger lattice parameters and higher critical superconducting transition temperatures (T_c). The EPC strength of MgB₂ with ∼2 wt.% graphene addition is even higher than that of the pure reference sample, as estimated from the Sommerfeld constant. The π gap was found to be expanded by graphene addition through the analysis of heat capacity data, and it is responsible for both the enhanced EPC strength and the weak dependence of T_c on the graphene content.     

冷却介质对商业纯钛 β→α 相转变组织及织构的影响

利用OM、ECC、EBSD、TEM等表征技术和显微硬度实验研究了经β固溶处理的商业纯钛板材在β→α相变过程中不同冷却介质对其组织演变、变体选择、织构遗传及力学性能的影响。结果表明：随着冷却速率的降低,相变组织依次呈细针状α′马氏体（水冷和液氮冷）、Widmanst?tten组织（空冷）及粗大晶粒（炉冷）,且冷却速率越快,则转变组织越细,进而其硬度值越高。在β→α冷却过程中,只有炉冷条件下由于出现了部分不满足Burgers关系的取向,导致其并不严格遵循Burgers取向关系。与原始组织相比,水冷和液氮冷条件下由于出现新的织构成分（<0001>//TD、<110>//ND）,导致其织构分布更分散;炉冷条件下由于发生了强烈变体选择而出现织构遗传现象,导致更强的相变织构。因此可以通过提高冷却速率来抑制变体选择,进而弱化相变织构。     

Ti600合金在(α+β)相区的热变形行为和本构模型

对具有片层状初始组织的Ti600合金的热变形行为进行了研究。变形温度范围为800~960 ℃,应变速率范围为10^-3~1 s^-1。随后提出了应变硬化指数（n）来表征流动软化和加工硬化之间的竞争。并且通过分析流变曲线和观察显微组织研究了该合金的软化行为。结果表明,变形参数对Ti600合金的流变行为有显著影响。当变形超过峰值应变之后,n值逐渐降低,动态软化过程开始占主导地位。微观组织分析表明：热变形过程中,α相的弯曲、破碎、动态回复和动态再结晶行为是造成Ti600合金软化的主要原因。最后基于实验数据,建立了3种本构模型,分别是应变补偿Arrhenius模型、Hensel-Spittel模型和修正的Arrhenius模型,来表征Ti600合金的流变行为。将3种模型预测的流变应力与实验结果进行比较,并计算其相关系数值和平均相对误差值来评估模型的准确性。3种模型的相关系数值分别为0.965、0.989和0.997,平均相对误差值分别为12.86%,9.74%和3.26%。这些结果表明,这3种模型都可以描述Ti600合金的流变行为,而修正的Arrhenius模型具有最高的预测精度。     

Electrochemical properties of LiNi0.8Co0.2?xAlxO2 (0≤x≤0.1) cathode particles prepared by spray pyrolysis from the spray solutions with and without organic additives

Fine-sized LiNi_0.8Co_0.2−xAl_xO₂ (0≤x≤0.1) cathode particles were prepared by spray pyrolysis from the spray solutions with and without organic additives. Citric acid, ethylene glycol, and Drying Control Chemical Additive (DCCA) were used as organic additives and improved the morphologies and electrochemical properties of the cathode particles. The LiNi_0.8Co_0.2−xAl_xO₂ (0≤x≤0.1) cathode particles obtained from the spray solutions with organic additives were of micro size and had slightly aggregated morphologies. The initial discharge capacities of the LiNi_0.8Co_0.2−xAl_xO₂ (0≤x≤0.1) cathode particles obtained from the spray solutions without organic additive changed from 169 mAhg⁻¹ to 190 mAhg⁻¹ when the x changed from 0 to 0.1. However, the initial discharge capacities of the cathode particles obtained from the spray solutions with organic additives changed from 196 mAhg⁻¹ to 218 mAhg⁻¹. The initial discharge capacity of the LiNi_0.8Co_0.15Al_0.05O₂ cathode particles obtained from the spray solution with organic additives was maintained after the 20th cycle at a current density of 0.1 C.