Ti−6Mo−5V−3Al−2Fe−2Zr合金热变形行为及热加工图

目的 建立近β钛合金Ti−6Mo−5V−3Al−2Fe−2Zr(质量分数)的热变形本构方程,绘制热加工图,确定该合金的流变失稳区和适宜加工区,为其在工业生产中热加工工艺参数的制定提供指导。方法 在变形温度700~ 850 ℃、应变速率0.000 5~0.5 s⁻¹、真应变0.7的条件下,对近β钛合金Ti−6Mo−5V−3Al−2Fe−2Zr进行热压缩实验;基于Arrhenius方程建立该合金的热变形本构方程,并对方程进行验证;根据Prasad失稳准则,构建该合金的热加工图。结果 该合金的流变应力随着变形温度的升高而减小,随着应变速率的增大而增大;其热变形激活能为226.29 kJ/mol,本构方程为;通过热变形本构方程得到的峰值应力计算值与实验值平均误差为4.21%。结论 建立的热变形本构方程预测了流变应力,描述了该合金的热变形行为;通过叠加合金的能量耗散图和流变失稳图,获得了该合金的热加工图。基于热加工图确定该合金的流变失稳区为变形温度700~755 ℃与784~850 ℃、应变速率0.5~0.05 s⁻¹,最佳加工区为变形温度836~850 ℃、应变速率0.000 5~0.005 s⁻¹。     

Phonon Vibration and Conduction of La2 − xSrxCuO4 − δ and La1.85 − xSr0.15 + xCu1 − xCoxO4 − δ

Polycrystalline samples La_{2 ? x} Sr _x CuO_{4 ? δ} (0.06 ≤ x ≤ 0.5) and La_{1.85 ? x} Sr_{0.15 + x} Cu_{1 ? x} Co _x O_{4 ? δ} (0 ≤ x ≤ 1) were synthesized by a conventional solid state reaction method. The structure, phonon vibration, and conduction were investigated by means of XRD, infrared (IR) spectra, and resistance. It is found that the increase of itinerant hole carriers could mask the in-plane ${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O(1)}}$ stretching vibration mode (689 cm^?1). The softening of the ${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O(1)}}$ phonon vibration mode gives an index of the weakening of ${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O}}$ hybridization. The distortion of CuO₆ octahedron and the microstructural inhomogeneity induced by Co doping lead to the widening of the IR absorption peaks.     

GH6159合金成分−组织−性能关联研究

目的 研究不同成分GH6159合金冷拉态和热处理态显微组织的变化情况,分析不同成分对合金室温和高温拉伸性能的影响规律,为GH6159合金成分优化与性能提升提供理论指导。方法 基于MP159合金成分,设计熔炼了4种不同成分的GH6159合金,经锻造开坯和热轧,进行了拉伸率为48%的冷拉变形和663 ℃/4 h的时效热处理,分别制成冷拉态和热处理态GH6159棒材,采用MTS 8810拉伸实验机进行室温和595 ℃的高温拉伸测试,获得了不同成分合金冷拉态和热处理态的室温和595 ℃高温拉伸性能,结合OLYMPUS−PM3光学显微镜和Tescan Mira 3 XMU扫描电子显微镜观察了显微组织的变化情况。结果 GH6159冷拉态棒材内存在大量的变形孪晶,热处理态组织内析出了弥散分布的强化相,合金拉伸性能主要受到基体元素和强化相元素的影响。结论 较高含量的Co、Cr、Ni基体元素有利于提高冷拉态GH6159合金的室温和高温拉伸强度,而Al、Ti、Nb强化相元素会提高热处理态GH6159合金的室温拉伸强度,但过高的Ti元素会降低合金强度,一定含量的Al、Ti、Nb元素有利于提高冷拉态和热处理态合金的高温塑性。     

定向凝固TiAl合金成分−组织−性能研究进展

TiAl合金由于其低密度和高比强度,在航空材料中展现出良好的应用前景。通过定向凝固控制TiAl合金晶体取向,有助于大幅提升合金高温性能和服役温度,促进TiAl合金在新一代航空发动机上的应用。综述了近年来TiAl合金定向凝固的研究方法和成分?组织?性能关系的研究进展,总结了国内外定向凝固TiAl合金的主要研究单位及研究主题,简要介绍了定向凝固方法与模壳材料的应用情况。从合金成分角度,分析并总结了α、β相稳定元素和其他常见元素对定向凝固组织和性能的作用;从力学性能角度,介绍了定向凝固高Nb?TiAl合金在高温拉伸、蠕变、高周疲劳性能上的优势及相关机理;从定向凝固工艺角度,归纳了生长速率和温度梯度对合金凝固路径、片层取向及宏观、微观偏析的影响。展望了定向凝固TiAl合金的未来发展方向。     

铸态Mg−2Sc−2Y−0.5Zr合金热压缩行为及热加工图

目的 研究铸态合金Mg?2Sc?2Y?0.5Zr合金热压缩行为及热加工图,根据合金的用途和再结晶程度,确定最佳热加工艺参数,为合金后续变形提供参考。方法 通过实验设计合金成分,称取一定质量的纯镁锭和二元中间合金,在真空熔炼炉中加热至760 ℃,保温至熔化,搅拌,静止,然后在钢磨具中空冷,得到合金锭。实际成分通过电感耦合等离子体原子发射光谱法测定;切取合适大小的铸锭进行X射线衍射实验。用于热压缩的铸态样品为圆柱形试样(?10 mm×15 mm) ,在进行热压缩实验前,对所有样品表面进行抛光。使用Gleeble?3800热压缩模拟试验机对铸态Mg?2Sc?2Y?0.5Zr合金进行热压缩试验,变形温度为573~723 K,应变速率为0.001~1 s^?1。经热压缩后将各试样立即进行水淬,以保持压缩变形组织。将压缩样品沿着纵轴切割压缩样品,然后抛光、蚀刻,并使用扫描显微镜进行检查,以观察微观结构的演变,计算该合金的变形激活能,并构建合金高温变形的本构方程,建立真应变为0.5时的热加工图。结果 得到了铸态Mg?2Sc?2Y?0.5Zr合金热变形本构方程及真应变为0.5时的热加工图,合金热变形发生了动态回复和动态再结晶,合金的热变形激活能Q为198.58 kJ/mol。结论 根据用途和再结晶程度,铸态Mg?2Sc?2Y?0.5Zr合金的最佳加工参数为变形温度623~673 K、应变速率0.001~0.01 s^?1,以及变形温度723 K、应变速率0.001~1 s^?1。     

Macroscopic magnetic properties in TlBa2Ca3Cu4O−δ−δ−δ single crystals

The four-CuO₂-layer TlBa2Ca₃Cu₄O_11– compound has a high superconducting transition temperature of 128 K and strong interlayer coupling. We have performed magnetic experiments on single crystals of TlBa₂Ca₃Cu₄O_11–, which include hysteresis loop, irreversibility line and time relaxation measurements. From these measurements, we observed the large critical current density, high irreversibility line and strongly temperature dependent flux creep rate in the TlBa₂Ca₃Cu₄O_11-gd single crystals.     

Hydrothermal synthesis and magnetic properties of CoxFe1−x/CoyLazFe3−y−zO4 composites

A series of iron–cobalt alloy and cobalt–ferrite composites doped with La³⁺ (Co_xFe_1−x/Co_yLa_zFe_3−y−zO₄) in which the Fe–Co alloy has either a bcc or a fcc structure and the oxide is a spinel phase, have been synthesized by using the disproportionation of Fe (OH)₂ and the reduction of Co (II) by Fe⁰ in a concentrated and hot KOH solution. when x ≤ 0.1, the structures of the Fe_xCo_1−x alloy and cobalt–ferrite are fcc structure; and when x ≥ 0.25, the structures of the Fe_xCo_1−x alloy is bcc structure. The fcc structure of alloy is favored for [KOH] close to 9 N, Co(II)/Fe(II) ratios between 0.5 and 0.9 and short reaction time of synthesis. And the bcc structure of the alloy is favored for [KOH] close to 1 N, Co(II)/Fe(II) ratios between 0.1 and 0.5 and long reaction time of synthesis. A low [KOH] favors nucleation leading to octahedral of 1 μm. And [KOH] of 9–12 N favors particle growth. The metal occurs in square particles of 100–150 nm included within the spinel. Powder X-ray diffraction (XRD), thermal gravity analysis (TGA) and different thermal analysis (DTA), scanning electron microscope (SEM), transmission electron micrograph (TEM) and vibrating sample magnetometer (VSM) were employed characterize the crystallite sizes, structure, morphology and magnetic properties of the composites. And the effect of the Co(II)/Fe (II) ratio (0 ≤ Co/Fe ≤ 1), concentration of KOH, reaction time and substitution Fe³⁺ ions by La³⁺ ions on structure, magnetic properties of the composites were investigated.     

轧制温度对Al−4.5Cu−1.5Mg−0.5Zr合金显微组织及性能影响

目的 优化加工工艺,改善合金的组织,提高合金的力学性能。方法 采用金相(OM)观察、拉伸试验和X射线衍射,分析在大应变轧制下冷轧结合T6态处理后板材的成形性能,引入Williamson-Hall模型和Taylor函数,分析合金内部位错密度的变化规律及其对力学性能的影响。结果 随着前期轧制温度从350 ℃升高到400 ℃,合金晶粒得到明显细化,再结晶充分,晶粒尺寸细小,晶界处第二相粗大;冷轧后晶粒破碎严重,晶粒的碎化方向与轧制方向垂直;在350 ℃时,合金内部的位错密度为1.62×10¹⁵ m^?2,位错密度对强度的贡献值为219.5 MPa,其抗拉强度最大为602 MPa、屈服强度为512 MPa、伸长率为12.6%。结论 Al?4.5Cu?1.5Mg?0.5Zr合金的晶粒组织明显细化,其力学性能得到提升。     

超声波−微波联合处理对CSNC−CSS膜的影响

目的 制备功能更优的包装膜，拓展纳米纤维素?淀粉包装膜的应用，研究超声波?微波协同作用对纳米纤维素?淀粉膜的影响。方法 利用玉米秸秆纳米纤维素(CSNC)和玉米秸秆淀粉(CSS)制备CSNC?CSS膜，并在制备过程中采用超声波?微波协同改性，探究不同超声波?微波协同处理体系对制备的CSNC?CSS膜各种性能的影响。结果 与未进行超声波?微波协同体系处理制备的CSNC?CSS膜进行对比发现，经过超声波?微波协同作用制备的CSNC?CSS膜的各种性能更加优异。其中，膜的抗拉强度由原来的14.92 MPa升至26.46 MPa，提高了约77.35%;断裂伸长率由原来的64.75%升至90.08%，提高了约39.12%;经过超声波?微波处理后，膜的透湿系数和透氧系数均有所下降，分别下降了约25.57%和41.45%，透光量有所增加，溶解时间有所缩短。结论 经超声波?微波协同作用后，CSNC?CSS膜具有更好的力学性能、阻湿性能和阻气性能，具有广阔的市场应用前景。     

纸浆纤维−聚碳酸酯复合材料

目的 采用可再生的纸浆纤维和功能塑料聚碳酸酯(PC)制备功能木塑复合材料，探究硼酸处理对复合材料相关性能的影响，进一步拓展材料在工程领域的应用。方法 配制质量分数为5%的硼酸溶液，将部分纸浆纤维放入硼酸溶液中浸渍2 h，将纸浆纤维与PC混合后，用双螺旋挤出机进行熔融加工，再用微型注塑机注塑成型,制备出复合材料。结果 经硼酸处理后的复合材料，在添加质量分数为30%的纸浆纤维时，复合材料的弹性模量达到4.31 GPa，比添加同样纤维含量的未经过硼酸处理的复合材料高16%:同时，与纯PC的弹性模量相比提高了90%。结论 采用硼酸处理可以提高纸浆纤维的热稳定性，可进一步提高复合材料的力学强度。PC是一种生活中常见的功能塑料，其本身具有优良的力学性能，硼酸的处理和纸浆纤维的加入使其力学性能进一步提升，有望作为结构材料应用于集装箱、托盘等方面，在包装领域有较好的应用前景。     

The HREM study of precipitates in an Al−Zn−Mg alloy

A study of precipitate phases in an Al–Zn–Mg alloy in the T74 condition has been conducted by means of high resolution electron microscopy. It has been observed that G.P. zones, and phases exist simultaneously in the matrix. The G.P. zones are plate-like forming on (111) matrix plane. The phase has a hexagonal structure witha=0.496 nm,c=1.403 nm and the orientation relationship with the matrix is . A new orientation relationship between the phase and the matrix is found to be .     

Raman scattering of magnetic excitations in Y1−x Prx Ba2Cu3−yAlyO7−δ single crystals

Magnetic excitations and their role for the superconductivity in cuprate superconductors have been widely discussed in the literature. Here, we present a study of Y_1–x Pr_x Ba₂Cu_3–yAl_yO_7– single crystals using Raman spectroscopy in an energy range of 50 – 10000 cm^–1 Raman shift. The high energy range is dominated by a two-magnon scattering process at 3J, where J is the superexchange energy. In the Pr-123 single crystal, we find J = 720 cm^–1, a damping of the one-magnon states = 200 cm^–1, and a resonance energy of 2.79_eV for the two-magnon excitation. The two-magnon peak shows a continuous increase of the one-magnon damping with decreasing x and a nearly constant J across the phase transition to the superconductor. Especially, we find a weak two-magnon peak for a superconductor with a T_c = 86 K.     

Crystallization kinetics of Zr-rich FexZr0−x0−x0−x(20 ⩽ x ⩽ 40) metallic glasses

The crystallization kinetics of the melt-spun Fe-Zr metallic glasses in the iron-rich region has been investigated by means of DSC and X-ray diffraction. The crystallization mode changes with iron concentration. In the lower iron region, 20 x 25, the Fe _x Zr100–x glasses crystallize into -Zr and Ti₂Ni-type FeZr₂ with an accompanying sharp and large exotherm at the first crystallization step and immediately after this step, they transform into orthorhombic FeZr₃. On the other hand, the alloys with 35 x 40 exhibit a gradual exotherm which initiates from a temperature far below the definite crystallization temperature (T _x). The Fe-Zr metallic glasses in this concentration region crystallize polymorphously into the oxygenstabilized Ti₂Ni-type FeZr₂ with accompanying relatively small and composite exotherms. The annealing at a temperature where the gradual exotherm occurs for the alloys with 30 x 40 does not cause any changes of X-ray halo pattern but results in the reduction of the heat of exotherm due to the crystallization.     

Thermoelectric Power Studies on YBa2−xCaxCu3O7−δ System

The temperature dependence of the thermoelectric power of calcium substituted YBa_2?x Ca _x Cu₃O_7?δ pellets with 0≤x≥1.5 is presented between 60 K and 300 K. A metal–insulator transition was reported earlier by us in this system and was attributed to the ionic size-dependent localization effect. While the sign of thermoelectric power of all the calcium substituted samples was found to be positive, its magnitude increases significantly with calcium content in YBCO. The normal state thermoelectric power data of substituted YBa_2?x Ca _x Cu₃O_7?δ (0≤x≥1.5) are discussed in light of a two-band model originally proposed by Gottwick et al. for heavy fermion systems and later modified by Forro et al.     

Preparation and characterization of in1−xGaxAsyP1−y epilayers by liquid-phase epitaxy

In_1–x Ga _x As _y P_1–y epilayers with three different solid compositions of ln_0.73Ga_0.27As_0.60P_1.40, In_0.59Ga_0.41As_0.87P_0.13 and ln_0.53Ga_0.47As were grown on (1 0 0) InP substrate at 623° C by the step cooling technique of liquid-phase epitaxy. From the optical transmission measurements, the corresponding wavelengths of the InGaAsP epilayers were 1.30, 1.55 and 1.69 m, respectively, which are in good agreement with those obtained from the calculations using Vegard's law. The full widths at half maximum of the photoluminescent spectra at 14 K of these layers were as low as 18.6, 22.5 and 7.9meV, respectively. The electron mobility of the InGaAsP epilayers is a function of the solid composition with the ln_0.53Ga_0.47As epilayer having the highest electron mobility. The mobility and concentration of this layer are 8,873cm²V^–1 sec^–1, 9.7×10¹⁵cm^–3 and 22,900 cm²V^–1 sec^–1, 8.5×10¹⁵cm^–3 at 300 and 77 K, respectively. The compensation ratio is between 2 and 5.     

Dielectric properties of the system Ba1−xLaxTi1−xCo x O3

The dielectric behaviour of compositions withx=0.01, 0.05, 0.10 and 0.20 in the system Ba_1–x La _x Ti-_1-x Co _x O₃ was studied in the temperature range 300–473 K. The compositions withx = 0.01 and 0.05 show a diffuse ferroelectric-paraelectric phase transition, while other compositions do not show this transition in this temperature range. The frequency dependence of dielectric constant and dielectric loss in the samples withx0.05 indicates that spacecharge polarization contributes significantly to their observed dielectric parameters.     

Room-temperature multiferroic properties and magnetoelectric coupling in Bi4−x Sm x Ti3−x Co x O12−δ ceramics

We present the structural, dielectric, ferroelectric, magnetic and magnetoelectric studies of lead free; single phase Bi_4?x Sm _x Ti_3?x Co _x O_12?δ (0 ≤ x ≤ 0.07) ceramics, synthesized using a standard solid-state reaction technique. Raman spectroscopy analysis reveals the relaxation of distortion in TiO₆ octahedron. Field emission scanning electron microscopy confirmed the growth of plate-like grains. It is observed that with the substitution of Sm³⁺ and Co³⁺ ions the dielectric constant, loss tangent and ferroelectric transition temperature decreases. Electrical dc resistivity, remnant polarization and magnetization increases with increasing Sm³⁺ and Co³⁺ contents. The magnetoelectric coupling co-efficient, α = 0.65 mV cm^?1 Oe^?1 is realized for Bi_4?x Sm _x Ti_3?x Co _x O_12?δ (x = 0.07) ceramic sample. Our results clearly demonstrate the lead free, multiferroic nature of Sm/Co-substituted Bi₄Ti₃O₁₂, which may find useful application in designing cost-effective electromagnetic devices.