Cr3C2粒径对等离子堆焊铁基合金层组织与耐磨性能的影响

在低碳钢表面利用等离子堆焊技术分别制备Fe50堆焊层及添加40％(质量分数)微米和纳米Cr₃C₂的(Fe50+40%微米/纳米Cr₃C₂)复合堆焊层,比较研究添加不同粒径的Cr₃C₂对Fe50合金堆焊层的显微组织与磨损性能的影响。采用X射线衍射仪(XRD)分析堆焊层的相组成,利用扫描电镜(SEM)和能谱分析仪(EDS)观察堆焊层的显微组织形貌及微区成分,通过显微硬度计测试了堆焊层的硬度分布,使用滑动磨损及冲击磨损试验机分别考察了复合堆焊层的磨损性能。结果表明:Fe50等离子堆焊层组织主要由柱状晶α-Fe及其间的网状共晶α-Fe+Cr₂₃C₆组成;而Fe+40%微米/纳米Cr₃C₂堆焊层凝固方式为过共晶,由大量的先共晶碳化物及其间细密、均匀的枝晶与共晶组织组成,并增加了γ-Fe、Cr₇C₃和未熔Cr₃C₂等相;但Fe+40%纳米Cr₃C₂涂层比Fe+40%微米Cr₃C₂涂层析出更多且细小、致密的先共晶碳化物。与Fe50等离子堆焊涂层相比,Fe+40%微米Cr₃C₂涂层的显微硬度、滑动磨损性能及冲击磨损性能分别提高了21%、1.5倍和0.8倍;而Fe+40%纳米Cr₃C₂涂层的显微硬度、滑动磨损性能及冲击磨损性能则分别提高了34.1%、2.4倍和1.7倍,表面的犁沟和剥落及塑性变形明显减少,耐磨性能显著提高。因此,添加纳米Cr₃C₂颗粒可以显著细化铁基合金等离子堆焊层的显微组织并提升其耐磨性能。     

激光熔敷Cr3Si/Cr2Ni3Si复合材料涂层组织与耐磨性研究

以Cr-Si-Ni合金粉末为原料、利用激光熔敷技术在A3低碳钢表面上制得了以金属硅化物Cr₃Si为增强相,以Cr₂Ni₃Si复杂金属硅化物为基体的快速凝固Cr₃Si/Cr₂Ni₃Si复合材料冶金涂层,分析了该涂层的显微组织,并分别在干滑动磨损及二体磨料磨损条件下测试了该涂层的耐磨性能。研究结果表明,由于激光熔敷Cr₃Si/Cr₂Ni₃Si快速凝固复合材料涂层组织细小、均匀,在滑动磨损过程中不易与对偶件粘着、在磨料磨损过程中具有很高的抗切削抗剥落能力,因而在干滑动磨损及二体磨料磨损条件下涂层均具有优良的耐磨性能。     

Al与γ－Al2O3润湿角的计算

本文应用金属的形核理论对目前无法用实验进行准确测定的易氧化金属Al与γ-Al₂O₃的润湿角进行了计算。计算结果发现Al与γ-Al₂O₃的润湿角在30°到50°这一范围之间,即30°<θ≤50°。     

Al2O3-SiO2纤维增强ZL108合金复合材料的强度特性

用低成本的Al₂O₃-SiO₂系纤维作为增强相,通过加压铸造法制作ZL108合金复合材料,并对该复合材料和ZL108合金进行不同温度下的时效处理和压缩试验。通过DSC、EPMA和TEM分析认为:经488K、0.5h时效处理(T6处理)的V_f 20%的复合材料在573K以下的压缩屈服强度低于ZL108合金,是由于基体中的Mg与Al₂O₃-SiO₂纤维在加压铸造过程中起化学反应而生成MgAl₂O₄,损耗了基体中的大量Mg,导致基体铝合金时效硬化效果很差,所以压缩屈服强度低下。623K、720h保温后的V_f 20%的复合材料的压缩屈服强度比ZL108合金要高得多,是由于在这种温度环境下对ZL108合金来说是过时效,所以纤维的增强怍用显得明显。在高温(673K)下V_f 20%的复合材料的屈服强度比ZL108台金高一倍左右。不论在什么温度场合下V_f5%的复合材料的屈服强度比V_f 20%的复合材料都低。     

Zr55Al10Ni5Cu30非晶合金晶化相转变的价电子结构分析

基于EET理论,计算了F-Zr₂(Ni,Cu)和tI-Zr₂Cu及tI-Zr₂(Cu,Ni)相的价电子结构,用最强键键合力n₁、结构单元总成键能力F和单位成键能力F_v分析了F-Zr₂Ni亚稳相向tI-Zr₂Cu型稳定相的转变过程。研究发现:F-Zr₂Ni的n^{F-Zr₂Ni₁值比tI-Zr₂Cu的ntI-Zr₂Cu₁值大115.36%,FF-Zr₂Ni_v值比tI-Zr₂Cu的FtI-Zr₂Cu_v值大34.03%;F-Zr₂(Ni0.3,Cu0.7)的nF-Zr₂(Ni0.3,Cu0.7)₁值比tI-Zr₂Cu的ntI-Zr₂Cu₁值大0.36%,FF-Zr₂(Ni0.3,Cu0.7)_v值比tI-Zr₂Cu的FF-Zr₂Ni}_v值大1.25%; tI-Zr₂(Cu0.6,Ni0.4)的n^{tI-Zr₂(Cu0.6,Ni0.4)₁值比F-Zr₂(Ni0.3,Cu0.7)的nF-Zr₂(Ni0.3,Cu0.7)}₁值大12.95%, F^{tI-Zr₂(Cu0.6,Ni0.4)_v值比F-Zr₂(Ni0.3,Cu0.7)的FF-Zr₂(Ni0.3,Cu0.7)}_v值大14.41%; 从价电子结构角度看,F-Zr₂Ni不能直接转变为tI-Zr₂Cu,F-Zr₂(Ni,Cu)不易分解重构为tI-Zr₂Cu;F-Zr₂(Ni0.3,Cu0.7)可分解并转变为tI-Zr₂(Cu0.6,Ni0.4)。     

一维TiO2纳米材料的制备及其光催化性能研究

采用水热法,通过改变水热温度成功制备出一系列一维TiO₂纳米管、纳米线和纳米带。运用X射线衍射、透射电子显微镜、N₂吸附-脱附和紫外-可见光谱等手段表征了材料的结构和性质,并考察了一维TiO₂样品光催化降解气相苯的活性。结果表明,一维TiO₂纳米材料具有较高的比表面积,光吸收出现明显的“蓝移”,光催化活性较P25有所提高,其中140 ℃水热温度下制备出的TiO₂纳米管的光催化活性最佳,80 min内对气相苯的去除率为77%,终产物CO₂的浓度为625 mg/m³。     

ZrO2在β"─Al2O3复合陶瓷中的作用

本文研究了四方和立方ZrO₂在与Na-β"-Al₂O₃的复合陶瓷中作为第二相所起的各种作用。结果说明ZrO₂对复合陶瓷具有细化晶粒、改善显微结构、提高强度和断裂韧性的作用,与此同时也在一定程度上降低离子电导率。在提高力学性能方面,四方ZrO₂除了具有与立方ZrO₂相同的弥散颗粒的作用外,相变所起的作用也是很显着的。ZrO₂-Na-β"-Al₂O₃复合陶瓷是一种有应用价值的固体电解质材料。     

SrI2∶Eu∶Cs晶体生长及闪烁性能

采用垂直布里奇曼法成功制备出尺寸为Φ25 mm×70 mm的SrI₂∶Eu∶Cs晶体,经加工后封装得到尺寸为10 mm×10 mm×10 mm的透明单晶,这是迄今为止Eu²⁺和Cs⁺双掺杂的最大尺寸SrI₂单晶,所用原料为国产原料。XRD测试结果表明,所得晶体为SrI₂正交相,空间群为Pbca。荧光光谱显示晶体的发射峰和激发峰分别位于440 nm和419 nm,属于典型Eu²⁺的5d→4f跃迁发射。X射线激发发射光谱显示该晶体只有一个位于440 nm的发射峰,与荧光光谱的结果一致。采用单指数拟合后得到晶体在370 nm激发波长下的荧光寿命约为1.3 μs。在¹³⁷Cs射线源激发下的γ能谱测试显示晶体的能量分辨率为5.5%,已基本满足实际使用的要求。     

单层和三层结构的PVDF基复合材料介电与储能特性

通过水热合成法制备CaCu₃Ti₄O₁₂球型颗粒填料,以PVDF为基底,采用溶液逐层涂覆法制备单层和三层结构的PVDF基复合材料。利用X-射线衍射仪和扫描电镜表征材料的微观组织结构,LRC测试仪和铁电综合测试工作站测试其电学性能,研究低填充浓度和多层结构对PVDF基复合材料微观结构、介电特性、极化强度、耐电压特性和储能特性的影响规律。结果表明,CaCu₃Ti₄O₁₂填料的尺寸约为200 nm,增加其填充浓度,可以提高单层PVDF/CaCu₃Ti₄O₁₂复合材料的介电特性与极化强度；在3.0vol.%填充量下,复合材料达到最大的介电常数13.2、介电损耗0.074和电位移极化强度4.04 μC/cm²；而在0.5vol.%的超低填充量下,复合材料达到最大的释放能量密度3.51 J/cm³。三层结构的PVDF基复合材料体系中,在上下层复合材料的高介电极化特性与中间层材料的击穿阻挡特性的协同作用下,获得了综合储能特性优化的PVDF基复合材料,使其在300 kV/mm的低电场强度下,达到最高的释放能量密度4.36 J/cm³。     

超声血流向量成像技术探讨颈动脉球部壁面剪切应力的影响因素

目的：运用超声血流向量成像(Vector Flow Imaging, V Flow)技术探讨颈动脉球部自体解剖结构及血流动力学因素对壁面剪切应力(Wall Shear Stress, WSS)的影响。方法：选取颈动脉超声检查正常患者 70例,将 V Flow感兴趣区置于颈总动脉分叉部及颈内动脉起始段。测量颈动脉球部与颈总动脉间角度(θ)、测量收缩末期颈动脉球部(Carotid Bulb, CB)膨大最明显处内径(D_CB)与颈总动脉末段内径(D_CCA)的比值(D_CB/D_CCA)、测量颈动脉球部分流量(Q_CB)与颈总动脉末段流量(Q_CCA)的比值(Q_CB/Q_CCA)、描记颈动脉球部血流紊乱区可视化面积(A_CB)以及测量颈动脉球部起始段内侧平均壁面剪切应力(WSSI-CB)和外侧平均壁面剪切应力(WSS_E-CB),并对上述各项参数进行统计学分析。结果：(1)颈动脉球部起始段 WSS_I-CB值为(0.88±0.30) Pa,外侧 WSS_E-CB值为(0.32±0.15) Pa,外侧壁明显小于内侧壁,差异有统计学意义(P<0.01)。(2)颈动脉球部与颈总动脉夹角 θ值为(24.5±12.1)°,与 WSS_E-CB相关系数为r=-0.171,二者无相关性且差异无统计学意义(P>0.05);颈动脉球部膨大最明显处内径与颈总动脉末段内径比值 D_CB/D_CCA为(0.66±0.09),与 WSS_E-CB值呈负相关,相关系数为r=-0.312,差异有统计学意义(P<0.05)。(3)颈动脉球部分流量与颈总动脉末段流量比值Q_CB/Q_CCA为(0.69±0.15),与 WSS_E-CB值呈正相关,相关系数为r=0.428,差异有统计学意义(P<0.01);颈动脉球部血流紊乱区面积 A_CB为(0.27±0.17) cm²,与 WSSE-CB值呈负相关,相关系数分别为 r=-0.545,差异有统计学意义(P< 0.01)。结论：颈动脉球部血流量、血流紊乱区面积及膨大程度是影响外侧壁面剪切应力 WSS的主要因素,而与颈动脉球部发出角度的关系并不密切。     

Effect of the composition on the bandgap width of high-κ MexTiyOz (Me = Hf, Ta, Sr) layers

To explore the possibility of bandgap engineering in Ti-oxide based insulators, we investigated the effect of added cations of another kind (Hf, Ta, Sr) on the optical absorption and photoconductivity of thin titanate films. A bandgap of 3.1-3.4 eV, typical for pure polycrystalline TiO₂, was found in crystallized Sr_xTi_yO_z of different composition as well as in amorphous Ta₂Ti₃O_z. By contrast, the gap width of Hf titanates increases starting from 3.5 eV for 30% Hf/(Hf + Ti) to 4.2 eV for 84% Hf/(Hf + Ti). We suggest that this gap widening is associated with reduced interaction between electron states of neighboring Ti cations as influenced by a wide-gap (E_g = 5.6 eV) HfO₂ sub-network.     

Chemical control of superconducting properties of (Y, Ca)(Sr, Ba)2Cu2.7Ga0.3O7?δ

The partial substitution of Ga at the Cu(1) (chain) sites of the YBa₂Cu₃O₇ structure allows synthesis at ambient pressure of Ba-free analogs, e.g., YSr₂Cu_2.7Ga_0.3O_7– . Materials with this composition have been found to be nonsuperconducting, but superconductivity has been induced by one or more of the following methods: Ca substitutions at the Y site; Ba substitutions at the Sr site; annealing in high-pressure oxygen. The influence of these chemical manipulations onT _c has been monitored and all methods have been found to enhanceT _c . The electronic effects of Ba substitutions have been deduced indirectly using powder neutron diffraction, and such substitutions appear to result in a redistribution of hole density into the Cu(1) sites from the superconducting CuO₂ planes.     

Two-gap superconductivity in R2Fe3Si5 (R=Lu,Sc) and Sc5Ir4Si10

R₂Fe₃Si₅ (R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T_c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R₂Fe₃Si₅ single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu₂Fe₃Si₅, we can reproduce C(T) below T_c, assuming two distinct energy gaps 2Δ ₁/k_BT_c = 4.4 and 2Δ ₂/k_BT_c = 1.1, with nearly equal weights, indicating that Lu₂Fe₃Si₅ is a two-gap superconductor similar to MgB₂. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc₂Fe₃Si₅ single crystals also shows the two-gap feature. R₅Ir₄Si₁₀ (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc₅Ir₄Si₁₀ single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.     

Two-gap superconductivity in R2Fe3Si5 (R=Lu,Sc) and Sc5Ir4Si10

Abstract

R₂Fe₃Si₅ (R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T_c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R₂Fe₃Si₅ single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu₂Fe₃Si₅, we can reproduce C(T) below T_c, assuming two distinct energy gaps 2Δ ₁/k_BT_c = 4.4 and 2Δ ₂/k_BT_c = 1.1, with nearly equal weights, indicating that Lu₂Fe₃Si₅ is a two-gap superconductor similar to MgB₂. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc₂Fe₃Si₅ single crystals also shows the two-gap feature. R₅Ir₄Si₁₀ (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc₅Ir₄Si₁₀ single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.     

First-principles study on electronic structure, phase stability, and optical properties of In2X2O7 (X═C, Si, Ge or Sn)

In₂Ge₂O₇ and In₂Si₂O₇ are commonly used as scintillation materials. More studies on In₂X₂O₇ (X═C, Si, Ge, or Sn) are important to explore the possibility of using these materials for optoelectronic devices. This work presents results dealing with structural properties, electronic structure, chemical bonding, carrier effective masses, and optical spectra of polymorphs of In₂X₂O₇ obtained from first-principles calculations. The monoclinic phase of In₂Ge₂O₇, cubic and monoclinic phases of In₂Si₂O₇, as well as cubic phase of In₂Sn₂O₇ are known in scientific literature. From the total energy calculations at high pressure/strain we have found that the monoclinic phase of In₂Si₂O₇, In₂Ge₂O₇, and In₂Sn₂O₇ can be transformed into the cubic phase. The cubic phase of In₂Ge₂O₇ and In₂Sn₂O₇ is found to be more stable than the monoclinic phase. However, the monoclinic phase of In₂C₂O₇ and In₂Si₂O₇ is more stable than the cubic phase. The phase stability study suggests that In₂C₂O₇ is not stable, and that it might dissociate into corresponding binary oxides. Effective masses of electrons and holes have been estimated. Analysis of optical properties shows that in Si solar cells In₂Si₂O₇ and In₂Sn₂O₇ can be used as antireflection coating layer.     

Some thermodynamic aspects of the high-temperature transition in doped V2O3

Measurements of the entropy change are reported for the high-temperature metal-insulator (MI) transitions in the (V_1–xCr_x)₂O₃ and (V_1–xAl_x)₂O₃ systems. It is emphasized that the entropy of the I phase exceeds that of the M phase. Evidence is presented to show that the M and I phases coexist over a narrow temperature range. The transformation is attended by enormous hysteresis effects; these indicate that the lattice plays an important role in the transition. The probable role of Cr³⁺ and Al³⁺ as a dopant in the V₂O₃ lattice is briefly discussed. A phase diagram for the dilute V₂O₃-Al₂O₃ alloy system is presented.     

The Study of Hole Distribution in High-Tc Tl- and Hg-based 1212 Type Cuprates via High-Resolution X-Ray Absorption Near Edge Structure

High resolution O K-edge and Cu L₃-edge X-ray absorption near-edge-structure (XANES) spectra of the high-T_c cuprates of (Tl_0.5Pb_0.5)Sr₂(Ca_1–xY_x)Cu₂O₇ (Tl-1212) and (Hg_0.5Pb_0.5)Sr₂(Ca_1–xY_x)Cu₂O₇ (Hg-1212) in powder form were measured using a bulk sensitive total-fluorescence-yield technique. Near the O 1s edge, the pre-edge peak with maxima at 528.3 eV is ascribed to the transitions to O 2p holes located in the CuO₂ planes. The intensity of this pre-edge peak increases with increasing doping level of Ca²⁺ into the Y³⁺ sites in Tl-1212 and Hg-1212. In the Cu L-edge absorption spectra, high-energy shoulders at around 933 eV are attributed to the transitions to the Cu(2p_3/2)^–13d¹⁰L states in the CuO₂ layers, where L denotes the O 2p ligand hole. The behavior of these shoulders in Tl-1212 and Hg-1212 correlates with that of the pre-edge peak at 528.3 eV in the O K-edge absorption spectra. The results can lead us to understand the hole distribution in high-T_c cuprates which will give a direction to find new high-T_c materials.     

Structural and magnetic study of nitrided Co74Fe8B12Si6 and Co74Fe4Mn4B12Si6 ribbons

The nitriding thermochemical treatment (NTT) is commonly used for steels. In this paper, the experimental conditions required for NTT, and the influence of such treatments on the structure and hysteresis loops of Co₇₄Fe₈B₁₂Si₆ and Co₇₄Fe₄Mn₄B₁₂Si₆ ribbons are reported. The results have been compared with those obtained with ribbons treated according to conventional thermal treatment (CTT) as well.     

Superconductivity at 103 K in CdBa2(Ca0.7Y0.3)Cu2Oy

A cadmium analogue of the mercury system with nominal composition CdBa₂(Ca_1–xY_x)Cu₂O_y has been synthesized. Thex=0 samples contain about 12 vol.% of the 1212 phase but are not superconducting. Thex=0.3 samples are superconducting atT _on = 103 K. The EDX analysis of 18 microcrystals shows a broad cationic distribution of the different components. The observed broad superconducting transition is attributed to the variousT _c of the different microcrystals.     

Effect of Sr and Sr-Ca substitution on the superconductivity of (Er0.76Ca0.24)Ba2(Cu2.76Co0.24)Oz

The structural and superconducting properties of (Er_1-xCa_x)Ba_2-ySr_y(Cu_2.76Co_0.24)O_z are investigated using X-ray diffraction, resistivity, ac susceptibility, and oxygen content measurements. Increasing the Sr content in (Er_0.76Ca_0.24)Ba_2-ySr_y(Cu_2.76Co_0.24)O_z lowers the oxygen content and decreases theT _c, which is attributed to the rearrangement of oxygen atoms in the basal plane. This suppression ofT _c at_{y =0.6} cannot be improved by appropriate hole doping with Ca in (Er_1-xCa_x)Ba_1.4Sr_0.6(Cu_2.76Co_0.24)O_z forx = 0.24-0.48.