铝基复合材料的Al-Cu合金中间层瞬间液相扩散连接

采用Al—Cu合金作为中间层研究了铝基复合材料(Al2O3p／6061Al)瞬间液相扩散连接接头的组织与力学性能。研究结果表明，在Al—Cu／A12O3p／6061Al接头中无明显的增强相偏聚区和增强相贫化区，且接头成分分布较为均匀；在Al—C。合金中间层厚度30μm、连接温度600℃、连接时间30min条件下，接头抗剪强度为130～140MPa,较Cu／A12O3p／6061Al接头抗剪强度提高45％。因此，采用Al—Cu中间层是改善铝基复合材料接头力学性能的有效途径。     

铝基复合材料瞬间液相扩散连接接头的组织与力学性能

采用扫描电镜、能谱仪及电子拉伸试验机系统地研究了Cu,Ag作为中间层铝基复合材料瞬间液相扩散连接接头的组织与力学性能。根据组织结构特点接头可分为增强相偏聚区、增强相贫化区和母材区。增强相偏聚区的组织主要为Al2O3颗粒和铝合金基体，并含有汪量的MgAl2O4化合物，对于Cu中间层接头还含有少量的Al2Cu化合物。连接温度、连接时间和中间层厚度对接头抗剪强度具有较明显的影响。在一定条件下，Cu,Ag中间层接头的抗剪强度分别为82－99MPa和86－109MPa。增强相偏聚区是接头最薄弱的区域，减少增强相的偏聚是进一步改善接头力学性能的重要途径。     

SiCP颗粒增强Al基复合材料的瞬间液相连接

采用Ni箔和Cu/Ni/Cu多层箔作中间层在923K进行了SiC颗粒增强铝基复合材料的瞬间液相连接.研究表明,无压连接时,接头强度随保温时间延长有所增高,但界面处会存在纯金属(无增强颗粒)区域和氧化物夹杂,是导致接头强度不高的主要原因.加压TLP连接则能有效改善界面组织和接头性能.采用Cu/Ni/Cu多层箔作中间层加压连接时接头强度可达189.6MPa,约为母材强度的85%.本文对压力的作用和复合材料TLP连接界面特性进行了讨论.     

SiCP颗粒增强Al基复合材料的瞬间液相连接

采用Ni箔和Cu/Ni/Cu多层箔作中间层在923K进行了SiC颗粒增强铝基复合材料的瞬间液相连接。研究表明,无压连接时,接头强度随保温时间延长有所增高,但界面处会存在纯金属（无增强颗粒）区域和氧化物夹杂,是导致接头强度不高的主要原因。加压TLP连接则能有效改善界面组织和接头性能。采用Cu/Ni/Cu多层箔作中间层加压连接时接头强度可达189．6MPa,约为母材强度的85％。本文对压力的作用和复合材料TLP连接界面特性进行了讨论。     

用Cu箔中间层瞬间液相连接SiCP/Al 复合材料的界面现象与连接强度

采用Cu箔作中间层,在温度为853K的条件下进行了SiCp/Al复合材料的瞬间液相（Transient Liquid-Phase bonding,TLP)连接,用扫描电镜观察了连接界面微观形貌,测定了接头的剪切强度,着重研究了连接时间和压力对界面结构和强度的影响。研究表明,不加压连接时,由于在界面处形成纯金属带,且氧化膜也难以去除,接头强度较低,约为母材强度的48%,接头剪切强度随连接时间延长而增高,连接时施加0.2MPa的压力即可显著提高接头强度,达到母材强度的70%,且强度随连接时间变化不大,试验还发现,用Cu箔中间层无压瞬间液相连接小增强相颗粒、高体积百分含量的SiCp/AlMMCs时,接头界面区域没有发现颗粒偏聚,本文对此进行了理论分析。     

SiC颗粒增强铝基复合材料的瞬间液相连接

铝基复合材料采用Cu箔、Ni箔和Cu/Ni/Cu多层箔作中间层进行瞬间液相连接。研究了保温时间和压力对铝基复合材料接头组织和性能的影响。研究发现，加压能有效改善铝基复合材料接头组织和性能；采用Cu/Ni/Cu多层箔作中间层时铝基复合材料接头强度最高，达189.6MPa，约为母材强度的84.6%。     

用Cu箔中间层瞬间液相连接SiCP/Al 复合材料的界面现象与连接强度

采用Cu箔作中间层,在温度为853K的条件下进行了SiCP/Al复合材料的瞬间液相(TransientLiquid-Phasebonding,TLP)连接,用扫描电镜观察了连接界面微观形貌,测定了接头的剪切强度,着重研究了连接时间和压力对界面结构和强度的影响.研究表明,不加压连接时,由于在界面处形成纯金属带,且氧化膜也难以去除,接头强度较低,约为母材强度的48%,接头剪切强度随连接时间延长而增高.连接时施加0.2MPa的压力即可显著提高接头强度,达到母材强度的70%,且强度随连接时间变化不大.试验还发现,用Cu箔中间层无压瞬间液相连接小增强相颗粒、高体积百分含量的SiCp/AlMMCs时,接头界面区域没有发现颗粒偏聚,本文对此进行了理论分析.     

Al-Si合金瞬间液相扩散连接接头组织与力学性能

采用扫描电镜、X射线衍射、能谱仪及电子拉伸试验机等测试方法研究了Cu箔作中间层瞬间液相扩散连接(TLP)Al-Si合金接头的组织和力学性能.结果表明,Al-Si合金基体中的Al元素与中间层Cu元素发生共晶反应形成液相,而合金中的Si对Al与Cu的相互作用有一定的阻碍.接头组织主要由α-Al、单晶Si及金属间化合物(CuAl2和Al4Cu9)组成,而金属间化合物的数量随连接时间的增加而减少.剪切试样沿着界面/基体处断裂.当温度为560℃时,随着连接时间的增加,接头抗剪强度先增大后减小,在120 min时达到最大值70.2 MPa;接头塑性和韧性提高,断口表面形貌由脆性特征转变为脆性和韧性共存的混合型断裂特征.     

Ti/Cu/Ti复合中间层扩散连接TiC-Al2O3/W18Cr4V接头组织分析

通过添加Ti/Cu/Ti复合中间层,控制加热温度1 130 ℃,保温1 h,连接压力15 MPa,实现陶瓷基复合材料TiC-Al2O3 与高速钢W18Cr4V的真空扩散连接,TiC-Al2O3/W18Cr4V接头抗剪强度达103 MPa.采用扫描电镜、X射线衍射、电子探针等测试方法分析了TiC-Al2O3/W18Cr4V扩散连接接头的微观组织结构和显微硬度分布.结果表明,Ti/Cu/Ti复合中间层与两侧基体TiC-Al2O3和W18Cr4V发生扩散结合,形成均匀致密、宽度为90 μm的扩散过渡区,过渡区显微硬度从3 400 HM逐渐降低到1 000 HM,形成的相结构主要有Ti3Al, CuTi2, Cu和TiC.     

亚微米级Al2O3p/6061Al铝基复合材料扩散焊接工艺

以亚微米级Al2O3p/6061 Al铝基复合材料为对象,研究了直接扩散焊与采用中间层扩散焊两种工艺焊接铝基复合材料的特点、机理,分析了中间层对接头强度的影响规律.结果表明,在铝基复合材料液、固温度区间,存在"临界温度区域",在此温度区域进行直接扩散焊接时,通过液相基体金属的浸润,使得在扩散接合面中增强相-增强相接触转化为增强相-基体-增强相的有机结合,获得高质量焊接接头;进一步研究发现,在扩散接合面上采用合适的基体中间层同样可以将增强相-增强相接触转化为增强相-基体-增强相的有机结合,同时增大"临界温度区域"范围,接头性能更加稳定,接头变形量进一步减小(＜2%).     

Structural, mechanical and corrosion properties of TiOxNy/ZrOxNy multilayer coatings

Results on the deposition and characterization of TiO_xN_y/ZrO_xN_y multilayers, with bilayer periods of 20 and 400 nm, are presented. The coatings were deposited on TiNiNb alloy substrates by the pulsed magnetron sputtering method. The elemental composition, hardness, adhesion and corrosion resistance of the coatings were analyzed.As resulted from the XPS analysis, the individual layers consisted of a mixture of titanium or zirconium oxynitrides and corresponding oxides. X-ray analysis revealed that the coatings were amorphous. Only slight differences between the microhardness and adhesion values of the coatings with small and large bilayer period Λ were found. The experiments also showed that the multilayered coatings improved the corrosion resistance of the uncoated alloy and reduced the amount of ion release in artificial body fluids.     

MOCVD growth and characterizations of BxAl1−xAs and BxAl1−x−yInyAs alloys

Zinc-blende B_xAl_1−xAs and B_xAl_1−x−yIn_yAs alloys have been grown on exactly oriented (0 0 1)GaAs substrates by low pressure metalorganic chemical vapor deposition (LP-MOCVD). The influence of susceptor coating, growth temperature and gas-phase boron mole fraction on boron incorporation into AlAs has been comprehensively investigated. It has been found that boron incorporation into AlAs could be enhanced and the optimal growth temperature range of B_xAl_1−xAs alloys changed from 580 °C to 610 °C when SiC-coated graphite susceptors were replaced by the non-coated ones. In this study, the maximum boron composition x of 2.8% was achieved for the pseudomorphically strained B_xAl_1−xAs alloys. AFM measurements show that RMS roughness of B_xAl_1−xAs alloys increased sharply with the increase of gas-phase boron mole fraction. Raman spectra of B_xAl_1−xAs alloys show a linear increase of the BAs shift with boron composition x. Based on BAlAs deposition, bulk B_xAl_1−x−yIn_yAs (x = 1.9%) quaternary alloy was grown lattice-matched to GaAs successfully. Moreover, 10-period BAlAs/GaAs and BAlInAs/GaAs MQW heterostructures were also demonstrated.     

生物医用NiTi形状记忆合金腐蚀研究进展

镍钛形状记忆合金(NiTi-SMA)具有较好的耐腐蚀和机械性能,在口腔和临床医学中有着大量而广泛的应用。NiTi-SMA腐蚀后释放Ni²⁺会引发细胞毒性和过敏反应,进一步提高NiTi-SMA的耐蚀性是目前生物医学材料领域发展的核心之一。本文对近年来国内外有关口腔医学和临床医学中常用NiTi-SMA的腐蚀研究现状进行了总结,同时也对NiTi-SMA增材制造及表面改性技术进行了评述,以期为开发高性能抗腐蚀生物医用NiTi-SMA提供一定的指导意义。     

Li掺杂Ba(Ti1/7Sn1/7Zr1/7Hf1/7Nb1/7Ga1/7Li(1/7-x))O3高熵陶瓷的制备及介电性能研究

近年来,在高熵合金基础上发展起来的高熵陶瓷逐渐引起了研究者的广泛关注,其出现为开发高性能的无机非金属材料提供了新的设计思路。本文采用固相法制备了BaMO3基钙钛矿型高熵陶瓷Ba(Ti1/7Sn1/7Zr1/7Hf1/7Nb1/7Ga1/7Li(1/7-x))O3 (x = 0, 2.3%, 5.3%, 8.3%, 11.3%),并研究了Li含量对高熵陶瓷物相结构、微观形貌及介电性能的影响。结果表明,Li含量对陶瓷结构的影响不大,陶瓷均保持立方钙钛矿结构,且无杂相产生;陶瓷的晶粒尺寸相对较均匀。当x = 0时,即B位七元等摩尔比Ba(Ti1/7Sn1/7Zr1/7Hf1/7Nb1/7Ga1/7Li1/7)O3高熵陶瓷,其介电常数达到了最大值2920 (@100 Hz),相较于已报道的不掺Li的六元高熵钙钛矿陶瓷Ba(Ti1/6Sn1/6Zr1/6Hf1/6Nb1/6Ga1/6)O3提升了近50倍。     

Ag/LaNixCo1-xO3触点材料的制备及电接触性能研究

本文运用溶胶-凝胶燃烧法合成了双钙钛矿型LaNixCo1-xO3(LNCO)纳米材料,利用粉末冶金和热挤压技术制备了相应的Ag/LNCO触点材料及元件样品。重点考察了不同Ni、Co含量对Ag/LNCO触点材料微观结构、物相组成、物理性能、力学性能及电寿命服役能力的影响,对其电弧侵蚀失效行为进行了研究,并与SnO2粉体增强Ag基触点材料进行对比。结果表明:溶胶凝胶法合成的LNCO纳米颗粒粒径为20-30 nm,经粉末冶金工艺制备的Ag/LaNi0.5Co0.5O3触点材料电学性能和电寿命都优于Ag/SnO2触点材料,其电阻率低至2.10 μΩ?cm,电寿命性能达到51287次。表明Ag/LaNi0.5Co0.5O3触点材料性能较佳,是一种可以取代Ag/CdO的新型触点材料。     

Hydrothermal synthesis of superconductors Ba1−xKxBiO3 and double perovskites Ba1−xKxBi1−yNayO3

Superconductors Ba_1−xK_xBiO₃ and body-centered double perovskites Ba_1−xK_xBi_1−yNa_yO₃ have been selectively synthesized by a facile hydrothermal route. The appropriate ratio and adding sequence of initial reagents, alkalinity, reaction temperature and time are the critical factors that influence the crystal growth of the compounds. The purity and homogeneity of the crystals were detected by the ICP, SEM, EDX and TEM studies. Magnetic measurements show that the superconducting transition temperatures T_C of Ba_1−xK_xBiO₃ decrease from 22 K (for x = 0.35) to 8 K (for x = 0.55) with increasing the K doping level.     

Magnetic phase diagrams of the TbRh2−xPdxPdxSi2 and TbRu2−xPdxSi2 systems

The a.c. susceptibility and high field magnetization on TbRh_2−xPd_xPd_xSi₂ and TbRu_2−xPd_xSi₂ compounds were investigated up to 140 kOe. The (T,x) magnetic phase diagrams were determined. For both systems, an increase in the Pd content causes a decrease in the Néel temperature and changes the magnetization curves.     

High strength and good ductility of casting Al-Cu alloy modified by PrxOy and LaxOy

A modified Al-Cu alloy with high tensile strength and ductility of about 574.0 MPa and 10.4%, respectively, was obtained by adding multiple rare earth oxides (Pr_xO_y and La_xO_y) as modifier. Compared with the unmodified Al-Cu alloy, the tensile strength and ductility of the modified sample were increased by 24.3% and 42.5%, respectively. The improvement both in the strength and ductility may attribute to the finer crystal grains and dendrites, more homogeneously distributed θ′ phase precipitates and the intermetallic compounds formed at the crystal grain boundaries as well as in the space of the dendrites.     

Si3N4/Ti/Cu/Ni/Cu/Ti/Si3N4二次部分瞬间液相连接强度

采用Ti/Cu／Ni中间层对Si3N4陶瓷进行二次部分瞬间液相(PTLP)连接，研究连接工艺参数对Si3N4／Ti/Cu／Ni连接强度的影响，同时研究了连接强度随试验温度的变化规律。结果表明，在该试验条件下，室温连接强度随着二次连接温度的提高和二次保温时间的延长而提高，改变连接工艺参数对Si3N4／Ti/Cu／Ni二次PTLP连接界面反应层厚度无明显影响；连接强度在试验温度400℃时达到最大，随后随试验温度升高，连接强度降低，但在800℃前，其高温强度具有很好的稳定性。     

Thermoelectric properties of Sn1−x−yTiySbxO2 ceramics

Thermoelectric properties of Sn_1−x−yTi_y Sb_xO₂ ceramics were investigated in detail. The addition of Sb into SnO₂ matrix increased the electric conductivity, σ. The increase in the σ value should be caused by the increase in the carrier concentration. The Seebeck coefficients of all the samples were negative, which means that these samples have n-type conduction. The samples of this study have porous structure. The maximum Z value of all the samples measured in this study was 2.4 × 10⁻⁵ K⁻¹.