Interfacial Microstructure and Reaction Phases of Solid State Bonded at SiC/V Joints

SiC was bonded to SiC using V foil at temperatures ranging from 1473 K to 1673 K for 1.8 to 64.8 × 10³ s and 30 MPa in vacuum. Interfacial reactions and microstructures were investigated using electron probe microanalyser and X-ray diffractometer. SiC begins to react with V at temperatures above 1473 K. Granular V₂C phase was formed at the V side of the reaction zone, while a layer of V₃Si phase was formed at the interface between V₂C and SiC after bonding at 1573 K for 1.8 and 7.2 × 10³ s. The same reaction structure can be observed at 1473 and 1673 K for 1.8 × 10³ s. Hexagonal V₅Si₃Cx (X < 1) phase was formed at the interface between V₃Si and SiC after bonding at 1573 K for 14.4 and 21.6 × 10³ s, and the interface structure of the joint became SiC/V₅Si₃Cx/V₃Si/V₂C + V/V. This microstructure represents a complete diffusion path which is correlated with the corresponding Si-V-C phase diagram. At the longer bonding time of 64.8 × 10³ s, V was completely consumed, and the joint showed the layer structure of SiC/V₅Si₃Cx/V₃Si/V₂C/V₃Si/V₅Si₃Cx/SiC.     

铝和氮化铝陶瓷结合强度与机理研究

在氮气气氛下、保温10min、948~1098K利用活性金属铸接方法制备铝/氮化铝陶瓷基板, 用力学试验机、扫描电子显微镜、高温金相光学显微镜和原子力显微镜对铝/氮化铝陶瓷的结合强度和机理进行研究. 结合温度低于973K时, 铝和氮化铝陶瓷之间的剥离强度随结合温度升高线性增大, 当结合温度超过973K时, 结合温度对强度影响很小, 铝和氮化铝陶瓷之间的结合强度约为49N/mm, 铝和氮化铝陶瓷之间的结合为物理湿润和化学反应湿润共同作用.     

AlN陶瓷研究新进展

AlN陶瓷在热、电、光和机械等方面具有非常良好的综合性能 ,可广泛应用于电子、冶金、机械、国防等领域。随着人们对AlN陶瓷研究的深入 ,它变得越来越重要。本文详细地综述了近年来AlN陶瓷在晶体缺陷、导热机理、粉末的制备及其水解和氧化、烧结及其应用等领域的研究进展 ,并展望了AlN未来的发展趋势。     

Lanxide技术合成AlN材料的反应过程及组织特征

本文分析了以Lanxide技术合成AlN的生长过程,发现AlN晶体生长具有明显的方向性,XRD分析表明：AlN晶体的生长方向为[0001]晶向.反应过程中AlN由基体表面向气氛中不断深入生长,形成了纤维状或称柱状晶体组织.反应初期Mg元素的挥发非常强烈,Mg蒸气参与表面反应,生成一层疏松的复相表层,有利于反应的深入进行.氮化过程中Si元素存在富集现象,造成宏观组织的成份不均匀性.     

Ni-Cr/Ti/瓷界面反应机制

采用磁控溅射技术,在Ni-Cr合金表面溅射一层Ti薄膜作为中间层,研究了Ni-Cr/Ti/瓷界面组织结构,产物种类、分布及反应机制。结果表明:Ni-Cr/Ti/瓷界面反应复杂,界面处形成的新物相有Ti2Ni,AlTi3,TiO2,SnCr0.14OX,NiCr2O4和Cr2O3。高温烤瓷过程中,Ti与Ni以稳定的化合物Ti2Ni形式结合,同时Ti与陶瓷中Al2O3反应生成AlTi3化合物,与SnO2和SiO2发生置换反应生成TiO2,TiO2与陶瓷中氧化物结合,更好的实现了Ni-Cr合金与陶瓷的连接。     

镁含量和硅对铁-锌铝镁合金固-液扩散偶中Fe-Al反应层的影响

在热浸镀锌中,铁基表面Fe-Al化合物层的形成会影响镀层的生长和质量。将Fe/(Zn-11%Al-3%Mg)和Fe/(Zn-11%Al-x%Mg-0.2%Si)扩散偶在600℃下进行25min的固-液扩散实验,利用扫描电子显微镜(SEM)和能谱仪(EDS)研究了镁含量和硅对铁-锌铝镁合金固-液界面Fe-Al合金层形成的影响。结果表明,Fe/(Zn-11%Al-3%Mg)固-液扩散偶反应层由FeAl3和Fe2Al5相层组成;随着Mg含量的增加,Fe/(Zn-11%Al-x%Mg-0.2%Si)扩散偶中反应层的厚度呈现先增加后减少再增加的变化趋势,当镁含量为3%时反应层厚度最薄;Fe/(Zn-11%Al-3%Mg)扩散偶中Fe-Al反应层的平均厚度比Fe/(Zn-11%Al-3%Mg-0.2%Si)扩散偶中反应层的厚度大60μm,证明Si元素起到抑制Fe-Al反应层形成的作用。研究结果为解释Super Dyma合金镀层中不形成明显的Fe-Al抑制层提供了实验依据。     

AZ31B镁合金/PRO500超高强度钢TIG熔钎连接界面反应特性及力学性能

利用TIG电弧作为热源开展AZ31B镁合金与超高强度钢PRO500熔钎连接实验,研究界面反应特性及力学性能。结果表明:AZ31B镁合金/PRO500钢能够利用TIG电弧熔钎焊实现有效连接;接头界面中各基体元素的氧化具有强烈的热力学自发性并在接头界面中形成氧化物聚集且包含AlFe3相的过渡区,其硬度介于两种基材之间;界面中靠近钎接位置的钢基体在焊接热循环作用下会出现回火软化现象;大的焊接热输入会导致界面过渡区中脆性化合物相增多,结合强度显著下降。     

Raman spectra of TiN/AlN superlattices

TiN (4.5 nm)/AlN (3, 6, 22 nm) superlattices deposited by DC magnetron sputtering on MgO(001) at a temperature of 850°C exhibit Raman signals. They indicate N and Ti vacancies (as in thick TiN) in TiN_1−x layers (x=3±2%). x is higher for the sample with 3-nm thick AlN layers, which is ascribed to N diffusion from AlN (standing close to the TiN interfaces) to TiN. In comparison to Raman peaks of thick AlN, there are split signals of wurzite AlN phase, and a signal from another phase, which might be defective rocksalt AlN standing close to the TiN interfaces. The Raman signals clearly show interactions between AlN and TiN layers.     

Comparison of microstructure and phase transformation for nanolayered CrN/AlN and TiN/AlN coatings at elevated temperatures in air environment

CrN/AlN and TiN/AlN multilayer coatings with modulation period of 4 nm and thickness ratio equal to 1.0 were manufactured by RF magnetron sputtering. Both films were annealed at temperatures of 800 °C in air for 1 h and then for an additional 9 h. Both coatings in as-deposited and after heat treatment were evaluated with a transmission electron microscope (TEM) equipped with EDS. After heat treatment at 800 °C for 1 h, a thick oxide layer around 260 nm was formed on the surface of the TiN/AlN coating. The oxide layer which formed on the coating was composed of three different regimes, including Al-enriched oxide with excess oxygen on the top surface, a crystalline Al-depleted TiO₂ layer 30-80 nm thick above the nitride coating and in between, mixed nano-crystalline Al₂O₃ and TiO₂ films. In comparison, only one oxide layer smaller than 50 nm in thickness was found in the annealed CrN/AlN coating. This amorphous or nanocrystalline oxide layer identified by EDS was a metal-deficient oxide, in which Al₂O₃ and Cr₂O₃ were mixed together forming a solid solution. As a result, the CrN/AlN coating exhibited superior stability compared to the TiN/AlN coating at elevated temperatures.     

原位反应结合碳化硅多孔陶瓷的制备与性能

以碳化硅(SiC)和氧化铝(Al₂O₃)为起始原料、石墨为造孔剂, 通过原位反应结合工艺制备SiC多孔陶瓷. XRD分析表明多孔陶瓷的主相是SiC, 结合相是莫来石与方石英; SEM观察到多孔陶瓷具有相互连通的开孔结构. 坯体在烧结前后具有很小的尺寸变化, 线收缩率约在±1.5%内. 多孔陶瓷的开口孔隙率随烧结温度和成型压力的增大而减小, 随石墨加入量的增加而增大; 而体密度具有相反的变化趋势. 随着石墨粒径的增大, 多孔陶瓷的孔径分布呈现双峰分布. 抗弯强度随烧结温度和成型压力的增大而增大, 随石墨加入量的增大而减小. 于1450℃保温4h烧成的样品在0～800℃的平均热膨胀系数为6.4×10^-6/K. 多孔陶瓷还表现出良好的透气性、抗高温氧化和耐酸腐蚀性, 但耐碱腐蚀性相对较差.     

碳化硅陶瓷和金属铌及不锈钢的扩散接合

研究了碳化硅陶瓷和金属Ｎｂ的相反应，显微组织结构和Ｎｂ２Ｃ、Ｎｂ５Ｓｉ３Ｃｘ，ＮｂＣ和ＮｂＳｉ２的形成过程，分析了反应相对霎头强度的影响。     

残余应力对Si3N4/S45C连接体强度的影响

本文主要就Si3N4／S45C连接体在插入软金属及附加热循环的情况下，使残余应力发生变化，而讨论其对抗弯强度的影响．其结果为：（1）Si3N4表面边缘处的拉伸应力是影响连接体强度的主要原因．（2）抗弯强度和残余应力具有σ0＝-1．63σ＋658．1的线性关系．（2）周期性热循环对连接体的残余应力及抗弯强度有较大的影响；即发生加工硬化等使残余应力上升，产生裂纹等导致强度下降．     

Effect of thermal cycling on the adhesion strength of Ti/Ni/Ag films on AlN substrate

The adhesion strength of Ti/Ni/Ag multi-layers on AlN substrates before and after thermal cycling treatment was studied. The Ti/Ni/Ag layers with thicknesses of 0.6, 1.0, and 0.2 μm, respectively, were deposited sequentially on bulk AlN substrates using direct current (DC) sputtering. Thermal cycling test (TCT) was conducted for 0, 15, 100, and 300 cycles to measure the adhesion strength of Ti/Ni/Ag on AlN. The adhesion strength of the deposited specimen increased slightly over 15 thermal cycles and increased abruptly after 100 thermal cycles. After 100 thermal cycles, Ti reacted with AlN substrate to form TiN and TiO. The formation of TiN and TiO at the Ti/AlN interface may be responsible for the increase of the adhesion strength after a large number of thermal cycles.     

电子能量损失谱及其在纳米多层膜研究中的应用

本文介绍了电子能量损失谱的基本原理、能量过滤成像分析及应用电子能量损失谱计算碳同素异构体的电子密度和sp^2 键结构的含量。同时应用透射电镜（TEM）和电镜配置的能量过滤成像系统（gatan imaging filter），结合电子能量损失谱研究类金刚石（a-C／Ta—C）和Al／AlN两种纳米多层膜的形态、结构和膜中各元素的分布。结果显示透射电镜观察配合电子能量损失谱在纳米多层膜表征中将会扮演一个重要角色。     

Al/Fe液-固界面扩散反应层生长动力学分析

采用镶嵌式技术制备了Al/Fe扩散偶,在铝熔点以上铁熔点以下进行扩散热处理,对Al/Fe液-固界面扩散反应层的生长动力学进行了分析,并建立了生长动力学方程。结果表明,Fe2Al5是热处理保温过程中唯一生成的新生相。在Fe2Al5连续单相层形成之前,其生长受Al原子和Fe原子的化学反应控制;一旦连续的Fe2Al5单相层形成,其生长则主要依赖于Al原子沿其晶界的扩散控制,且伴随着其晶粒尺寸的长大。在800℃以下热处理,可忽略晶粒长大对原子扩散的影响,其生长动力学方程为:y=2020.96exp(-78490/RT)t0.25。但当热处理温度超过铁熔点的0.7倍后,则不能忽略晶粒长大的影响,应适当减小生长动力学方程中的生长指数值。     

Effects of AlN layer thickness on magnetic anisotropy and transport phenomena of CoPt/AlN layered structure

The magnetic anisotropy was studied as a function of the AlN layer thickness in [AlN(x nm)/CoPt(2 nm)]5/AlN(x nm) layered structure (x is AlN layer thickness, and 5 is the number of multilayer series). The multilayered film was deposited by a sputtering apparatus equipped with two pairs of facing targets. It was found that, in the range of AlN layer thickness below 30 nm, CoPt/AlN multilayers transform from an enhanced in-plane magnetic anisotropy to perpendicular magnetic anisotropy (PMA) through thermal annealing in vacuum, with an optimized AlN thickness of 10 nm for strong PMA. However, beyond this thickness range, the PMA did not occur, and thermal annealing only results in magnetic isotropy in both parallel and perpendicular directions. The related structure analysis revealed that smooth interface and good texture of CoPt (111) make positive contributions to interface anisotropy energy and magnetocrystalline anisotropy energy for producing PMA in CoPt/AlN layered structure. In addition, the transport phenomena were also studied by using a four-probe method.     

Direct Comparison between Tensile Strength and Flexural Strength of Ceramic/Metal Brazing Joint

A design of the sandwich joint,steel/ceramic/steel,was made for direct comparison be-tween tensile and flexural strength ofceramic/metal joint.The flexural strength is abouttwice as high as the tensile strength for the samejoint.The results also showed that the flexural testis more excellent than tensile test for joint with ahigh interracial bond strength.     

SiC/AlN复合球体的制备与表征

以粉煤灰和碳黑为原料n(SiO2)/n(C)=4.2,采用微波加热碳热还原法在1300℃下制备了SiC/AlN复合球体。利用X射线衍射仪(XRD)、拉曼光谱(RS)和扫描电子显微镜(SEM)对SiC/AlN复合球体的形貌和结构进行了表征,并分析了其形成机理。结果表明,以炭黑球为模板,粉煤灰提供Si源和Al源,通过微波加热碳热还原氮化反应可以制得具有梯度结构的SiC/AlN复合球体。所制备的SiC/AlN复合球体具有AlN-多型体的外壳、SiC纳米线过渡层和SiC晶须与花朵状SiC晶体构成的核心。     

AlN/EG纳米流体的制备及稳定性研究

通过两步法制备了氮化铝/乙二醇(Al N/EG)纳米流体,研究了超声分散时间、p H值、分散剂种类及添加量3种因素对其稳定性的影响。结果表明,超声分散时间太长或太短都不利于流体的稳定性,实验中取30 min最好;酸溶液的加入使Al N/EG纳米流体稳定性急剧恶化;碱溶液的加入也使Al N/EG纳米流体稳定性恶化,但速度较酸的加入慢。适量分散剂PVP的加入能够改善Al N/EG纳米流体的稳定性。     

A Method for the Strength Prediction of Porous Ceramics

We present a fracture model for ceramic materials, according to which ceramics is regarded as a porous inhomogeneous material with a composite structure. The role of pores as stress raisers is taken into account, and their size, geometric shape, and orientation with respect to the direction of the maximum tensile stresses are shown to be important factors. The stress on the pore surface at the places of highest stress concentration, which is equal to the ultimate strength of the ceramics bonding phase, was taken as limiting (failure) stress. Probable pore sizes and shapes have been considered in terms of filler crystal size and volume content. A fracture model and a method for the mathematical determination of the strength of ceramics have been proposed, the method taking into account the strength of the constituents, their volume content, and the shape and size of possible internal defects.