Al2O3-SiO2/AZ91D镁基复合材料制备及界面反应机理研究

采用硅酸铝纤维和镁合金制备出结构紧密的Al2O3-SiO2/AZ91D镁基复合材料。介绍了复合材料的制备工艺,适宜的挤压铸造工艺为预制体温度650℃、模具温度550℃、浇注温度760℃和30～50MPa压力。XRD、SEM、EDS和光学金相显微镜OM等分析结果表明,复合材料主要由Mg、β-Mg17Al12、MgO、AlPO4、3Al2O3·2SiO2和Mg2Si等结晶相组成;镁与硅酸铝纤维反应生成MgO和汉字状Mg2Si等产物;基体镁与硅酸铝纤维的界面形成较紧密的结合层。     

不同Al含量Mo(Si_(1-x),Al_x)_2材料的高温氧化行为

以MoSi2、Mo和Al粉末为原料,采用真空热压烧结制备不同Al含量的Mo(Si1-x,Alx)2材料,考察Al含量对MoSi2材料微观结构和高温氧化行为的影响。结果表明,当x=0和0.05时,Mo(Si1-x,Alx)2材料主要由呈C11b结构的MoSi2组成;当x=0.1时,该材料主要由呈C40结构的Mo(Si0.9,Al0.1)2和MoSi2组成;当x=0.2~0.4时,该材料由呈C40结构的Mo(Si1-x,Alx)2相组成。随着Al含量的增加,Mo(Si,Al)2晶格膨胀增大。1200℃氧化时,不同Al含量Mo(Si1-x,Alx)2材料的氧化动力学均呈抛物线规律;Mo(Si,Al)2中Al含量越高,氧化增量越大,抗氧化能力越低。当x=0和0.05时,材料表面氧化生成了连续致密的SiO2氧化膜;当x=0.1时,氧化层由SiO2·Al2O3混合氧化膜组成;当x=0.2~0.4时,材料表面氧化生成连续的Al2O3氧化膜。由于Si和Al的扩散,氧化膜与Mo(Si1-x,Alx)2界面处形成了Mo5(Si,Al)3过渡区。     

Cu含量对Al2O3·SiO2sf/Al-Cu复合材料耐磨性能的影响

通过挤压铸造的方法制备出了不同Cu含量的系列Al2O3·SiO2sf/Al-Cu复合材料.摩擦磨损实验结果表明,Cu的加入降低了复合材料的摩擦系数;且随着Cu含量的增加,Al2O3·SiO2sf/Al-Cu复合材料的耐磨性能先增加后降低.在磨损过程中,Al2O3·SiO2纤维增强相牢固地镶嵌在基体里并形成支架,起到保护基体而提高复合材料耐磨性能的作用.Al2O3·SiO2sf/Al复合材料的磨损机制主要为黏着磨损,Al2O3·SiO2afAl-Cu复合材料的磨损机制为黏着磨损为主并伴有磨粒磨损.     

Si4+和F-掺杂对LiNi1/3Co1/3Mn1/3O2结构和电化学性能的影响

以Li2CO3、NiO、Co2O3、MnO2、LiF和SiO2为原料,采用机械力活化固相法制备了Si4+和F-掺杂的锂离子电池正极材料LiNi1/3Co 1/3Mn1/3O2.通过X射线衍射(XRD)、扫描电镜(SEM)和电化学性能测试等技术研究了LiNi1/3Co1/3Mn1/3O2的结构特征、形貌及电化学性能等.结...     

CeO2对渗Si层组织和耐磨性能的影响

采用料浆包渗法,以SiO2粉为Si源,纯Al粉为还原剂,NaF和NH4Cl作为复合活化剂,Al2O3为惰性添加剂,蛋白质(鸡蛋清)为粘结剂,在Cu表面预先镀Ni层随后900℃、12h表面渗Si,制备渗Si层.分别研究了CeO2和Al粉含量对渗Si层组织和摩擦性能的影响.结果表明:当铝粉含量20％时,CeO2含量由3％增加到6％,渗层组织为Ni2Si+ NiSi相;当CeO2含量6％时,铝粉含量由20％增加到30％,渗层组织变化过程:Ni2Si+ NiSi→NiAl→Ni2Al3相,包渗过程由渗硅向渗铝转变;两种渗层的最小摩擦系数都约为纯铜的1/5.     

烧结助剂对高气孔率SiC陶瓷结构和性能的影响

由叔丁醇、丙烯酰胺和SiC粉及烧结助剂组成固相含量为10%(体积分数)的陶瓷浆料,采用凝胶注模成型和无压烧结工艺制备多孔SiC陶瓷,研究Al2O3和Al2O3+SiO2这两种烧结助剂体系对多孔SiC陶瓷的气孔率、显微结构和力学性能的影响。结果表明:Al2O3+SiO2复合烧结助剂明显改善SiC陶瓷的烧结性能,与采用单一的Al2O3烧结助剂相比,SiC样品的烧结温度和莫来石的生成温度均降低50℃左右;两种不同的烧结助剂制成的试样中的气孔均呈很窄的单峰分布,中位孔径为2μm左右;随烧结温度的升高压缩强度增大,而气孔率变化不大;以Al2O3+SiO2为烧结助剂、在1 400℃烧结的试样的气孔率和强度分别达到70.57%和17.74 MPa。     

溶胶-凝胶法制备三维Cf/Mullite复合材料的工艺与性能

利用SiO2-Al2O3双相Sol-gel技术制备出三维编织碳纤维增强莫来石复合材料(3D-BCf/3Al2O3·2SiO2).研究表明,以AlCl3·6H2O,(CH2)6N4和硅溶胶为原料的Sol-gel工艺能制备出高反应活性的SiO2-Al2O3复合粉体,它在1 300℃N2中煅烧可生成莫来石.所得3D-BCf/3Al2O3·2SiO2的密度为1.642 g/cm3,弯曲强度和断裂韧性分别为257.9 MPa和12.2 MPa·m1/2.材料中较多的孔隙是材料密度和弯曲强度不高的原因所在.     

Al2O3-SiO2/AZ91D镁基复合材料的制备及其性能研究

采用硅酸铝纤维和镁合金制备出结构紧密的Al2O3-SiO2/AZ91D镁基复合材料.适宜的挤压铸造工艺为:预制体温度650 ℃、模具温度550 ℃、浇注温度760 ℃和压力30～50 MPa.XRD、SEM、EDS和OM等分析结果表明,复合材料主要由Mg、β-Mg17Al12、MgO、AlPO4、3Al2O3·2SiO2和Mg2Si等结晶相组成;镁与硅酸铝纤维反应生成MgO和汉字状Mg2Si等产物;基体镁与硅酸铝纤维的界面形成比较紧密的结合层.与镁合金相比,复合材料的硬度和油摩擦性能有较大提高.     

无压浸渗制备SiCp/Al-7Si-5Mg铝基复合材料的反应过程及热物理性能（英文）

采用无压浸渗法制备出了体积分数为55%~70%的SiCp/Al复合材料,并对其反应机理、组织形貌以及热物理性能进行了研究。XRD及热力学分析表明:复合材料在制备的过程中最可能发生的界面反应为SiO2(s)+Al(l)+MgO(s)→MgAl2O4(s)+Si(s),提高Si元素的活度可以有效抑制有害界面产物Al4C3的生成;金相显微分析表明:复合材料组织均匀,结构致密,在复合材料制备过程中易产生浸渗缺陷;热物理研究表明:浸渗缺陷较少,结构致密的复合材料其最佳热导(TC)和热膨胀系数(CTE)分别为170.2 W/(m·K)和6.64×10-6K-1。     

Behavior of calcium silicate hydrate in aluminate solution

Using calcium hydroxide and sodium silicate as starting materials, two kinds of calcium silicate hydrates, CaO · SiO2 · H2O and 2CaO · SiO2 · 1.17H2O, were hydro-thermally synthesized at 120 ℃. The reaction rule of calcium silicate hydrate in aluminate solution was investigated. The result shows that CaO · SiO2 · H2O is more stable than 2CaO · SiO2 · 1.17H2 O in aluminate solution and its stability increases with the increase of reaction temperature but decreases with the increase of caustic concentration. The reaction between calcium silicate hydrate and aluminate solution is mainly through two routes. In the first case, Al replaces partial Si in calcium silicate hydrate, meanwhile 3CaO · Al2 O3 · xSiO2 · (6-2x) H2 O (hydro-garnet) is formed and some SiO2 enters the solution. In the second case, calcium silicate hydrate can react directly with aluminate solution, forming hydro-garnet and Na2O · Al2O3 · 2SiO2 · nH2O (DSP). The desilication reaction of aluminate solution containing silicate could contribute partially to forming DSP.     

Elastic Modulus Evolution and Behavior of Si/Mullite/BSAS-Based Environmental Barrier Coatings Exposed to High Temperature in Water Vapor Environment

Si-based ceramics (e.g., SiC and Si₃N₄) are known as promising high-temperature structural materials in various components where metals/alloys reached their ultimate performances (e.g., advanced gas turbine engines and structural components of future hypersonic vehicles). To alleviate the surface recession that Si-based ceramics undergo in a high-temperature environmental attack (e.g., H₂O vapor), appropriate refractory oxides are engineered to serve as environmental barrier coatings (EBCs). The current state-of-the-art EBCs multilayer system comprises a silicon (Si) bond coat, mullite (3Al₂O₃·2SiO₂) interlayer and (1 ? x)BaO·xSrO·Al₂O₃·2SiO₂, 0 ?? x ?? 1 (BSAS) top coat. In this article, the role of high-temperature exposure (1300 °C) performed in H₂O vapor environment (for time intervals up to 500 h) on the elastic moduli of air plasma sprayed Si/mullite/BSAS layers deposited on SiC substrates was investigated via depth-sensing indentation. Laser-ultrasonics was employed to evaluate the E values of as-sprayed BSAS coatings as an attempt to validate the indentation results. Fully crystalline, crack-free, and near-crack-free as-sprayed EBCs were engineered under controlled deposition conditions. The absence of phase transformation and stability of the low elastic modulus values (e.g., ~60-70 GPa) retained by the BSAS top layers after harsh environmental exposure provides a plausible explanation for the almost crack-free coatings observed. The relationships between the measured elastic moduli of the EBCs and their microstructural behavior during the high-temperature exposure are discussed.     

Preparation and characterization of biomorphic SiC hollow fibers from wood by chemical vapor infiltration

Biomorphic SiC hollow fibers were prepared by the reactive infiltration of SiO vapor into basswood-derived charcoal. Gaseous SiO was produced from a SiO₂/Si powder mixture in Ar at elevated temperatures. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform-infrared spectroscopy were employed to characterize the structural morphology and phase compositions of the final products. The results show that the tubular cells in bulk charcoal are converted into lots of SiC hollow fibers with pore diameters of 10–50 μm and lengths ranging from hundreds of μm to several mm. Resulting SiC hollow fibers consist of β-SiC with a minute amount of α-SiC. The formation mechanism of SiC hollow fibers is based on the gas–solid reaction between SiO and carbon.     

New environmental barrier coating system on carbon-fiber reinforced silicon carbide composites

Carbon-fiber-reinforced silicon carbide composites (C/SiC) are promising materials for high-temperature, light weight structural components. However, a protective coating and environmental barrier coating (EBC) are necessary to prevent the oxidation of the carbon and the reaction of the formed silica scale with water vapor. Current EBC systems use multiple layers, each serving unique requirements. However, any mismatch in the coefficients of thermal expansion (CTE) creates internal stresses and might lead to crack formation. In this case, oxygen and water vapor penetrate through the EBC, reducing the lifetime of the component. Mullite (Al₆Si₂O₁₃) is used in many known EBC systems on silicon-based ceramics either as an EBC itself or as a bondcoat. Due to its low CTE and its sufficient thermal cycling behavior, mullite was chosen in this investigation as a first layer. As mullite suffers loss of SiO₂ when exposed to water vapor at high temperatures, an additional protective top coat is needed to complete the EBC system. Different oxides were evaluated to serve as top coat, especially high-temperature oxides with low coefficients of thermal expansion (LCTE). An EBC containing mullite as bondcoat and the LCTE oxide La₂Hf₂O₇ as a top coat is proposed. Both layers were applied via atmospheric plasma spraying. In this paper, results of the influence of processing conditions on the microstructure of single mullite and LCTE oxide layers as well as mullite/LCTE oxide systems are presented. Special emphasis was directed toward the crystallinity of the mullite layer and, in the top layer, toward low porosity and reduced crack density.     

不同粒度的碳化硅磨料氧化性研究

本文用热重分析仪、X射线衍射仪和扫描电子显微镜（SEM）研究了两种不同粒度（0．28-104．71μm,39．81～954．99μm）的碳化硅粉体在20-1400℃温度范围内非等温氧化的特性,结果表明：（1）粒度较小的1#试样的比表面积是2#试样的20多倍,1#试样氧化开始温度为560℃,而2#试样的氧化开始温度为870μ,1#试样在1400℃的氧化增重率为2．36％,2#试样的增重率为1．14％。这表明在相同实验条件下,碳化硅粒度越小,活性越高,氧化程度越高。（2）粒度较小的碳化硅氧化产物为方石英。（3）SEM表明SiC表面生成SiO2保护膜可封闭部分气孔,阻止O2向内扩散,为保护性氧化。     

铜互连多层膜系中自对准CuSiN层的微结构及其热稳定性

通过等离子体与Cu膜表面的分步反应合成了厚约4 nm的CuSiN自对准层.采用高分辨透射电子显微术(HRTEM)、纳米电子束探针能谱(EDS)和X射线衍射(XRD)表征CuSiN和Si/SiO2/TaN/Ta/Cu(CuSiN)/SiC:H/SiOC:H多层膜基体系的微结构和热稳定性.表明CuSiN层两侧分别出现SiN和Cu(Si)层,显著提高Cu/SiC:H/SiOC:H结构的热稳定性,其机制是在500℃退火温度条件下CuSiN层仍能够稳定存在,从而阻碍了Cu原子向SiC:H/SiOC:H介质薄膜体内的扩散.     

Failure of thermal barrier coating systems under cyclic thermomechanical loading

The failure mechanisms of thermal barrier coating (TBC) systems applied on gas turbine blades and vanes are investigated using thermomechanical fatigue (TMF) tests and finite element (FE) modeling. TMF tests were performed at two levels of applied mechanical strain, namely five times and three times the critical in-service mechanical strain of an industrial gas turbine. TMF testing under the higher mechanical strain of air plasma-sprayed (APS) and electron beam–physical vapor deposition (EB-PVD) coated samples showed that both systems failed after a similar number of cycles by cracks that initiated at the bond coat/thermally grown oxide (TGO) interface and propagated through the bond coat to the substrate. When the applied mechanical strain was decreased, cracking of the bond coat in EB-PVD coated systems was suppressed, the life of the coated system increased significantly and delamination of the top-coat was observed. A subsequent FE analysis showed that, by subjecting the system to the higher mechanical strain, significant tensile stresses develop in the TGO and the bond coat that are thought to be responsible for the observed crack initiation and propagation. The FE model also predicts that cracking initiates at specific geometric features of the rough interface of a PS coated system, which was confirmed by metallographic examination of failed samples. The decrease of the applied mechanical strain and hence of the developed stresses led to the suppression of failure by bond coat cracking and activate delamination. These results outline the importance of designing TMF tests and selecting the appropriate mechanical loading in order to accelerate testing and still trigger the same failure mechanisms as observed in-service.     

Cf／ZrC—ZrB2-SiC—C超高温陶瓷复合材料的显微结构表征

利用X-射线衍射、扫描电子显微镜和透射电子显微镜对Cf／ZrC-ZrB2-SiC-C超高温陶瓷复合材料的相组成、纤维／热解碳层的界面特征和超高温陶瓷基体的显微结构特征进行了表征。在碳纤维表面有一层厚度为2～3μm石墨化程度较高的热解碳界面层,该界面层可以避免采用PIP工艺制备超高温陶瓷基体时可能对碳纤维造成的损伤。热解碳层与碳纤维之间为弱机械结合,其界面间分布着20～30nm的ZrC纳米颗粒。Cf／ZrC—ZrB2-SiC—C超高温陶瓷复合材料基体主要由ZrC,ZrB2,SiC和石墨相（Cg）组成。基体中石墨的（002）面沿着ZrC,ZrB2或SiC的表面生长。在石墨与ZrB2和石墨与SiC的界面没有观察到取向关系,界面处既没有反应层也没有非晶相存在。在石墨与ZrC之间存在ZrC（111）／／Cg（002）,ZrC[110]／／Cr[010]的取向关系。ZrB,和SiC之间也没有界面反应和非晶层存在。     

Ni71CrSi中间层钎焊连接C／C复合材料与镍基高温合金GH3044

以Ni71CrSi为中间层存1180℃×30min的钎焊条件下,对C／C复合材料和镍基高温合金进行钎焊试验。,研究了Ni7lCrSi对C／C复合材料和表面SiC改性的C／C复合材料的润湿性。利用扫捕电子显微镜、能谱分析仪、万能试验机和做米压痕仪分别对接头的界面组织、显微硬度和剪圳断裂过程进行了研究。结果表明,表面未改性的C／C复合材料在连接过程中直接失效,而表而SiC改性的C／C复合材料与镍基合金的接头连接良好,且接头剪切强度达到35．08MPa,断裂方式呈假塑性断裂。机理分析表明,镍基钎料较好地润湿表面SiC改性的C／C复合材料,接头的显做硬度分布旱中问高两边低的变化趋势,且形成了表面改性C／C／Ni（s．s）＋Cr7C3＋Ni3Si／Ni（s．s）＋cr3c2＋Ni3Si／Ni（s．s）＋cr3c2＋MC＋Ni3Si／Ni3Si＋MC＋Ni（s．s）／GH3044界面结构。     

THE INFLUENCE OF Mo DIFFUSION ON THE THERMAL BEHAVIOR OF TBCs ON Ni_3Al BASED ALLOY IC-6

Conventional two-layered structure thermal barrier coatings (TBCs) were prepared onto γ'-Ni3Al based alloy IC-6 by electron beam physical vapor deposition (EB-PVD). Isothermal oxidation and thermal cycling tests were carried out to investigate the effect of Mo content at the interface between bond coat and ceramic top coat caused by diffusion. It has been found that the alloy coated with TBCs presented the lowest oxidation weight gain value for the reason that the ceramic top coat in TBC system can effectively stop Mo oxides evaporating. The life time of TBCs has close relation with Mo content at the interface between the bond coat and top coat. Spaliation of ceramic top coat occurred during thermal cyclic testing when Mo atoms accumulated at the interface up to certain amount to decline the combination between the bond coat and top coat.     

高温拉压环境下DZ125高温合金的热障涂层失效

采用电子束物理气相沉积法（EB-PVD）在定向凝固Ni基高温合金DZ125基体上制备了NiCoCrAlY粘结层和YSZ陶瓷层，研究了高温拉压环境下热障涂层的失效模式，并对其进行了有限元分析。实验结果表明，热障涂层的失效与仅受热载荷作用下的有很大不同，仅有热载荷作用下的热障涂层裂纹多萌生于热氧化层（TGO）内部，进而扩展引起热障涂层的失效。而高温拉压试验后热障涂层体系存在两种裂纹，分别萌生于TGO／粘结层界面和粘结层／扩散层界面附近。有限元模拟结果显示TGO／陶瓷层和TGO／粘结层处存在应力状态的转变和应力值的突变，径向应力的突变导致了界面分离现象的产生，而轴向应力的突变加速了垂直于界面裂纹的扩展，并导致了试样的最终断裂。