Multi-composition oxidation resistant coating for SiC-coated carbon/carbon composites at high temperature

This work proposes a multi-composition oxidation resistant coating for SiC-coated carbon/carbon (C/C) composites by slurry method using the mixture of Y₂O₃, ZrO₂, Al₂O₃, Si and C. XRD analysis shows that the phases of the composite coating are composed of SiC, Al₂O₃, Y₂O₃, ZrO₂, Al₄SiC₄ and Y₃Al₂(AlO₄)₃. SEM analysis of the cross section of the coating displays the microstructure with 500 μm thickness which filled the porous SiC. Oxidation test shows that, after 19 h oxidation in air at 1873 K, the weight loss of the coated SiC-C/C is only 1.76%. The oxidation of the coated C/C composites was primarily due to the reaction of C/C matrix and oxygen diffusing through the penetrable cracks and bubble holes in the coating.     

超重力熔铸Y2O3-Al2O3-SiO2玻璃的晶化行为研究

研究了以超重力熔铸方法制备的Y₂O₃-Al₂O₃-SiO₂玻璃的晶化行为, 并结合相图分析了热处理条件对晶化过程的影响规律。实验结果表明, Y₂O₃-Al₂O₃-SiO₂玻璃的晶化行为与热处理温度和SiO₂含量密切相关。当热处理温度为1050℃时, 晶化后样品的相组成沿超重力场方向呈现出梯度分布, 自上而下分别为Al₆Si₂O₁₃玻璃陶瓷、纯玻璃相、χ-Al₂O₃玻璃陶瓷。当退火温度为1100℃时, 析出晶相主要为Y₃Al₅O₁₂及Y₂Si₂O₇; 退火温度为1200℃时主要析出Y₃Al₅O₁₂。因此, 以超重力熔铸法制备YAS玻璃结合后续热处理的工艺, 提供了一种快速制备YAS基微晶玻璃的新方法。     

A New Unidirectional Solidified Ceramic Eutectic with High Strength at High Temperature

New eutectic composites such as Al₂O₃/Er₃Al₅O₁₂ or Al₂O₃/GdAlO₃ have recently been fabricated by unidirectional solidification. The eutectic composite has a new microstructure, in which continuous networks of Al₂O₃ phases and oxide compounds (Er₃Al₅O₁₂ or GdAlO₃) interpenetrate without grain boundaries. The eutectic composite is thermally stable and has the following properties. In case of Al₂O₃/Er₃Al₅O₁₂ composite,

1. The flexural strength at room temperature can be maintained up to 2073 K (just below its melting point of about 2130 K),

2. The compressive flow stress at 1873 K and a strain rate of 10^-4/sec is about 8 times higher than that of sintered composites of the same composition,

3. It shows neither weight gain nor grain growth, even upon heating at 1973 K in an air atmosphere for 500 hours. In case of Al₂O₃/GdAlO₃ composite, and

4. It shows substantial plastic deformation at 1873 K with a flexural yield stress of about 700 MPa. It is found that the plastic deformation occurred by dislocation motion in each phase.     

光悬浮区熔定向凝固Al2O3/Er3Al5O12和Al2O3/Yb3Al5O12共晶陶瓷的制备与性能研究

本研究探索了光悬浮区熔法制备Al₂O₃/Er₃Al₅O₁₂(ErAG)和Al₂O₃/Yb₃Al₅O₁₂(YbAG) 定向凝固共晶陶瓷。在10 mm/h的抽拉速率下成功获得了凝固组织均匀、内部无裂纹或孔洞的高质量共晶陶瓷。通过高分辨三维X射线衍射仪研究了Al₂O₃和RE₃Al₅O₁₂在三维空间的分布与组织结构; 利用电子背散射衍射技术分析了定向凝固末期Al₂O₃和RE₃Al₅O₁₂两相的晶体学择优取向和相界面关系。力学性能表征结果显示, Al₂O₃/ErAG和Al₂O₃/YbAG具有优异的力学性能, 二者的维氏硬度分别为(13.5±0.4)和(12.8±0.1) GPa;断裂韧性分别为(3.0±0.2)和(3.2±0.1) MPa·m^1/2。     

稀土氧化物对SPS烧结AlN陶瓷电性能的影响

以AlN粉末为原料, 添加稀土氧化物(Sm₂O₃、Y₂O₃), 在氮气气氛下, 采用SPS烧结方法制备AlN陶瓷, 研究稀土氧化物的掺杂对AlN烧结试样相组成、微观结构和电性能的影响。实验表明: Sm₂O₃、Y₂O₃与Al₂O₃反应生成的液相稀土金属铝酸盐会提高AlN陶瓷致密度, 且在晶界处形成导电通路降低了AlN陶瓷电阻率。随着Sm₂O₃掺杂量的增加, 晶界相逐渐由Sm₄Al₂O₉过渡到SmAlO₃, 且Sm₄Al₂O₉对电阻率贡献最大。其中, 3wt% Sm₂O₃掺杂AlN陶瓷电阻率最低, 为      

纤维预热温度对连续Al2O3f/Al复合材料力学性能的影响

选用Nextel610型Al₂O₃纤维为增强体、ZL210A连续氧化铝合金为基体,采用真空压力浸渗法制备纤维增强铝基复合材料(Al₂O_3f/Al),纤维的体积分数为40%,预热温度分别为500、530、560和600℃,研究了纤维预热温度对Al₂O_3f/Al复合材料的微观组织、纤维损伤和力学性能的影响。结果表明：随着纤维预热温度的提高复合材料的致密度随之提高,最大达到99.2%,材料的组织缺陷最少,纤维的分布均匀;随着纤维预热温度的提高从复合材料中萃取出来的Al₂O₃纤维的拉伸强度不断降低,纤维预热温度为600℃的复合材料中Al₂O₃纤维的拉伸强度仅为1150 MPa,纤维表面粗糙,有大尺寸附着物。纤维的预热温度对Al₂O_3f/Al复合材料的拉伸强度有显著的影响。预热温度为500、530、560和600℃的复合材料其拉伸强度分别对应于298、465、498和452 MPa。组织缺陷、纤维损伤和界面结合强度,是影响连续Al₂O_3f/Al复合材料强度的主要因素。     

纳米Al2O3-碳纤维多尺度增强聚酰胺基复合材料的制备及力学性能

采用叠层模压法制备了纳米Al₂O₃-碳纤维织物多尺度增强聚酰胺基（nano Al₂O₃-CFF/PA6）复合材料层压板。借助场发射扫描电子显微镜（FESEM）、同步热分析仪（TGA/DSC）和FTIR,研究了模压温度、压力和纳米Al₂O₃加入量等因素对nano Al₂O₃-CFF/PA6复合材料力学性能的影响。研究表明：在模压温度为230℃、模压压力为3 MPa和保压时间为15 min时,CFF/PA6层压板的弯曲强度为250.3 MPa,层间剪切强度为87.6 MPa,平行层厚方向的冲击强度为41.2 MPa,垂直层厚方向为9.6 MPa。当基体中的Al₂O₃含量达到6wt%时,nano Al₂O₃-CFF/PA6层压板的弯曲强度为387.6 MPa,层间剪切强度为35.7 MPa,平行和垂直层厚方向的冲击强度分别为80.3 MPa和25.6 MPa。     

Improvement of the tensile strength of Al18B4O33w/Al composite at elevated temperatures by change of interfacial state

In general, it is very difficult to obtain obviously reinforced effect in discontinuously reinforced aluminum matrix composites at the temperature above 400 °C. In the present study, we report an effective method to improve the high-temperature tensile strength of Al₁₈B₄O₃₃w/Al composite by change of interfacial state. The pure aluminum matrix composites reinforced by Al₁₈B₄O₃₃w with different ZnAl₂O₄ coating contents were fabricated by squeeze casting. The results indicate that ZnAl₂O₄ coating of the whiskers can effectively improve the high-temperature tensile strength of Al₁₈B₄O₃₃w/Al composite, although the tensile strength of the composite decreases with increasing the tensile temperature. On the basis of fractograph analysis, the fracture mechanism of the composites at elevated temperatures was investigated.     

Processing and Characterization of Fiber Reinforced Intermetallic Matrix Composites

A series of intermetallic matrix composites reinforced with Al₂O₃ based fibers were fabricated by pressure casting. The Al₂O₃ based fibers used were DuPont's 20 μm diameter Fiber FP and PRD-166 fiber, Mitsui's 10 μm diameter Almax fiber, and Saphikon's 125 μm diameter single crystal Al₂O₃ fiber. The intermetallic matrices employed were alloys based on Ni₃Al, NiAl, Fe₃Al, Ti₃Al+TiAl, and Nb₂Al+NbAl₃. Optical, scanning and transmission electron microscopy were used to investigate the microstructure of the composites and the fibers. Tensile testing was conducted to determine the Weibull mean strength of the fibers in the as-received and heat treated conditions. The effect of fiber gage length on the Weibull mean strength of the PRD-166 and Fiber FP was evaluated. Indentation tests were performed to determine the effect of alloying additions on the fiber/matrix bond strength in shear in Saphikon fiber reinforced Ni₃Al composites.     

Morphology control and luminescent property of Y3Al5O12:Tb particles prepared by spray pyrolysis

A spray pyrolysis process was used to prepare spherical yttrium aluminum garnet (Y₃Al₅O₁₂:Tb) phosphor particles with enhanced luminescence properties. The aim of the process was to improve the morphology and luminescent intensity of the Y₃Al₅O₁₂:Tb phosphor particles by modifying the precursor solution. The particles produced from a nitrate aqueous solution were spherical with a hollow structure that was deformed by the post treatment at 1400 °C. To avoid the hollowness, the nitrate solution was modified by the addition of an NH₄OH solution so that a polycation solution could be obtained. Compared with the hollow particles prepared from the nitrate aqueous solution, the Y₃Al₅O₁₂:Tb particles with the spherical morphology and nonaggregated structure, even after the post treatment, were successfully prepared and found to have an improved photoluminescence and cathodoluminescence intensity.     

三维网络结构Al2O3陶瓷/高铬铸铁复合材料干摩擦磨损性能

采用往复式滑动摩擦磨损（SRV）试验机研究了高铬铸铁及三维网络结构Al₂O₃陶瓷增强高铬铸铁复合材料的干摩擦磨损性能,测量了高铬铸铁和Al₂O₃陶瓷/高铬铸铁复合材料在不同摩擦频率及载荷下的摩擦系数和磨损率;用扫描电镜观察磨损表面形貌,并分析了三维网络Al₂O₃陶瓷对复合材料磨损机制的影响。结果表明：陶瓷Al₂O₃与高铬铸铁基体之间具有良好的界面结合,复合材料的摩擦系数随摩擦频率和载荷的变化保持稳定,耐磨性远优于高铬铸铁,而且随着摩擦频率和载荷的增加,Al₂O₃陶瓷/高铬铸铁复合材料的抗磨损性能明显提高,这是由于复合材料中Al₂O₃与高铬铸铁相之间三维空间结构和良好的界面结合有利于摩擦载荷的传递;三维Al₂O₃陶瓷骨架在磨损表面形成硬的网络突体并起承载作用,能有效保护金属基体;磨损机制为氧化磨损及磨粒磨损共同作用。     

Processing, microstructure and properties of C40 Mo(Si,Al)2/Al2O3 composites

The C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composites were prepared by spark plasma sintering (SPS) of mechanically alloyed (MA) powders. The Mo(Si_0.75Al_0.25)₂/0–20 vol.% Al₂O₃ materials, showing micron and submicron composite structure, possess a hardness of 13.9–14.6 GPa but a poor toughness of 1.78–1.80 MPa m^1/2. The addition of 30 vol.% Al₂O₃ leads to the formation of the micron C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composite with an intergranular distribution of Al₂O₃, that results in a drop of the hardness to 10.2 GPa and an improvement of the toughness to 3.67 MPa m^1/2. The transition of the cleavage facets to the intergranular fracture with the addition of Al₂O₃ is assumed as the main toughening mechanism.     

The influence of substrate chemistry on the adhesion of electrolessly deposited Ni(P) on metal oxide coated ceramics

The adhesion of electrolessly deposited Ni(P) on alumina ceramic substrates which were coated with thin SiO₂, SnO₂, TiO₂, Al₂O₃, Y₂O₃, ZrO₂ and (In,Sn)O_x (ITO) films was studied. The adhesion was measured with the aid of the 90° peel test. Strong adhesion of Ni(P) was found for the substrates with ZrO₂ and Al₂O₃ coatings and weak adhesion for the substrates with SiO₂, TiO₂, SnO₂, Y₂O₃ and ITO coatings. The fracture path and the type of interfacial bonding were analysed using scanning electron microscopy, energy-dispersive analysis of X-rays and X-ray photoelectron spectroscopy. In the case of the strongly adhering samples, fracture took place through the metal layer and along the interface. In the case of the weakly adhering samples only interfacial failure was observed between the Ni(P) layer and the metal oxide coating. Cross-section transmission electron microscopy studies of the interfaces suggested that the differences in peel energy values are caused by differences in micromechanical interlocking at the metal oxide-Ni(P) interface. In addition, a weak boundary layer which was found to be present at the Ni(P)-alumina interface was absent in the case of the strongly adhering samples with the ZrO₂ substrate coating.     

三维网络Al2O3增强球墨铸铁基复合材料摩擦磨损性能

采用SRV摩擦磨损试验机研究了球墨铸铁及三维网络Al₂O₃增强球墨铸铁基复合材料的干摩擦磨损性能, 测量了球墨铸铁和复合材料在不同摩擦频率及载荷下的摩擦系数和磨损率; 用扫描电镜观察磨损表面形貌, 并分析了三维网络Al₂O₃对复合材料磨损机制的影响。结果表明: 陶瓷与金属基体之间具有良好界面结合的三维网络Al₂O₃/球墨鋳铁复合材料, 其摩擦系数随载荷和摩擦频率的变化保持稳定; 复合材料的耐磨性能远优于球墨铸铁, 而且随着摩擦频率和载荷的增加, 复合材料的抗磨损性能明显提高。这是由于复合材料中陶瓷与金属相之间三维空间结构和良好的界面结合有利于摩擦载荷的传递; 金属基体中的石墨减摩作用保持摩擦系数的稳定; 三维陶瓷骨架在磨损表面形成硬的微突体并起承载作用, 制约了基体的塑性变形和高温软化, 有利于磨损表面氧化膜的留存。     

几种不同改性剂对稻草/丙烯腈-丁二烯-苯乙烯复合材料性能的影响

以稻草纤维及丙烯腈-丁二烯-苯乙烯（ABS）为原料,分别以活性炭、Al₂O₃、SiO₂和硅烷偶联剂为增强改性剂,通过混炼-模压工艺制备了改性剂-稻草/ABS复合材料,对比研究了几种不同增强改性剂的增强效果及其增强机制。结果表明：硅烷偶联剂对稻草/ABS复合材料的增强效果较差,活性炭、Al₂O₃和SiO₂对稻草/ABS复合材料的增强均优于硅烷偶联剂,其中Al₂O₃的增强效果最佳。当Al₂O₃的添加量（Al₂O₃∶ABS质量比）为5%时,Al₂O₃-稻草/ABS复合材料的拉伸、弯曲及冲击强度分别达到最大值27.719 MPa、61.05 MPa和26.53 kJ/m²;当无机物添加量（无机物∶ABS质量比）为5%时,复合材料的耐水性能表现为：5% Al₂O₃ > 5%活性炭 > 5% SiO₂ > 未添加,与复合材料的力学性能梯度相符;改性剂-稻草/ABS复合材料的流变性能则表现为：5%活性炭 > 5% Al₂O₃ > 5% SiO₂ > 未添加。     

Effect of volume fraction of carbon fibers on wear behavior of Al/Al2O3/C hybrid metal matrix composites

Wear behavior of Al/Al₂O₃/C hybrid metal matrix composites fabricated by squeeze casting method was characterized. The effects of volume fraction of carbon fiber on wear behavior of hybrid composites was investigated. Wear behavior of Al/Al₂O₃/C composites was characterized by the dry spindle wear test under various sliding speeds.

The wear resistance of Al/Al₂O₃/C composites was remarkably improved over Al/Al₂O₃ composites by adding carbon fibers to Al/Al₂O₃/C composites. Specifically, at the intermediate sliding speed the wear resistance of Al/Al₂O₃/C composites containing 8 vol.% carbon fiber was found to be better than that of the rest of the carbon hybrid composites. From fractographic studies, damaged sections in wear surfaces of hybrid composites at intermediate sliding speed were not observed due to the formation of solid lubrication film. The solid lubrication film which was formed as a result of adding carbon fibers improved the wear resistance of carbon hybrid composites because this film reduced the high friction force between MMCs and counter material.     

碳纤维表面改性增强Fe3Al-Al2O3复合材料的制备及组织性能

采用溶胶-凝胶分散和热压烧结制备了短切碳纤维（CF_s）/Fe₃Al-Al₂O₃复合材料。分别通过电化学镀Cu和化学气相沉积SiC对CF_s表面修饰和改性,研究了Cu镀层和SiC涂层对CF_s/Fe₃Al-Al₂O₃复合材料显微组织、相组成、力学性能及断裂行为的影响。结果表明,未修饰的CF_s在Fe₃Al-Al₂O₃基体中受到严重侵蚀,CF_s/Fe₃Al-Al₂O₃复合材料致密度低,抗弯强度仅为239.0 MPa,与Fe₃Al-Al₂O₃强度相当;表面镀Cu可有效保护CF_s不被侵蚀,同时提高了CF_s/Fe₃Al-Al₂O₃复合材料的烧结致密性和界面结合强度,从而明显提高了复合材料的断裂强度,但断裂过程中纤维拔出较短;CF_s表面沉积SiC的CF_s/Fe₃Al-Al₂O₃复合材料组织均匀致密,表面涂层完整,且与纤维及基体之间结合力相当,断裂过程中,涂层既可随纤维一起拔出基体,也可与CF_s分离而留在基体之中,SiC涂层与纤维及基体之间的弱相互作用很大程度上促进了纤维脱黏和拔出,从而促进CF_s/Fe₃Al-Al₂O₃复合材料韧化所需的渐进破坏机制。      

层状硅酸钇改性SiCf/SiC复合材料湿氧化行为研究

研究了层状硅酸钇的引入对SiC_f/SiC复合材料湿氧化行为的影响。首先通过硝酸钇乙醇溶液浸渍热解法向碳化硅纤维引入Y₂O₃, 再采用化学气相渗透法沉积SiC。层状Y₂Si₂O₇主要通过Y₂O₃与沉积过程中的SiC反应转化而成。研究发现, Y₂Si₂O₇在1400 ℃湿氧环境条件下发生富集, 在氧化层表面形成保护层。氧化80 h后, 单层和多层Y₂Si₂O₇改性的SiC_f/SiC复合材料强度保留率分别达到60.38%和71.93%, 而没有改性的SiC_f/SiC复合材料强度保留率仅为50.11%。结果表明: 层状Y₂Si₂O₇的引入可显著提升SiC_f/SiC复合材料在湿氧环境的抗氧化性能。     

基于气动悬浮激光加热技术YAG熔体高温热物理性能评测

钇铝石榴石Y₃Al₅O₁₂(Yttrium Aluminum Garnet, 简记为YAG)材料具有优异的光、热和电学性能, 引起了广泛关注。但高熔点和冷却过程中复杂的相选择机制, 使YAG熔体特别是熔点以下过冷区内的热物理性能参数获得困难。利用自主搭建的气动悬浮无容器激光加热装置, 基于受迫振动和光学描影等原理, 在1750~2650 K宽达900 K的温区内, 评测了YAG熔体的黏度、表面张力和密度。研究表明, 与Al₂O₃熔体相比, YAG熔体密度具有更高的温度敏感性, 具有高约1倍的平均线膨胀系数; 不同于表面张力随温度变化不敏感的Al₂O₃熔体, YAG熔体的表面张力随温度升高产生略微降低; 与Al₂O₃熔体的黏温关系相比, 在熔点以下的过冷区内发现YAG熔体具有更陡峭的黏温变化趋势。     

Y_2W_3O_(12)/Ni复合材料的制备及热膨胀性能

为研究Ni基Y2W3O12复合材料的热学性能,首先,采用二次焙烧法制备了负膨胀材料Y2W3O12;然后,将Y2W3O12与金属Ni进行混合,并在1 200℃、50 MPa的条件下热压烧结制得40vol%Y2W3O12/Ni复合材料;最后,对复合材料的成分及热膨胀性能进行了研究。结果表明:在热压烧结过程中,由于Ni的还原性比W差,相对于对比试样40vol%Y2W3O12/Cr复合材料中发生的复杂化学反应,40vol%Y2W3O12/Ni复合材料的两相之间并未发生反应,使40vol%Y2W3O12/Ni复合材料保持了较低的热膨胀系数;经数次循环退火释放热应力及去除Y2W3O12相的结晶水后,40vol%Y2W3O12/Ni复合材料在170~800℃温度范围内的热膨胀系数趋于稳定,约为3.4×10-6 K-1,与理论设计值4.0×10-6 K-1相近。