定向凝固铸造用氧化铝型壳热强度性能研究

通过矿化剂及矿化剂加入量、各组元含量对型壳热强度的影响研究,研制一种电熔莫来石加矿化剂的硅溶胶型壳.该型壳具有很高的热强度,其1550℃的抗弯强度由电熔刚玉加矿化剂型壳的4.99MPa提高到13.65MPa,为单晶叶片用薄壁型壳的研制奠定基础.经定向叶片生产验证,效果优良.     

氧化铝定向凝固高温型壳性能探讨

对型壳基体材料和矿化剂配比进行了试验研究,分析矿化剂的加入对氧化铝型壳高温性能的影响,探讨了二次莫莱石化能明显提高氧化铝型壳高温性能的主要原因。结果表明,氧化铝型壳可以应用于定向和单晶叶片的实际生产。     

定向凝固用陶瓷型壳高温力学性能研究现状

简述了高温合金定向凝固用陶瓷型壳的工况,重点介绍了在浆料中添加矿化剂和粒度小于10 μm超细氧化铝粉等提高型壳材料的化学反应活性以促进型壳中莫来石的形成,进而提高陶瓷型壳的高温强度和抗蠕变性能的措施.还有采用非连续纤维和连续纤维强化型壳,提高其强度和抗蠕变性能的方法.并通过提高型壳孔隙率和在面层形成阻挡层的方法提高型壳的抗热震性能.同时,指出了定向凝固用陶瓷型壳存在的一些问题,论述了其发展方向.     

水平热型连铸定向凝固设备研究

设计制造了氩气气氛保护下的水平热型连铸定向凝固设备,该设备将水平连续铸造与定向凝固技术结合起来,集熔炼、保温、净化、凝固于一体,可制备出表面光洁、质量优异的定向凝固线材。介绍了该设备的结构组成、工作原理。     

定向凝固过程中型芯型壳温度场数值模拟

以空心涡轮叶片作为典型件,开展了定向凝固过程中叶片、陶瓷型芯和陶瓷型壳温度场的数值模拟研究,分析了陶瓷在定向凝固过程中的膨胀特点,对空心叶片铸造过程中陶瓷型芯的定位进行了设计。     

高温合金定向凝固用陶瓷型壳的铸型反应和导热性

介绍了陶瓷型壳和高温合金中的活性元素发生的化学反应,重点描述了陶瓷型壳中的SiO2和Al2O3与合金元素中的Nd、Hf、C、Al、Cr等的化学反应状况,由于非硅基粘结剂不含易于反应的SiO2,从而降低或消除铸型反应.此外,在陶瓷型壳中涂高辐射率涂层、添加金属氧化物和导热体等方法可以提高定向凝固过程中固-液界面凝固前沿的温度梯度.     

型壳耐火材料对无余量定向凝固叶片铸件质量的影响

本文阐述了电熔莫来石结合刚玉制成的型壳材料的显微结构和烧结特点,以及对型壳性能的影响。研究了定向凝固过程中型壳表面层耐火材料杂质和液态金属杂质对叶片铸件表面质量的影响。结果表明:电熔莫来石结合刚玉型壳材料是一种理想的适用于定向凝固型壳的耐火材料。     

定向凝固过程中型芯、型壳温度场数值模拟

以空心涡轮叶片作为典型件，开展了定向凝固过程中叶片、陶瓷型芯和陶瓷型壳温度场的数值模拟，分析了陶瓷在定向凝固过程中的膨胀特点，对空心叶片铸造过程中陶瓷型芯的定位进行了设计。     

型壳参数对定向凝固两相区温度梯度的影响

采用数值模拟与实验验证相结合的方法研究了型壳不同预热温度和厚度对凝固两相区温度梯度的影响.型壳预热温度对温度梯度的影响主要表现在凝固前期;型壳厚度对温度梯度的影响主要体现在凝固后期热量的散失方式上.结果表明,在型壳的预热温度从1450℃增加到1550℃的过程中,平均温度梯度不断增大,最大值为42.1℃/cm;分别考察了4～8mm厚度型壳的凝固过程,平均温度梯度先增大后减小,当型壳厚度超过一定范围时,温度梯度的变化很小,在厚度为6mm时达到最大值43.8℃/cm.     

固溶温度对一种定向凝固镍基合金中温蠕变性能的影响

通过对一种定向凝固合金进行不同温度的固溶处理、蠕变性能测试及组织形貌观察,研究了固溶温度对枝晶臂/间区域的成分偏析及持久性能的影响。结果表明:经1230℃固溶及时效处理后,合金在枝晶干/间区域存在明显的成分偏析和组织不均匀性,粗大γ'相存在于枝晶间区域,细小γ'相存在于枝晶干区域,碳化物呈条状分布在枝晶间区域。合金经1260℃固溶及时效处理后,可明显降低合金中元素的偏析程度,并消除了合金在枝晶间区域存在中的粗大γ'相,使高体积分数细小立方γ'相均匀分布在枝晶间和枝晶干区域,并有细小粒状碳化物沿晶界析出,抑制晶界滑移,因此,可大幅度改善合金的中温蠕变性能。合金在中温蠕变期间的变形特征是位错在基体中滑移和剪切γ'相,并在γ'/γ两相界面形成位错网。蠕变后期,由于沿与应力轴呈45!角的晶界承受载荷的最大剪切应力,故裂纹易于在与应力轴呈45!角的倾斜晶界处萌生与扩展。     

Solidification microstructure of laser remelted Al2O3ZrO2 eutectic

Surface resolidification experiments using a high power CO₂-laser have been performed on an Al₂O₃ZrO₂ containing 36.8 at.% ZrO₂ eutectic alloy at beam velocities between 0.3 and 8 mm·s⁻¹. The local growth rate has been measured by observation of the orientation of the microstructure using scanning electron microscopy. In the whole range of velocities, the structure is essentially a regular lamellar eutectic and the value of the growth productλ²V was found to be ≈ 9.6·10⁻¹⁷ m³·s⁻¹. The measured eutectic spacings were compared with Jackson and Hunt model. Using thermophysical properties from the literature, the measured spacings were more than four times larger than the calculated ones. Assuming all parameters of the growth relationship except the diffusion coefficient to be of the right order of magnitude or to have a negligible influence, agreement is found when using a larger liquid diffusion coefficient,D_L≈5·10⁻¹⁰m²·s⁻¹.     

国外多孔基体氧化铝/氧化铝复合材料工程应用进展

氧化铝/氧化铝复合材料(Al2O3/Al2O3)是20世纪90年代兴起的一类连续陶瓷纤维增强陶瓷基复合材料,已经发展为与SiC/SiC、C/SiC等非氧化物陶瓷基复合材料并列的一类陶瓷基复合材料。与非氧化物陶瓷基复合材料相比,Al2O3/Al2O3具有长时抗氧化、高温耐腐蚀、低成本等独特优势,已经在航空发动机、地面燃气轮机等军民两用热结构材料领域展现出广阔的应用前景。本文从材料应用的角度出发,系统分析阐述了目前在Al2O3/Al2O3占主导地位的多孔基体Al2O3/Al2O3(P-Al2O3/Al2O3)的增韧机制、成型工艺和性能特点,重点归纳了国外近年来P-Al2O3/Al2O3的工程化应用进展及前景,最后指出了P-Al2O3/Al2O3存在的局限性并展望了未来发展方向,旨在为国内Al2O3/Al2O3体系发展提供借鉴和参考。     

MoS2 coated with Al2O3 for Ni-MoS2/Al2O3 composite coatings by pulse electrodeposition

The MoS₂ powders were coated with Al₂O₃ (5 wt.%) through controlling hydrolysis of Al (NO₃)₃·9H₂O. MoS₂ powder coated with Al₂O₃ was written as MoS₂/Al₂O₃ hereinafter. MoS₂/Al₂O₃ powders were put into Ni plating electrolyte bath. Cetyltrimethylammonium bromide (CTAB) — the surfactant was also put into the bath. The experiment proves that MoS₂/Al₂O₃ particles were absorbed onto the Ni plate. The amount of MoS₂/Al₂O₃ deposited on Ni plate rises with the increasing concentration of MoS₂/Al₂O₃ in the bath. The microhardness, micro-surface, phase and the tribological property of the MoS₂/Al₂O₃ multi-plating coating were measured and analyzed. The performances of microhardness and wear resistance of the Ni-MoS₂/Al₂O₃ composite are better than those of Ni-MoS₂ composite.     

Al2O3-Sm2O3-CeO2电解质的性能（英文）

采用溶胶-凝胶法和低温燃烧技术制备Ce1-xSmxO2（x=0,0.1,0.2,0.3）和掺杂Sm和（2%-8%）Al2O3的二氧化铈;研究其合成、结构、致密化、导电性和热膨胀等性能,并利用XRD研究其结构和相组成。结果表明,于1300°C烧结球团,获得致密的陶瓷,于1250°C在Ce0.8Sm0.2O0.2中加入2%和4%的Al2O3以促进烧结。利用扫描电子显微镜观察烧结后球团的表面形貌,使用双探针交流阻抗谱研究总离子电导率。     

Magnetic properties of Al2O3-Cr2O3 solid solutions

Solid solution ceramics (Al₂O₃)_x(Cr₂O₃)_1−x with different x in the range of 0 < x < 1 were synthesized via traditional ceramic production method. X-ray diffraction results and Rietveld refinements indicated that all samples possessed rhomb-centered structure and continuous solid solutions were synthesized. The samples were composed of irregular grains with several micrometers in diameter. Temperature dependence of magnetization measurements showed monotonous decreasing Néel temperature with increasing x and percolation effect happened with threshold of x = 0.65. As x became higher, weak ferromagnetism was observed in the samples. Field dependence of magnetization measurements further confirmed the weak ferromagnetism in the samples with x = 0.7, 0.8 and 0.9.     

Scratching of Al2O3 under pre-stressing

Pre-stressing scratching tests have been preformed on polished surfaces of Al₂O₃ ceramic under a Rockwell diamond indenter which moved with uniform speed and constant normal load to investigate how the pre-stress contributes to the material removal mechanism. With the measurement of acoustic emission signals as well as indenter tangential forces, surface damages and cross-section of grooves of Al₂O₃ ceramic were evaluated under the action of different values of pre-stress. It was found that the scratched groove width was increased with the increasing of pre-stress when same normal loads were applied. The existence of pre-stress tends to restrain the crack propagation along the direction of pre-stress, and obvious plastic deformation at the bottom of scratched groove has been observed. Moreover, the fluctuation of tangential force was obviously enhanced, and the magnitude of tangential force in the test of pre-stress was higher than that of without pre-stress. The acoustic emission signals showed that fewer damages were produced in the process of scratching with an appropriate pre-stress. However, the continuing increase of pre-stress would aggravate the machining process.     

Microstructural constraints for creep in SiC-whisker-reinforced Al2O3

New and published creep data obtained on a SiC-whisker-reinforced Al₂O₃ composite have been analyzed in terms of an effective grain size and a threshold/critical stress. These concepts allow the formation of a consistent picture of the high-temperature deformation of these composites. For low volume fractions of whiskers, before the formation of a point-contact percolative limit is reached, deformation proceeds via grain-boundary sliding after the applied stress exceeds a temperature-dependent threshold stress. In this regime, the nominal grain size is the most important microstructural feature. For larger volume fractions of whiskers, up to the critical volume fraction for formation of facet-to-facet contact, whiskers inhibit grain-boundary sliding and deformation proceeds by means of pure diffusion. In this regime, the most important microstructural feature is an effective grain size, i.e. the spacing between the whiskers. Deformation proceeds until the stress reaches a temperature-dependent critical stress. At this point, damage occurs by unaccommodated grain-boundary sliding and creep is no longer in a steady state.     

La2O3对钢基陶瓷涂层组织与性能的影响

采用热化学反应法在中碳钢(45钢)基体上,以稀土氧化镧(La2O3)为添加剂,制备A12O3陶瓷涂层,并对其组织和性能进行测试和分析.结果表明:稀土氧化镧(La2O3)可以改善陶瓷涂层的组织及性能,陶瓷涂层的硬度和耐蚀性明显提高;添加了稀土氧化镧(La2O3)的A12O3陶瓷涂层,在900℃固化时有MgFeZr3O4、MgSiO3等新相生成;当陶瓷涂层中稀土添加剂(La2O3)含量约为1.19％时,涂层组织更加致密,涂层与基体的冶金结合更加明显,涂层耐蚀性能更好.