刚玉-莫来石材料高温断裂性能

为了研究刚玉-莫来石材料的高温断裂和变形性能,采用三点弯曲法研究了红柱石、板状刚玉、电熔莫来石3种不同骨料刚玉-莫来石材料的高温抗折强度和应力-应变曲线,并从材料的显微结构得到解释.以红柱石为骨料的材料形成薄膜状莫来石-刚玉结构,未发现玻璃相存在;其强度最高温度点在1000 ℃,高低温强度相差不大;800～1400 ℃应力-应变曲线分别显示出弹性、塑性特点.以板状刚玉为骨料的材料,基质由粒状刚玉、少量柱状薄膜状莫来石和微量玻璃相组成;其强度最高温度点在800 ℃,高低温强度相差很大;800～1400 ℃应力-应变曲线分别显示出弹性、塑性和粘滞流动3个阶段.以电熔莫来石为骨料的材料,性能与红柱石骨料接近,只是强度最高温度点在800 ℃,断裂前的变形量稍大.莫来石充当了莫来石晶种的作用,形成刚玉莫来石网状结构.     

莫来石-刚玉多孔陶瓷支撑体的制备与性能

以高岭土和氧化铝为原料,通过聚合物辅助挤出成型法制备了管状莫来石-刚玉多孔陶瓷支撑体.研究造孔剂添加量和烧结温度对支撑体相组成、机械强度、微观结构及孔结构的影响,结果显示通过优化制备条件可以获得高气孔率、高强度、孔径分布均匀、透气度好,且具有良好抗热震性能的多孔陶瓷支撑体.     

ZrO2溶胶对刚玉-莫来石复相陶瓷性能的影响

研究了ZrO2溶胶对刚玉-莫来石复相陶瓷性能和微观结构的影响.结果表明在已有刚玉-莫来石质材料技术的基础上,采用溶胶-凝胶法引入ZrO2,可使ZrO2在主体材料中形成亚微米包裹薄膜,可控制ZrO2的分布,使ZrO2在主体材料中均匀分布,达到定量均匀掺入的目的,从而可获得微观结构可控、晶粒尺寸大小均匀,使ZrO2的作用得以充分发挥,不仅可提高材料的抗热震性,而且可提高材料的高温强度及蠕变性.另外,对于加入氧化锆溶胶的试样,氧化锆粒子的应力诱导相变增韧和微裂纹增韧是刚玉-莫来石质材料热震稳定性提高的主要原因.     

莫来石-碳硅石泡沫陶瓷过滤器的研制

以碳化硅、高岭土、氧化铝粉为主要原料,制备具有较好流变性的水基陶瓷料浆,将其浸渍在泡沫塑料上,制成涂层均匀的泡沫体,最终烧制成具有气孔率高、容重小、强度好、抗热震性强的莫来石-碳硅石质泡沫陶瓷过滤器。研究了氟化钙和氧化铝的加入量、烧成温度等对泡沫陶瓷过滤器工艺性能的影响。试验发现,氧化铝含量为15%,CaF2加入量为4%,在1450℃条件下烧制的陶瓷制品外观结构致密均匀,其主晶相为碳硅石相和莫来石相,抗弯强度可达1.11MPa,抗热震性可达5次。     

烧结温度对莫来石刚玉复相材料微观结构的影响

以铝型材厂阳极氧化废渣和粘土为主要原料研制莫来石刚玉复相材料,探讨不同烧结温度对复相材料的影响,分别采用XRD和SEM表征样品的晶相结构和显微结构.结果表明烧结温度可显著改变样品中晶相的组成和各晶相的相对含量;各样品主要存在莫来石固溶体相和刚玉相两种结晶相,其中莫来石固溶体为主晶相,在不同温度下有两种组成(Al4.544Si1.456O9.728和Al4.59Si1.41O9.70);随烧结温度的升高,莫来石含量逐渐增多,至1650℃,试样中莫来石含量为100%.扫描电镜下莫来石呈针柱状交织,晶体发育良好,预示得到的材料具有良好的宏观力学性能.     

微弧等离子喷涂制备莫来石/金属复合热障涂层

运用微弧等离子喷涂制备了莫来石/金属复合热障涂层.研究了涂层的微观结构、结合强度、隔热性能和抗热震性能.复合涂层结构为莫来石颗粒被"包裹"在金属层片状结构中;涂层的结合强度大于30 MPa.随着涂层中莫来石含量的增加,涂层的隔热性能有所提高,随涂层表面温度的升高,涂层的隔热温度也不断提高,涂层的最高隔热温度为125℃.1 150℃的水淬热震试验表明,基体变形是导致涂层失效的重要原因之一,随着涂层中莫来石含量的增加,涂层的抗热震次数先增加后减小,粉末中莫来石含量为40%的涂层的抗热震性能最好,抗热震次数最多为72次.     

激光重熔Al2O3-13ωt%TiO2陶瓷涂层组织结构与热震性能

分析了激光重熔过程对Al2O3-13ωt%TiO2陶瓷涂层的物相结构变化、显微硬度和抗热震性能影响.结果表明:激光重熔过程可以获得稳定的α-Al2O3,且激光重熔工艺能够提高涂层的显微硬度和抗热震性能.     

高强低导热莫来石-刚玉轻质砖的制备

以高铝矾土、硅灰、聚苯乙烯球作原料,用凝胶注模工艺制备高强轻质莫来石-刚玉材料,确定最佳pH值和分散剂用量,并研究了烧成后样品的强度、气孔率、热导率、物相组成和微观结构.结果表明:最佳pH值为9,分散剂加入量为0.33%,当球料比为4:1 (mL·g~(-1))时,1550 ℃烧结出的样品密度为0.37 g/cm~3,气孔率达87.37%,热导率仅0.22 W/(m·K),强度高达2.17 MPa;材料主晶相为莫来石,并含有少量刚玉相,晶粒细小,气孔分布均匀,孔壁薄而完整并有封闭小气孔.     

硅酸盐溶液中ZL101等离子体电解氧化膜形成过程的研究

以硅酸盐溶液为电解液,对ZL101合金进行等离子体电解氧化(PEO)处理,分析膜层的形成过程和膜层的组成和结构。结果表明,PEO初始阶段的膜层分别在初生α相和共晶体上独立形成,Si相上无等离子体放电产生,Si在临近α相的等离子体放电产生高温下氧化,形成SiO2进入膜层。初生α相的膜层以Al2O3为主,含有少量的SiO2。而共晶体的膜层中SiO2含量显著高于Al2O3。ZL101的PEO膜主要成分为γ-Al2O3、α-Al2O3,SiO2及莫来石(3Al2O3.2SiO2)。随着PEO处理时间的增加,γ-Al2O3逐渐向α-Al2O3转化,膜层中α-Al2O3量增加。     

莫来石连续纤维制备工艺

以微米Al2O3和纳米SiO2为原料,添加成型添加剂PVB,制备出了多晶莫来石纤维.借助差热-失重分析(DSC-TGA)、X射线衍射(XRD)及扫描电镜(SEM)分别对纤维的固相反应、相组成及表面形貌等进行了研究.DSC-FGA表明,在600℃以下PVB被完全排出,在1200℃左右纳米SiO2发生从非晶质到鳞石英的晶形转变,XRD分析显示1400℃以下没有莫来石生成,1500℃生成少量莫来石,1500℃到1600℃时,莫来石大量生成,纤维完全莫来石化,并从动力学上说明了Al2O3和SiO2是一步反应生成莫来石.通过SEM观察,由于PVB的大量挥发,使制得的纤维表面粗糙,脆性增加.     

Effects of SiC and MgO on alumina-based ceramic foams filters

Alumina-based foam ceramic filters were fabricated by using alumina, SiC, magnesia powder as major materials. It has been found that this ceramic filter has a uniform macrostructure for filtering molten metals. The influences of SiC and magnesia content, the sintering temperatures on ceramic properties were discussed. Aluminabased foam ceramic filters containing 2.2 mass% magnesia and 7.6 mass% SiC has a compressive strength of 1.36 MPa and a thermal shock resistance of 5 times. Its main phases after 1 hour sintering at 1 500℃ consist of alumina,silicon carbide, spinel and mullite.     

莫来石纤维对氧化铝陶瓷性能的影响

选用莫来石纤维为增强体,通过添加适量的烧结助剂,制备莫来石纤维增强氧化铝陶瓷基复合材料,探讨了不同烧结温度和不同纤维含量对复合材料性能的影响规律.结果表明:莫来石纤维增强氧化铝陶瓷基复合材料的相对密度、弯曲强度和断裂韧性随烧结温度和纤维含量的增加先增大后减小,当烧结温度为1450 ℃、纤维含量为15%时,复合材料的弯曲强度、断裂韧性最高,复合材料弯曲强度和断裂韧性分别达到502.36 MPa和3.48 MPa·m~(1/2),比基体材料分别提高63.8%和54.7%;相对密度达到98.41%.纤维的拔出和脱粘消耗了大量的能量,是莫来石纤维增强氧化铝陶瓷复合材料力学性能提高的主要原因.     

添加TiC对Al_2O_3陶瓷热震行为的影响

热压制备了纯Al2O3陶瓷和Al2O3-30wt%TiC复合陶瓷。研究发现TiC的添加改善了氧化铝陶瓷的力学性能;由于强度的增加使复合陶瓷的临界温差提高了50℃,残余强度都比纯氧化铝的高;韧性的提高使复合陶瓷的热震循环疲劳性能得到改善,复合陶瓷的热震裂纹扩展较曲折。     

酸洗粉煤灰烧结莫来石陶瓷及其力学性能

以酸洗粉煤灰为原料,铝溶胶为铝源,烧结制备了莫来石陶瓷。利用X射线衍射和场发射扫描电镜等分析了莫来石陶瓷的晶体结构与微观形貌,研究了烧结温度和铝溶胶添加量对莫来石陶瓷的烧结行为、析晶过程以及力学性能的影响。结果表明:随着烧结温度升高,陶瓷体积密度、莫来石含量以及抗弯强度先增大后减小;随着铝溶胶添加量增大,陶瓷体积密度和莫来石含量持续增大,但抗弯强度和维氏硬度先增大后减小。酸洗粉煤灰中添加17.7%铝溶胶,1200℃烧结时莫来石陶瓷综合性能最佳,体积密度为2.67 g/cm^3,结晶度和莫来石含量分别为83.4%和50.2%,陶瓷抗弯强度和维氏硬度分别达到137.6 MPa和7.97 GPa。     

Mullite shell mould for casting of advanced CG and SX components in nickel based superalloys

Abstract

Mullite base shell mould system is used for casting of superalloys in columnar and single crystal grains in temperature range of 1480–1550°C. The colloidal silica gel+mullite filler with and without fine alumina slurries was prepared followed by two shell moulds: one without alumina (shell system I) and the other with alumina (shell system II). Shell made with slurry system II resulted in increase in green strength by 10% and fired (950°C) strength by 125% respectively. Sag resistance capability was observed more for shell system II for tested temperatures from 1500 to 1650°C. Dimensional stability of low pressure turbine blade cast at 1550°C was also studied. No shell bulging effect was observed for both shell moulds. The importance of mullite filler material for shell mould to be used for investment casting and its capability to withstand high temperature without metal mould reaction have been highlighted.     

Properties of alumina-based ceramic cores

Fused corundum is a rather promising raw material for preparing an alumina-based ceramic core due to its excellent high temperature resistance and chemical inertness.In this study,alumina-based ceramic cores were prepared using fused corundum as the matrix material,and the effect of varying silica powder contents on the properties of the alumina-based ceramic cores,including the sintering shrinkage,the flexural strength,and the high temperature deformation was investigated.The mineralization mechanisms of the silica on the alumina-based ceramic core were also analyzed.The optimum addition amount of silica in this experiment is 8% in weight.At that moment,the aluminum-based core has both a low sintering shrinkage coefficient of 0.66% and better properties:the room temperature flexural strength is 22.19 MPa,the high temperature flexural strength is 21.54 MPa,the high temperature deformation is 0.93 mm,and the residual flexural strength is 47.41 MPa.     

型壳材料对高温合金叶片组织和性能的影响

采用数值模拟方法并结合试验,研究了型壳材料对高温合金叶片组织和性能的影响。结果表明,无陶瓷保温棉时,氧化铝型壳铸件的冷却速率大于莫来石型壳,氧化铝型壳铸件组织及性能较优;有陶瓷保温棉时,氧化铝型壳铸件叶根处冷却速率略低于莫来石型壳铸件,叶身处冷却速率高于莫来石型壳铸件,莫来石型壳铸件叶根处组织及性能比氧化铝型壳铸件略优,叶身组织及性能比氧化铝型壳铸件略差。有陶瓷保温棉时的铸件叶根组织数值模拟结果和试验结果符合。     

Formation and Surface Structural Features of Crystalline Ceramic Nanocomposite Coatings on Aluminium Using Lithium Sulphate with Silicate Additive

We have synthesized a series of the ceramic coatings by anodization of aluminium using lithium sulphate and sodium silicate additive.Our experiments show that the present coatings are nanocomposites in nature,consisting of a mixture of nanocrystalline alumina,silica,aluminium silicate and mullite; the formation of alumina was similar to conventional anodizing technology,while the formation of mullite was attributed to an addition of sodium silicate.The microhardness of the coatings progressively increased with the increasing current density up to 0.2 A/cm2,which could mainly be attributed to the decrease of porosity in the interfacial region of the oxides up to the range.From the performance of the coatings against corrosion(Tafel/Nyquist plots),it was inferred that the coatings fabricated by lithium sulphate–sodium silicate bath have enhanced corrosion resistance(Rp=3.12 kΩ),as well as better microhardness value than that of the lithium sulphate bath alone(Rp=660.96 Ω) which confirm the perception that the silica particles included in the anodized alumina matrices randomly.Presence of Al,Si and O indicated that the electrolyte components had been intensively incorporated into the coatings.     

低红外发射率陶瓷层/金属层/陶瓷层复合薄膜高温性能研究

目的研究热处理工艺对陶瓷层/金属层/陶瓷层复合薄膜低红外发射性能的影响,并分析复合薄膜的有效工作温度。方法采用多弧离子镀方法在Ni基K424合金基底上制备了AlCrN/Cr/AlCrN和AlCrSiN/Cr/AlCrSiN两种复合薄膜,分别在700~800℃和800~900℃大气环境下对样品进行了热处理。利用X射线衍射仪、场发射高分辨率透射电子显微镜、X射线光电子能谱仪、电子探针显微分析仪、辉光放电质谱仪和傅里叶变换红外光谱仪,对样品的微观结构、化学组成和表面辐射特性进行了分析。通过建模计算了两种样品在不同温度下的氧化活化能和扩散系数,对比了其抗氧化性能和抗扩散性能。结果样品中的陶瓷层呈纳米晶-非晶结构特征,AlCrN和AlCrSiN陶瓷层中的纳米晶分别为hcp-Cr2N和hcp-AlN。非晶AlCrN介质会在750℃结晶形成面心立方相的Cr(Al)N,加入Si元素可以将其结晶温度提高至850℃。在氧化初期,由于纳米晶的不同,AlCrN和AlCrSiN陶瓷层的表面分别形成富Cr和富Al的氧化层,而由于fcc-Cr(Al)N的形成,以及氧化铬和氧化铝之间极高的溶解度,最终样品表面会形成铝、铬混合的氧化层。当非晶AlCrN介质结晶后,O元素通过晶界深入样品内部导致样品的红外发射率急剧增大,使其低发射特性失效。同时,结晶后的复合薄膜中陶瓷层的氧化活化能降低,Ni元素的扩散系数增大。结论纳米晶-非晶结构的陶瓷层具有更优异的抗氧化性能和抗扩散性能,加入Si元素可以提高样品的抗氧化性能,AlCrSiN/Cr/AlCrSiN复合薄膜可应用于850℃以下的低红外发射率应用。