多元稀土氧化物掺杂二氧化锆基陶瓷材料的热物理性能

稀土氧化物(RE)掺杂氧化钇稳定二氧化锆(YSZ)是提高传统YSZ热障涂层隔热性能和高温稳定性的有效途径之一。在1500 ℃高温固相反应烧结24 h制得Gd₂O₃和Yb₂O₃多元稀土氧化物掺杂的YSZ(含3.5%Y₂O₃(摩尔分数))(GY-YSZ)陶瓷材料。采用XRD研究了GY-YSZ 陶瓷材料的晶体结构和物相组成; 采用激光脉冲法研究了Gd₂O₃和Yb₂O₃掺杂对GY-YSZ 陶瓷材料的热物理性能的影响规律。研究发现, 掺杂2.0%~3.0%Gd₂O₃和Yb₂O₃(摩尔分数)后GY-YSZ的热导率为0.90~1.15 W·(m·K)-1, 比YSZ降低30%以上, 显示了良好的隔热性能。稀土氧化物掺杂对YSZ陶瓷材料热物理性能的影响机制为: 掺杂Gd₂O₃和Yb₂O₃导致YSZ中单斜相(M)、 四方相(T)和立方相(C)含量发生变化, 同时YSZ晶格发生畸变。      

EB-PVD热障涂层对高温合金基体断裂特征影响的研究

采用EB－PVD方法在K3合金上（包括铸态和经标准热处理两种状态）沉积了由NiCoCrAlY金属粘结层和YSZ涂层顶层组成的双层结构的热障涂层,对未涂层和涂层试样的拉伸性能进行了评估,并分析了涂层的制备和中间处理过程中的基体的微观结构的变化。结果表明,在热障涂层的沉积以及中间处理过程中（真空前处理及后处理）,基体的铸态组织得到改善,产生了析出强化,使得在铸态K3合金基体上沉积热障兴层后基体的拉伸强度由800MPa提高到1050MPa,而在经过标准热处理的合金基体上沉积热障涂层对基体的力学性能几乎没有影响。     

EB-PVD在热障涂层中的研究及应用

EB-PVD是以高能电子束为热源的一种蒸发镀膜技术.在真空的环境下,高能离子束轰击靶材(金属,陶瓷等),使其融化、升华、蒸发,最后沉积在基片上.由于EB-PVD技术具有蒸发和沉积速率高,涂层致密,化学成分易于精确控制,可得到柱状晶组织,无污染,热效率高,基片与薄膜之间有较强的结合力等诸多优点,已被广泛应用于国防和民用领域.本文介绍了EB-PVD技术在制备热障涂层时优势、不足与改进措施.     

纳米ZrO2热障涂层热震性能研究

为了研究纳米热障涂层的热震性能,采用等离子喷涂工艺制备了纳米Y2O3-ZrO2(YSZ)热障涂层,并测试了涂层的热震性能.借助扫描电镜和X射线衍射等手段分析了涂层的物相构成和组织结构.结果表明,涂层中保留未完全熔融的小尺寸颗粒,且存在大量的孔径＜1 μm的微孔,该结构对提高涂层的热震性能极为有利.纳米涂层抗热震性能显著优于常规热障涂层,从室温至1 000℃,经800次热循环,涂层无明显的脱落现象.     

等离子喷涂用Y2O3稳定ZrO2空心球形粉末制备技术及涂层性能的研究现状

原始粉末是影响等离子喷涂热障涂层组织结构和性能的主要因素之一。Y_2O_3稳定ZrO_2(Yttria stabilized zirconia,YSZ)空心球形粉末综合了熔融破碎粉末的预合金化效果好和团聚烧结粉末的流动性好的优点。采用该粉末制备的YSZ热障涂层的隔热性能、抗热震性能以及抗烧结性能等均显著提高,是目前综合性能最为优异的热障涂层之一。结合国内外研究情况,文章主要介绍了喷雾干燥法、等离子球化法以及模板法制备等离子喷涂用YSZ空心球形粉末的原理和优缺点;同时,对等离子喷涂过程中YSZ空心球形粉末熔滴的飞行特性、铺展凝固行为以及YSZ空心球形粉末制备涂层组织结构及性能的研究进行了概述;最后,指出了目前研究中存在的问题并对其未来的研究方向进行了展望。     

Gd2Zr2O7陶瓷的高温热物理性能及Gd2Zr2O7-8YSZ双涂层制备

通过高温固相合成方法制备了烧绿石结构Gd₂Zr₂O₇陶瓷材料,研究了其高温相稳定性和热物理性能。采用电子束物理气相沉积方法制备了Gd₂Zr₂O₇-8YSZ(8%Y₂O₃-ZrO₂)双陶瓷层结构热障涂层,分析了涂层顶层的晶体结构和原子数量比。结果表明,Gd₂Zr₂O₇在室温至1500℃范围内具有良好的相稳定性,比第一代热障涂层8YSZ的高温相稳定区间提高250℃以上。Gd₂Zr₂O₇块材的热膨胀系数在100~1500℃范围内介于8.8×10^-6~11.0×10^-6 K^-1之间,与8YSZ接近; 在1000~1400℃高温区间,热导率约为1.0 W(m·K)^-1,比8YSZ降低一半左右。沉积制得的Gd₂Zr₂O₇涂层化学成分符合化学计量比,为烧绿石结构,涂层呈现典型的柱状晶结构。     

EB-PVD 热障涂层的热循环失效机理

采用电子束物理气相沉积方法(EB—PVD)在NiCrAlY粘结层上沉积Y2O3部分稳定的ZrO2陶瓷层。对样品进行了1050C的热循环实验。结果表明,沉积态陶瓷层表面比较致密．其柱状晶粒簇拥成团,晶粒簇间存在间隙。随着热循环不断进行,陶瓷层表面变得疏松,晶粒簇间距增大,相邻较大的间隙互相连接成微裂纹。并逐渐横向及纵向扩展。1050C循环200次,粘结层氧化物是均匀连续的—薄层,主要由Al2O3组成;循环300次后,出现了NiO、尖晶石等氧化物。根据显微结构观察和EDS、XRD分析结果,提出了EB—PVD热障涂层热循环的失效机理。     

Oxidation and Hot Corrosion of Gadient Thermal Barrier Coatings Prepared by EB—PVD

The performances of gradient thermal barrier coatings (GTBCs)produced by EB-PVD were evaluated by isothermal oxidation and cyclic hot corrosion(HTHC) tests.Compared with conventional two-layered TBCs, the GTBCs exhibite better resistance to not only oxidation but also hot-corrosion.Adense Al2O3 layer in the GTBCs effectively prohibites inward diffusion of Oand S and outward diffusion of Al and Cr during the tests.On the other hand ,an “inlaid“ interface ,resulting from oxidation of the Al along the columnar grains of the bond coat,enhances the adherence of Al2O3 layer.Failure of the GTBC finally occurred by cracking at the interface between the bond coat and Al2O3 layer, due to the combined effect of sulfidation of the bond coat and thermal cycling.     

钇稳定氧化锆纳米粉体烧结工艺的研究

实验研究了钇全稳定氧化锆(8YSZ)纳米粉体的烧结工艺,根据阿基米德原理测瓷体密度,通过测定烧结前后瓷片尺寸获得烧结线收缩率,使用扫描电子显微镜观测样品微观形貌,并探讨了纳米粉体烧结的致密化过程,分析了烧结工艺对致密度和晶粒大小的影响,得到了8YSZ纳米粉体合理的烧结工艺为:采用两步烧结,首先升温到1500℃,升温速率为3℃/min,然后降低温度到1450℃,烧结时间为4h.结果显示,采用该工艺,可以得到相对密度98%,晶粒尺寸小于3μm的性能优异的8YSZ瓷体.研究发现,粉体粒度对烧结性能影响较大,纳米粉体比普通粉体具有较低的开始烧结温度,双粒度混合粉体可以进一步提高其烧结性能.     

电子束沉积SiC/ZrO2热防护层的结构优化及其抗热震性能

高性能辐射热防护层是高超声速飞行器金属热防护系统的重要组成部分。为获得高性能的热防护层,利用L5 EB-PVD电子束物理气相沉积设备在Haynes 214镍基合金表面沉积了SiC/ZrO2防护层,测试了其在热循环条件下的抗热震性能;通过分析其沉积温度及厚度对残余热应力的影响,确定了热防护层的沉积工艺参数。结果表明:热防护层在800℃和900℃循环80次后未出现明显的宏观裂纹;1000℃循环60次后,SiC表面层应力集中区出现裂纹,在交变热应力作用下,裂纹不断扩展形成网状龟裂纹,最终导致热防护层剥落;热膨胀系数不匹配导致热防护层在急冷急热热震过程中产生热应力是导致其失效的主要原因。     

纳米多孔薄膜孔结构的非破坏性表征

对纳米多孔低介电常数薄膜孔洞率、孔径、孔径分布和孔洞连通性等孔结构的表征有助于理解薄膜的结构和提高其性能。近年来开展了利用与特殊X射线反射联用的小角中子散射、小角X 射线散射、椭偏测孔仪、正电子湮没谱和表面声波谱等非破坏性方法表征多孔低介电常数薄膜孔结构的研究。介绍了这些方法的基本原理,综述了利用这些方法研究低介电常数介质薄膜及其集成工艺的进展,总结了这些方法表征多孔薄膜孔结构的特征。     

Oxidation and Hot Corrosion of Gradient Thermal Barrier Coatings Prepared by EB-PVD

The performances of gradient thermal barrier coatings (GTBCs) produced by EB-PVD were evaluated by isothermal oxidation and cyclic hot corrosion (HTHC) tests. Compared with conventional two-layered TBCs, the GTBCs exhibite better resistance to not only oxidation but also hot-corrosion. A dense Al2O3 layer in the GTBCs effectively prohibites inward diffusion of O and S and outward diffusion of Al and Cr during the tests. On the other hand, an "inlaid" interface, resulting from oxidation of the Al along the columnar grains of the bond coat, enhances the adherence of AI2O3 layer. Failure of the GTBC finally occurred by cracking at the interface between the bond coat and AI2O3 layer, due to the combined effect of sulfidation of the bond coat and thermal cvcling.     

Surface Adsorption in a Surfactant/Clay Mineral Solution

The complexes formed in aqueous mixture suspensions of the synthetic clay mineral Laponite and cetyltrimethylammonium bromide (CTAB) have been investigated by small-angle neutron scattering (SANS). All suspensions were prepared with a constant initial concentration of Laponite, but the amount of CTAB was varied. The SANS intensity patterns verify that suspended Laponite in dilute suspension is in the form of disks of diameter 30nm and thickness 1 nm. SANS indicates that this disk morphology, with the same diameter but with a thickness of about 4 nm, is retained for the suspended complexes, even if the CTAB in the aqueous medium is in considerable excess. SANS and chemical analysis show that a complex must adsorb CTAB to an amount corresponding to at least two multiples of the clay's cation exchange capacity to be dispersed. The amount of CTAB adsorbed as a function of CTAB in the precursor solution is discussed. We also report the effect the presence of clay on CTAB micelle formation as a function of CTAB concentration.     

PVD thermal barrier coating systems for Mo–Si–B alloys

Abstract

Oxidation protective layers with chemical compositions of Mo–70Al, Mo–46Si–24B, Mo–37Si–15B and Mo–47Si–24Al (at.-%) were deposited on Mo–9Si–8B specimens by magnetron sputtering. After pre-oxidation of the coated samples, ceramic topcoats of yttria partially stabilized zirconia (YSZ) and gadolinium zirconate (GZO) were applied using electron-beam physical vapour deposition. Both as-deposited YSZ and GZO topcoats exhibited good adhesion to the pre-oxidised bond coats. The different thermal barrier coating (TBC) systems were exposed to air at 1000 °C for periods between 20 and 100 h. The YSZ topcoat was tightly-adherent to the borosilicate scale grown on the Mo–46Si–24B bond coat after 20 h of exposure. Similar results were obtained for GZO topcoats deposited on Mo–46Si–24B and Mo–37Si–15B bond coats. The TBC system consisting of GZO topcoat and Mo–47Si–24Al bond coat, which formed a mixed scale of silica and mullite-like oxides, survived 100 h at 1000 °C. However, after this exposure time, the bond coats were approaching their lifetime due to the low layer thickness (5–10 μm). Oxidation of the Mo–Si–B substrate at unprotected areas around the suspension hole of the samples caused severe deterioration of the Mo–70Al bond coat and substantial degradation of the outer region of the GZO topcoat due to chemical reactions with MoO₃.