物相组成对硅酸镱涂层显微结构和耐蚀性能的影响研究

陶瓷基复合材料(Ceramic matrix composites CMCs)被视为新一代航空发动机热端部件的主要候选材料。然而,陶瓷基复合材料在服役过程中会受到高温水蒸气腐蚀,从而导致材料性能急剧下降。在CMCs表面制备环境障碍涂层(Environmental barrier coating,EBC)可有效解决这一难题。稀土硅酸盐具有高熔点、与CMCs匹配的热膨胀系数和良好的耐蚀性能等特点,是最具应用潜力的环境障碍涂层材料。大气等离子体喷涂技术是制备稀土硅酸盐环境障碍涂层的常见方法。本文通过固相反应法制备了不同物相组成的硅酸镱粉体,并采用大气等离子体喷涂方法制备了富Yb_2O_3(YS0.75)和富Yb_2Si_2O_7(YS1.25)两种涂层,比较研究了涂层的相组成、微观结构和耐高温水蒸气腐蚀性能。研究发现,YS0.75涂层主要由Yb_2O_3和Yb_2SiO_5相组成,结晶度较高,层状结构明显,涂层内有较多裂纹。YS1.25涂层主要由Yb_2SiO_5和Yb2Si2O7相组成,结晶度较低,片层间结合紧密,涂层含有较多球型气孔。不同物相组成的硅酸镱涂层经1400oC高温水蒸气腐蚀后表面均生成Yb_2SiO_5层。富Yb_2O_3涂层具有更好的耐水蒸气耐蚀性能。     

二硅化钼改性硅酸镱环境障涂层的高温抗氧化行为及机理

新一代高推重比航空发动机的发展对环境障涂层（EBCs）的服役寿命和温度提出了苛刻的要求。稀土硅酸盐作为EBCs材料应用于面层,在服役过程中易产生纵向裂纹,为腐蚀性介质的侵蚀提供通道,严重影响EBCs的寿命。二硅化钼（MoSi2）具有优异的高温性能,有望改善稀土硅酸盐 EBCs体系的高温性能。本工作中采用MoSi2改性Yb2SiO5面层,通过真空等离子喷涂技术（VPS）分别制备了Yb2SiO5-XMoSi2（X=0,5和10vol.%）为面层,Yb2Si2O7为中间层,Si为粘结层的三种环境障涂层体系。研究了涂层在1350 ℃长时间氧化前后显微结构演化过程。结果发现,掺杂MoSi2涂层体系在高温氧化500 h后仍能保持结构完整且面层裂纹减少。原因在于,MoSi2可消耗氧化剂,减缓涂层内部TGO的增长速率,反应产物Yb2Si2O7与中间层成分一致,具有较好的化学相容性,有效改善了涂层体系的高温性能。     

等离子喷涂纳米ZrO2热障涂层的组织及性能研究

采用大气等离子喷涂技术制备纳米ZrO2热障涂层,采用金相显微镜、X射线衍射仪、拉伸试验机等对涂层组织及性能进行了研究。结果表明,纳米ZrO2热障涂层组织均匀,面层内孔隙较小、呈近圆形,孔隙率为9.6%;涂层由t-ZrO2单相组成,其平均结合强度和平均剪切强度较传统微米ZrO2热障涂层分别提高63.5%和50.5%,分别达到46.63MPa和23.97MPa;同时涂层具有优异的抗腐蚀性能和耐湿热能力,腐蚀和湿热试验后涂层完整、表面清洁,无新相生成。     

Er0.5Yb1.5Si2O7 环境障涂层高温CMAS 熔盐腐蚀行为研究

硅基陶瓷材料以其优异的性能成为新一代航空发动机热端的候选材料,其在恶劣的服役环境中需要环境 障涂层 ( Environmental Barrier Coating, EBC ) 的保护。以稀土硅酸盐为面层的第三代EBC 是目前研究的热点之 一。采用大气等离子喷涂工艺制备了Er0.5Yb1.5Si2O7 环境障涂层面层样品,研究涂层在钙镁铝硅酸盐(CaO-MgOAl2O3- SiO2, CMAS) 覆盖浓度15 mg/cm2、保温温度1350 ℃、保温时间5 h 的腐蚀条件下的腐蚀行为。研究发现 Er0.5Yb1.5Si2O7 涂层与CMAS 反应后产物为磷灰石相Ca2(Er0.25Yb0.75)8(SiO4)6O2 与Er0.5Yb1.5Si2O7 相,涂层顶部残留 CMAS 熔盐,内部出现反应区和渗透区。     

Cr_7C_3-(Ni,Cr)_3(Al,Cr)热喷涂涂层残余应力状态及其来源分析

采用热喷涂方法在灰铸铁基体沉积Cr_7C_3-(Ni,Cr)_3(Al,Cr)涂层。通过X射线衍射(XRD)、扫描电子显微镜(SEM)分析涂层的形貌及结构,涂层厚度约235μm,涂层主要相成分为Cr_7C_3相和Ni_3Al相。纳米压痕仪测定涂层硬度为16.022±2.125 GPa,弹性模量为247.75±16.873 GPa。利用sin~2ψ法分析Cr_7C_3相在(522)晶面在不同夹角(Ψ=0°、±9°、±18°、±27°、±36°和±45°)下的残余应力。结果表明涂层表面为残余压应力,残余应力大约为-1375.9MPa,其中本征应力为主要来源约-1267.9 MPa,热应力为次要来源约-108 MPa。     

不同喷涂工艺对Cr~(3+)掺杂Al_2O_3陶瓷涂层相结构及发光性能影响研究

通过火焰喷涂工艺和等离子喷涂工艺制备了Cr~(3+)掺杂Al_2O_3陶瓷涂层。采用扫描电镜、X射线衍射、荧光光谱仪等方法表征了涂层的微观形貌、孔隙率、相结构及发光性能等。对比两种不同工艺制备的Cr~(3+)掺杂Al_2O_3陶瓷涂层性能结果表明:等离子喷涂制备的涂层形貌、颗粒熔化状态、厚度均一性均优于火焰喷涂涂层,但火焰喷涂工艺涂层的发光性能远优于等离子工艺涂层,其原因是火焰喷涂制备的涂层中Al_2O_3粒子的熔融状态更差,保留了更多的α-Al_2O_3相,未熔粒子部分将以喷涂原粉中稳定的α-Al_2O_3结构存在涂层中进而影响其光学性能。     

大气等离子喷涂工艺对纳米结构和传统Yb2SiO5 涂层微观结构的影响

纳米材料由于具有一些独特的效果而表现出了独特的性能,纳米结构稀土硅酸盐被认为是很有前景的环境 障碍涂层 ( EBC ) 材料之一。稀土硅酸盐材料中Yb2SiO5 因其卓越的高温相稳定性、对水蒸气环境的耐久性、低 热导率以及优秀的化学稳定性受到了研究者们的广泛关注。本文研究了大气等离子喷涂工艺 ( APS ) 参数对纳米 结构和传统Yb2SiO5 涂层微观结构的影响,并研究了相同大气等离子喷涂工艺下,纳米结构Yb2SiO5 喂料和传统 Yb2SiO5 喂料对涂层微观结构的影响,分析了APS 制备过程中不同结构喂料对涂层结构影响机制。结果表明：相 同喷涂参数制备的纳米结构Yb2SiO5 涂层孔隙率低于传统Yb2SiO5 涂层,以及纳米结构Yb2SiO5 涂层的铺展性和 融化度均优于传统Yb2SiO5 涂层,表明纳米结构Yb2SiO5 涂层为很有前途的环境障碍涂层之一。     

Al2O3 含量对 YSZ 热障涂层性能的影响

Al_2O_3等氧化物对YSZ热障涂层的高温使用性能有一定的影响。本文用HVOF喷涂Ni Co Cr Al Y合金粘结层,APS喷涂YSZ陶瓷面层,制备了Al_2O_3含量为0.01~0.64wt%的YSZ涂层。比较了不同Al_2O_3含量的YSZ涂层在1100℃下的热震性能和抗烧结性能,并探讨Al_2O_3对涂层的影响机理。结果表明相较于高纯YSZ涂层,随着涂层中Al_2O_3含量升高,涂层的抗热震性能降低,且Al_2O_3促进YSZ涂层的烧结。Al_2O_3含量在小于0.01wt%-0.12wt%区间内时,对涂层抗热震和抗烧结性能有显著影响,含量继续增加至0.64%时,对性能影响减缓。显微组织观察与EDS检测结果表明涂层中Al_2O_3并未在熔融颗粒界面处偏聚,但在颗粒内部有局部偏析。由此推测,含Al_2O_3的YSZ涂层热震失效的原因可能是Al_2O_3在YSZ颗粒内部偏析,并影响涂层的烧结性能,导致裂纹容易萌生和扩展。     

连接层和退火对 HVAF 喷涂Cr3C2-NiCr 涂层性能的影响

本文使用HVOF和HVAF技术在铜合金上喷涂Cr_3C_2-50wt%Ni Cr涂层,并就NiCr连接层和退火对HVAF喷涂层的耐磨性和耐腐蚀性进行研究。通过对涂层物相组成、显微结构、力学性能、摩擦磨损性能以及电化学动力学曲线进行测试。结果发现:HVAF喷涂层具有比HVOF更高的结合强度,且磨损体积差异较小,但致密的HVOF喷涂层其耐腐蚀性能优于HVAF喷涂层;NiCr连接层的添加提高了复合涂层的结合强度,且致密的连接层结构可阻碍腐蚀液向基体的侵蚀,使复合涂层的耐腐蚀性能提升;退火处理通过消除涂层内部缺陷提高组织致密性,使得耐腐蚀性增强,并且退火处理降低了涂层内部残余应力,导致涂层结合强度和耐磨性能提升;300℃磨损条件下,喷涂层的磨损机制包括黏着磨损、磨粒磨损和局部氧化磨损。     

重型燃气轮机用La_2(Zr_(0.7)Ce_(0.3))_2O_7/YSZ双层热障涂层热循环性能研究

重型发电燃气轮机低排放、高效率的发展目标,要求燃气轮机透平的进气温度不断提高。热障涂层作为保护金属热端部件的重要手段,是实现这一目标的关键技术之一。目前世界上最先进的J级燃气轮机的透平进口温度已经达到1600℃,热端部件表面温度超过1250℃,传统的YSZ热障涂层已经不能满足这一发展需求,因此迫切需要开发温度更高、热导率更低的新型热障涂层。本文对La_2(Zr_(0.7)Ce_(0.3))_2O_7(以下简称LZ7C3)热障涂层在重型发电燃气轮机中的应用进行了初步验证。结果表明,LZ7C3涂层具有比常规YSZ热障涂层更低的热导率(0.79～0.48Wm~(-1)K~(-1),相对传统YSZ涂层下降30%以上),且在1250℃的高温火焰台架试验中表现出优良的热循环寿命( 7370次),具有良好的应用前景。     

Corrosion Resistance of Sintered NdFeB Permanent Magnet With Ni-P/Tio22 Composite Film

The Ni-P/TiO₂ composite film on sintered NdFeB permanent magnet was investigated by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), and energy dispersive X-ray spectrometer (EDX). The corrosion resistance of Ni-P/TiO₂ film coated on NdFeB magnet, in 0.5 mol/L NaCl solution, was studied by potentiodynamic polarization, salt spray test and electrochemical impedance spectroscopy (EIS) techniques. The self-corrosion current density (i_corr) and the polarization resistance (R_p) of Ni-P/TiO₂ film are 0. 22 μA/cm² (about 14% of that of Ni-P coating), and 120 kΩ • cm² (about 2 times of that of Ni-P coating), respectively. The anti-salt spray time of Ni-P/TiO₂ film is about 2.5 times of that of the Ni-P coating. The results indicate that Ni-P/Ti0₂ film has a better corrosion resistance than Ni-P coating, and the composite film increases the corrosion resistance of NdFeB magnet markedly.     

Influence of LaCl3 addition on microstructure and properties of nickel-electroplating coating

The influence of rare earth chloride LaCl3 ·7H2O addition on the microstructural features, phase structure, corrosion resistance and microhardness of nickel-electroplating was investigated. The Watts-type with different additive amounts of LaCl3·7H2O(0-1.2g/L) were used in the experiment. Surface morphologies of coatings were examined by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) was used to measure the coatings’ grain size and the microstructure of coatings was detected by X-ray diffraction (XRD). Corrosive investigation was carried out in 3.5 wt.% NaCl solution. The microhardness values of the coatings with different amounts of LaCl 3·7H2O were measured, and the mechanism of the variation in microhardness was studied. Results showed that the addition of rare earth lanthanum refined the grain size and improved the surface consistency of the coatings, meanwhile the microhardness and corrosion property of coatings were improved and achieved a maximum with arround 1.0g/L LaCl 3·7H2O addition in electrolyte. The preferred growth orientation of lanthanum doped coating was crystal face (200), meanwhile the La2 Ni7 phase was detected in the nickel coating by XRD and this was due to the induced co-deposition of elements La and Ni. The reason maybe was that the special out-layer electronic structure of element La raised the polarization of Ni cathode deposition, accelerated the nucleation of Ni and reduced hydrogen evolution from cathode surface.     

Photoluminescent properties of Ca2Gd8（SiO4）6O2： Dy^3＋ phosphor films prepared by sol-gel process

There are growing interests on phosphor thin films owing to their potential application in high-resolution devices such as cathode ray tubes and flat panel display devices. The solution-based sol-gel method is one of the most important techniques for the synthesis of various functional coating films. Compounds with the apatite structure are very suitable host lattices for various luminescent ions. Ca2RE8（SiO4）6O2 （ RE=Y, Gd, La ） is a kind of ternary rare-earth-metal silicate with oxyapatite structure, which has been used as host material for the luminescence of various rare earth and mercury-like ions. In this article, Ca2Gd8（SiO4）6O2：Dy^3＋phosphor films were dip-coated on quartz glass substrates through the sol-gel process. X-ray diffraction （XRD）, atomic force microscopy （AFM）, photoluminescence （PL） spectra, as well as lifetimes were used to characterize the resulting films. AFM study revealed that the phosphor films consisted of homogeneous particles. The Dy^3＋ showed its characteristic emission in crystalline phosphor films, i.e., ^4F9/2-^6H15/2 and ^4F9/2-^6H13/2.     

Oxidation Resistance of Niobium Coated with Titanium Disilicide

Coatings based on TiSi₂ have been used to protect niobium alloys from corrosion at temperatures up to 1300°C. Kinetic oxidation curves are given for these coatings on niobium. The phase compositions of the coatings have been determined and also of the layers formed during oxidation. EPMA has been applied to the element distributions in the coating, from which it is concluded that the silicon is mobile. The high resistance to oxygen of coatings based on TiSi₂ is due to the formation of films of TiO₂ and SiO₂ on them.     

Effects of incorporation of micro and nano Al2O3 layers on thermal shock behaviour of YSZ thermal barrier coatings

In the present paper, thermal shock behaviour of usual YSZ and layered composite TBCs was evaluated. The layered composite TBCs used in this study were YSZ/micro Al₂O₃ and YSZ/nano Al₂O₃ in which Al₂O₃ was as a topcoat on the YSZ layer. In addition, coating microstructures were investigated using scanning electron microscope; EDS and X-ray diffraction techniques before and after thermal shock test. The results showed that incorporation of a nano Al₂O₃ oxygen barrier layer caused better thermal shock resistance, while micro Al₂O₃ layer on the top of YSZ sample resulted in sooner coating failure, compared to the usual TBC coating. Also, the thermal shock behaviour and failure mechanism of mentioned coatings were investigated.     

Oxidation Resistance of Niobium Coated with Titanium Disilicide

Coatings based on TiSi₂ have been used to protect niobium alloys from corrosion at temperatures up to 1300°C. Kinetic oxidation curves are given for these coatings on niobium. The phase compositions of the coatings have been determined and also of the layers formed during oxidation. EPMA has been applied to the element distributions in the coating, from which it is concluded that the silicon is mobile. The high resistance to oxygen of coatings based on TiSi₂ is due to the formation of films of TiO₂ and SiO₂ on them.