Yb_2SiO_5稀土硅酸盐环境障涂层研究进展

环境障涂层体系历经三代的发展,稀土硅酸盐因其具有低热膨胀系数、优良的抗水氧腐蚀性能与相稳定性,且与中间层莫来石化学相容性好,已成为研究热点。本文重点论述稀土硅酸盐Yb_2SiO_5环境障涂层的制备方法、涂层形貌、相结构影响以及裂纹机制、抗高温水蒸气腐蚀及抗CMAS腐蚀性能的研究进展。并指出了以Yb_2SiO_5为代表的稀土硅酸盐体系值得关注的问题及未来环境障涂层的发展趋势。     

热喷涂技术沉积环境屏障涂层（EBC）的评估

目前研究的环境屏障涂层用于防护在富含水蒸气的燃烧环境中使用的涡轮发动机部件,为实现本目的需要致密、无裂纹并且具有较好粘结力的涂层。本文对沉积Yb_2Si_2O_7和Si环境屏障涂层的不同热喷涂技术进行了评估。由于快速凝固导致的玻璃化转变以及含硅物质的蒸发,使得耐火硅酸盐材料的等离子喷涂很复杂。硅在喷涂过程中,尤其是在大气环境下,容易被氧化,因此低密度硅的等离子喷涂工艺也需要细致的优化。本文采用了大气等离子喷涂(APS)、超音速火焰喷涂(HVOF)及等离子物理气相沉积(PS-PVD)分别制备了Yb2Si2O7涂层。分析了涂层的微观组织结构、非晶含量以及相组成,针对工艺参数和材料性能,讨论了每种喷涂技术相比于其他喷涂方法的优点和缺点。     

两步法制备纳米硅酸镱晶须的研究

硅酸镱(Yb_(2)Si_(2)O_(7))是重要的环境障涂层材料之一,具有非常好的高温热稳定性。研究中,采用两步法,以硝酸镱和正硅酸乙酯为原材料,得到硅酸镱晶须。通过SEM对所制备的材料进行形貌分析,结果表明,通过改变工艺参数使得硅酸镱晶须由形貌不规则的短棒状,颗粒状变为晶须状。硅酸镱晶须有望应用到高温结构材料中,提高结构材料的韧性和高温使用寿命。     

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。     

热冲击条件下硅酸镱环境障涂层组织演变研究

硅酸镱是重要的环境障涂层 (EBC) 材料, 本文采用等离子喷涂方法制备硅酸镱涂层, 对其进行了热冲击 考核, 包括纯燃气和含钙离子水汽热冲击, 并初步研究了经过热冲击的涂层组织演变行为。 结果表明, 高温下双 硅酸镱相容易发生向单硅酸镱相的转变, 这可能是因为涂层材料和水汽发生了反应。 在 1350 ℃燃气环境下, 涂 层表层发生了明显的烧结现象。 在含钙离子水汽热冲击（加热温度 1250 ℃） 条件下, 硅酸镱涂层表层形成了鼓 泡特征, 同时受到了钙离子腐蚀。 本文通过对涂层显微组织的分析, 提供了可能的组织演变与化学反应机制。     

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。     

多元稀土掺杂ZrO_2粉末制备与涂层性能研究

稀土掺杂氧化锆热障涂层广泛应用于燃气轮机和航空发动机中以满足其对使用性能和服役寿命的更高要求。本文利用稀土氧化物粉末和氧化锆粉末为原料,采用固相合成法制备了La_2O_3-Gd_2O_3-Yb_2O_3-Y_2O_3-ZrO_2粉末,利用大气等离子喷涂制备LaGYYSZ涂层,利用场发射扫描电镜、X射线衍射和激光拉曼光谱研究了粉末及涂层微观形貌、相结构。结果表明,所制备的La GYYZ粉末基本呈规则实心球,且球形度良好,粒径均匀,其分布范围为30~90μm,且流动性较好,具有良好的高温相稳定性,满足大气等离子喷涂工艺的要求。粉末和涂层均呈四方相/立方相结构,涂层孔隙率13%。在相同测试条件下,LaGYYSZ涂层的隔热性能更优异,较8YSZ涂层提高了18%。     

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/Al_2O_3涂层制备工艺与发光性能研究

采用烧结破碎法可制备适用于热喷涂的Cr/Al_2O_3的粉末,分别采用大气等离子喷涂和火焰喷涂制备了Cr/Al_2O_3发光涂层,研究了粉体和不同喷涂方法制备的涂层组织形貌、相结构及发光性能。结果表明:所制备的Cr/Al_2O_3粉末呈现α-Al_2O_3的单相结构;火焰喷涂涂层呈现粉红色,表面粗糙度Ra 8.8μm和孔隙率21.5%,涂层以α-Al_2O_3相为主;等离子喷涂的涂层呈现灰白色,较低的表面粗糙度Ra 6.1μm和孔隙率8.3%,涂层以γ-Al_2O_3相为主;粉体和两种涂层均可呈现红宝石单晶R线发射,发射峰为693nm和694nm。     

高能等离子喷涂纳米Al203-13％TiO2涂层的组织与耐蚀性能

本文采用高能等离子喷涂方法制备了纳米Al2O3-13％TiO2涂层.通过X射线衍射法(XRD)分析了涂层物相成分,利用电子显微镜观察涂层截面组织形貌,并检测涂层盐雾腐蚀性能与人造海水耐蚀性能.结果表明:该涂层显微组织结构不同于普通等离子喷涂的Al2O3-13％TiO2涂层;涂层在人造海水环境下平均腐蚀率为0.025g/...     

Microstructure of silicon nitride ceramics sintered with rare-earth oxides

Microstructures of Si₃N₄ with crystallized grain boundaries of rare-earth silicates were investigated. β-Si₃N₄ grains in samples sintered with Yb₂O₃ were more elongated than those sintered with Dy₂O₃. Amorphous thin layers between crystallized grain boundaries of silicate and Si₃N₄ grains were recognized for both specimens sintered with Dy₂O₃ and with Yb₂O₃. In the sample sintered with Dy₂O₃, very clean grain boundaries between Si₃N₄ grains which did not contain the heavy elements were frequently recognized, while samples with Yb₂O₃ had an amorphous grain boundary phase containing Yb. Unusual structures with distorted lattice images in regions rich in Si and O were discovered in crystalline Dy-silicate phases.     

Influence of Electrolyte Chemistry on Morphology and Corrosion Resistance of Micro Arc Oxidation Coatings Deposited on Magnesium

In the present work, micro arc oxidation (MAO) coatings were synthesized on magnesium substrate employing 11 different electrolyte compositions containing systematically varied concentrations of sodium silicate (Na₂SiO₃), potassium hydroxide (KOH), and sodium aluminate (NaAlO₂). The resultant coatings were subjected to coating thickness measurement, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), image analysis, and three-dimensional (3-D) optical profilometry. The corrosion performance of the coatings was evaluated by conducting potentiodynamic polarization tests in 3.5 wt pct NaCl solution. The inter-relationships between the electrolyte chemistry and the resulting chemistry and porosity of the coating, on one hand, and with the aqueous corrosion behavior of the coating, on the other, were studied. The changes in pore morphology and pore distribution in the coatings were found to be significantly influenced by the electrolyte composition. The coatings can have either through-thickness pores or pores in the near surface region alone depending on the electrolyte composition. The deleterious role of KOH especially when its concentration is >20 pct of total electrolyte constituents promoting the formation of large and deep pores in the coating was demonstrated. A reasonable correlation indicating the increasing pore volume implying the increased corrosion was noticed.     

Effects of Duty Cycle,Current Frequency,and Current Density on Corrosion Behavior of the Plasma Electrolytic Oxidation Coatings on 6061 Al Alloy in Artificial Seawater

In this study, the effects of duty cycle, current frequency, and current density on corrosion behavior of the plasma electrolytic oxidation (PEO) coatings on 6061 Al alloy in artificial seawater (3.5 wt pct NaCl solution) were investigated. To serve this purpose, the electrical parameters of a unipolar pulsed current were applied during the PEO process on 6061 Al alloy in alkaline silicate electrolyte with and without Al₂O₃ nanoparticles. The coating morphology and microstructure were characterized by the scanning electron microscopy. The corrosion behavior and electrochemical response of the specimens treated by plasma electrolytic oxidation were analyzed by the electrochemical impedance spectroscopy and the potentiodynamic polarization in artificial seawater. It was found that PEO coatings formed in the presence of Al₂O₃ nanoparticle had lower porosity and exhibited better corrosion behavior compared with the coatings formed in the absence of Al₂O₃ nanoparticle in the structure. This can be attributed to the nanoparticles’ incorporation and penetration through the PEO coatings. On the other hand, the decrease in the current density and increases in the duty cycle and frequency lead to further reduction of the nanoparticles’ incorporation and distribution on the coating surface.

     

电弧喷涂含陶瓷颗粒铝基复合涂层的微结构和性能

采用5052半硬铝带分别包覆Al_2O_3、SiC、B_4C、TiC陶瓷颗粒制备的粉芯丝材进行电弧喷涂试验,制备了含陶瓷颗粒的铝基复合涂层。利用光学显微镜、XRD分析了涂层的微观组织和相结构,测试了复合涂层的显微硬度、耐磨性及耐腐蚀性。研究结果表明,制备的铝基复合涂层中含有一定数量的未熔陶瓷颗粒,涂层较为致密,无明显缺陷。含陶瓷铝基涂层的物相主要由Al和所添加的陶瓷相构成,其中在含B_4C陶瓷涂层中还存在Al_3BC、Al_4C_3和AlB_2等新相。陶瓷颗粒的加入有利于提高铝基复合涂层的显微硬度,其中B_4C的加入使涂层中基体相显微硬度提高了1.5倍,这是由于B_4C陶瓷和Al反应生成Al_3BC、Al_4C_3和AlB_2硬质相。复合涂层的耐磨性均优于纯铝涂层,摩擦磨损的形式主要为粘着磨损。动电位极化腐蚀试验表明,含SiC和TiC陶瓷涂层具有较低的腐蚀电流,耐蚀性较好,含SiC陶瓷的复合涂层出现了明显的钝化现象。     

Oxidation and corrosion resistance of TiAl3 coatings

Titanium aluminides based on TiAl, TiAl₃ and Ti₃Al are potential materials for high temperature aerospace applications. Their low density, high temperature creep resistance, high temperature strength and high oxidation resistance make them excellent coating materials. However these coatings are likely to be subjected to high temperature and corrosive environments during service. Hence it is aimed to study the oxidation and corrosion resistance of TiAl₃ coatings on various types of substrates. In the present work, TiAl₃ is coated on high speed steel, stainless steel 304, stainless steel 316, copper and aluminum substrates by physical vapor deposition technique. X-ray diffraction analysis confirms the presence of TiAl₃ phase. The hardness studies reveal that better hardness can be achieved with thick coatings. The oxidation behavior of the coatings is studied by carrying out step stress experiments at elevated temperatures. Coated samples are heated up from 400°C in the steps of 100°C for 1h in each step to 1000°C. The mass gain caused by oxidation was determined. The oxidation curve drawn as a function of mass gain versus temperature reveals that TiAl₃ film started to oxidize above 800°C, where as oxidation of the uncoated substrates began at a much lower temperature of 550°C. The excellent oxidation resistance of the coatings can be attributed to the formation of an amorphous Al₂O₃ film. Scanning electron microscope (SEM) and EDAX analysis confirm the presence of an amorphous Al₂O₃ film. The corrosion behavior of TiAl₃ coatings are investigated by the polarization resistance experiments in NaCl aqueous solution at ambient temperature. According to the Tafel plot analysis, the coatings show lower corrosion rate than the untreated substrates. The major corrosion in the coatings arose from electrolyte penetration into the pores of the coatings. In fact, a dense coating showed a high corrosion resistance in an aqueous medium.     

Toughening of MoSi2 with a ductile (niobium) reinforcement

The effect of interfacial reactions and Y₂O₃ coatings on toughening of MoSi₂ by ductile phase Nb reinforcements has been investigated. In the absence of coating the interfacial reaction layer exhibits parabolic growth with Mo₅Si₃, (Mo, Nb)₅Si₃, (Nb, Mo)₅Si₃ and Nb₅Si₃ phases forming. In precracked laminates subjected to tensile loads the ductile phase deformation is partially constrained, with debonding occurring within the interfacial reaction zone. Dense Y₂O₃ coating inhibits interdiffusion and results in more extensive debonding. In either case, significant toughening is expected with measured work of rupture values χ ≈ 5.7 to 6.3. Bulk composite MoSi₂ reinforced with 20 vol.% Nb particles subjected to a chevron-notched three point flexure test had a work of rupture almost five times larger than the unreinforced MoSi₂ matrix.     

Analysis of zinc coatings on the basis of the iron-zinc phase diagram

The structure of zinc coatings is studied on the basis of the iron-zinc phase diagram, and the coating properties are compared. Corrosion tests indicate that diffusional zinc coatings are preferable in challenging operating conditions. Their structure consists mainly of intermetallides (iron-zinc phases) whose corrosion resistance is greater than that of pure zinc, primarily on account of passivation by zinc ferrites (ZnFeO₂, ZnFe₂O₄), as well as ZnO. The coating life in various aggressive media is considered, together with the main applications of zinc coatings.     

Experimental study of phase equilibria in the PbO-Al2O3-SiO2 system

Equilibrium phase relations in the PbO-Al₂O₃-SiO₂ system have been investigated experimentally by means of high-temperature equilibration, quenching, and electron probe X-ray microanalysis (EPMA). The system has 21 primary phase fields including three monoxides (PbO, Al₂O₃, and SiO₂), seven binary compounds (Al₆Si₂O₁₃, PbAl₂O₄, PbAl₁₂O₁₉, Pb₂Al₂O₅, PbSiO₃, Pb₂SiO₄, and Pb₄SiO₆), and eleven ternary compounds (PbAl₂Si₂O₈, Pb₃Al₁₀SiO₂₀, Pb₄Al₂Si₂O₁₁, Pb₄Al₄SiO₁₂, Pb₄Al₄Si₃O₁₆, Pb₄Al₄Si₅O₂₀, Pb₅Al₂Si₁₀O₂₈, Pb₆Al₂Si₆O₂₁, Pb₈Al₂Si₄O₁₉, Pb₁₂Al₂Si₁₇O₄₉, and Pb₁₂Al₂Si₂₀O₅₅). Three new ternary compounds, Pb₄Al₄SiO₁₂, Pb₄Al₄Si₅O₂₀, and Pb₁₂Al₂Si₁₇O₄₉, were observed and characterized by EPMA. No extensive solid solution in any of the compounds was found in the present study. The liquidus isotherms were experimentally determined in most of the primary phase fields in the temperature range from 923 to 1873 K, and the ternary phase diagram of the PbO-Al₂O₃-SiO₂ system has been constructed.