Fabrication of nano-sized oxide composite coatings and photo-electric conversion/electron storage characteristics

Titanium dioxide TiO₂ can be used as a photo-anode to give generated electrons to the metal substrate under illumination. The transition metal oxide such as iron oxide Fe₂O₃ can be used to store electrons generated by the photo-electric conversion function of TiO₂ under the illuminated situation while the electrons are discharged from the transition metal oxide to the metal substrate in the dark. In this paper, coatings of nano-sized composite of TiO₂ and Fe₂O₃ were fabricated by the Warm Spray process, in which the feedstock powder is accelerated by a supersonic gas jet with speed above 1.0 km s^- 1 and temperature between 800 and 2500 K, and then impacted onto the target substrate continuously to form coatings. The coatings of TiO₂ and Fe₂O₃ nano-composite fabricated by Warm Spray showed no thermal deterioration such as phase transformation and particle growth of the feedstock during the spray process. The coatings fabricated by the Warm Spray had larger photo-current and the electron charge/discharge capacity than that by a conventional HVOF process. In addition, these characteristics were improved by decreasing the primary particle size of TiO₂ and Fe₂O₃.     

Salt spray corrosion test of micro-plasma oxidation ceramic coatings on Ti alloy

Ceramic coatings were prepared on Ti-6Al-4V alloy in NaAlO2 solution by micro-plasma oxidation (MPO). The salt spray teste of tne coated samples and the substrates were carried out in a salt spray test machine. The phase composition and surface morphology of the coatings were investigated by XRD and SEM. Severe corrosion occurred on the substrate surface, while there were no obvious corrosion phenomena on the coated samples. The coatings were composed of Al2TiO5 and a little α-Al2O3 and rutile TiO2, and the salt spray test did not change the composition of the coatings. The weight loss rate of the coatings decreased with increasing MPO time because of the increase in density and thickness of the coatings. The surface morphology of the coatings was influenced by salt spray corrosion test Among the coated samples, the coating prepared for 2 h has the best corrosion resistance under salt spray test.     

Grinding of nanostructural ceramic coatings: damage evaluation

This paper investigates the damage, mainly surface and subsurface cracks, in ground n-Al₂O₃/13TiO₂ and n-WC/12Co coatings. Surface cracks are formed under some special conditions. The presence and formation of the surface cracks are studied.Subsurface damage, especially cracks, of the ground components greatly influences their performance and life in service. The effects of the grinding conditions such as material removal rate, wheel grit size and bond materials on the subsurface damage, especially subsurface cracks, are investigated. The difference of material properties of these two coatings also influences the subsurface cracks. Different from bulk samples, large quantities of defects inherited from the thermal spray process play a significant role in the initiation and development of the cracks, present the crack configurations more complex than the typically reported system of median and lateral cracks observed in ground bulk ceramics. This complexity is analyzed.     

Novel thermal barrier coatings that are resistant to high-temperature attack by glassy deposits

Airborne sand particles that deposit on thermal barrier coatings (TBCs) in gas-turbine engines melt and form calcium–magnesium–aluminosilicate (CMAS) glass, which attacks the TBCs. A new approach for mitigating CMAS attack on TBCs is presented, where up to 20 mol.% Al₂O₃ and 5 mol.% TiO₂ in the form of a solid solution is incorporated into Y₂O₃-stabilized ZrO₂ (YSZ) TBCs. The fabrication of such TBCs with engineered chemistries is made possible by the solution-precursor plasma spray (SPPS) process, which is uniquely suited for depositing coatings of metastable ceramics with extended solid-solubilities. Here, the TBC serves as a reservoir of Al and Ti solutes, which are incorporated into the molten CMAS glass that is in contact with the TBC. This results in the crystallization of the CMAS glass and the attendant arrest of the penetrating CMAS front. This approach could also be used to mitigate attack by other types of foreign deposits (salt, ash, and contaminants) on TBCs.     

Effect of some parameters on microstructure and hardness of alumina coatings prepared by the air plasma spraying process

The spraying distance, substrate temperature, coating thickness and surface roughness of substrate during deposition play an important role on the plasma spray coating process and effect the final properties of the coatings. Al₂O₃ coatings on AISI 304 L stainless steel substrate were prepared to investigate the effects on the coating of these parameters. The results indicated that the parameters such as the spraying distance, substrate temperature, coating thickness and substrate roughness were fairly effected the hardness, porosity and surface roughness of Al₂O₃ coatings. The lowest surface roughness and the lowest porosity and the highest hardness values of Al₂O₃ coating were obtained for the spraying distance of 12 cm and the surface roughness of 3.28 μm and the substrate temperature of 500 °C. It also found that the increases of coating thickness were lowered the hardness and enhanced the porosity and the coating roughness.     

Oxidation behavior of ceramic coatings on Ti–6Al–4V by micro-plasma oxidation

Compound ceramic coatings prepared on Ti–6Al–4V alloy by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO₂ solution were oxidized under different temperature in air. The phase composition and surface morphology of the coatings before and after oxidation were investigated by X-ray diffractometry and scanning electron microscopy, respectively. Meantime, the weight gains and the high temperature oxidation characteristics of the coated samples were investigated. The results show that the coatings prepared by MPO were composed of a large amount of Al₂TiO₅ and a little -Al₂O₃ and rutile TiO₂. And the oxidation process of the coated samples included the decomposition of the Al₂TiO₅ in the coating, the oxidation of the substrate and the changes of the coating structure. After high temperature oxidation, the increase of -Al₂O₃ in the coating was due to the decomposition of Al₂TiO₅, whereas the increase of rutile TiO₂ in the coating was attributable to both the decomposition of Al₂TiO₅ and the oxidation of the Ti substrate. The main crystalline of the coatings became rutile TiO₂ after the oxidation of 1000 °C for 1 h. The decomposition of Al₂TiO₅ in the coating occurred at 900 and 1000 °C, and its half decomposition time was less than 1 h at 1000 °C. Increasing oxidation temperature or extending oxidation time, the weight gains of coated samples was increased to different extent. However, the weigh gains of the coated samples was much lower than that of the substrate, so the ceramic coatings improved the oxidation resistance of Ti alloy greatly under the experimental conditions.     

Thermal cycle behavior of plasma sprayed La2O3, Y2O3 stabilized ZrO2 coatings

The effects of La₂O₃ addition on thermal conductivity, phase stability and thermal cycle life of Y₂O₃ stabilized ZrO₂ plasma sprayed coatings were investigated. Although low thermal conductivity as well as high resistance to sintering was achieved by La₂O₃ addition, it tended to also result in lower phase stability and thermal cycle life of the coatings. Optimization of the composition and structure of the coatings improved these properties, and the optimized coatings showed prolonged thermal cycle life.     

树脂金刚石砂轮加工氧化铝陶瓷的磨削工艺试验研究

为改善氧化铝陶瓷的磨削效果,分别使用粒度尺寸125~150 μm和38~45 μm的金刚石制备树脂结合剂砂轮,并进行磨削实验,研究表面粗糙度、材料去除方式和材料去除比例随磨削参数的变化规律,观察并分析氧化铝陶瓷磨削后的表面微观形貌。结果表明:氧化铝陶瓷的表面粗糙度可以达到R_a 0.418 μm,材料去除比例可达到95%;用粒度尺寸38~45 μm的金刚石制备的树脂结合剂砂轮在切深≤ 2 μm,工件移动速度为0.15 m/min加工时,材料由延性域的塑性去除转变为脆性去除。优化后的加工工艺为先以磨料粒度尺寸125~150 μm的树脂金刚石砂轮在切深为4 μm时进行初步加工,再用磨料粒度尺寸38~45 μm的树脂金刚石砂轮进行光磨,可以兼顾高效与精密两方面的要求。      

氧化硼对保护渣中TiO2溶解动力学的影响

含钛钢连铸过程中,部分TiO₂夹杂物进入保护渣,导致渣性能恶化,进而影响铸坯质量。采用旋转法,研究了TiO₂在保护渣中的溶解速率与旋转速度、温度、B₂O₃含量等因素的关系。结果表明,TiO₂在保护渣中溶解速率与棒旋转的角速度的平方根成正比;且在温度升高时,TiO₂在保护渣中的溶解速率有明显的上升;在w(B₂O₃)=0～9%时,随着B₂O₃含量上升,TiO₂溶解速率升高,溶解活化能由162.99降至123.95 J/mol,但B₂O₃含量对溶解速率的影响要明显小于温度的影响。以上研究结果较好阐明了TiO₂在保护渣中的溶解机理,为含钛钢连铸过程提供一定的参考。     

保护渣对铝钛系夹杂物溶解的吸收规律

以CaO-SiO₂-Al₂O₃-Na₂O-CaF₂-MgO为基础渣系,采用旋转动力学方法研究了不同碱度、BaO质量分数(0~15%)、B₂O₃质量分数(0~15%)对连铸保护渣吸收Al₂O₃或TiO₂速率的影响以及吸收前后矿相变化。结果表明,保护渣吸收TiO₂的速率要远大于吸收Al₂O₃的速率;添加BaO或B₂O₃后均能提高保护渣吸收Al₂O₃和TiO₂的能力;保护渣主要物相为钙镁黄长石(2CaO·MgO·2SiO₂)、钙铝黄长石(2CaO·Al₂O₃·2SiO₂)、枪晶石(3CaO·2SiO₂·CaF₂)及玻璃相(Na₂O·Al₂O₃·SiO₂);添加BaO后,钙镁黄长石转变为重硅酸钡钙镁(2CaO·MgO·2SiO₂·BaO),并抑制黄长石和枪晶石晶体长大;当添加B₂O₃的质量分数不低于10%,保护渣形成的物相为玻璃相。试验条件下,不同碱度的保护渣和添加B₂O₃的保护渣中TiO₂仍以TiO₂形式存在,而在添加BaO的保护渣中,TiO₂形成钙钛矿。     

纳米结构金属陶瓷(n-WC/Co)涂层材料精密磨削的试验研究

本文对纳米结构金属陶瓷（n-WC/Co）涂层材料在金刚石砂轮精密磨削过程中的磨削力进行了较详细的试验研究。对常规结构金属陶瓷(n-WC/Co）和n-WC/Co涂层材料的磨削力作了对比磨削试验,分析了磨削工艺参数如砂轮磨削深度,工件进给速度,金刚石砂轮结合剂类型和磨粒尺寸以及被磨试件材料特性等对磨削力的影响,结合被磨试件表面的扫描电镜（SEM）的观察,分析了n-WC/Co涂层材料磨削的材料去除机理,研究结果表明：在相同磨削条件下,纳米结构陶瓷涂层的磨削力始终高于常规结构陶瓷涂层的磨削力;在其它磨削条件相同的情况下,用金属结合剂砂轮磨削工件所需的磨削力要比树脂结合剂砂轮,陶瓷结合剂砂轮所需的磨削力大些,磨粒尺寸小的砂轮磨削工件所需的总磨削力要比磨粒尺寸在的砂轮所需的磨削力大些,磨削力随砂轮磨削深度,工件进给速度的增加而增大;一般情况下,n-WC/Co涂层材料精密磨削过程的材料去除机理中,占主导方式的是塑性成形的材料去除方式。     

Microstructure and composition analysis in plasma sprayed coatings of Al2O3/ZrSiO4 mixtures

Plasma spraying of Al₂O₃/ZrSiO₄ was performed using spray dried and plasma spheroidised powder feedstock. The mixtures were sprayed using different spray stand-off distances and plasma power levels. X-Ray diffraction (XRD) was used to characterise the phase composition and scanning electron microscopy (SEM) examined the morphology of the sprayed surface and polished cross-sections. The results showed that the plasma spray process parameters played an important role in the final outcome of microstructures of the coatings. The coatings produced with spheroidised powders displayed a much denser structure than those produced with the spray-dried powders. The phase composition analysis showed the presence of amorphous phases in addition to crystalline alumina, zircon and tetragonal (t) zirconia (ZrO₂). Transmission electron microscopy (TEM) showed that amorphous phases and t-ZrO₂ crystals with particle size 100–200 nm could coexist within a single splat due to the relatively low local cooling rate.     

Aerosol Spray Pyrolysis Synthesis of Porous Anatase TiO_2 Microspheres with Tailored Photocatalytic Activity

Porous titanium dioxide(TiO_2) microspheres(MS) were prepared by a facile ultrasonic spray pyrolysis process with commercial colloidal silica as a sacrificial template. The morphology structure, Brunauer–Emmett–Teller surface areas and pore size distribution of TiO_2 microspheres were studied by changing the content and diameter of the silica template in detail. These porous micro-sized MS are composed of anatase TiO_2 nanocrystallites of 5–10 nm and have unique bimodal mesopores. The largest specific surface area of 112.3 m~2/g has been achieved using 60 wt% 20 nm silica as a template.When used as photocatalysts, the best photocatalytic activity of the as-prepared porous MS is comparable to commercial P25 nanopowders. Moreover, the micro-size and tailored properties from the design that appear during the ultrasonic spray pyrolysis process give these porous MS a promising application in photocatalytic reaction.     

Microcrack formation in plasma sprayed thermal barrier coatings

Air plasma sprayed ZrO₂–8wt%Y₂O₃ thermal barrier coatings were deposited under tightly controlled conditions. The lengths and orientations of the horizontal cracks and vertical cracks in these coatings were characterized in detail, and process/structure maps of the crack distribution as a function of particle and substrate states were constructed. A fully coupled thermo-mechanical finite element model was used to study the buildup of stresses during splat solidification, and to understand the effect of deposition conditions on crack formation during plasma spray deposition. The model also showed that surface roughness plays a key role in determining the magnitude of maximum stresses, and that only roughness features on the scale of splat thickness are important in providing locations of maximum stress concentration.     

NiCrAlY/Al-Al2O3/Ti2AlNb高温抗氧化和力学性能研究

采用电弧离子镀技水在NiCrAlY涂层与O相Ti₂AlNb合金之间沉积不同Al:Al₂O₃比例的Al-Al₂O₃薄膜作为扩散阻挡层.研究了900℃下恒温氧化500 h后NiCrAlY/Al-Al₂O₃/Ti₂AlNb体系中Al-Al₂O₃层阻挡合金元素互扩散的行为,以及对涂层氧化动力学曲线的影响.结果表明,没有添加扩散阻挡层的NiCrAlY/Ti₂AlNb体系,涂层和基体之间的元素互扩散十分严重,涂层丧失抗氧化能力;而添加扩散阻挡层的材料体系,涂层和基体之间的元素互扩散受到抑制,涂层的长期抗高温氧化性能得到提高.对于3Al-Al₂O₃,1Al-Al₂O₃和0Al-Al₂O₃ 3种扩散阻挡层,综合比较材料体系的抗氧化性能、阻挡层阻挡涂层和基体元素互扩散能力、以及涂层和基体之间结合力,当1Al-Al₂O₃薄膜作为扩散阻挡层时,材料性能最优异.同时,本文利用扩散阻挡系数简洁定量地表示出不同Al:Al₂O₃比例阻挡层的阻挡扩散能力.     

Isothermal oxidation of air plasma spray NiCrAlY bond coatings

The isothermal oxidation behaviors of plasma-sprayed NiCrAlY bond coatings (Ni22Cr10Al1Y and Ni31Cr11Al 0.6Y) have been evaluated. Two unique microstructures, oxide stringers and improperly flattened zones, can be observed in the air plasma spray (APS) bond coatings. The structures and chemical compositions of the oxide stringers were examined by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Improperly flattened zones had a high density of open pores. These features affected the oxidation behaviors in both the transient and the steady-state stages. In the transient oxidation stage, NiO, Cr₂O₃ and -Al₂O₃ were observed on the surface simultaneously. The oxide stringers and improperly flattened zones had an especially high density of NiO and Cr₂O₃, which implied that these regions had inherently lower contents of Al. During steady-state oxidation, a continuous -Al₂O₃ layer reduced the diffusion rate of oxygen and, thus, the rate of isothermal oxidation became low. As the oxidation time was increased, depletions of Al, the formation of NiAl₂O₄ layers and the formation of Cr₂O₃ subsequently occurred. Hemispherical protrusions were also detected on the surface after cooling to room temperature.     

Microscopic observation of degradation behavior in yttria and ceria stabilized zirconia thermal barrier coatings under hot corrosion

In this study, the effects of yttria stabilizer replacement with ceria on hot corrosion properties of thermal barrier coatings (TBCs) have been investigated in microscopic respects. Yttria stabilized zirconia (YSZ; ZrO₂–8 wt.%Y₂O₃) and ceria stabilized zirconia (CSZ; ZrO₂–25 wt.%CeO₂–2.5 wt.%Y₂O₃) thermal barrier coatings (TBCs) were fabricated to have similar microstructures, followed by hot corrosion tests with a NaVO₃ salt at 900 °C. Very dense YSZ TBCs with porosities below 4% were also fabricated in order to investigate the effects of coating defects on hot corrosion behavior. Results revealed that CSZ TBCs were better resistant to hot corrosion environment than YSZ TBCs in terms of phase stability and overall damage by the salt. From studies on microscopic failure behavior, it was found that YSZ and CSZ TBCs showed a different degradation behavior and that coating defects, such as pores, microcracks and splat boundaries, play important roles as effective paths for the salt in hot corrosion. From the present results, a possible microscopic degradation mechanism and effects of coating microstructures for zirconia-based TBCs under hot corrosion are discussed.     

化学机械抛光304不锈钢用抛光液成分研究

由于304不锈钢的优良特性,未来其将成为柔性显示器衬底的主要材料之一。为提高304不锈钢化学机械抛光的速率和质量,研究不同氧化剂在不同质量浓度或体积浓度及不同pH值下, 对材料去除率和表面粗糙度的影响。结果表明:氧化剂Fe₂O₃、H₂O₂、FeCl₃都在pH=2时抛光效果最佳,氧化剂KMnO₄在pH=10时抛光效果达到最佳。在最佳的pH值下进行抛光,H₂O₂的体积浓度为10 mL/L时,表面粗糙度R_a最好,为4 nm;在FeCl₃质量浓度为4.0 g/L时,材料去除率最高,为209 nm/min。      

Preparation of ceramic coatings on inner surface of steel tubes using a combined technique of hot-dipping and plasma electrolytic oxidation

A new method for inner surface modification of steel tubes, named a combined technique of hot-dipping and plasma electrolytic oxidation (PEO) was proposed and demonstrated in this paper. In this work, metallurgically bonded ceramic coatings on inner surface of steel tubes were obtained using this method. In the combined process, aluminum coatings on steel were firstly prepared by the hot-dip process and then metallurgically bonded ceramic coatings were obtained on the aluminum coatings by PEO. The element distribution, phase composition and morphology of the aluminide layer and the ceramic coatings were characterized by SEM/EDX and XRD. The corrosion resistance of the ceramic coatings were also studied. The results show that, after hot-dip treatment, the coating layers consist of two layers, where Al, Fe_xAl _(1−x) were detected from external topcoat to the aluminide/steel substrate. Then after PEO process, uniform Al₂O₃ ceramic coatings have been deposited on inner surface of steel tubes. The ceramic coatings are mainly composed of -Al₂O₃ and γ-Al₂O₃ phase. The compound coatings show favorable corrosion resistance property. The investigations indicate that the combination of hot-dipping and plasma electrolytic oxidation proves a promising technique for inner surface modification of steel tubes for protective purposes.     

等离子喷涂La2(Zr0.7Ce0.3)2O7热障涂层的抗热震性能

采用等离子喷涂制备了La₂(Zr_0.7Ce_0.3)₂O₇（LZ7C3）热障涂层,并对涂层的微观组织、相结构、成分、相稳定性、涂层热导率以及抗热震性能进行了研究.结果表明,LZ7C3涂层由单相烧绿石结构物质组成,高温稳定性较好;涂层的热导率较块材下降约20%,这是由于涂层具有较高的孔隙率所致:涂层在不同温度范围的热震寿命和失效机制不同,在室温至约1000℃间的热震寿命为116 cyc,涂层失效方式以片状剥落为主:在室温至1100℃间的热震寿命为53 cyc,涂层失效方式为片状剥落和层状撕裂;在室温至1200℃间的热震寿命为3 cyc,涂层失效方式以层状撕裂为主.