YPSZ纳米结构热喷涂粉末材料工艺优化研究

热等离子体喷涂制备YPSZ纳米结构涂层必须首先进行YPSZ纳米结构粉末材料的研究.本文采用浆料分散、喷雾干燥、热处理的方法制备适于热等离子体喷涂纳米结构涂层的球形、致密YPSZ纳米结构粉末材料.测定浆料的粘度、沉降高度曲线表征浆料的均匀性和稳定性,利用扫描电子显微镜、x射线衍射分析对粉末材料的微观组织及相结构进行分析,利用热重/差热分析对热处理工艺过程进行分析.结果表明:采用优化的工艺成功制备出球形、结构均匀、致密的YPSZ纳米结构粉末材料,适于热喷涂制备YPSZ纳米结构涂层.     

热喷涂用纳米结构Al_2O_3/TiO_2/SiO_2团聚体粉末的研究

对喷雾干燥和不同温度热处理后Al2O3/TiO2/SiO2纳米团聚体粉末的流动性、松装密度及振实密度进行了测试,对喷雾干燥后的粉末进行了热重-差热分析,通过扫描电镜观察了粉末颗粒形貌和大小,采用X射线衍射分析了不同温度热处理后粉末的相组成,并对粉末的综合性能进行了比较。实验结果表明:在1000～1450℃热处理后的Al2O3/TiO2/SiO2纳米团聚体粉末颗粒仍近似球形,粒径在10～100μm之间。随着热处理温度升高,纳米团聚体大颗粒表面发生塌陷,大颗粒之间发生连接,大颗粒内部纳米颗粒明显长大。低于1250℃热处理后的粉末流动性好,振实密度高,适于等离子体喷涂制备纳米结构涂层。     

热处理对喷雾干燥制备的Al2O3纳米团聚体粉末的影响

对喷雾干燥和经不同温度热处理后的Al2O3纳米团聚体粉末的松装密度及振实密度进行了测试,通过扫描电镜观察分析了团聚体粉末颗粒的大小和形貌以及纳米晶颗粒的大小,采用X射线衍射分析了热处理后粉末的相组成.实验结果表明,在1050～1250℃热处理后的Al2O3纳米团聚体粉末颗粒仍近似球形,粒径在10～90μm之间.随着热处理温度升高,纳米团聚体大颗粒表面发生塌陷,大颗粒之间发生连接,大颗粒内部纳米颗粒明显长大.低于1250℃热处理后的粉末流动性好,振实密度高,适于等离子体喷涂制备纳米结构涂层.     

纳米YSZ热喷涂粉末的制备及其性能

基于纳米涂层的优异性能,研究了纳米YSZ热喷涂粉末的制备工艺。喷雾干燥造粒后,分别用霍尔漏斗法和电子扫描显微镜对团聚体粉末的流动性、松装密度及微观形貌进行了测试与分析。研究发现,固含量越高,粉末的流动性及松装密度性能越好,但过高的固含量反而会影响造粒效果;在固含量一定的情况下,黏结剂含量适中的浆料造粒后团聚体粉末的流动性更好。为了得到性能更好的团聚体粉末,合理的后续处理方法是在电流300A,电压40V条件下进行等离子致密化。     

二硅化钼喷涂粉末的制备及其涂层组织结构

以粒度为1~2μm的MoSi₂粉末为原料,采用喷雾干燥和真空烧结制备了喷涂用MoSi₂团聚粉末. 分别用平均粒度为9.68μm的MoSi₂粉末和团聚造粒MoSi₂粉末(38~72μm)为喂料, 大气等离子喷涂制备了二硅化钼涂层,分析了涂层的微观组织结构. 研究结果表明,喷雾干燥造粒后的近球形粉末在1300℃真空烧结1h后,粉末流动性和松装密度分别为17.1s/50g和2.16g/cm³,比烧结前分别增加了57.0%和46.0%.平均粒度为9.68μm 的MoSi₂粉末制备的涂层主要是由Mo和Mo₅Si₃等富钼相组成. 团聚粉末制备的涂层主要由MoSi₂相组成,涂层较致密, 内部出现了类似“网状”的组织结构.     

热喷涂用纳米结构Cr_2O_3大颗粒粉末的研究

纳米晶Cr_2O_3粉末经过球磨、制浆、喷雾干燥和热处理(?)聚成适用于热喷涂的大颗粒球形粉末,采用不同的粘结剂浓度和(?)含量配制浆料,并在不同喷雾干燥条件和热处理温度下对原始Cr_2O_3纳米粉末进行了再处理,测量了(?)聚体粉末的松(?)密度、振实密度及流动性,并用扫描电镜对粉末的形貌进行了观察分析,讨论了粉末制备工艺条件对粉末性能的影响。结果表明;喷雾干燥后粉末基本上为球形,颗粒平均尺寸在45～75μm范围内。粉末的流动性和表观密度良好,满足热喷涂的要求。     

反应火焰喷涂TiC/Fe复合涂层显微结构研究

采用前驱体碳化复合技术制备Ti-Fe-C系反应喷涂复合粉末,通过反应火焰喷涂技术成功制备了TiC/Fe基金属陶瓷复合涂层.利用XRD和SEM对喷涂粉末和涂层的成分、组织结构进行了分析,考察了喷涂粉末粒度、Ti的加入方式对涂层组织结构的影响.研究结果表明:所制备的TiC/Fe复合涂层由不同含量TiC颗粒分布于晶粒内部而形成的晶内型复合强化片层组织叠加而成,TiC颗粒呈纳米级;喷涂粉末粒度较大时,制备的涂层中出现有害相Fe2Ti,片层厚度较大,孔隙率高;以纯Ti粉为Ti源制备的喷涂粉末和以TiFe粉为Ti源制备的喷涂粉末相比较,其涂层中硬质相TiC含量较少,孔隙率较大.     

溶液注入热等离子体中直接制备纳米结构热障涂层

采用一种新的方法,将Y2O3稳定的ZrO2前驱体溶液雾化注入直流等离子体中直接制备热障涂层.扫描电镜、透射电镜、X射线衍射分析、激光闪烁法分别观察分析了涂层的显微组织、纳米晶粒、相结构和热导率,排水法、冷热冲击法分别检测了涂层密度和热循环性能.实验结果显示等离子体喷涂液体制备出来的热障涂层不具有层状组织,晶粒尺寸小于100nm,组成相为四方相,硬度为350左右,热导率在1.2～1.5 W/m·K范围,涂层中存在16%左右的孔隙率,具有比常规微米结构热障涂层更优越的热循环性能.分析结果表明液体注入热等离子体中的雾化沉积既区别于物理化学气相沉积,又区别于粉末注入热等离子体中的熔化沉积,属于表面工程技术下的交叉领域.     

等离子喷涂氧化锆纳米涂层显微结构研究

利用大气等离子喷涂（APS）技术,在不锈钢基体上制备了氧化锆纳米结构涂层.运用XRD、SEM与TEM等分析手段对喷涂用粉末原料和涂层的显微结构、物相组成进行了观察和确定.实验结果表明,纳米氧化锆粉末经喷雾造粒后的颗粒粒径主要分布在15～40μm之间,流动性好,适合于等离子喷涂用.等离子喷涂氧化锆纳米涂层颗粒分布在60～120nm之间,晶粒发育良好.涂层物相由四方和立方相氧化锆所组成.氧化锆纳米涂层的气孔率约为7％,结合强度为45MPa。     

等离子喷涂氧化锆纳米涂层的组织结构与性能

研究了用纳米粉制备热障涂层的组织及性能与工艺参数的影响关系,对涂层制备具有指导作用.采用等离子喷涂方法以二次造粒的纳米ZrO2为喂料制备了熔炼隔离热障涂层,并利用X衍射物相分析、SEM、TEM、金相等分析手段观测了涂层的物相构成、组织结构和孔隙率.结果表明,涂层主要以四方相和立方相构成,并含有少量的单斜相.在喷涂过程中粉末熔化状况良好,涂层含有网状微裂纹,涂层致密度可达96%,比普通二氧化锆等离子喷涂层高.     

NiAl-B composites with nanocrystalline intermetallic matrix produced by mechanical alloying and consolidation

Powder mixtures with equiatomic Ni–Al stoichiometry and with the addition of 5, 10, 20 and 30 vol% of boron were mechanically alloyed in a high-energy SPEX mill. Differential scanning calorimetry (DSC) was used for examination of the thermal behaviour of the milled powders. The mechanically alloyed powders and powders after DSC examinations were investigated by X-ray diffraction (XRD). For all the powder mixtures, a nanocrystalline NiAl intermetallic phase was formed during milling. With the increase of boron concentration in the mixtures, more intense refinement of the NiAl grain size during mechanical alloying was observed. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) examinations showed that the produced powders have composite structure, with boron particles uniformly distributed in the nanocrystalline NiAl intermetallic matrix. The density of the composite powders decreases with the increase of boron content, following the rule of mixture.The produced powders were subjected to consolidation by hot-pressing at 800 °C under the pressure of 7.7 GPa for 180 s. The produced bulk materials were investigated by XRD, SEM and EDS as well as characterised by hardness, density and open porosity measurements. It was found that during applied consolidation process the nanocrystalline structure of the NiAl matrix was maintained. The average hardness of the bulk composite samples is in the range of 10.58–12.6 GPa, depending on boron content, increases with the increase of boron content, and is higher than that of the NiAl intermetallic reference sample (9.53 GPa). The density of the bulk composite samples is the same as that of the corresponding powders after milling, decreases with the increase of boron content and is lower than that of the NiAl reference sample. To the best of our knowledge, the NiAl-B composites with nanocrystalline intermetallic matrix have been produced for the first time.     

Thermal stability and oxidation behavior of Al-containing nanocrystalline powders produced by cryomilling

Al-containing nanostructured coatings provide excellent protection from high temperature corrosion. Aluminum oxide scales generally provide better oxidation resistance and yield lower oxidation rates than other oxide scale compositions. In this study, nanocrystalline 316L stainless steel containing 6 wt.% Al was synthesized using cryogenic milling (cryomilling). Complete alloying was obtained after 32 h of milling and the average grain size was found to be 7 nm. High temperature thermal stability and oxidation kinetics of the alloyed powders were examined. The powder demonstrated good grain growth stability at 500 °C, at which point, the powders had been heat treated for 120 h and the average grain size was found to be 11.4 nm. The oxidation kinetics of the powder were studied for 48 h at 500, 800, and 1,000 °C, respectively. For comparison, conventional 316LSS powder was also tested. Nanocrystalline 316LSS-6 wt.% Al showed lower weight gain than the conventional 316LSS powders. During the oxidation of nanocrystalline 316LSS-6 wt. % Al at 500 °C, protective aluminum oxide scale formed at the surface. At 800 °C and 1,000 °C, most of the nanocrystalline 316LSS-6 wt.% Al particles showed completed outer aluminum oxide scale. However, at 800 and 1,000 °C, some particles showed growth of chromium oxide scale underneath the aluminum oxide scale. In those samples, Al depletion was also observed due to a non-homogenous distribution of Al during cryomilling. The activation energy of the oxidation reaction was calculated and was found to be affected by the enhancement of the grain boundary diffusion in nanostructured particles.     

Preparing of nanostructured Al2O3–TiO2–ZrO2 composite powders and plasma spraying nanostructured composite coating

Nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders for plasma spraying were prepared by spray drying granulation technology. The effects of processing parameters on the microstructure and properties of composite powders were investigated. The results show that with increasing the slurry solid content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the binder content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the spray drying temperature, the particle size of powders increases, and the bulk density and flowability of powders increases firstly and then decreases. The most appropriate spray drying parameters are the slurry solid content of 40 wt.%, the binder content of 2.0 wt.% and the spray drying temperature of 250 °C. The nanostructured composite coating was successfully prepared by using the as-prepared nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders as feedstocks. The nanostructured coating possessed higher hardness and toughness compared with the conventional microstructured one, which was attributed to the use of the nanostructured composite powders feedstocks.     

Overview on the Development of Nanostructured Thermal Barrier Coatings

Thermal barrier coatings （TBCs） have successfully been used in gas turbine engines for increasing operation temperature and improving engine efficiency. Over the past thirty years, a variety of TBC materials and TBC deposition techniques have been developed. Recently, nanostructured TBCs emerge with the potential of commercial applications in various industries. In this paper, TBC materials and TBC deposition techniques such as air plasma spray （APS）, electron beam physical vapor deposition （EB-PVD）, laser assisted chemical vapor deposition （LACVD） are briefly reviewed. Nanostructured 7-8 wt pct yttria stabilized zirconia （7-8YSZ）TBC by air plasma spraying of powder and new TBC with novel structure deposited by solution precursor plasma spray （SPPS） are compared. Plasma spray conditions, coating forming mechanisms, microstructures,phase compositions, thermal conductivities, and thermal cycling lives of the APS nanostructured TBC and the SPPS nanostructured TBC are discussed. Research opportunities and challenges of nanostructured TBCs deposited by air plasma spray are prospected.     

Plasma spheroidization of nickel powders in a plasma reactor

Thermal spray coatings of surfaces with metal, alloy and ceramic materials for protection against corrosion, erosion and wear is an intense field of research. The technique involves injection of the powder into a plasma flame, melting, acceleration of the powder particles, impact and bonding with the substrate. Feedstock powders of metals, alloys and ceramics for thermal spray applications have to meet several requirements. Particle shape, size and its distribution, powder flow characteristics and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. For smooth and uniform feeding of powders into plasma jet, the powder particles have to be spherical in shape. High temperatures and steep temperatures present in thermal plasma is exploited to spheroidize particles in the present investigation. Nickel powder particles in the size range from 40–100 μm were spheroidized using plasma processing. SEM and optical micrographs showed spherical shape of processed particles.     

Synthesis of ceramic oxide powders by microwave plasma pyrolysis

Ceramic powders prepared pyrolytically exhibit homogeneity and, in most cases, small grain sizes. The energy efficiency of electrically heated systems performing the pyrolysis in a stream of carrier gas is poor. Similar considerations concerning energy demand are valid for spray drying of suspensions. This situation can be improved using a microwave plasma as a source for thermal energy. The process described in this paper works with any aqueous solution of salts used as starting material in ceramics. The process was demonstrated by the synthesis of alumina, zirconia, and zirconia-based ceramic powders; where an energy efficiency of more than 80% was found. For the powder synthesis, aqueous solutions of the nitrates were used as starting materials. Through proper selection of conditions for synthesis, it is possible to obtain nanocrystalline powders, as demonstrated by electron microscopy. Because of the extreme conditions associated with plasma during synthesis, it is possible to prepare nonequilibrium structures and solid solutions in systems in which nearly no equilibrium solubility exists.     

不同Ti／Ba摩尔比的钛酸钡纳米晶粉体的Sol—gel法制备与表征

采用Ｓｏｌ－ｇｅｌ法制备了不同Ｔｉ／Ｂａ摩尔比的ＢａｙＴｉｘＯ３（ｘ／ｙ＝０．９９０,１．０００,１．０１０,１．０２０,１．０４５）纳米晶粉体。应用热分析、Ｘ射线粉末衍射、激光和透射电镜等技术对干凝胶热分解历程和粉体性能进行了研究,发现随Ｔｉ／Ｂａ摩尔比的增加,粉体的平均晶粒尺寸、晶体结构和粉体粒度分布各呈现规律性变化。本文并对这些规律性变化进行了初步讨论     

Synthesis and Characterizations of Nanocrystalline WC-Co Composite Powders by a Unique Ball Milling Process

In order to explore the high efficiency of fabricating nanocrystalline WC-Co composite powders, this paper presented a unique high energy ball milling process with variable rotation rate and repeatious circulation, by which nanocrystalline WC-10Co-0.8VC-0.2Cr3C2 (wt pct) composite powders with mean grain size of 25 nm were prepared in 32 min, and the quantity of the powders for a batch was as much as 800 grams. The as-prepared powders were analyzed and characterized by chemical analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA). The results show that high energy ball milling with variable rotation rates and repeatious circulation could be used to produce nanocrystalline WC-Co powder composites with high efficiency. The compositions of the powders meet its specifications with low impurity content. The mean grain size decreases, lattice distortion and system energy increase with increasing the milling time. The morphology of nanocrystalline WC