电解等离子体法制备Al2O3陶瓷层及其特性研究

利用电弧喷铝并重熔后进行电解等离子体处理(EPP)的方法在Q235钢基体上制备出呈冶金结 合的Al₂O₃陶瓷层.利用XRD，SEM和EDS等手段对陶瓷层的成分和显 微组织进行了分析， 测定了陶瓷层的耐蚀性能和耐磨性能.实验结果表明，陶瓷层主要由α-Al₂O3，γ-Al₂O₃，θ-Al₂O₃以及一 些非晶相组成，组织致密，耐蚀性能和耐磨性能良好. 关键词： 电解等离子体处理 陶瓷层 复合技术 生长机理     

管状铝质材料的等离子体电解沉积行为研究

对管状铝质材料的等离子体电解沉积行为进行了研究.测试了不同工作电压和不同电极放置模式条件下铝管内部不同位置的电位分布，并通过显微分析观察，对比了不同电极放置模式对铝管内外壁陶瓷沉积层生长情况的影响.结果表明，不同的电极放置模式下，铝管内外壁陶瓷沉积层生长情况有很大差异.这是因为不同的电极放置模式对铝管内的电场分布具有很大影响，进而影响到铝管内外壁陶瓷层的沉积过程.只有外电极时，由于电场屏蔽作用，不能在铝管内壁形成均匀陶瓷层；在铝管内部加入辅助中心电极后，铝管内部产生均匀电场，这有利于在其内壁形成均匀的陶瓷层. 关键词： 等离子体电解沉积 铝管 表面改性 陶瓷层     

Al3O3N纳米线的制备与表征

在H2+Ar混合气氛中加入少许N2+O2气氛,采用直流电弧等离子体法制备了Al3O3N纳米线.用XRD,SEM,TEM,HRTEM测定了纳米线的成分、形貌特征、显微结构等.Al3O3N纳米线直径分布为25-110 nm,长度达5.5μm.Al3O3N纳米线是尖晶石结构.另外,对Al3O3N纳米线的生长机理进行了研究.     

Cr3+:Al2O3透明多晶陶瓷光谱特性分析

对透光性良好的Cr3+:Al2O3透明多晶陶瓷的光谱性能进行了研究,其吸收光谱中吸收峰与单晶红宝石相一致,按吸收光谱和Tanabe-Sugano能级图,算出其晶场强度参数Dq及Racah参数B分别为1792cm-1,689cm-1,Dq/B=2.6,陶瓷中Cr3+离子所处格位的晶体场强比单晶弱一些,但Cr3+:Al2O3透明陶瓷仍属于强场晶体材料;当Cr3+掺杂浓度到达0.8wt%时,陶瓷的发射谱仍保持较好的R线发射;随Cr3+掺杂浓度的增大,激发峰位发生"红移".在Cr3+:Al2O3透明多晶陶瓷的荧光谱上,发现一个波长为670nm的发射峰,经激发谱确认为Cr3+的发射峰.     

原子层沉积制备Al2O3薄膜的光学性能研究

研究了原子层沉积制备氧化铝薄膜的光学性能。以三甲基铝(TMA)和水为前聚体,分别在基板温度为250℃和300℃的K9和石英玻璃衬底上沉积了Al2O3光学薄膜。采用分光光度计,X射线光电子能谱(XPS),X射线衍射(XRD),原子力显微镜(AFM),扫描电子显微镜(SEM)等分析手段对薄膜的微结构、表面形貌和光学特性进行了研究。结果表明,原子层沉积法制备的Al2O3薄膜在退火前后均呈现无定形结构,元素成分接近化学计量比,其表面粗糙度小于1.2nm,聚集密度高于0.97,光学非均匀性优于1%。同时在中紫外到近红外均有很好的光学性能,适合作为中间折射率和低折射率材料在光学薄膜中得到应用。     

冲击载荷下Al2O3陶瓷的失效与破碎特性

作为典型的脆性材料,陶瓷对变形具有高度敏感性,在强动载荷下具有完全不同于延性金属材料的损伤、破坏行为等力学响应特性。采用分离式霍普金森杆测试系统对Al_2O_3陶瓷进行了冲击加载试验,获得了陶瓷的动态抗拉/压力学性能,以及材料破碎特性随应变率的变化关系。利用能量守恒和动力学的理论方法,对脆性陶瓷材料在不同应变率下的力学特性和碎片尺度进行了深入研究。结果表明:在冲击载荷作用下,Al_2O_3陶瓷的抗拉和抗压强度均与应变率呈正相关。Al_2O_3陶瓷试样在一维应力波作用下的破碎颗粒尺寸差异较大,随着加载应变率的增加,破碎的陶瓷颗粒总数增大,颗粒平均粒径减小,应力集中的影响逐渐减弱。采用DID模型模拟的脆性材料碎片尺度与实验结果比较吻合,Grady模型源于韧性材料的推广,与实验结果的偏差较大。     

Preparation and properties of ceramic coating on Q235 carbon steel by plasma electrolytic oxidation

Ceramic coating was achieved on Q235 carbon steel by PEO (plasma electrolytic oxidation, PEO) without any pretreatment in sodium aluminate system. The discharge process as well as the accompanied surface morphology evolution was analyzed. The phase and elemental composition of the coatings were also investigated. The corrosion, mechanical and tribological properties of the ceramic coating were primarily studied. It is found that the coating surface was porous and the thickness of the coating was about 120 μm. The coating mainly consisted of FeAl₂O₄, Fe₃O₄ and a little γ-A1₂O₃. The corrosion current of the coated sample was 3.082 × 10⁻⁷ A/cm², which was decreased by two orders of magnitude compared with the uncoated one. The micro hardness of the ceramic coating was 1210 Hv, which was about three times as that of the uncoated sample. The friction coefficient of coated sample was also well improved. Investigations revealed that PEO provided a promising technique for preparation of protective ceramic coatings on steels.     

Different spray processes for different Al2O3 coating properties

Among the different coating technologies, a thermal spray has a leading position because of its versatility: an extremely wide variety of materials can be deposited to protect back materials from wear, corrosion, thermal flux, etc. For example, atmospheric plasma spray is a rather well-established process but some other ones, such as flame technology, can also be used with lower economical impact. After a respective optimization of the processing parameters, both plasma and wire flame thermal processes were tested to form Al₂O₃ coatings. For each process, in-flight particle conditions, coating cross-section micro-structures and coating properties were successively determined. The experimental parameters were correlated to in-flight particle characteristics and to coating micro-structure and compared to resulting coating features. The evolution of particle velocity and temperature showed well-marked trends and the mean values were dependent on the spray process. The results emphasized the difference of spray system in terms of kinetic and thermal transfers to the particles. Then, the differences observed on in-flight particle characteristics can be used to explain the differences observed in coating properties, such as porosity content and hardness.     

Preparation of ceramic coating on Ti substrate by plasma electrolytic oxidation in different electrolytes and evaluation of its corrosion resistance: Part II

The aim of this work is to discuss the growth characteristics and corrosion behavior of the prepared ceramic coatings on titanium by plasma electrolytic oxidation (PEO) technique in different electrolytes. PEO process was carried out on titanium under constant voltage regime using a pulse power supply. Three kinds of electrolytes, phosphate, silicate and borate based solutions, were used to evaluate the influence of electrolyte composition on the structure, surface morphology, phase composition and corrosion behavior of prepared ceramic oxide films (titania). The phase composition of the coatings was investigated by X-ray diffraction. Scanning electron microscopy was employed to evaluate the growth and surface morphology of coatings. Elements of coatings were investigated with energy dispersive spectrometer. Corrosion behavior of the coatings was also examined by potentiodynamic polarization and electrochemical impedance spectroscopy. The spark voltage of oxide films had a significant effect on the surface morphology, size and homogeneity of micro-pores, thickness and corrosion properties of coatings.     

SHS等离子喷涂制备FeAl2O4-Al2O3-Fe纳米复合涂层的研究

利用SHS等离子喷涂技术,将经过机械团聚法制备的Fe2O3-Al复合粉体送入等离子焰流,沉积出厚度约为400 μm的复合涂层.利用XRD,SEM 和TEM等检测手段对涂层的成分和组织进行了分析,测定了涂层的显微硬度、断裂韧性以及耐磨性.结果表明涂层为具有纳米结构的FeAl2O4-Al2O3-Fe纳米复合组织;涂层的显微硬度为HV100g870;断裂韧性是普通Al2O3涂层的2倍;无润滑磨损的耐磨性是普通Al2O3涂层的2.5倍.     

Preparation of ceramic coating on Ti substrate by Plasma electrolytic oxidation in different electrolytes and evaluation of its corrosion resistance

Ceramic oxide coatings (titania) were produced on Ti by micro-arc oxidation in different aluminate and carbonate based electrolytes. This process was conducted under constant pulsed DC voltage condition. The effect of KOH and NaF in aluminate based solution was also studied. The surface morphology, growth and phase composition of coatings were investigated using scanning electron microscope and X-ray diffraction. Corrosion behavior of the coatings was also examined by potentiodynamic polarization and electrochemical impedance spectroscopy. It was found that the sparking initiation voltage (spark voltage) had a significant effect on the form and properties of coatings. Coatings obtained from potassium aluminate based solution had a lower spark voltage, higher surface homogeneity and a better corrosion resistance than the carbonate based solution. Addition of NaF instead of KOH had improper effects on the homogeneity and adhesion of coatings which in turn caused a poor corrosion protection behavior of the oxide layer. AC impedance curves showed two time constants which is an indication of the coatings with an outer porous layer and an inner compact layer.     

Silicon solar cells with Al2O3 antireflection coating

The paper presents the possibility of using Al₂O₃ antireflection coatings deposited by atomic layer deposition ALD. The ALD method is based on alternate pulsing of the precursor gases and vapors onto the substrate surface and then chemisorption or surface reaction of the precursors. The reactor is purged with an inert gas between the precursor pulses. The Al₂O₃ thin film in structure of the finished solar cells can play the role of both antireflection and passivation layer which will simplify the process. For this research 50×50 mm monocrystalline silicon solar cells with one bus bar have been used. The metallic contacts were prepared by screen printing method and Al₂O₃ antireflection coating by ALD method. Results and their analysis allow to conclude that the Al₂O₃ antireflection coating deposited by ALD has a significant impact on the optoelectronic properties of the silicon solar cell. For about 80 nm of Al₂O₃ the best results were obtained in the wavelength range of 400 to 800 nm reducing the reflection to less than 1%. The difference in the solar cells efficiency between with and without antireflection coating was 5.28%. The LBIC scan measurements may indicate a positive influence of the thin film Al₂O₃ on the bulk passivation of the silicon.     

Structure and mechanical properties of ceramic coatings fabricated by plasma electrolytic oxidation on aluminized steel

Ceramic coatings were formed by plasma electrolytic oxidation (PEO) on aluminized steel. Characteristics of the average anodic voltages versus treatment time were observed during the PEO process. The micrographs, compositions and mechanical properties of ceramic coatings were investigated. The results show that the anodic voltage profile for processing of aluminized steel is similar to that for processing bulk Al alloy during early PEO stages and that the thickness of ceramic coating increases approximately linearly with the Al layer consumption. Once the Al layer is completely transformed, the FeAl intermetallic layer begins to participate in the PEO process. At this point, the anodic voltage of aluminized steel descends, and the thickness of ceramic coating grows more slowly. At the same time, some micro-cracks are observed at the Al₂O₃/FeAl interface. The final ceramic coating mainly consists of γ-Al₂O₃, mullite, and α-Al₂O₃ phases. PEO ceramic coatings have excellent elastic recovery and high load supporting performance. Nanohardness of ceramic coating reaches about 19.6 GPa.     

Preparation and characterization of a novel Si-incorporated ceramic film on pure titanium by plasma electrolytic oxidation

A Si-incorporated bioactive ceramic film was prepared on pure titanium by plasma electrolytic oxidation (PEO) in a new bath containing Ca²⁺, H₂PO₄⁻ and SiO₃²⁻. The film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS). The apatite-induced ability of PEO film was evaluated by soaking in a simulated body fluid (SBF) for various periods. The results showed that Si-incorporated PEO film present a porous microstructure, the pore size is around 1–5 μm. The film mainly consists of anatase and rutile and a small amount of CaHPO₄ and CaO, besides, bioactive compounds such as CaSiO₃ and SiO₂, also exist in the Si-incorporated PEO film. After immersion in SBF for 28 days, not only the surface layer but also the pores inside the Si-incorporated PEO film were completely filled by apatite crystals, whereas on the surface of a benchmark PEO film free of Si just present small piles of apatite crystals. Silicon incorporated into the PEO film provided more heterogeneous nucleation sites for apatite deposition and hence increased remarkably bioactivity of the PEO film.