Characterization of ceramic sol-gel coatings as an alternative chemical conversion treatment on commercial carbon steel

Sol-gel yttria-stabilized zirconia (YSZ) thin films were prepared on commercial carbon steel sheets by dip-coating technique followed by a low temperature heat treatment (473, 573, and 673 K for 1 h) in order to improve both corrosion properties and adhesion. For comparison, zirconia (ZrO₂) coatings have been also analyzed. Electrochemical techniques, Fourier Transform Infrared (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the anticorrosion behavior of the coatings in a 3.5 wt% NaCl solution. The adhesion with a polyester organic coating was evaluated by the pull-off technique. The typical thickness of the deposited layers ranged from 1 to 1.3 μm depending on process parameters. The obtained results indicated that sol-gel ZrO₂ and YSZ coatings without an organic coating can act as protective barriers against wet corrosion during the first hours, but they fail when the time exposure is longer than 1 day. However, when synthesized films were used as a pre-treatment and an organic coating was added (top-coated), the anticorrosive and adhesion properties were strongly affected by the temperature of the treatment, and an increase in both properties was observed at higher temperatures. The structural and morphological characteristics of the coating provide an explanation of the role of each film in the electrochemical behavior in this aggressive medium. Comparing both systems, YSZ displayed greater protective and adhesion values than exhibited for ZrO₂ which can be correlated with the stabilization of the cubic phase.     

不锈钢纯黑色转化膜的制备工艺及性能表征

介绍了一种不锈钢黑色转化工艺。研究了温度和着色液主要组分对转化工艺的影响,并对黑色转化膜的成分、耐磨性、耐热性、耐蚀性等性能进行分析。得到不锈钢着黑色的最佳工艺条件为:铬酸酐175g/L,浓硫酸275mL/L,添加剂A225g/L,温度80°C。铬酸酐——浓硫酸复配组成影响转化膜的色泽和均匀性。随添加剂A含量的增加,转化膜颜色依次为灰、黑、蓝。不锈钢黑色转化膜的主要成分是Fe2O3和Cr2O3,膜厚为0.478μm,膜层黑度深,光亮度、耐热性和机械加工性能优异,耐腐蚀性和耐磨性均优于不锈钢基体。     

凝胶--封孔法制备不锈钢表面陶瓷膜层

为改善不锈钢的抗高温氧化性和耐磨性,拓宽其应用范围,采用凝胶－－封也法在不锈钢表面制得陶瓷膜层。介绍了该方法的工艺过程,探讨了电沉积及封孔机理以及各因素对成膜过程的影响。该方法所得陶瓷膜层光滑平整,具有好的耐磨性及抗高温氧化性。     

The properties of hydroxyapatite ceramic coatings produced by plasma electrolytic oxidation

Calcium phosphate coatings produced on the surface of Ti6Al4V by plasma electrolytic oxidation (PEO) using different concentrations of hydroxyapatite (HA) in a 0.12 M Na₃PO₄ (NAP) electrolyte solution was investigated. It was found that the amount of calcium phosphate particles infiltrated into the coating layer as well as the thickness and the surface roughness of the coating increased with increasing HA concentration. The porosity of the ceramic coatings indicated an inverse relationship with the concentration of HA particles dispersed in the NAP solution. The result also demonstrates that higher scratch adhesive strength was achieved using 1.5 g/L HA solution, producing a critical load of 2099 mN, while 0 g/L HA only produced a critical load of 1247 mN. The adhesion becomes independent of thickness when the concentration of HA exceeds 1.5 g/L. The failure of the coating was characterized by large periodic hemispherical chipping, while intermittent delamination was noticed with the coating embedded with HA particles. This study demonstrate the viability of using PEO to produce a thin layer of HA ceramic coating on Ti6Al4V suitable for biomedical applications.     

Preparation of coatings on alumina ceramic for wettability

To improve the wetting ability between ceramic and metal, titanium and copper coatings on alumina ceramics were prepared by infiltration of molten salt and electroless plating, respectively. A Ti/Cu bi-layer was also obtained by combining the two methods. The preparation process was optimized. The phase composition of the coatings was analyzed by X-ray diffraction (XRD). And the wettability of the titanium coating was investigated. The results showed that the copper droplet was easily spread on the surface of titanium coated alumina. The titanium coated alumina was well composited with high chromium white cast iron and the interface between ceramic and metal was well combined.     

NaF添加剂对铝合金等离子电解氧化陶瓷膜形成的影响

研究了Na2SiO3-KOH电解溶液中添加NaF对铝合金等离子电解氧化陶瓷膜形成的影响。研究表明：电解溶液中加入NaF可加速氧化物陶瓷膜的形成，提高其硬度。NaF的最佳加入量为0．5～0．75g／L。     

钢铁表面复合转化膜的制备

为研究一种无磷涂装前金属表面处理技术,提出了以氟锆酸、硝酸锰和KH-792[即N-(2-氨乙基)-3-氨丙基三甲氧基硅烷]为原料在钢铁表面形成复合转化膜的方法。通过单因素实验确定了最佳工艺条件为:氟锆酸5.5 g/L,硝酸锰2.0 g/L,KH-7922.5 g/L,p H 2.5,室温,成膜时间10 min。通过扫描电镜观察到在钢铁表面形成了完整而致密的转化膜,由能谱分析结果推测其化学组成可能为Me ZrF₆·nH₂O·[NH₂(CH₂)₂NH(CH₂)₃SiO₃)]_m(Me)_n(其中Me为Fe或Mn)。该转化膜的单位面积质量为3.152 6 g/m²,耐3%NaCl溶液浸泡时间为180 min。成膜液的疲劳度优于锌系磷化液和锆化液。     

氧化剂对钢铁表面氟铁酸盐转化膜的影响

通过中性盐雾试验,研究了过氧化氢、钼酸钠、澳酸钾、碘酸钾和过硫酸铵等氧化剂对Q195冷轧钢表面所形成的氟铁酸盐转化膜耐蚀性的影响.结果表明,氧化剂为过硫酸按时,形成的转化膜效果最好,其质量浓度为7 g/L时,转化膜的耐盐雾时间可达到8h.过硫酸按的加入使氟铁酸盐转化膜的形成加快,形成的无定形结构亦使得膜层耐蚀性能更好.     

Hydrogenated amorphous carbon films deposited on 316L stainless steel

Research on hydrogen amorphous carbon films (a-C:H), which possess the diamond-like characteristic, has been stimulated for many years by need to simultaneously optimizing the mechanical, optical and biological properties, and by challenges related to the deposition of a-C:H films on medical implants. In the present work, we investigate the structure, optical and mechanical properties (hardness, elastic modulus and stress) of a-C:H films deposited on 316L stainless steel substrate by the radio frequency plasma enhanced chemical vapor deposition (RF PECVD). The negative self-bias voltages significantly influence on temperature of steel substrates during the deposition process and films properties. Specifically, the high energetic deposition leads also to stabilization of the sp² content and thermally-activated relaxation in the stress of a-C:H films. Presented correlation between the obtained results and literature analysis let deem the Raman spectra as a good tool to control the properties of implants made of 316L stainless steel with a-C:H film for general use.     

Slurry erosion behavior of thermally sprayed ceramic nanocomposite coatings on turbine steel

The aim of the present study is to investigate the slurry erosion behavior of nano-yttria-stabilized zirconia (YSZ) reinforced Cr₃C₂–25NiCr ceramic nanocomposite coatings deposited on turbine steel. The Cr₃C₂–25NiCr coating powder, 95% (Cr₃C₂–25NiCr) + 5% YSZ, and 90% (Cr₃C₂–25NiCr) + 10% YSZ nanocomposite coating powder deposited on CA6NM steel samples by using high-velocity oxy-fuel coating technique. L₉ orthogonal array Taguchi method was used to design the experiment. Erosion tests were performed on erosion test rig under hydro accelerated conditions at different levels of various parameters. Erosion tests and analysis of variance resulted that for coated samples, velocity is the major influencing factor followed by slurry concentration, impact angle, and particle size. Velocity was the largest contributor to the mass loss, whereas particle size has the least contribution to mass loss of the coated samples. The scanning electron microscopy analysis of eroded samples revealed that craters, micropores, platelets, plowing, spalling, and so on were responsible for the mass loss of uncoated and coated samples. The incorporation of YSZ nanoparticles decreased the porosity; erodent particles cannot penetrate more deeply inside the workpiece and resulted in less erosion. It has been resulted that 95% (Cr₃C₂–25NiCr) + 5% YSZ and 90% (Cr₃C₂–25NiCr) + 10% YSZ ceramic nanocomposite coatings exhibited better erosion resistance as compared to Cr₃C₂–25NiCr coatings due to high microhardness and low porosity.     

Electroactive polymer films for stainless steel corrosion protection

Electroactive polymer films of polyaniline, poly-o-toluidine and a composite of both were deposited on stainless steel and their performance as protective coatings against corrosion was evaluated. Open circuit potential and potentiodynamic studies of the polymer-coated stainless steel in a corrosive medium showed a significant shift in the corrosion potential towards more positive values. Mechanical characteristics of the films were evaluated by means of microhardness measurements, revealing nonelastic films in all cases and low hardness values that increased from polyaniline to poly-o-toluidine to the composite. The best results were obtained in the case of the polyaniline-o-toluidine composite.     

Preparation and characterization of multilayer coatings on tool steel

This work is focused on the design and preparation of ZrO2-, TiN- and TiAlN-based multilayer using a combination of different strategies. Films have been deposited onto stainless and tool steels with the aim of characterizing the coatings as well as analyzing their behavior in order to optimize service capacity, extend working life and minimize production costs. The results of the study revealed compatibility among the techniques through the optimal combination of layers in terms of thickness and densification thus leading to an optimization of the properties of multilayer coatings.     

铜基表面陶瓷涂层的制备与耐蚀性能研究

以Al2O3、TiO2和ZnO为骨料,钠水玻璃为粘接剂,在纯铜表面用热化学反应法制备了陶瓷涂层。X射线分析发现,陶瓷涂层热固化后,涂层内产生了NiAl2O4、Al2SiO5等新相,它提高了涂层与基体的结合强度。腐蚀实验表明,封孔后陶瓷涂层的耐酸、耐碱、耐盐等性能分别比纯铜基体提高了3.9、12.3和6.3倍;极化曲线表明,陶瓷涂层有明显的钝化区,其抗电化学腐蚀能力增强,抗盐雾腐蚀性比基体提高了5.0倍。     

陶瓷基纳米二氧化钛膜的制备与性能研究

控制钛氧有机物水解条件合成稳定的纳米二氧化钛胶体,X射线衍射和扫描电子显微镜研究表明,该胶体的胶粒为锐钛矿型晶体,晶粒大小约12nm。将制得的纳米二氧化钛胶体喷涂于陶瓷表面,经焙烧处理得到陶瓷基纳米二氧化钛膜。扫描电子显微镜和气相光催化反应实验显示,陶瓷基纳米二氧化钛膜由致密的球形纳米二氧化钛粒子组成,光照下具有好的分解有机物的能力和光诱导亲水性,其光催化分解有机物的反应属于动力学一级反应。此陶瓷材料拥有良好的自洁净功能和光诱导亲水性。     

Growth of nano-textured graphene coatings across highly porous stainless steel supports towards corrosion resistant coatings

In this paper, we demonstrated for the first time the growth of 3D networks of graphene nano-flakes across porous stainless steel substrates of micron sized metal fibres, and its anti-corrosion properties. The controlled formation of graphene-grade coatings in the form of single sheets to complex and homogeneously distributed 2–4 μm long nano-pillars is demonstrated by Scanning Electron Microscopy. The morphology and stability of these structures are shown to be particularly related to the temperature and feed gas flow rate during the growth. The number of layers across the graphene materials was calculated from the Raman spectra and is shown to range between 3 and more than 15 depending on the growth conditions and to be particularly related to the time and flow rate of the experiment. The presence of the graphene was shown to massively enhance the specific surface area of the material and to contribute to the increased corrosion resistance and electrical conductivity of the material without compromising the properties or structure of the native stainless steel materials. This new approach opens up a new route to the facile fabrication of advanced surface coatings with potential applications in developing new thermal exchangers, separation and bio-compatible materials.     

镍基高温合金陶瓷涂层的制备及性能表征

以Cr2O3粉、玻璃料及黏土为原料制成料浆,通过喷涂将其涂覆在镍基高温合金GH44的表面,采用热化学反应法于1050°C保温10min,熔烧制备出高温陶瓷涂层。通过扫描电镜和X射线衍射分析了高温陶瓷涂层的表面和截面形貌以及相组成,对涂覆陶瓷涂层的镍基合金的抗热震性能、抗氧化性能以及高温疲劳性能进行了测试。结果表明,陶瓷涂层结构致密,与基体结合牢固,具有良好的抗热震性能。涂覆陶瓷涂层的镍基合金其高温抗氧化性相对于基体提高了6倍以上,其高温疲劳性能明显改善。     

Study of CNx films on 316L stainless steel for orthodontic application

In order to improve the friction property and corrosion resistance of 316L stainless steel (316LSS) in orthodontic application, carbon nitride (CNx) films were synthesized by using IBAD technique at a set of assisted N ion beam currents. X-ray photoelectron spectroscopy and Raman spectroscopy were used to characterize the bonding state and the microstructure of the CNx films. Results of tribological tests indicated that the 316LSS coated by CNx films exhibited lower friction coefficients than the uncoated one both in air and in artificial saliva. The electrochemical tests in artificial saliva confirmed that the corrosion resistance of 316LSS was evidently improved after coated with CNx films.     

Black ceramic coatings on Ti alloy with enhanced high absorptivity and high emissivity by plasma electrolytic oxidation

A black ceramic coating with high absorptivity and emissivity was successfully prepared on TA7 (Ti-5Al-2.5Sn) in a hybrid electrolyte solution by plasma electrolytic oxidation for improving the imaging precision of optical system. The influence of electrolyte components and technical parameters on the composition, structure, and optical properties was investigated. The results show the coatings with typically porous structure are mainly composed of O, P, Si, Ti, V, Fe, and Ni. The corresponding amorhous oxide in the outer layer endows the coating with strong absorption in the visible light and infrared areas, and the crystallized TiO₂ indwelling the inner layer contributes to the strong UV absorption property. In addition, the micropores of the coatings have different size ranges corresponding to the wavelengths, facilitating the increase of absorptivity and emissivity in some degree. The absorptivity and emissivity can be adjusted by electrolyte components and technical parameters. The coating presents the best absorptivity of 0.962 and emissivity of 0.950 in the electrolyte solution of 3 g/L NH₄VO₃, 5 g/L FeSO₄, and 5 g/L C₄H₆O₄Ni under 400 V for 10 minutes.