Thick c-BN coatings - Preparation, properties and application tests

Due to the outstanding properties of cubic boron nitride (c-BN) - c-BN is the second hardest of all known materials, has a high wear resistance and a high thermal stability - this material is very promising for a broad range of applications, especially for cutting tools, both as bulk and as a coating material. The state-of-the-art is the use of sintered cutting inserts with c-BN grains. Such c-BN grains are synthesized in an expensive high-pressure-high-temperature process.The requirements for cutting tools continuously increase in production engineering and this leads to a strong demand for new super hard tool coatings. Cubic boron nitride coatings could be an attractive solution. Unfortunately, the preparation of thick c-BN coatings, on the μm scale, is difficult, due to some serious drawbacks and has been successful only in the last years for a few research groups worldwide.PVD processes allow the preparation of c-BN films thicker than 2 μm on silicon and 1 μm c-BN top layers on pre-coated cemented carbide cutting inserts. Measurements of mechanical properties like hardness and Young's modulus reveal that the properties of the c-BN coatings, with hardness of about 60 GPa, are nearly identical to those of c-BN bulk material.Results of systematic turning and milling tests of different coatings in combination with a c-BN top-layer on cemented carbide cutting inserts will be presented in detail. The new results confirm the high potential of c-BN coatings on cutting tools.     

含氟聚丙烯酸酯自分层乳胶涂料的制备与性能

为制备通过一次涂布而形成多层的自分层涂料,实现对基材的有效保护,通过种子乳液聚合制备了含氟与纯丙烯酸酯两种乳液,并将其复配成可自分层的乳胶涂料。分别用傅里叶变换红外光谱仪(FT-IR)、光学显微镜和动态力学谱仪(DMA)对涂膜进行了表征。结果表明,随共聚单体中甲基丙烯酸三氟乙酯(TFEMA)的含量增大,涂膜不透明性增大,光学显微镜表明涂膜出现分层现象;FT-IR分析表明,涂膜的上下表面—CF3的含量不同,上表面有更多的含氟单体;DMA分析表明,力学内耗峰随含氟乳液用量比例增多而变宽,也说明涂膜已产生相分离,得到了自分层涂料。     

Preparation and high-temperature tribological properties of CrAlVYN-Ag nanocomposite coatings

CrAlVYN-Ag coatings were successfully deposited by introducing the elements of V and Ag into CrAlYN hard coatings. Their microstructure and mechanical property as a function of the annealing temperature were investigated from room temperature (RT) (～25°C) to 800°C. Besides, the worn surfaces were analyzed after combined effects of temperature and friction to figure out the wear mechanisms at different temperatures. The coatings exhibited special surface morphologies and Ag diffusion after annealing at different temperatures. In addition, the x-ray diffraction results showed that the coatings suffered obvious oxidation once the temperature exceeded 600°C; as a result of this, the coating hardness decreased sharply. The friction coefficients were relatively high during the tribological tests from RT to 400°C because the abrasive wear mechanisms played a dominant role. The lower friction coefficients obtained at 600 and 700°C were mainly due to the self-lubricating mechanisms. However, the coating exhibited higher friction coefficient at 800°C, which was mainly ascribed to the severe oxidation wear of the coating.     

BAS系微晶玻璃抗氧化涂层的制备与性能

利用2层不同软化温度和不同热膨胀系数的BaO-Al₂O₃-SiO₂(BAS)系微晶玻璃, 采用浆料涂覆—浸渍—多层共烧的方法制备了2种双层同组分和1种双层不同组分的C_f/SiC复合材料抗氧化涂层。3种结构的BAS系微晶玻璃涂层完整、 无明显缺陷, 涂层与C_f/SiC复合材料的结合状态良好, 有助于提高C_f/SiC复合材料的抗氧化性能。双层不同组分的BAS系微晶玻璃涂层在1200~1350 ℃范围内对提高C_f/SiC复合材料抗氧化性能的作用显著, 失重速率和失重量均明显减小。与未包覆涂层的复合材料相比, 包覆双层不同组分涂层的复合材料经历600次(每次保温10 min)热冲击后的失重降低了1/2~2/3, 保留的强度提高了7~15倍。      

Nanocrystalline diamond coatings for mechanical seals applications

A mechanical seal is a type of seal used in rotating equipment, such as pumps and compressors. It consists of a mechanism that assists the connection of the rotating shaft to the housings of the equipments, preventing leakage or avoiding contamination. A common cause of failure of these devices is end face wear out, thus the use of a hard, smooth and wear resistant coating such as nanocrystalline diamond would be of great importance to improve their working performance and increase their lifetime. In this paper, different diamond coatings were deposited by the HFCVD process, using different deposition conditions. Additionally, the as-grown films were characterized for, quality, morphology and microstructure using scanning electron microscopy (SEM) and Raman spectroscopy. The topography and the roughness of the films were characterized by atomic force microscopy (AFM).     

Plasma-sprayed self-sealing ceramic coatings: Materials chemistry and high temperature protective properties

The principal theoretical and experimental data relating to the structure and the protective action of self-sealing ceramic coatings (SSCCs) used to prevent non-aqueous corrosion phenomena (T ? 900 K) on metallic surfaces in chemically aggressive environments (oxidation, carburization, nitridation, sulphidation, attack by molten metals etc.) are reviewed. The plasma spray process used to deposit SSCCs is described and some of their properties are summarized. The results obtained in an investigation of the protective efficiency of SSCCs on Incoloy 825 and titanium substrates, which are particularly susceptible to metal dusting and oxidation-nitridation corrosion phenomena, are reported. It is hoped that the work described in this paper will stimulate new approaches to the development and characterization of these novel protective coatings as it is necessary to optimize the prevention of non-aqueous corrosion in many applications.     

Preparation and optical properties of titania/epoxy nanocomposite coatings

This work reports the preparation of TiO₂/Epoxy nanocomposites coatings with high refractive index and optical transparency. Highly dispersed titania nanoparticles were synthesized by sol-gel method at room temperature. The TiO₂ nanoparticles can be dispersed directly into the polymer without the use of organic surfactant. Nanocomposite coating with refractive index of 1.668 can be obtained by adding 30 wt% TiO₂ nanoparticles into the polymer matrix. All coatings with different amount of TiO₂ exhibit excellent optical transparency of more than 90%. Although higher refractive index of the nanocomposite can be obtained by increasing the content of TiO₂ nanoparticles, cracks also appear in the surface of the hybrid coating.     

Preparation of electroplated Ni-P-ultrafine diamond, Ni-P-carbon nanotubes composite coatings and their corrosion properties

Ni-P-ultrafine diamond (UFD) and Ni-P-carbon nanotubes (CNTs) composite coatings were deposited by electroplating at 76°C. The relation between the content of the incorporation and the amount of the UFD and CNTs in the electroplating solution was investigated. The corrosion behavior of the composite coatings was evaluated by polarization curves and electrochemical impedance spectroscopy in 0.1 M NaCl and 0.5 M H₂SO₄ solutions. It was found that increasing the UFD content in the coatings displays better corrosion performance, while a contrary result for the CNTs incorporated alloys was found due to the special structural state. The results show the incorporation of UFD and CNTs in Ni-P coatings is advantageous for forming better passive films.     

SBR-SiO2超疏水涂层的制备与性能

利用羟基硅油(HSO)对白炭黑(SiO2)进行疏水改性,并用过氧化二异丙苯(DCP)对丁苯橡胶(SBR)胶浆进行适度交联,通过粒子填充法制备了超疏水SBR-SiO2涂层。研究了HSO、SiO2和DCP用量及交联条件对涂层成膜性能和润湿性能的影响,探讨了涂层热氧老化和紫外光老化过程中超疏水性能的变化。结果表明,当m(HSO)∶m(SiO2)=1∶1、HSO-SiO2用量为3.5g、DCP用量为0.25g、交联温度为155℃、交联时间为20min时,涂层成膜性能好,接触角为157.0°,且热氧老化和紫外光老化后仍保持较好的超疏水性。扫描电镜照片表明涂层具有微纳米多尺度粗糙结构。     

水性聚苯胺/叔氟丙烯酸酯复合防腐涂层的制备及性能

为研究水性聚苯胺/叔氟丙烯酸酯（PANI/VFAc）复合涂层对Q235钢防腐蚀性能的影响,首先,以叔碳酸乙烯酯（Veova 10）和甲基丙烯酸十二氟庚酯（DFMA）为功能单体合成了VFAc乳液,并将其与PANI乳液混合后涂刷在Q235钢表面,制备了PANI/VFAc复合涂层;然后,采用TEM和FTIR对VFAc的结构进行了表征,采用XPS和接触角（CA）研究了复合涂层的表面性能,采用电化学方法研究了不同改性丙烯酸酯乳液对复合涂层防腐蚀性能的影响。结果表明:PANI/VFAc复合涂层的水接触角为97.56°,湿附着力等级为0,涂层表现出较好的疏水性;其腐蚀电流密度为8.72×10-8 A·cm-2,电化学阻抗达到106 Ω·cm2。所得结论表明PANI/VFAc复合涂层对Q235钢具有良好的防腐蚀性能。      

镁合金超疏水环氧复合涂层的制备与性能EI北大核心CSCD

传统的超疏水表面的制备过程比较复杂,机械稳定性差,这严重制约了超疏水表面的实际应用。采用“黏合剂+纳米粒子”的方法,在镁合金表面制备一种无氟、持久稳定的超疏水环氧复合涂层。接触角测试结果表明,复合涂层的接触角最高可达160.2°,且在3.5%(质量分数)NaCl溶液中浸泡30天后,接触角仍然高达103°;EIS结果表明,在5个加速老化循环周期后,复合涂层的|Z|_(0.01 Hz)仍高于10^(9)Ω·cm^(2),展现出优异的耐盐雾性能和耐蚀性能;摩擦磨损实验结果显示,在19.6 N的载荷下机械摩擦8 h后,复合涂层的|Z|_(0.01 Hz)高达1.84×10^(9)Ω·cm^(2)。通过“空气垫”的屏障作用,复合涂层能够为镁合金提供高效且持久的腐蚀防护,“黏合剂+纳米粒子”策略为超疏水涂层的制备提供了新的思路。     

Electrolytic deposition of titania films as interference coatings on biomedical implants: Microstructure,chemistry and nano-mechanical properties

TiO₂ films with uniform thickness were electrolytically deposited on AISI 316L stainless steel and Ti6Al4V substrates for potential use as color coded biocompatible coatings on biomedical implants. Deposition occurred via a peroxoprecursor method from solutions containing TiCl₄ and H₂O₂. By optimizing electrolyte formulation and deposition parameters, thin stoichiometric titania films with almost uniform thickness-dependent interference colors, similar as known from the color anodization processes of Ti-alloys, were obtained. Crack-free films were found up to 140 nm on AISI 316L and up to 190 nm on Ti6Al4V substrates. After thermal annealing at 450 °C of as-deposited amorphous peroxotitanium hydrate films, Raman and transmission electron microscopy showed highly stoichiometric, nanocrystalline anatase films. Chemical depth profiling was performed by glow-discharge optical emission spectrometry (GD-OES), showing clearly a densification and loss of water during annealing. On AISI 316L, GD-OES revealed stoichiometric TiO₂ films containing a small Fe (3–4 at.%) and Cr (1 at.%) contamination due to thermal diffusion from the substrate. On Ti6Al4V, the comparison between electrolytic TiO₂ films and color-anodization in different sulfuric and phosphoric acid containing electrolytes showed significant higher purity of electrolytic films, absent of V, Al, S, P contaminations as they were found in anodic oxides (4–6 at.% Al, 1–2 at.% V), especially V and S being problematic in biomedical applications. Annealing greatly increased the mechanical properties of the green films. A nano-hardness of 5.5–6.6 GPa, elastic modules close to substrate modules, excellent adhesion and very ductile behavior were found from nanoindentation and scratch tests. Based on thickness uniformity, high purity and good mechanical properties, electrolytic TiO₂ films are not only attractive as biocompatible colored coatings on non-anodizable biomedical alloys such as AISI 316L and CoCrMo, but also for Ti-alloys that are anodized for protective as well as coding reasons prior to implantation.     

一种三层雷达吸波涂层的制备和性能

在磁性金属微粉的雷达吸波涂层中引入导电纤维层具有减轻质量和展宽吸收频带作用,本文采用磁性金属微粉和短导电纤维制备了一种三层雷达吸波材料.研究表明,三层的相对顺序对吸波涂层的带宽与峰值具有明显影响,在面密度为2.50 kg/m2的条件下,当导电纤维层位于表层时带宽最大,在8～18 GHz频段范围内反射率小于-10 dB的带宽达7 GHz.     

Sliding wear performance of metallic laser coatings against composite PTFE seals

Laser coatings are frequently used in applications where they slide against various elastomeric and polymeric seals or guide bands in different environments. Examples of such applications include hydraulics, maritime propulsion systems and components in pulp & paper industry. In this study highly corrosion resistant Inconel 625 (DIN Mat. No. 2.4856) and Thermanit 2509 super duplex stainless steel (～1.4501) coatings manufactured by novel coaxial hot‐wire laser cladding technique are tested in dry conditions at room temperature against various composite polytetrafluoroethylene (PTFE) seals. Despite only small difference in coating surface hardness, ～1.4501 and 2.4856 show significant differences in wear and friction performance against various seals. For instance, ～1.4501 is superior to 2.4856 against glass fiber and MoS₂ reinforced PTFE in terms of wear resistance and friction characteristics, whereas 2.4856 performs better against bronze reinforced PTFE seal. The reference Stellite laser coating, which is the hardest counter surface in this study, exhibits the best wear behavior against all the seal materials tested. The differences in wear performances are explained by cohesive and adhesive wear mechanisms.     

Preparation and investigation of the structure and properties of Al2O3 plasma-detonation coatings

Using a specially designed and constructed plasmatron, combining the plasma and detonation technologies, aluminum oxide coatings with high adhesion and strength (19.8 GPa) were obtained for the first time. The samples were studied by the transmission electron microscopy and X-ray diffraction methods and characterized for the first time by the Rutherford backscattering and proton elastic resonance measurements. It was found that the aluminum oxide coatings are composed of 0.20–0.25 μm crystallites, belonging to the α-, β-, γ-, and δ-Al₂O₃ crystal modifications, and have a transition region containing AlFe nanocrystals with a size of 20–40 nm and a considerable dislocation density. The aluminum oxide coatings exhibit significant carbonization, with a maximum carbon concentration on the surface reaching 20 at. %. The relative phase composition calculated using the X-ray diffraction data is as follows: γ-Al₂O₃, 60%; α-Al₂O₃, 30%; β-and δ-Al₂O₃, balance to 100%.     

Y_2Si_2O_7晶须增强MoSi_2复合涂层的制备及性能

采用水热电泳沉积法在C/C-SiC复合材料表面制备了Y2Si2O7晶须增强MoSi2复合抗氧化外涂层。采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)对涂层的相组成和显微结构进行了表征。研究了Y2Si2O7晶须对复合涂层显微结构和抗氧化性能的影响。结果表明:Y2Si2O7晶须对复合涂层的显微结构和抗氧化性能有较大的影响。与MoSi2/SiC涂层相比,Y2Si2O7-MoSi2/SiC复合涂层均匀、致密,无显微裂纹。在静态空气氧化过程中,Y2Si2O7晶须有效阻止了外涂层的开裂,提高了涂层的抗氧化性能。该复合涂层试样在1773 K下氧化100 h,失重仅为0.73%,相应的失重速率仅为1.48×10-5g.cm-2.h-1。     

Failure mode and interface chemistry of localized coatings on brass

The behaviour of partly coated aluminium brass has been examined under accelerated laboratory and under natural conditions. Acrylic (Incralac) coatings are found to have a good life and to provide a long-term protection of brass surfaces. Analysis of failed interfaces by photoelectron spectroscopy showed that acidic conditions developed beneath the coating and contributed to a partial weakening of the bond strength. Eventually the crevice conditions drift back towards neutral and there is little further loss of strength.