Corrosion Behaviors of P110 Steel and Chromium Coating in CO_2-saturated Simulated Oilfield Brine

The protective chromium coating was prepared on P110 steel by employing pack cementation.The corrosion behaviors of P110 steel and the obtained coating in CO2-saturated simulated oilfield brine were studied by static complete immersion tests and electrochemical measurements.The corrosion attacks of the samples were determined by mass loss,corroded surface morphologies,corrosion products,and results of electrochemical measurements.The experimental results showed that the coating was uniform,continuous and compact.The chromium coating was slightly corroded,and the mass loss and corrosion rate of the coating were far lower than those of P110 steel.Chromium coating has higher self-corroding potential and lower corrosion current density than P110 steel in accordance with the electrochemical tests results.Taken as a whole,chromizing treatment has significantly improved the corrosion resistance of P110 steel.

Microstructures and wear resistance of chromium coatings on P110 steel fabricated by pack cementation

In order to obtain a high-performance surface on P110 steel that can meet the requirements in oil/gas field environment, the chromium coatings were fabricated by pack cementation. The chromium coatings differed in with/without the addition of La2O3. Scanning electron microscope （SEM）, energy dispersive X-ray spectrometer （EDS）, X-ray diffractometer （XRD） and microhardness tester were employed to investigate the surface morphologies, surface element distributions, microstructures, phase constitutions and microhardness of the coatings. Friction-wear tests of the P110 steel substrate and the coatings were conducted in air at ambient temperature and humidity. The results show that ＇uniform and continuous coatings are formed on P110 steel regardless of adding La2O3 or not. The chromium coatings consist of Cr23C6, Cr7C3, and （Cr, Fe）7C3. The La2O3-added chromium coating is more beneficial in terms of surface morphology, microstructure, thickness and microharduess as compared with the coating without adding La2O3. Chromizing treatment significantly improves the surface hardness and wear resistance of the P110 steel. The wear resistance of the tested samples can be sorted in the following sequence： La2O3-coating 〉 no RE-coating 〉bare P110 steel.

Improvement of stability of trivalent chromium electroplating of Ti based IrO_2+Ta_2O_5 coating anodes

The preparation process and properties of the thermally prepared Ti anodes coated with IrO2+Ta2O5 was studied. The structure and morphologies of the IrO2+Ta2O5 coatings were determined by XRD and SEM. Their electrochemical properties were studied by polarization curve and cyclic voltammetry. Trivalent chromium electroplating using Ti/IrO2+Ta2O5 anodes is carried out and the results were analyzed. Results show that this anode exhibits excellent electrochemical activity and stability in sulfate electrolysis. The electrocatalytic activity is determined not only by the content of IrO2 but also the structure and morphology of the anode coatings. The electroplating results indicats that Ti/IrO2+Ta2O5 anodes have excellent capabilities and merits in improving the stability of trivalent chromium electroplating in sulfate system.

Microstructure and corrosion resistance of high-chromium iron-base coating by plasma cladding

A new type of high-chromium iron-base coating was fabricated on substrate of hardened and tempered grade C steel by plasma cladding with Fe-Cr-C alloy powders. The coating has fine microstructure and is metallurgically bonded to the grade C steel substrate. The corrosion resistance of the coating in solutions of 0. 5 mol/L H2SO4 , 3.5 % NaCl and seawater was evaluated utilizing the electrochemical polarization corrosion-test method. Because of the inherent excellent corrosion- resisting properties of the constituting phase and the fine microstucture, the plasma clad coating exhibits excellent corrosion resistance in the water solutions of 0. 5 mol/L H2S04, 3.5% NaCl and seawater.

Preparation and Property of Chromium Carbide Thermal Diffusion Coating on Cold Working Die Materials

Thermal diffusion （TD） salt bath chromizing of cold working dies was studied. Firstly, it obtained an ideal salt bath formula by comparing with a variety of formulas, and then obtained the influence rule of coating thickness based on studying of some process parameters. The microstructure morphologies and phase structures of the TD chromizing coating were investigated by X-ray diffraction （XRD）, energy-dispersive spectrometry （EDS） and other modern analysis methods. Meanwhile, it carried out a system of testing and analysis of coating, such as hardness, wear resistance, etc.

Tribological Characteristics of Chromium-active Carbon Electroplated Composite Coatings

A process of chromium electroplating using a standard bath with additives and active carbon particles was reported,and the tribological behaviors of the composite coatings using the pin-on-disk tester and the table wear tester were investigated.Experimental results indicate that the electroplated chromium-active carbon composite coatings exhibited the low friction coefficient and excellent anti-wear properties when compared with the normal chromium electroplated ones.The formation of active carbon particles within the chromium matrices can be explained by SEM analysis and the mechanisms of wear resistance of the composite coatings were studied.

Preparation and Characterization of Plasma-Sprayed Ultrafine Chromium Oxide Coatings

Ultrafine chromium oxide coatings were prepared by plasma spraying with ultrafine feedstock. Processing parameters of plasma spraying were optimized. Optical microscope （OM） was used to observe the microstructure of the ultrafine chromium oxide coatings. Scanning electron microscopy （SEM） was used to observe the morphology and particle size of ultrafine powder feedstock as well as to examine the microstructure of the chromium oxide coating. In addition, hardness and bonding strength of the ultrafine chromium oxide coatings were measured. The results showed that the optimized plasma spraying parameters were suitable for ultrafine chromium oxide coating and the properties and microstructure of the optimized ultrafine chromium oxide coating were superior compared to conventional chromium oxide wear resistant coatings.

Study of a New Chromium-Free Conversion Coating Formed on ZnAl Alloy

A new chromium-free conversion film was obtained on surface of a ZnAl alloy by chemical conversion process. Influence of the additives in treating solution containing cerium salt on the corrosion protection of the conversion film formed on zinc alloy was investigated. Corrosion tests and electrochemical measurements in sodium chloride solution were performed . The microstructure and composition of the coatings were examined by means of SEM, EDS and XRD. It was found that the corrosion protection capabilities of the conversion film are markedly increased with the cerium nitride plus additives (hydrogen fluoride acid and an organic inhibitor) treating process. The modified conversion film is an organic/inorganic composite coating and is much more corrosion resistant than the conventional chromate conversion coating and the single cerium conversion coating.

The Effect of Chemical Composition and Thermal Sprayed Method on the Chromium and Tungsten Carbides Coatings Microstructure

The microstructure, phase consistence and microhardness of thermal sprayed coatings were investigated. The tungsten and chromium carbide coatings and also composite NiCrSiB coating were analyzed. The microstructure of coatings were observed by using optical microscopy (MO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Almost equiaxial carbide particles settled inside the surrounded material of coating were found. The cracks propagating thorough the particles and along boundaries between the particles and surrounded material were observed. This phenomenon was connected with the porosity of coatings. The decarburization process was detected in coatings by phase composition investigation using X-ray method. The decarburization process was the reason due to which beside initial Cr3C2 the Cr7C3 and Cr23C6 particles were found. In the tungsten coatings beside the initial WC carbides the W2Cones were found.

LASER ALLOYING ON CHROMIUM-COATED SURFACE OF NODULAR CAST IRON

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Sliding wear characteristics of solid lubricant coating on titanium alloy surface modified by laser texturing and ternary hard coatings

Titanium alloys are poor in wear resistance and it is not suitable under sliding conditions even with lubrication because ofits severe adhesive wear tendency.The surface modifications through texturing and surface coating were used to enhance the surfaceproperties of the titanium alloy substrate.Hard and wear resistant coatings such as TiAlN and AlCrN were applied over texturedtitanium alloy surfaces with chromium as interlayer.To improve the friction and wear resisting performance of hard coatings further,solid lubricant,molybdenum disulphide(MoS2),was deposited on dimples made over hard coatings.Unidirectional sliding weartests were performed with pin on disc contact geometry,to evaluate the tribological performance of coated substrates.The tests wereperformed under three different normal loads for a period of40min at sliding velocity of2m/s.The tribological behaviours ofmulti-layer coatings such as coating structure,friction coefficient and specific wear rate were investigated and analyzed.The lowerfriction coefficient of approximately0.1was found at the early sliding stage,which reduces the material transfer and increases thewear life.Although,the friction coefficient increased to high values after MoS2coating was partially removed,substrate was stillprotected against wear by underlying hard composite layer.

Thickness Dependence of Structural and Optical Properties of Chromium Thin Films as an Infrared Reflector for Solar-thermal Conversion Applications

The thermal emittance of Cr film, as an IR reflector, was investigated for the use in SSAC. The Cr thin films with different thicknesses were deposited on silicon wafers, optical quartz and stainless steel substrates by cathodic arc ion plating technology as a metallic IR reflector layer in SSAC. The thickness of Cr thin films was optimized to achieve the minimum thermal emittance. The effects of structural, microstructural, optical, surface and cross-sectional morphological properties of Cr thin films were investigated on the emittance. An optimal thickness about 450 nm of the Cr thin film for the lowest total thermal emittance of 0.05 was obtained. The experimental results suggested that the Cr metallic thin film with optimal thickness could be used as an effective infrared reflector for the development of SSAC structure.

Impact of Corrosive Liquid on Trivalent Chromium over Aluminium Alloys

Considering aviation and space sectors, aluminium alloys are commonly used due to its excellent mechanical and physical properties. Though satellite hard-ware is confined to controlled environment, it requires anticorrosive treatment over metal substrate followed by a systematic coating scheme. The trivalent chromium coating was deposited over three aluminium alloys namely AA6063, AA7075 and AA6082. The variation in corrosion resistance property of trivalent chromium over each aluminium alloy has been studied in detail. The Neutral Salt Spray (NSS) test result shows that trivalent chromium coating over AA7075 alloy is affected by pitting corrosion compared to other two alloys. In addition to that, NSS test also proves that thickness of the layer does not have any influence corrosion resistance property of trivalent chromium coating. Furthermore, ions in trivalent chromium coating was identified using Secondary Neutral Mass Spectroscopy (SNMS) and degradation of coating in a corrosive liquid studied using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) instrument to understand mechanism of corrosion. The results indicated that both coating and substrate is involved in corrosion process. The number of elements dissolved in to salt solution reveals the weak ionic bonding of coating towards substrates. In comparison, AA7075 alloy has weaker bonding than AA6082 and AA6063 series. The alloying elements such as zinc and copper are removed from substrate by corrosive solution.

Process of pulse electrodeposition nanocrystalline chromium from trivalent chromium bath

Nanocrystalline chromium coating was prepared by pulse electrodeposition from trivalent chromium bath containing carboxylate-urea as complexing agent. The effects of electrodeposition parameters such as current density,bath temperature and solution concentration on the thickness and electrodeposition velocity of Cr deposited films were investigated. The crystallographic structures,morphology and chemical composition of Cr deposited films were analyzed by means of XRD,SEM and EDS. The results indicate that the deposited films with thickness up to 11.2 μm possess a smooth and clean appearance,and the grain size is less than 100 nm. The coating is pure chromium and the Cr deposit has face-centered cubic(fcc) structure and exhibits a(210) growth preference. Both the electrodeposition velocity and thickness exist maximum under different concentration complex agents,ureas,acetates,different temperatures and current densities. Compared with direct current electrodeposition,the thicker coating and finer grains can be obtained at lower temperature and current density by pulse electrodeposition. The electrodepostion velocity is about 0.24 μm/min,which is faster than that by direct current electrodeposition. In 1 mol/L H2SO4,3.5% NaCl and 10% NaOH solution,corrosion potential of Cr pulse-deposited film is about 100 mV higher than that of direct current. Corrosion and passivation current densities are lower and the nanocrystalline exhibits better corrosion resistance.

Influence of process parameters on thickness and wear resistance of rare earth modified chromium coatings on P110 steel synthesized by pack cementation

The pack cementation was employed to produce rare earth modified chromium coatings on P110 steel aiming at improving its performance and increasing the usage lifetime during operation. The orthogonal array design （OAD） was applied to set experiments. Contents of NH4Cl, types of RE, contents of RE, test temperature and soaking time were the main factors, and each factor was endowed with four levels. While the range analysis and analysis of variance were used to investigate the results of OAD tests on thickness and wear resistance. The results indicated that for a promising coating with higher thickness value and excellent anti-wear property, the test temperature was the most significant process factor. The potential promising conditions for chromizing treatment were： adding 1% NH4Cl and 1% LaCl3, maintaining the test temperature at 1000 oC for 8 h. The results of verification showed that the coating formed under the optimal process parameter had a valid thickness of 28 μm and a reduction of 0.32 mg in wear resistance test.

Preparation of Chromium Oxide Coatings on Aluminum Borate Whiskers by a Hydrothermal Deposition Process

Aluminum borate whiskers (9Al 2O 3·2B 2O 3) can be used to reinforce aluminum alloys to produce light and strong composites. However, the adverse interfacial reactions between the whiskers and the aluminum alloys inhibit their practical uses; therefore, a protective coating is needed on whiskers. In this work, aluminum borate whiskers were coated with chromium coating deposits in a hydrothermal solution containing CrCl 3, Na 2C 4H 4O 6, NaPH 2O 2, and H 3BO 3. The presence of the impurity P in the hydrothermal deposits can be avoided by reducing the amount of NaPH 2O 2 in the coating solution. Thermodynamic analysis was used to discuss the behavior of ions in the coating process. The subsequent heating of the hydrothermal products in air at 800 ℃ yielded smooth Cr 2O 3 films with a thickness of 0.060.07 μm.

外场快速修复用六价铬转化膜的性能

外场装备损伤部位快速修复可维持装备服役期间的功能性及寿命。文章对比分析了AA7B04铝合金表面损伤部位及六价铬转化膜再修复样品的表面微观组织、化学成分、电化学性能、酸性盐雾性能。研究结果表明,自主研发六价铬溶液可有效修复划痕样品。划痕修复部位形成一层致密薄膜,且主要成分包括Cr、F、O、K等元素;对比分析拉曼光谱结果,划痕修复部位存在显著的六价铬CrO_(4)^(2-)(847 cm^(-1));电化学阻抗谱结果证明再修复样品在10-2Hz处阻抗膜值为5.09×10^(5)Ω⋅cm^(-2),比划痕样品提高了5倍;电动位极化曲线显示再修复样品自腐蚀电流密度为10^(-5.5)A·cm^(-2),与划痕样品相比下降了1个数量级;此外,再修复样品耐酸性盐雾周期超过336 h,样品表面无腐蚀点,表面盐雾评级达到10级,失重法表征的腐蚀速度比划痕样品下降1个数量级。

硝酸镧含量对锌铝涂层组织结构和耐蚀性的影响

以稀土硝酸镧为添加剂,用硅烷钝化液代替铬酐,通过添加不量的硝酸镧制备了水性无铬锌铝涂层。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱(EDS)分析、中性盐雾试验和极化曲线等对含硝酸镧涂层试样的结构和性能进行了评价。结果表明:含5g/L硝酸镧(指其在B组分中的质量浓度)涂层试样的耐蚀性最好,适量的镧盐可以改善涂层结构,使涂层均匀致密;硝酸镧钝化处理可以显著降低涂层试样的腐蚀电流,提高腐蚀电位,抑制腐蚀速率,提高涂层的耐蚀性。硝酸镧也可以作为物理屏障,阻止腐蚀介质渗透到涂层中,但它不改变极化曲线的形状。水性无铬锌铝涂层中硝酸镧的最佳用量为5g/L。

镀铬层表面微坑阵列PDMS掩膜电解加工研究

以聚二甲基硅氧烷(PDMS)为掩膜的微细电解加工能高效地加工出群微坑阵列,从而改善表面摩擦学性能,提高零件使用寿命,但因电场边缘效应,得到的微坑阵列尺寸均匀性较差。针对这一现象,采用厚层PDMS模板并利用高压静液进行掩膜电解加工,探究工艺参数对铬层表面的微坑阵列尺寸与加工精度的影响,并在耐磨的镀铬层表面进行加工以进一步验证铬层表面摩擦学性能,分析微坑尺寸对镀铬层表面摩擦性能的影响。结果表明,在占空比100%、直流电压30 V、加工时间30 s时,可加工出平均直径和深度分别为106.23μm和15.33μm的微坑阵列,在此基础上探究加工的减磨效果,发现不同直径的微坑阵列均在5μm的深度时达到最佳减磨效果。

硅钢含铬绝缘涂层的红外光谱研究

基于傅里叶变换衰减全反射红外光谱法(ATR-FTIR)研究不同烘烤固化方式和工艺对无取向硅钢含铬绝缘涂层部分性能的变动,讨论了涂层厚度、红外加热方式和固化程度对含铬涂层红外光谱的影响。结果发现:ATR-FTIR可作为硅钢含铬绝缘涂层测试表征的重要方法,可规避涂层厚度、色泽波动所致影响;红外谱图中915 cm-1附近的吸收峰,可作为涂层中是否含有[Cr6+]的判断依据;1585 cm-1附近的吸收峰可作为硅钢含铬涂层成膜物质(丙烯酸树脂与三价铬交联形成复合盐)的特征峰参照。