电解液成分对等离子体电解氧化TC4合金腐蚀行为和摩擦学性能的影响（英文）

在TC4合金表面制备4种典型等离子体电解氧化(PEO)涂层,研究电解质组成对PEO涂层腐蚀行为和摩擦学性能的影响。结果表明,PEO涂层的腐蚀行为和摩擦学性能与电解质成分密切相关。在含NaH₂PO₂的电解液中制备的PEO涂层由于内氧化膜较致密而具有最好的耐蚀性能,而在含NaAlO₂的电解液中制备的PEO涂层由于含有Al₂O₃而具有最好的摩擦学性能。为制备具有良好耐蚀性和耐磨性的PEO涂层,以NaH₂PO₂和NaAlO₂为电解液主要成分制备了复合PEO涂层。     

Investigations of the Failure in Boilers Economizer Tubes Used in Power Plants

In this study, failure of a high pressure economizer tube of a boiler used in gas-Mazut combined cycle power plants was studied. Failure analysis of the tube was accomplished by taking into account visual inspection, thickness measurement, and hardness testing as well as microstructural observations using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). Optical microscopy images indicate that there is no phase transformation during service, and ferrite-pearlite remained. The results of XRD also revealed Iron sulfate (FeSO₄) and Iron hydroxide sulfate (FeOH(SO₄)) phases formed on the steel surface. A considerable amount of Sulfur was also detected on the outer surface of the tube by EDS analysis. Dew-point corrosion was found to be the principal reason for the failure of the examined tube while it has been left out-of-service.     

Determination of biocorrosion of low alloy steel by sulfate‐reducing Desulfotomaculum sp. isolated from crude oil field

In this study corrosion behavior of low alloy steel, in the presence of anaerobic sulfate‐reducing Desulfotomaculum sp. which was isolated from an oil production well, was investigated. In order to determine corrosion rates and mechanisms, mass loss measurements and electrochemical polarization studies were performed without and with bacteria in the culture medium. Scanning electron microscopic observations and energy dispersive X‐ray spectra (EDS) analysis were made on steel coupons. The effect of iron concentration on corrosion behavior was determined by Tafel extrapolation method. In a sterile culture medium, as the FeSO₄ · 7H₂O concentration increased, corrosion potential (E_cor) values shifted towards more anodic potentials and corrosion current density (I_cor) values increased considerably. After inoculation of sulfate‐reducing bacteria (SRB), E_cor shifted towards cathodic values. I_cor values increased with increasing incubation time for 10 and 100 mg/L concentrations of FeSO₄ · 7H₂O. Results have shown that the corrosion activity changed due to several factors such as bacterial metabolites, ferrous sulfide, hydrogen sulfide, iron phosphide, and cathodic depolarization effect.     

Electroless Ni-P and Ni-P-Al2O3 Nanocomposite Coatings and Their Corrosion and Wear Resistance

In an effort to utilize beneficial aspects of nanoparticles in providing corrosion and wear resistance, electroless Ni-P and Ni-P-Al₂O₃ nanocomposite coatings were produced. Alumina particles with various contents from 5 to 20 g/L in bath were co-deposited within Ni-P deposits on mild steel (ms) substrate. Coatings were characterized by scanning electron microscopy (SEM) for morphology, energy dispersive analysis of x-ray EDAX for analyzing elemental composition and x-ray diffractometry for investigating the structural changes of their components. Electrochemical and immersion measurements were used to analyze corrosion behavior of the coatings in 3.5% NaCl solution. Wear resistance of the coating was measured by pin-on-disc method. The results indicated that the Ni-P-Al₂O₃ coatings provide the high hardness as compare to the Ni-P coating. Corrosion and wear resistance of coatings is observed to be superior to that of ms. Corrosion protection properties of the coatings are found to be affected with continuous exposure to the electrolyte. Coating with high concentration of alumina is exhibiting high wear resistance than Ni-P coating. Wear mechanism in case of Ni-P coating appears to be adhesive type and seems to change to abrasive type on introduction of alumina.     

Abrasive wear/corrosion properties and TEM analysis of Al2O3 coatings fabricated using plasma electrolysis

Alumina coatings were deposited on Al alloy substrates using an electrolytic plasma technique, based on a dielectric barrier discharge created during anodic oxidation in an aqueous electrolyte. The substrate material (BS Al 6082) was biased anodically with an unbalanced AC high voltage. During processing, a plasma current density of 100 mA/cm² was used, at which a coating deposition rate of 1.67 μm/min was achieved. Coating abrasive wear and corrosion properties were assessed by conducting dry and wet rubber wheel abrasive tests and potentiodynamic polarization experiments, respectively. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate the coating microstructure, and the coating/substrate interface. The property test results show that the coatings possess excellent abrasive wear and corrosion resistance. XRD analyses indicate that the coatings consist of α- and γ-Al₂O₃. An amorphous+nanocrystalline inner layer (1.5-μm thick) and a nanocrystalline (50–60 nm) intermediate layer in the coating were observed by TEM. The higher resistance to wear and corrosion can in part be attributed to the presence of these interlayers.     

Microstructure refinement and alloying of WC-CoCr coatings by electron beam treatment

The corrosion and wear behaviour of HVOF (high velocity oxygen fuel) sprayed WC-CoCr (cermet) coatings were investigated before and after electron beam (EB) remelting. In this regard, the coatings were deposited on INCONEL 617 substrate. The mentioned Ni-based alloy is well known for its good corrosion behaviour in chloride containing media but exhibits not enough good wear properties.The paper investigates the influence of EB-remelting process on sliding wear respectively on corrosion resistance in 1 M NaCl solution of the alloyed surface. Scanning electron microscopy (SEM) and X-Ray Diffraction (XRD) were performed before respectively after the EB-treatment in order to investigate the coating morphology as well as the phase modification achieved through the alloying process. Tribological tests concerning the sliding wear behaviour of the tested materials revealed a significant decrease of the wear rate for both the as-sprayed coating respectively the alloyed surface in comparison with the base material. However, the as-sprayed cermet coating exhibits the lowest wear rate among the investigated samples.The microhardness of the alloyed surface was higher (1100 HV₀₃) in comparison with that of the as-sprayed cermet coating (905 HV₀₃) as a result of new phase formation (especially the η-Co₄W₂C). The corrosion behaviour in salt water of the EB remelted surface was also considerably improved in contrast to the as-sprayed cermet coating.     

纳米Si3N4 对TC4钛合金微弧氧化层微观结构和性能的影响

在基电解液中加入氮化硅纳米颗粒,对TC4钛合金进行微弧氧化（MAO）处理,研究了Si₃N₄浓度对微弧氧化层表面形貌、耐蚀性和耐磨性的影响。添加Si₃N₄的MAO层呈现多孔结构,当Si₃N₄浓度为1 g/L时,涂层厚度最大,且经过7 d的酸腐蚀试验,该涂层的耐蚀性良好,腐蚀速率最低,约为0.057 mg·cm^-2·d^-1。随着Si₃N₄的加入,MAO涂层的抗菌性能先升高后降低。当Si₃N₄的添加量为1 g/L时,该MAO层的抗菌性能最好。Si₃N₄的加入能明显提高涂层在模拟海水中的耐磨性。当Si₃N₄的添加量为3和4 g/L时,所得涂层的摩擦系数低且稳定,且添加3 g/L Si₃N₄制备来的MAO涂层表现出优异的耐磨性。     

Corrosion Behavior of PEO Coatings Formed on AZ31 Alloy in Phosphate-Based Electrolytes with Calcium Acetate Additive

The PEO coating started on magnesium AZ31 using a unipolar DC power source. The coating was generated in the electrolyte based on Na₃PO₄·12H₂O and KOH with calcium acetate as additive. The x-ray diffraction method showed some phases containing calcium and phosphate, which was created in the presence of additive. Also, the EDS tests of the sample’s surfaces proved the existence of calcium on the surface. Based on the electrochemical tests results, the most corrosion resistance belongs to the sample with calcium acetate additive. In fact, the results of the EIS tests showed the coating with calcium acetate has the highest resistance but the lowest capacitance. However, this state belongs to the surface morphology, the lower porosity, and surface chemical composition.     

Investigation of wear and corrosion resistance of nanocomposite coating formed on AZ31B Mg alloy by plasma electrolytic oxidation

Ceramic-WC coatings were prepared on AZ31 B Mg alloy by plasma electrolytic oxidation (PEO) from a phosphate based bath containing suspended tungsten carbide nanoparticles at various process times. Scanning electron microscope results indicated that increase of coating time and incorporation of tungsten carbide into the ceramic coating during the PEO process led to a decrease in the number and diameter of coating pores. Phase analysis showed that the nanocomposite coating was composed of MgO, Mg₃(PO₄)₂ and WC. Tribological properties and corrosion behaviour of uncoated AZ31 B Mg alloy and ceramic coatings were evaluated using a pin-on-disc tribometer and potentiodynamic polarisation technique in 3.5% NaCl solution, respectively. The wear and electrochemical tests showed that wear and corrosion resistance of ceramic-WC nanocomposite coatings were better than ceramic only ones. In addition, wear and corrosion behaviour of coatings improved with increasing the coating time.     

Development of permanganate assisted manganese phosphate coating on mild steel

Manganese phosphate coatings are widely used as pretreatment for corrosion and wear resistance of numerous automotive components. Manganese phosphating formulations are established with various additives to improve the coating weight besides achieving the required amount of iron dissolution in a shorter time. The aim of our investigation is to use permanganate as an additive to increase iron dissolution and to achieve subsequent improvement in the quality of manganese phosphate coating. Manganese carbonate, phosphoric acid, nitric acid are used to create a basic formulation in which permanganate concentration is varied. The composition of the final formulation is optimised by giving due consideration to higher iron dissolution and improved coating weight. The resultant coating is characterised with polarisation, electrochemical impedance spectroscopy (EIS), FT-IR, XRD, SEM and EDX. The kinetics of the coating formation is also followed using potential–time measurement for all the experimental baths. Kinetic studies showed earlier attainment of point of incipient precipitation of manganese phosphate coating in the optimised formulation when compared to other formulation under investigation. The study revealed that the addition of KMnO₄ in the manganese phosphating bath enabled an increase in the rate of metal dissolution, and enrichment of ferrous ion concentration at the metal/solution interface thus, favoured precipitation of corrosion and wear resistant Hureaulite ((Mn,Fe)₅H₂(PO₄)₄.4H₂O). For a given coating weight, addition of KMnO₄ substantially reduced the processing time.     

ZM5镁合金无铬前处理化学镀镍层的性能

采用优化的Na4P2O7+Na2SO4+NaNO3体系的化学蚀刻无铬前处理化学镀镍工艺,在ZM5镁合金上制备Ni-P镀层。利用扫描电镜、能谱仪、X射线衍射仪分析镀层的微观形貌、成分和相结构。通过电化学方法和摩擦磨损试验评价了镀层的耐蚀性和耐磨性。结果表明:无铬前处理工艺制备的镀层中P的质量分数为12.90%。与ASTM标准的含铬前处理工艺得到的镀层的耐蚀性和耐磨性相比,无铬前处理得到的镀层的自腐蚀电位为-0.506V,腐蚀电流密度为2.132×10-6 A/cm2,接近ASTM工艺含铬前处理得到的镀层的耐蚀性能;同时其磨损率为3.056×10-4 mg/s,与ASTM工艺的1.778×10-3 mg/s相比,其抗摩擦磨损性能明显优于含铬前处理的镀层。无铬前处理化学镀镍显著提高了ZM5镁合金的耐蚀性和耐磨性。     

西南地区某输油管道外腐蚀分析

目的研究西南地区某输油管道外腐蚀行为。方法现场检测,对土壤理化性质及腐蚀产物成分进行室内分析。结果开挖点A的土壤呈弱碱性,土壤腐蚀性弱,管道发生轻微均匀腐蚀,腐蚀产物主要为FeO(OH),Fe(OH)3和Fe3O4等铁的氧化物,对应的阴极反应为吸氧反应;开挖点B的土壤酸性强,硫酸根离子浓度高,土壤腐蚀性强,管道发生严重坑蚀,腐蚀产物主要成分为FeSO4·7H2O及少量碱式硫酸铁,对应的阴极反应以析氢反应为主。结论开挖点土壤的理化性质差异,导致管道的腐蚀形态、腐蚀产物和腐蚀机理显著不同。     

Wear and corrosion resistant coatings on surface of cast A356 aluminum alloy by plasma electrolytic oxidation in moderately concentrated aluminate electrolytes

Plasma electrolytic oxidation of a cast A356 aluminum alloy was carried out in aluminate electrolytes to develop wear and corrosion resistant coatings. Different concentrations of 2, 16 and 24 g/L NaAlO₂ solutions and a silicate electrolyte (for comparison) were employed for the investigation. Wear performance and corrosion resistance of the coatings were evaluated by WC (tungsten carbide) ball-on-flat dry sliding tests and electrochemical methods, respectively. The results show that the coating formed for a short duration of 480 s in 24 g/L NaAlO₂ solution generated the best protection. The coating sustained 30 N load for sliding time of 1800 s, showing very low wear rate of ～4.5×10^?7 mm³/(N·m). A low corrosion current density of ～8.81×10^?9 A/cm² was also recorded. Despite low α-Al₂O₃ content of the coating, the compact and nearly single layer nature of the coating guaranteed the excellent performances.     

氟化钾对AZ91D镁合金微弧氧化膜的生长及微观结构的影响

通过在NaOH和Na_2SiO_3组成的基础电解液中,分别不加及加入KF,对AZ91D镁合金进行微弧氧化处理,研究了KF的有无对镁合金微弧氧化膜的生长、微观结构及耐蚀性能的影响。结果表明:与不加KF相比,加入KF后,试样的起弧电压明显降低,击穿变得剧烈,试样表面火花较大,膜层的生长速率明显提高,膜层厚度显著增大,表面孔隙率稍有增大,但表面微孔数量减少。KF的加入有利于MgF_2、MgAl_2O_4的生成,与同样来自电解液的Si、O两元素相比,F~-更易被基体中的Mg所吸附,也容易通过已成膜层迁移到膜层的内部。电解液中含有KF时,膜层厚度显著增大,MgAl_2O_4物相含量增加,并生成新物相MgF_2,这些都有利于膜层耐蚀性的提高。     

电解液组分对镁合金微弧氧化成膜及膜层耐蚀性的影响

基于单纯形重心设计改变Na₂SiO₃、NaOH、KF和NaAlO₂ 4种组分的搭配,在AZ91D镁合金上进行微弧氧化处理,研究了电解液配方对膜层成膜及耐蚀性能的影响。结果表明,所得到的回归方程非常显著,预测精度高。帕累托分析显示,4种电解质均对膜层耐蚀性影响显著。通过响应面分析可知,增大主盐Na₂SiO₃或者NaAlO₂的浓度可以显著提高膜层的耐蚀性。但二者复合却不利于耐蚀性的提高。主盐对于提高膜层成膜性及耐蚀性至关重要。当电解液中无主盐时,膜层的成膜性及耐蚀性都很差。当电解液中含有主盐时,适当增加NaOH与KF的浓度,膜层耐蚀性提高。通过Pearson相关分析可知,膜层耐蚀性主要受致密度及孔隙率的影响,同时也受膜厚、物相等其他特征参量的影响。而电解液各组分通过影响上述微观结构特征参量从而影响膜层性能。     

Ce(SO4)2浓度对电喷镀Ni-W-Ce合金镀层性能影响

为了研究Ce(SO4)2浓度与合金镀层表面性能的关系,采用喷射电沉积法制备了一系列Ni-W-Ce合金镀层工件。用扫描电镜(SEM)观察了镀层的表面结构,并用能谱仪(EDS)检测镀层中的元素组成。XRD分析表明,镀层存在晶格畸变。LEXT4100激光共焦显微镜观察磨损痕迹,发现磨损机理发生了变化。结果表明,添加Ce(SO4)2改善了涂层的表面微观形貌,当浓度为0.5g/L时,涂层的表面质量最佳。同时,显微硬度、耐磨性和耐腐蚀性随浓度的增加呈现先好后坏的规律。当Ce(SO4)2浓度为0.5g/L时,显微硬度达到峰值519.69HV0.1。此时,镀层耐磨性最好,其耐磨性表征参数均取得最小值。且镀层的耐蚀性也最好,腐蚀电位为-0.5537V,电弧电抗半径最小。     

Wear and Corrosion Behavior of Zr-Doped DLC on Ti-13Zr-13Nb Biomedical Alloy

Zirconium (Zr)-doped DLC was deposited on biomedical titanium alloy Ti-13Nb-13Zr by a combination of plasma-enhanced chemical vapor deposition and magnetron sputtering. The concentration of Zr in the films was varied by changing the parameters of the bi-polar pulsed power supply and the Ar/CH₄ gas composition. The coatings were characterized for composition, morphology, nanohardness, corrosion resistance in simulated body fluid (SBF) and tribological properties. X-ray photoelectron spectroscopy (XPS) studies on the samples were used to estimate the concentration of Zr in the films. XPS and micro-Raman studies were used to find the variation of I _D/I _G ratio with Zr concentration. These studies show that the disorder in the film increased with increasing Zr concentration as deduced from the I _D/I _G ratio. Nanohardness measurements showed no clear dependence of hardness and Young’s modulus on Zr concentration. Reciprocating wear studies showed a low coefficient of friction (0.04) at 1 N load and it increased toward 0.4 at higher loads. The wear volume was lower at all loads on the coated samples. The wear mechanism changed from abrasive wear on the substrate to adhesive wear after coating. The corrosion current in SBF was unaffected by the coating and corrosion potential moved toward nobler (more positive) values.     

HVAF工艺参数对铝基非晶合金涂层性能的影响

针对铝基非晶合金形成能力弱的问题,采用超音速火焰喷涂(HVAF)工艺制备出铝基非晶合金涂层,研究了优化工艺参数对涂层孔隙率和非晶含量的影响,并评价了涂层的耐蚀和耐磨性能。 结果表明:在合适的喷涂厚度下,提高喷枪移动速率及降低送粉速度,可有效提高涂层的致密度与非晶含量,进而明显提升了涂层的耐蚀和耐磨性能。 在优化的工艺参数下得到的铝基非晶涂层孔隙率为 0. 12%,非晶含量为 83. 7%时,点蚀电位可提高到-0. 3 V_SCE ,腐蚀电流密度降低一个数量级,磨损速率仅为 5. 6×10 ^-4 mm ³N ^-1m ^-1 。     

A Black Phosphate Conversion Coating on Steel Surface Using Antimony(III)-Tartrate as an Additive

A novel black phosphate conversion coating was formed on steel surface through a Zn-Mn phosphating bath containing mainly ZnO, H₃PO₄, Mn(H₂PO₄)₂, and Ca(NO₃)₂, where antimony(III)-tartrate was used as the blackening agent of phosphatization. The surface morphology and composition of the coating were characterized by scanning electron microscopy, energy dispersion spectroscopy, and x-ray photoelectron spectroscopy. Corrosion resistance of the coating was studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy. The pH value of the solution had significant influence on the formation and corrosion resistance of the coating. The experimental results indicated that the Sb plays a vital role in the blackening of phosphate conversion coating. The optimal concentration of antimony(III)-tartrate in the phosphating bath used in this experiment was 1.0 g L^?1, as higher values reduced the corrosion resistance of the coating. In addition, by saponification and oil seals, the corrosion duration of the black phosphate coating in a copper sulfate spot test can be as long as 20 min.     

Ni-WC涂层在饱和H2S溶液中的磨损和腐蚀行为

为了提高深海石油钻采工具的耐磨耐蚀性能,利用等离子转移弧堆焊(PTA)在不锈钢表面制备了不同球形碳化钨(WC)含量的镍(Ni)基涂层,并研究了该涂层在饱和硫化氢(H₂S)溶液中的耐磨损与腐蚀性能。通过X射线衍射仪、扫描电子显微镜、X射线光电子能谱仪等方法研究了涂层的表界面形貌和组成结构。利用显微硬度测试仪和摩擦磨损测试仪研究了涂层的耐磨损性能。通过极化曲线和3D光学轮廓仪等方法研究了涂层在H₂S溶液中的腐蚀速率和点蚀分布。结果显示,球形WC粉末的Ni基合金颗粒经过离子转移电弧堆焊在合金钢表面形成的涂层,其主要成分为WC,W₂C,Ni和Ni₃Fe。但WC的体积分数对于涂层的耐磨耐蚀性能影响较大,当WC的体积分数为60%时(Ni-60%WC),涂层在H₂S溶液中的耐磨与耐蚀性能均优于单纯的Ni基涂层和Ni-30%WC涂层。因此,文中研究为深海石油钻采工具的表面防护提供了一种新的思路和选择。