二次铝灰烧制镁铝尖晶石固相反应动力学及材料耐水蚀性能

以再生铝行业二次铝灰为主要原料,开展二次铝灰烧结制备镁铝尖晶石材料的研究。材料物相分析表明:二次铝灰可以烧结制备镁铝尖晶石材料。根据适宜的原料配比,在不同温度条件下烧结制备材料,进一步探讨烧结温度对材料耐水蚀性能的影响。二次铝灰烧结制备镁铝尖晶石材料的晶化反应表观活化能Ea=104.54 kJ/mol。在1200~1500℃烧结3 h,材料水化反应动力学方程依次为:(1-(1-5.76η)^(1/2)2=kt,(1-(1-6.15η)^(1/2)2=kt,(1-(1-6.43η)^(1/2)2=kt和(1-(1-6.34η)^(1/2)2=kt;1400℃烧结3 h,材料水化率为8.83%,达不到高耐水性材料标准(0.2%)要求。

17-4PH不锈钢表面激光熔覆Stellite6涂层组织及耐水蚀性能

为提高17-4PH不锈钢的耐水蚀性能,利用激光熔覆方法在其表面制备了Stelite6合金涂层。研究了涂层的微观组织形貌、相组成以及元素扩散行为,分析了涂层的硬度分布和耐水蚀性能。结果表明,Stellite6涂层微观组织由平面晶、胞状和柱状晶、树枝晶以及等轴晶组成,物相组成包括面心立方(FCC)结构的γ-Co固溶体和M_(23)C_6、Cr_7C_3、CoC_x等,Fe、Co元素在基体和涂层间的扩散明显。Stellite6涂层的最高硬度为561HV,平均硬度约为基材的1.4倍。多道多层熔覆时,搭接区存在软化现象,横向硬度分布出现周期性波动。在压力为80 Mpa、温度为80℃、水流冲蚀时间为30h的条件下,基材表面发生了严重的材料破坏,而Stellite6涂层表面基本保留了初始形貌,涂层的耐水蚀性能相比基材的有了显著提高。

Fabrication and anti-corrosion performance of superhydrophobic silane film on sintered NdFeB

An eco-friendly superhydrophobic protective film(DTMS/TEOS silane film)was fabricated on sintered NdFeB substrate through the utilization of electrochemically assisted deposition technology.The structure,properties,and film-forming mechanism of dodecyltrime-thoxysilane(DTMS)/tetraethoxysilane(TEOS)silane films were comprehensively analyzed using Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS).Based on the test results,it can be determined that this film has a superhydrophobic property with a hydrophobicity angle of 152°.This special property can be attributed to the long alkyl chains in the DTMS molecule,the rough morphology,and the low surface energy of the DTMS/TEOS silane film.The surface of sintered NdFeB is coated with a layered three-dimensional network silane film that forms through the condensation of silanol substances.This film provides excellent corrosion resistance to the sintered NdFeB substrate,reducing its corrosion current density to 2.02×10~(-6)A/cm~2.Moreover,the impact of film on the magnetic characteristics of sintered NdFeB was assessed and found to be minimal.

1Cr12Ni2W1Mo1V不锈钢表面等离子堆焊司太立熔覆层的组织及性能

为提高1Cr12Ni2W1Mo1V不锈钢的耐水蚀性能,采用等离子堆焊方法在其表面制备司太立熔覆层。研究了涂层的显微组织和显微硬度分布,分析了涂层的抗微粒冲蚀性能和耐水蚀性能。结果表明:司太立熔覆层与基体材料冶金结合良好,熔覆层组织细小、分布均匀,基体为枝晶状Co-Cr固溶体,枝晶间较均匀地分布着黑色碳化物,主要为M7C3和少量WC颗粒;司太立熔覆层的平均显微硬度(382.38 HV4.9 N)约为基材平均硬度(195.29HV4.9 N)的1.96倍,最高硬度值达到了421.00 HV4.9 N;堆焊第2层的硬度明显高于第1层的;司太立熔覆层合金的抗微粒冲蚀性能优于基材,其水蚀速度比基材小,在基材1Cr12Ni2W1Mo1V上堆焊司太立合金能有效提高其耐水蚀性能。

Surface modification of NiTi alloy by sol-gel derived porous TiO_(2)film

Titania films with nano-sized pores were prepared on the NaOH？HCl pretreated NiTi alloy substrate by sol？gel method.A crack-free film is obtained for the sample with a dense inner layer and a porous outside layer（sample TC1＋1）.The X-ray diffraction shows that the titania films are composed of anatase,and a little Ni4Ti3 phase in the heat treated substrate is also detected.The X-ray photoelectron spectroscopy results indicate that the titania film completely covered the NiTi substrate for sample TC1＋1.The sample TC1＋1 is hydrophilic with a contact angle about 20°,and UV illumination treatment for 15 min further decreases the contact angle to（9.2±3.2）°.The potentiodynamic polarization test in 0.9% NaCl solution reveals a better corrosion resistance of sample TC1＋1 than the polished NiTi sample.

Corrosion resistance of in-situ Mg-Al hydrotalcite conversion film on AZ31 magnesium alloy by one-step formation

In situ growth of nano-sized layered double hydroxides （LDH） conversion film on AZ31 alloy was synthesized by a urea hydrolysis method. The formation mechanism of the film was proposed. Firstly, the dissolved Mg2＋ ions deposited into a precursor film consisted of MgCO3 and Mgs（CO3）4（OH）2·4H2O; secondly, the precursor translated into the crystalline Mg（OH）2 in alkaline conditions; finally, the Mg2＋ ions in Mg（OH）z were replaced by A13＋ ions, Mg（OH）2 translated into the more stable LDH structure, simultaneously, the OH- ions in the interlayer were exchanged by CO32-, thus led to the formation of the LDH （Mg6Alz（OHh6CO3·4H2O） film. The results indicated that the LDH film characterized by interlocking plate-like nanostructures and ion-exchange ability significantly improved the corrosion resistance of the AZ31 Mg alloy.

Electric field assisted chemical conversion process of AZ91D magnesium alloy in HCO_3^-/CO_3^(2-) solution

A new method for synthesizing Mg-Al hydrotalcite conversion coating on AZ91D Mg alloy was developed by the application of electric field （EF）. By using EF technique, the formation time of the coating can be significantly reduced. The SEM results indicate that a continuous and compact Mg-Al hydrotalcite coating is formed on the surface of Mg alloy after short time EF treatment. However, a long time treatment would make the coating partially exfoliate. The corrosion current density （Jcor ） of the coated sample （EF1＋1 h） is approximately two orders of magnitude lower than that of Mg alloy substrate. The test of electrochemical impedance spectroscopy （EIS） and immersion corrosion also suggest that the coating can effectively protect Mg alloy against corrosion.

Structure and corrosion resistance of modified micro-arc oxidation coating on AZ31B magnesium alloy

A hydrophobic surface was fabricated on a micro-arc oxidation (MAO) treated AZ31 Mg alloys via surface modification with myristic acid. The effects of modification time on the wettability of the coatings were investigated using the contact angle measuring device. The surface morphologies and structure of the coatings were evaluated using SEM, XRD and FT-IR. The corrosion resistance was investigated by potentiodynamic polarization curves and long-term immersion test. The results showed that the water contact angle (CA) increases gradually with modification time from 0 to 5 h, the highest CA reaches 138° after being modified for 5 h, and the number and size of the micro pores are decreased. The modification method hardly alters crystalline structure of the MAO coating, but improves the corrosion resistance based on the much positive potential and low current density. Moreover, the corrosion resistance and hydrophobicity can be enhanced with increasing the alkyl chain. The wetting and spreading for the alkylcarboxylate with low surface energy become easier on the micro-porous surface, and alkylcarboxylate monolayer will be formed through bidentate bonding, which changes the surface micropores to a sealing or semi-sealing structure and makes the MAO coating dense and hydrophobic. All the results demonstrate that the modification process improves the corrosion protection ability of the MAO coating on AZ31B Mg alloy.

Effect of cooling conditions on corrosion resistance of friction stir welded 2219-T62 aluminum alloy thick plate joint

Friction stir welding (FSW) with water cooling and air cooling was used to weld 2219-T62 aluminum alloy joints with a thickness of 20 mm. The effect of cooling conditions on the corrosion resistance of joints in 3.5% NaCl solution was investigated using the open circuit potential (OCP), the potentiodynamic polarization, and the corrosion morphology after immersing for different time. And the precipitates distribution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that the weld nugget zone (WNZ) owning positive potential, lower corrosion current density and fine and uniform precipitates, is much more difficult to corrode than the heat affected zone (HAZ) and the base metal (BM). Compared with air-cooled joint, the water-cooled joint has better corrosion resistance. In addition, the results of microstructure observation show that the potential, distribution and size of second phase particles determine the corrosion resistance of FSW AA2219 alloy joints in chlorine-contained solution.

Enhanced corrosion resistance of micro-arc oxidation coated magnesium alloy by superhydrophobic Mg-Al layered double hydroxide coating

To further enhance the corrosion resistance of the porous micro-arc oxidation(MAO) ceramic layers on AZ31 magnesium alloy, superhydrophobic Mg-Al layered double hydroxide(LDH) coating was fabricated on MAO-coated AZ31 alloy by using in-situ growth method followed by surface modification with stearic acid. The characteristics of different coatings were investigated by XRD, SEM and EDS. The effect of the hydrothermal treatment time on the formation of the LDH coatings was studied. The results demonstrated that the micro-pores and cracks of MAO coating were gradually sealed via in-situ growing LDH with prolonging hydrothermal treating time. Electrochemical measurement displayed that the lowest corrosion current density, the most positive corrosion potential and the highest impedance modulus were observed for superhydrophobic LDH/MAO coating compared with those of MAO coating and LDH/MAO coating. Immersion experiment proved that the superhydrophobic LDH/MAO coating with the active anti-corrosion capability significantly enhanced the long-term corrosion protection for MAO coated alloy.

Properties of hydrophobic carbon-PTFE composite coating with high corrosion resistance by facile preparation on pure Ti

Composite coatings consisting of carbon and polytetrafluoroethylene(PTFE) were prepared on Ti alloy substrate by a simple two-step process of hydrothermal and impregnation. The morphology, composition, hydrophobic and corrosion properties of the composite coatings were characterized by scanning electron microscopy(SEM), Fourier transform infrared spectroscopy(FTIR), water contact angle method, X-ray photoelectron spectroscopy(XPS) and electrochemical technique, respectively. The effect of PTFE content on the corrosion properties of the composite coatings was studied. It is found that the composite coating film exhibits a full coverage with uniformly distributed PTFE when 0.1 mol/L of glucose is used as carbon source and 20 wt.% PTFE suspension as impregnating solution. The coating with 20 wt.% PTFE has a good bonding strength with Ti plate and exhibits excellent hydrophobic property with a water contact angle of 142.3° as well as superior corrosion resistance with corrosion current density as low as 0.0045 μA/cm^2. With regard to its excellent hydrophobicity and corrosion resistance, the carbon-PTFE composite coating may find potential application in automobiles and metal corrosion industries.

Electrochemical characteristics of electroplating and impregnation Ni-P/SiC/PTFE composite coating on 316L stainless steel

Ni-P/SiC/PTFE coating was obtained on the surface of 316L stainless steel by electrodeposition of Ni-P/SiC coating and immersion of PTFE(polytetrafluoroethylene).The surface morphology and composition were analyzed by scanning electron microscope and energy dispersive spectrometer.The corrosion resistance of the coating in 0.5 mol/L H2SO4+2×10−6 HF solution was studied by electrochemical method.Surface contact angle was used to test the hydrophobic properties of the coating.The results indicated that the Ni-P/SiC/PTFE coating prepared on the surface of stainless steel was uniform and compact,which significantly improved the self-corrosion potential of stainless steel.The self-corrosion current density decreased from 7.62 to 0.008μA/cm2.The durability performance of coating was tested under 0.6 V voltage and the stable corrosion current density value was 0.19μA/cm2,then wetting angle was tested after durability experiment and the value is 134.5°.

17-4PH不锈钢表面激光熔覆Stellite6合金涂层高周疲劳行为研究

利用半导体激光器在汽轮机末级叶片材料17-4PH不锈钢表面激光熔覆Stellite6合金涂层,然后分别制备17-4PH不锈钢、17-4PH不锈钢表面激光熔覆和17-4PH不锈钢表面激光熔覆后经550℃×6h热处理的疲劳试样,进行高周拉压疲劳试验,并对疲劳断口进行扫描电镜(SEM)分析。试验结果表明:在107循环周次条件下,基材17-4PH不锈钢的疲劳极限为470MPa,基材表面激光熔覆Stellite6合金涂层试样的疲劳极限下降到380MPa,而基材表面激光熔覆Stellite6合金涂层经过热处理后的试样可达到440MPa;基材17-4PH不锈钢的裂纹源通常位于表面、近表面或内部缺陷处,裂纹扩展区具有明显的疲劳辉纹特征,瞬断区为韧窝特征;而熔覆试样的裂纹源位于熔覆层侧的缺陷处或熔覆层与基体的界面结合处,然后向熔覆层和基体两侧扩展,熔覆层侧呈脆性沿晶断裂,基体呈韧性疲劳断裂。