Ni-P/Ni-W-P双层镀层宏观和微观耐蚀性研究

采用恒电位极化法结合特殊点微观扫描的方法研究了Ni-P/Ni-W-P双层化学镀层的宏观与微观耐蚀性能。研究表明,Ni-P/Ni-W-P双层镀层的阳极极化曲线具有相当稳定的钝化区,较之相同配方的Ni-W-P单层镀层具有更小的维钝电流密度。两种镀层的腐蚀都是由胞状物开始,并逐渐向边界扩展。

元素Cr、Ni对不锈钢耐蚀性能影响

奥氏体不锈钢06Cr19Ni10广泛应用于高压电气行业,其耐蚀性是重要的使用性能,本文选取三类不同化学成分的不锈钢板,结合微观组织结构,通过电化学腐蚀和盐雾腐蚀系统分析,研究了三类不锈钢的耐蚀性能,结果表明,随着Cr与Ni含量的增加,不锈钢的耐蚀性能提高,本试验为指导生产提供了技术依据。

Microstructure and corrosion behavior of as-cast ADC12 alloy with rare earth Yb addition and hot extrusion

The effects of rare earth ytterbium(Yb)addition and hot extrusion on the microstructure and corrosion behavior of as-cast ADC12 were studied by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD).The experimental results demonstrate that both the Si phase andβ-Al5FeSi phase in the alloy with 0.9 wt%Yb have been remarkably refined,and the Al3Yb intermetallic compound has also been obtained.The Si,β-Al5FeSi,and rare earth phases are further refined in the alloy at 0.9 wt%Yb and hot extrusion.The results of the immersion corrosion tests and electrochemical experiments show that the corrosion current density(8.56μA/cm2)of the alloy with 0.9 wt%Yb addition and hot extrusion is 50.6%lower than the untreated alloy(17.33μA/cm2),and the polarization resistance(9252Ω·cm2)was 71.3%higher than the untreated alloy(2654Ω·cm2).The corrosion in the cathode phase in the micro-battery was refined to varying degrees attributable to the addition of Yb and hot extrusion,where the cathode reaction in the corrosion process caused a decrease of the corrosion rate.

Effect of platform temperature on microstructure and corrosion resistance of selective laser melted Al-Mg-Sc alloy plate

The Al-3.40Mg-1.08Sc alloy plates were manufactured by selective laser melting(SLM) at platform temperatures of 35 ℃ and 200 ℃, respectively, and the corrosion performance of them was studied along height direction. The results show that the corrosion resistance of the alloy plate built at platform temperature of 35 ℃ along height direction is basically the same due to a uniform microstructure;While the corrosion resistance of the alloy plate built at platform temperature of 200 ℃ along height direction is different. The evolution of microstructure and the distribution of secondary phases are investigated, and the results show that the Cu-rich phases in alloy play a key role on corrosion performance. At higher platform temperature, the cooling rate is relative slow and a certain degree of in situ ageing leads to the significantly different distribution of Cu-rich phases along grain boundary. Specimens built at the platform temperature of 200 ℃ are inclined to locate at the crossed grain boundary, rather than continuous segregation of Cu-rich phases along grain boundary that is built at platform temperature of 35 ℃. Therefore, the corrosion resistance of Al-3.40Mg-1.08Sc alloy plate manufactured at platform temperature of 200 ℃ is higher, and presents a gradually decreasing trend along height direction.

Effect of high-speed laser cladding on microstructure and corrosion resistance of CoCrFeNiMo_(0.2) high-entropy alloy

In order to study the corrosion resistance of high-speed laser cladding(HLC) coating while improving production efficiency,a CoCrFeNiMo_(0.2)high-entropy alloy(HEA) coating was prepared by HLC.The optimized parameters of HLC are laser power of 880 W,scanning speed of 18 m/min,overlapping ratio of 60%,and powder feed speed of 3 r/min.Then,the surface roughness,microstructure,phase composition,element distribution,and electrochemical properties in 3.5 wt% NaCl solution of the coatings were analyzed,respectively.The local surface roughness of the CoCrFeNiMo_(0.2)HEA coating was found to be 15.53 μm.A distinct metallurgical bond could be observed between the coating and the substrate.Compared to the conventional laser cladding(CLC),the results of electrochemical tests showed that CoCrFeNiMo_(0.2)HEA coating exhibited a significant passivation.The corrosion current density of 5.4411 × 10^(-6)A·cm^(-2) and the corrosion potential of-0.7445 V for the HLC coating were calculated by the Tafel extrapolation method.The CLC coating’s corrosion current density and corrosion potential are 2.7083×10^(-5)A·cm^(-2) and-0.9685 V,respectively.The HLC coating shows a superior corrosion resistance,crucially due to the uniform and fine grains.Under various complex and harsh working conditions,this method can be widely used in the field of repairing and remanufacturing of corro sion-proof workpiece s.

Nickel composite plating with fly ash as inert particle

The Ni/FA composite plating was realized by electrodeposition with fly ash （FA） as inert particles. The main compositions of FA are 72% SiO2 and 25% A1203 in the size of 3-7 Ixm. Electrodeposition was performed in Watts bath containing FA with concentrations of 5, 20, 50 g/L, current densities of 2 and 4 A/dm2, temperature of 50 ~C and magnetic stirring of 250 r/min. Scanning electron microscope （SEM＋EDX）, electrochemical and mechanical technique were used to study morphology, composition and properties of coating. FA content in deposit is dependent on the FA concentration in solution, as well as the plating parameters. Since FA particles were incorporated in the coating, the mechanical and electrochemical properties of the coating were increased. The microhardness of Ni/FA composite plating reaches HV 430 in comparison with HV 198 of pure Ni coating. It was confirmed by electrochemical measurement that the corrosion resistance of Ni/FA composite coating was higher than that of pure Ni.

Effects of KMnO_4 on microstructure and corrosion resistance of microarc oxidation coatings on 2024 aluminum alloy

Microarc oxidation （MAO） coatings were prepared on 2024 aluminum alloy in a Na2SiO3-KOH electrolyte with KNinO4 addition varying from 0 to 4 g/L. The microstructure and phases of the coatings were characterized by scanning electron microscopy （SEM） and X-ray diffractometry （XRD）, respectively. The corrosion resistance of MAO coatings was evaluated by electrochemical potentiodynamic polarization in 5% （mass fraction） NaCl solution. The results show that when KMnO4 is added into base electrolyte, the growth speed of oxide coatings is increased obviously. The main phase of oxide coatings is Al2O3, and the contents of MnO2 and MnEA104 phases are increased at the top of oxide coatings with increasing the concentration of KMnO4. The solute elements participate in forming the oxide coatings. When a proper concentration of KMnO4 （2.5 g/L） is added into the base solution, the micropores of the MAO coatings are small and compact, and the corrosion resistance of oxide coatings is increased largely.