Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《中国腐蚀与防护学报》
Abstract: The evolution of corrosion product film formed on X80 pipeline steel in artificial solution, which simulate the soil medium at Ku'erle area, with different immersion time was studied by immersion tests, while the morphology and phase constituent of the corrosion product film was characterized by means of scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. The effect of corrosion product film on the pitting corrosion of X80 pipeline steel was investigated by cyclic polarization curves and electrochemical impedance spectroscopy (EIS). The experimental results showed that the thickness and compactness of corrosion product film gradually increased with increasing immersion time. After immersion for 168 h, the corrosion product film was clearly divided into two layers. The pitting of X80 pipeline steel may be hindered or inhibited by the corrosion product film, which may reduce the probability of pitting initiation, and increase the resistance to pitting growth.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract: The Ni-Fe alloy coating with Ce was electroplated on the 20# steel by adjusting the concentration of CeCl3 in plating solution with the rare earth cerium salt CeCl3 as the additive. The relevant microstructure and corrosion behavior in 3.5%NaCl solution of coatings were studied by means of SEM, EDS and XRD, as well as electrochemical polarization curve and impedance spectroscopy. The results indicate that rare earth additive in acidic bath is extremely favor of the generation of sol Ce(OH)3, but restrains the generation of (FeOH) and Fe(OH)2 etc. With cathodic adsorptive characteristics the adsorption of Ce(OH)3 would compete with the adsorption of (FeOH). The former is preferentially absorpt on the surface of material, which restrains the generation of Fe. On the other hand, the addition of CeCl3 improves the current efficiency greatly, so as to increase the deposition rate. When concentration of CeCl3 is 3 g/L, the coating with better quality and better corrosion resistance would be obtained with the content of Fe controlled to about 16%.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract: Nanocrystalline Fe-Ni-Cr alloy coating was plated on brass from a bath containing trivalent chromium plating solution by using pulsed electrodeposition method. Then the surface morphology, chemical composition and microstructure of the coating were characterized by means of SEM with EDS and XRD. The corrosion behavior of the coating in 5%H2SO4 solution was examined by polarization curve measurements in comparison to the traditional 304 stainless steel. The results showed that: the electrodeposited Fe-Ni-Cr coating was nanocrystalline with grain size in a range of 10~40 nm and a composition of 25.52% Cr, 59.61% Fe and 6.55% Ni. In 5%H2SO4 solution the free corrosion potential increased nearly 30 mV, corrosion current density reduced by nearly 1/8 and passive current reduced by nearly one-tenth for the Fe-Ni-Cr alloy coating in comparison to 304 steel.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract: Nanocrystalline Fe-Ni-Cr alloy coatings were deposited on brass substrate by pulse electroplating with variant pulse frequencies, which then were characterized by SEM and EDS, as well as by XRD. The polarization curve and AC impedance of the coating were examined by electrochemical workstation. The results show that the coating prepared by pulse frequency 5000 Hz is nanocrystalline with mean grain size ca 12 nm, as well as a much smooth and uniform surface morphology, of which the corrosion current density, corrosion potential and the charge transfer resistance in 3.5%NaCl solution were -200 mV, 0.12 μA/cm2, 2500 Ω/cm2 respectively. It is believed that proper pulse frequencies may be beneficial to increase the number of nucleation sites of the deposits resulting in a coating with fine grain sized nanocrystallites, and better corrosion resistance.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract: The effect of heat treatment temperature on the microstructural evolution of electroless plated Ni-P coatings was investigated using X-ray diffraction (XRD) analysis. The results showed that the as plated electroless Ni-P coating is amorphous. After heat treatment at 350 ℃, Ni-P coatings turn into crystalline state, while Ni3P phase appeared at 400 ℃. With the increasing heat treatment temperature, the Ca2 + atomic percentage of the formed fouling scales reduced firstly at 300 ℃, and then increased at 350 and 400 ℃. After heat treatment at 300 ℃, the internal stress and hydrogen embrittleness of the coating was eliminated, thereby, the anti- fouling performance and corrosion resistance of the coating was enhanced.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract: X80 pipeline steel was nitridated by plasma nitriding and then its electrochemical corrosion behavior in 3.5%NaCl solution was studied by means of polarization curves and impedance spectroscopy. As compared to the bare X80 steel, the nitriding steels exhibit a remarkable increment in hardness, which increases with the rising nitriding temperature; the nitriding steels possess higher corrosion resistance with a lower corrosion current density by about one order of magnitude. The formation of ε phase (Fe3N) with a small amount of γ ' phase (Fe4N) dominates on the surface of the steel nitridated at 450 ℃, resulting in a maximium in corrosion potential about -214 mV and a minimum in corrosion current density about 0.56 μA/cm2, respectively, togeter with the hardness increase to about 810 HV. Only the γ 'phase forms on the surface of the steel nitridated at 570 ℃, which contributes to the hardness increase to 930 HV and a obvious decrease of corrosion resistance. The plasma nitriding temperature determines the phase constitutes of the surface nitriding layer and affects greatly its hardness and corrosion resistance.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract: The corrosion resistance of X80 pipeline steel modified by using plasma nitriding technique was investigated in a simulated soil solution of the Yingtan area in the south-east of China. The results show that the as-plasma nitriding treated steel exhibit higher corrosion resistance rather than the bare X80 steel. The nitriding treatment resulted in the formation of a surface layer composed of nitrides of ε phase and γ ' phase as well as solved nitrogen, which could not only shift the corrosion potential positively, but also reduce greatly the corrosion current density, thus lowering the corrosion velocity. The corrosion current density of the as-plasma nitriding treated steel increases with the increasing immersion time. However, for the long term, micro-pores and cracks could occur in the corrosion product film, thereby the corrosion was accelerated.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract: Effect of temperature on corrosion behavior of X70 pipeline steel in high pH solution (0.5 mol/L Na2CO3+0.5 mol/L NaHCO3) was studied by means of potentiodynamic polarization, electrochemical impedance spectroscopy and Mott- Schottky measurements. Results showed that the pitting potential, passive current density and the polarization resistance of X70 pipeline steel all decreased with the increase of temperature. In the experimental temperature range, the formed passive film consisted mainly of Fe2O3 and Fe3O4 with features of n-type semiconductor. With the rising temperature, the thickness and donor density of the passive film increased, correspondingly, corrosion tendency of the steel increased. Therefore, the stability of the passive film decreased with the increasing temperature, which weakened the corrosion resistance of the X70 steel.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract: Cu-Co-Fe alloys have excellent properties such as high strength, high electrical conductivity and giant magneto resistance (GMR). These alloys are promising candidates to be used as electric contactors, integrated circuit lead frame, wires & cables, ferromagnetism materials. However, the manufacturing of Cu-Co-Fe alloys is extremely difficult due to the presence of metastable miscibility gap in the liquid state. The liquid-liquid decomposition generally leads to serious phase segregated microstructure during the conventional solidification process. Studies in recent years reveal that rapid solidification techniques can effectively suppress the liquid phase separation. In this work, rapid solidification experiment is carried out with Cu-10%Co-10%Fe (mass fraction) alloy by using the high pressure gas atomization technique. Powders having composite microstructure with the Fe-Co-rich particles homogeneously dispersing in the Cu matrix are obtained. A model is developed to describe the microstructure evolution in an atomized droplet of Cu-Co-Fe alloy during the liquid-liquid phase transformation. The microstructure formation is simulated by coupling the thermodynamic and kinetic calculations. The favorable agreements between the calculated and experimental results for the powders of different sizes indicate that the model describes the microstructure evolution in the atomized droplets of Cu-Co-Fe alloy well. The results demonstrate that the effect of the Marangoni migration and Ostwald coarsening of the Fe-Co-rich droplets are very week under the rapid cooling conditions of gas atomization. For Cu-10%Co-10%Fe powders with diameter less than 220 mm, the average radius Ra and number density N of the Fe-Co-rich particles depend exponentially on the powder diameter d.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract: By using high energy ball- milling and vacuum hot-pressed sintering techniques, ultrafine grained carbide cement WC-2.5TiC-10Co were prepared, and the effect of grain growth inhibitors Cr3C2, VC, TaC and NbC on microstructures and mechanical properties were studied by X- ray diffractometer, field emission scanning electron microscope (FESEM) and mechanical performance test. The results indicates that the particle size of the WC powder can be reduced to less than 0.2 mm from 0.6 mm after 30 h of high energy ball-milling at a rotation speed of 350 r/min and ball/powder ratio of 10: 1. After vacuum hot-pressed sintering at 1410℃ for 1h, no new reactive product formed revealed by XRD. When 0.45 % Cr3C2, 0.3 %VC, 0.5 %TaC or NbC were added to the carbide cement, a small quantity of abnormally coarsened WC grains occurred, while the fractured surfaces display loose and smooth. Analyzing the fractured surfaces indicate that cleavage cracking in coarsened WC grains was caused by concentrated stress and become the source of materials fracture. When the contents of inhibitors Cr3C2 and VC were both more increased 0.1%, the grain size of WC can be reduced less than 0.5 mm. In such a case, the fractured surfaces are intimate and step-like, while the bending strength can be increased by 20%. Inhibitors TaC and NbC have not pronounced effect on the preventing the WC grain growth, while the addition of NbC is most effective in improving the relative density of the carbide cement.