Papers by Keyword: Corrosion Behaviour

Abstract: Cobalt-based Stellite 6 alloy rely primarily on carbides, forming in the Co matrix and grain boundaries, for their strength and the distribution, size and shape of carbides depend on processing conditions. We have employed microstructure and corrosion behavior of Stellite 6 by combustion synthesis and vacuum induction melting with scanning electron microscopy, electron probe microscopy analysis. The results show that there are significant uniformity on microstructure and corrosion behavior of Stellite 6 by different techniques. The combustion synthesis has more advantages over conventional manufacturing process for Stellite 6.

Abstract: Ni–SiC nanocomposite coatings with reinforcing SiC nano-particulates were prepared by electrodeposition on MB8 wrought magnesium alloys. The microstructure, chemical compositions, hardness, corrosion resistance, and wear resistance of resulting composites were investigated respectively. This article details the state of the art in coating technologies, applied to magnesium based substrates for improved corrosion and wear resistance.The experimental results show that, uniform and compact coatings with good corrosion resistance can be obtained on MB8 wrought magnesium alloys. The wear resistance of the coatings were observed to be superior to hard chromium coatings.

Abstract: Potentiodynamic electrochemical tests and surface analysis technics, such as scanning electronic microscope (SEM), energy dispersive spectrum (EDS) and X-ray diffraction analysis (XRD), were applied to investigate the microstructure and corrosion behavior of Ag-Cu-Zn-Ni alloys in Na2S solution. The results reveal that the α-Ag phase is the main matrix of the studied silver alloys. The second phase of Ag-4Cu-0.3Ni and Ag-3Cu-Zn-0.3Ni/Ag-6Cu-Zn-0.3Ni are respectively CuNi and CuNi(Zn) phases. The second phases of Ag-6Cu-Zn-0.3Ni are well-distributed, which leads to an improvement in the corrosion resistance in Na2S solution.

Abstract: The corrosion behavior of Zr53.5Cu26.5Ni5Al12Ag3 bulk amorphous alloy in 3.5% NaCl solution was investigated by using potentiodynamic polarization experiments and electrochemical impedance spectroscopy (EIS). The results show that Zr53.5Cu26.5Ni5Al12Ag3 bulk amorphous alloy has the better corrosion resistance than its corresponding crystal alloy. During the bath in the 3.5% NaCl solution at 25°C, Zr53.5Cu26.5Ni5Al12Ag3 alloy has the lower corrosion current density than the corresponding crystal alloy. After 100h, the corrosion current densities of Zr53.5Cu26.5Ni5Al12Ag3 and the corresponding crystal alloy are 3.8415×10-8A/cm2 and 5.2827×10-7A/cm2, respectively. The results of EIS test indicate that Zr53.5Cu26.5Ni5Al12Ag3 bulk amorphous alloy has the excellent corrosion resistance because passive film with stable structure formed on the surface in 3.5% NaCl solution. With an increase in the immersion time, the passive film becomes thicker. It leads to impedance resistance and corrosion resistance decrease. The surface of Zr53.5Cu26.5Ni5Al12Ag3 bulk amorphous alloy in 3.5% NaCl solution for 100h was analyzed by SEM and EDS. The results show that the corrosive pitting can be found at both the amorphous alloy and the corresponding crystal alloy. However, the amorphous alloy has the better corrosive pitting resistance than the crystal one because the corrosion products formed by selective dissolving of Zr and Al elements. Moreover, the addition of Ag element helps to improve the corrosion resistance of the amorphous alloy greatly.

Abstract: The corrosion behavior of reinforcing steel bar HPB235 in concrete structure in 0.5% NaCl solution was investigated and its mechanical properties were tested before and after corrosion. The results showed that, with corrosion time increasing from 240h to 720h, the corrosion rate increases and the corrosion becomes heavier and heavier, but the corrosion scale is not changed obviously in compositions. After 720h, the yield strength is decreased by less than 5%, but the tensile strength and the elongation are decreased by more than 10%.

Abstract: There were little works about electrochemical corrosion behaviors that appeared in high H₂S and CO₂ containing environment. In this work, the electrochemical behaviors of tubular steel API-P110 in buffered acidic NaCl solutions saturated with high H₂S and CO₂ containing gases, were investigated by potentiodynamic sweep technique. Analysis of the results shows corrosion density declines with increasing CO₂ content in H₂S/CO₂. The corrosion potential of steel moves towards more negatively with the increase of CO₂ content in H₂S/CO₂. In pH 2.9 solution, Passivity appears in high H₂S and CO₂, but no passivity shows in due to decreasing in high H₂S. In pH 5.3 solution, cathodic liming density comes out and increases with the increasing CO₂ content in H₂S/CO₂, however, no cathodic liming density comes out in H₂S.

Abstract: The Corrosion behaviour of Mg-7.3Al alloy in buffered chloride solutions was investigated in the paper. The corrosion resistances of Mg-7.3Al alloy were evaluated in different borate capacity and pH by immersion test and polarization curves. The influences of immersion time, pH and buffer borate capacity were analyzed. The results revealed that the corrosion rate of Mg-7.3Al alloy depends on the pH of corrosive solution and has no relationship with buffer capacity. In the pH 6.5 and 2g / L buffer solution, the morphologies of Mg-7.3Al alloy consist of porous pits and protuberant second phases. There are seriously corroded area and macro-uncorroded area or protuberant second phases on the sample surface. The corossion potentials of the mg alloy is kept the same value in the pH 9 solution, regardless of borate capacity is 1g/Lor 2g/L, which are higher than that in the neutural chloride solution or acid solution (pH=6.5). Borate may play an inhibition role for mg alloy by the quick corrosion test of polarisation curves.

Abstract: TiN coating was deposited on 3Cr2W8V alloy by PVD and then processed with electron beam surface alloying process. The microstructure, microhardness, friction coefficient, amount of wear and corrosion resistance of electron beam treated specimens were investigated. It is shown that the electron beam treated specimens can improve the properties of material. The coating has an average microhardness of approximately HV800, the friction coefficient of electron beam irradiation treated specimens is considerably lower than that of TiN coating. When the electron beam irradiate times is appropriate, the roughness of surface will much lower, and it will achieve polishing effects. The corrosion behavior of the composite coating in 3.5% Nacl solution at room temperature was also determined using a potentiont state system. In comparion with the corrosion potential for 3Cr2W8V alloy, the corrosion potentials of TiN coating and electron beam treated specimen are increased respectively. The electron beam treated specimen has the lowest corrosion current density as well as the highest corrosion potential showing an improved corrosion resistance compared with 3Cr2W8V alloy.

Abstract: In the present study, effect of sintering temperature and atmosphere on corrosion behavior of 316L stainless steel specimens manufactured by metal injection molding (MIM) process were investigated. Sintering experiments were carried out at 1320°C, 1370°C and 1375°C under various sintering atmospheres, i.e. Ar+H₂, Ar, N₂+H₂ or N₂. The corrosion behavior of as-sintered specimens was studied by weight loss immersion test in 5%HCl solution. The results indicated that a better corrosion resistance was accompanied higher density, finer and rounder surface pores. The specimens sintered under Ar+H₂ atmosphere at 1370°C had little susceptibility to intergranular corrosion.

Abstract: To study the corrosion behaviors on the rod and tube materials used in oil well is very important for prolonging oil well repairing periods, lowering oil production maintenance costs and increasing oil production efficiency. Through selecting some kinds of tube and rod materials which are always used in oilfield, chemical corrosion experiment and electrochemical corrosion experiment were carried out under different conditions. The results show that the corrosion rates are accelerated with material prestress increasing, liquid mineralization rate and temperature rising. The nitrified materials have better corrosive resistance than untreated materials. The electrochemical corrosion experiment results show that the electrode potentials of four materials (45, 20CrMo, J55, N80) have tiny difference and don’t exceed 20mV. The bimetallic corrosion tests show that the couple corrosion of the four selected materials pair can be ignored under short period and oxygen conditions.