Papers by Keyword: Corrosion Behaviour

Abstract: In this paper, the magnesium alloy AZ91D as biological implant material was treated by micro-arc oxidation. The effects on the coating growth of oxidation time and terminal voltages in zirconium solution and silicate solution were investigated respectively. Immersion and electrochemical tests were applied to study the corrosion behavior of AZ91D alloy in Hank’s solution. The results revealed that the coating thickness increases and the corrosion rate in immersion test decreases as the extension of oxidation time and the rising of terminal voltage. The corrosion rate of the alloy in the immersion test treated in zirconium solution varies with the terminal voltages and that in silicate solution depends on the coating thickness. In the polarization curves test, the corrosion current of the MAO treated alloy is two orders of magnitude lower than that of original samples and the polarization curves in zirconium solution show bigger anode and cathode polarizability which indicates that the MAO coating has a strong blocking effect of the corrosion. The corrosion resistance of MAO treated magnesium AZ91D improves significantly.

Abstract: The corrosion resistance of Ultra-fine grain (UFG) chromium bronze, prepared by Equal-channel angular pressing (ECAP), was investigated at room temperature and atmospheric pressure by electrochemistry technique and immersion experiment. The electrochemistry experiment showed that ECAP processing don’t change the corrosion nature of chromiun bronze, the corrosion potential of UFG chromium bronze is a little more positive than that of CG chromium bronze, the differences are in the range of 10mV-20mV. Meantime, the immersion experiment showed that the UFG chromium bronze is more resistant to corrosion than its CG counterpart. The difference between UFG chromium bronze and its CG counterpart is also significant in terms of corrosion morphology. Though the structure is uniform corrosion, the microstructure is honeycomb-like morphology for CG chromium bronze and the corrosion pit is deeper. The shallower corrosion pits are displayed for UFG chromium bronze and grain drop off in local region.

Abstract: The corrosion behaviors of 304 stainless steel (304SS) which has been cut and 304SS which has not been cut in two different solutions were investigated using polarization curve and electrochemical impedance spectroscopy (EIS) methods. The results show that 304SS which has been cut and 304SS which has not been cut have the similar corrosion voltage in two different solutions. However, the corrosion velocity of 304SS which has been cut is more than 304SS which has not been cut both in the two solutions and the corrosion behaviors of two 304SS in the water solution are better than in the water which has little oil.

Abstract: Individual and combined additions of elements like Si, Sb, Sr are carried out to AZ91 alloy and its microstructure, mechanical properties especially creep properties and corrosion behavior are investigated. In general, additions of the above elements improve the mechanical properties. Further, the results show these alloying elements introduce thermally stable intermetallics and thereby improve the creep performance. Among various additions, Sb addition provides highest creep resistance. With the Si and Sr additions, the corrosion resistance of AZ91 alloy is improved. Detailed micro-mechanisms are also studied and they are correlated with the properties studied.

Abstract: With the development of the ECAP technology, the corrosion behavior of the UFG materials has been investigated in some degree. Two categories of corrosion behaviors of UFG material were discussed in this paper. The large proportion of the non-equilibrium grain boundaries and high residual stress inside of the grain were regarded as the key to affect the corrosion behavior of the UFG materials. The corrosion behavior was also affected by the ECAP factors especially the press pass number and the pressing temperature. Finally some prospects of making UFG materials combined with high mechanical property and good corrosion resistance by ECAP technology were expounded.

Abstract: The corrosion behavior of ultra-fine grain (UFG) copper bulk prepared by equal channel angular pressing (ECAP) was studied in 3.5% NaCl solution. The effect of ECAP deformation on the copper corrosion is controversial in the literature, and worth to verify by means of various experimental techniques. Corrosion performances of UFG copper were investigated in comparison with that in recrystallized coarse grain (CG) copper by polarization curves, Tafel extrapolation method, electrochemical impedance spectroscopy(EIS). The shape of polarization curves and type of corrosive attack remains the same in the UFG and the coarse-grain state. UFG copper exhibited a lower corrosion current and high self-corrosion potential in comparison with CG copper. Electrochemical experimental results showed that UFG copper increased in resistance to corrosion compared with CG copper. This decrease in corrosion resistance was mainly attributed to the more compact corrosion film of UFG copper. The compact passive film led to decrease of the diffusion capability of ions within the corrosion film and corrosion rate.

Abstract: Today’s global exploration of oil and gas leads to a range of highly corrosive environment that, in turn, require corrosion resistant high nickel content alloys for Oil Country Tubular Goods. Aimed at the problem of oil tube corrosion in environment with high content of H2S and CO2, the corrosion behavior of two nickel based alloys in 15%NaCl solution containing H2S/CO2 in high temperature and high pressure environments were researched. The pitting corrosion behavior of Ni-based alloys were investigated in FeCl3 solution by polarization curve and immersion test. The scanning electron microscopy(SEM), energy disperse spectroscopy(EDS) were applied to analyse the microstructure and corrosion performance of the samples. The results showed that the pitting-resistant of G3 was superior to Incoloy825.With the experimental temperature increasing, the corrosion rates increased and some slight corrosion pits appeared on the surface of Incoloy 825, Its maximum corrosion rate was 0.018mm/a. XRD showed that the corrosion films formed on nickel base alloys were consist of NiS, FeS and the oxides of Ni and Cr. The polarization curves showed that there were different corrosion behavior of two alloys, the anodic curve of G3 has an obvious passivation region, and there has higher pitting potential .

Abstract: Cubic oxides with pyrochlore and garnet structures are promising matrices for long-lived actinides immobilization. Their isomorphic capacity with respect to An and REE was determined. To predict the long-term behavior of these matrices under their underground disposal radiation stability of synthetic pyrochlores and garnets was studied. Most of titanate phases have the critical (amorphization) doses close to 0.2 displacements per atom at 298 K. This value is significantly higher for Sn- and Zr-rich pyrochlores. Corrosion behavior of the pyrochlore- and garnet-composed matrices was investigated. The lowest actinides leach rates were observed in water and alkaline solutions most typical for underground waste repositories. Amorphization of the phases has a low influence on their corrosion behavior in solutions. Possibility for joint incorporation of actinides and Tc into zirconate- and titanate-based matrices with the pyrochlore structure is discussed.

Abstract: The ribbon samples for Cu60Zr30Ti10 (at. %) with a thickness of 50 μm and a width of 13 μm were prepared by melt spinning at the wheel speed of 30 m/s. The glassy structure was confirmed by X-ray diffraction (XRD) using Cu Kα radiation. The corrosion property and corrosion mechanism in 1 M HCl, 1 M NaCl, and 0.5 M H2SO4 solutions were investigated by electrochemical polarization measurement. The corrosion mechanisms are dominated by the pitting corrosion in H2SO4 solution and the pitting and uniform corrosion in HCl and NaCl solutions. In addition, the corrosion resistance in H2SO4 solution is better than that in HCl and NaCl solutions. Cu60Zr30Ti10 glassy alloy in H2SO4 solution is nobler than in HCl and NaCl solutions.

Abstract: SiCp/Al composite was fabricated by the method of pressureless-infiltration. In atmospheric environment, the atmospheric corrosion behavior of SiCp/Al composites (ZL101+49%SiC+5%Mg) was studied by mass loss, optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR), respectivelhy.The results show that the corrosion rate of the SiCp/Al composites increases with increasing of time in atmospheric environment. Pitting corrosion is the main characteristic of SiCp/Al composite, and corrosion area gradually extends around with time increasing. At last, sheet like corrosion substrates distribute in the surface of n the SiCp/Al composites. Amorphous Al2O3 and amorphous AlxSO4yOHz are the main corrosion products.