Papers by Keyword: Corrosion

Abstract: In this study, microstructure and corrosion behaviour of homogenized Mg-4Zn-1La magnesium alloy was investigated. Mg-4Zn-1La alloy was produced by low-pressure die casting method. Homogenization treatments were performed at 350 °C and 400 °C for 12, 18, 24 and 48 hours, followed by rapid cooling in water at room temperature. Microstructure characterizations showed that La addition led to a formation of semi-continuous network structure and islands of second phases which identified as T-phase (Mg₇Zn₃RE). A significant amount of second phase dissolution and an increase in a-Mg grain size with increasing both homogenization time and temperature was observed. Homogenization treatment led to an improvement in corrosion resistance of Mg-4Zn-1La alloy. Homogenization at 400 °C resulted in better corrosion resistance than homogenization at 350 °C for all homogenization duration.

Abstract: In recent years, more and more attention has been paid to the effect of stray current on the properties of cement-base materials in subway engineering. In the actual service process, reinforced cement-based systems suffer from various erosive conditions, the degradation mechanisms in reinforced cement-based systems due to the combined effects of stray current and environmental multi-factors have been a serious problem in civil engineering for many years. This paper reviews the research achievements on the properties of cement-based materials under the multi-factor coupling conditions such as stray current and soft water, chloride ion, sulfate, stress, freezing and thawing cycle and so on. Furthermore, the improvement of cement-based materials on stray current resistance is also generalized in it. Prospects of cement-based materials for durability under environment multi-factor coupling actions are also presented.

Abstract: Corrosion protection of equipment, apparatus and thermal-stressed metal structures (which refer to equipment of fuel and power industries) operated under conditions of chemical manufacturing processes is the prime industrial target. Corrosive medium causes changes in material structure and properties resulting in decreased strength and premature damage of equipment [1].The subject of research is the system of thermal resistant protective coating for extreme operation conditions.The objective of the study is technology development of protective organic coating with predictable properties within the long-term operation of real gas-compressor units. The research resulted in improved procedure of thermogradient coatings application with positive progress due to the modification of layers of heat-resistant paintwork materials [2].

Abstract: Cyclic voltammetry and potentiostatic polarization have been applied to study the electrochemical behavior and to determine the corrosion resistance of nitinol, which surface was modified with silicon using plasma-immersion ion implantation, in 0.9% NaCl solution and in artificial blood plasma. It was found out that continuous, and also homogeneous in composition, thin Si-containing layers are resistant to corrosion damage at high positive potentials in artificial physiological solutions due to the formation of stable passive films. Breakdown potential Eb of Si-modified NiTi depends on the character of silicon and Ni distribution at the alloy surface, Eb values amounted to 0.9–1.5 V (Ag/AgCl/KCl sat.) for the alloy samples with continuous Si-containing surface layers and with decreased Ni surface concentration.

Abstract: Fiber-Metal-Laminates (FML) show superior dynamic mechanical properties combined with low densities. The mechanical performance of for example commercially available fiber-metal-laminate, glass laminate aluminum reinforced epoxy, can be improved by the substitution of glass fibers with carbon fibers. However, carbon fiber reinforced aluminum laminate introduces a mismatch of coefficients of thermal expansion and the possibility of galvanic corrosion. The fiber-metal-laminate is altered by the integration of an elastomer interlayer which is desired to solve both problems. The high electrical resistance is supposed to inhibit the corrosion. This study focuses on the effect of galvanic corrosion caused by neutral salt spray tests on fiber-metal-laminates, the influence of an elastomer interlayer and the quantification of the residual mechanical properties. The galvanic corrosion affects the interfaces of the laminates, therefore in this study edge shear tests and flexural tests were carried out to quantify the residual properties and thereby the corrosive damage. The elastomer interlayer was found to inhibit galvanic corrosion in the salt spray chamber, whereas the fiber-metal-laminate without interlayer showed corrosive damage. Furthermore, the mechanical properties of the fiber-metal-laminate with elastomer interlayer remained constant after the corrosion tests, whilst the fiber-metal-laminate’s properties decreased with corrosive loads.

Abstract: With the increase of environmental restrictions, chromium and cadmium-based coatings have been replaced by zinc layers. These coatings can be obtained through electrodeposition, whose industrially established pH range is from 5.0 to 5.8, and stirring speed is uncontrolled, which has led to part rejections. In addition, the corrosion resistance of zinc coatings is inferior to cadmium and chromium coatings, which has boosted the research of zinc composite coatings. The proposed work presents the performance of zinc-bentonite composite coatings in regards to corrosion relating to pH variation and stirring speed. The samples were degreased for 5 minutes in a commercial degreasing solution at a temperature of 55 °C, with magnetic stirring and, posteriorly, submitted to a pickling process with a duration of 1 to 2 minutes in a commercial bath, followed by a washing process with deionized water. The electrolyte used for electrodeposition was a zinc bath with a chemical composition of 85 g/l ZnCl₂, 210 g/l KCl and 25 g/l H₃BO₃. For the zinc-bentonite electrodepositions 20 g/l of bentonite nanoparticles was added to the bath. Zinc and zinc-bentonite coatings were characterized by scanning electron microscopy, open circuit potential and potentiodynamic polarization. This work shows that a 5.2 pH is the most recommended for the zinc electrodeposition process. Potentiodynamic polarization tests indicated that pure zinc coatings developed in the stirring speed of 380 rpm and zinc-bentonite produced in the stirring speed of 710 rpm showed the best results.

Abstract: Recent studies have focused on the development of metastable beta-type Ti alloys with non-toxic elements such as Nb, Ta, Mo and Zr for biomedical applications. These alloys present low modulus, good mechanical compatibility and good corrosion resistance. Moreover, the processing variables can be controlled to produce microstructures with specific properties. In this regard, the objective of this work was to analyze the electrochemical behavior of Ti-13Nb-12Mo alloy hot forged and aged at 500 °C/24 h. The microstructure was analyzed by transmission electron microscopy. The corrosion tests were carried out under a NaCl solution at a temperature of 25 °C. The results showed that under the conditions studied Ti-12Mo-13Nb alloy exhibited passivation, which is desirable for corrosion resistance. Therefore the alloy is a potential alternative for the of Ti-6Al-4V used in orthopedic implants.

Abstract: The pack-cementation is one of economical, efficient coating processes for Fe-base alloys. It can provide good protection against high-temperature oxidation and corrosion. In this study, the high-temperature corrosion behavior of the aluminized diffusion-coating on low-carbon T20 steel (Fe-2.0Cr-0.5Mo-0.8Mn-0.3S in at.%) was studied at 800 °C in N₂/H₂O/H₂S-mixed gas. The aluminized coating consisted of Fe₃Al. The aluminized T20 steel after corrosion at 800 °C for 10~100h in N₂/H₂O/H₂S-mixed gases, the scale formed on the Fe₃Al coating consisted primarily of α-Al₂O₃, Al₂S₃, FeAl₂O₄ and FeO, with relatively slow scaling rates. The Fe₃Al intermetallics has reasonable corrosion-and oxidation-resistance, because it can form a protective alumina scale. Without the aluminized diffusion-coating, T20 steel corroded fast with serious scale failure. At the surface, coarse FeS grains with cracks formed. Since FeS has a very high concentration of cation vacancies, it grew fast through the outward diffusion of Fe²⁺ ions.

Abstract: This study aimed to understand the effect of a different binder on fundamental properties and corrosion behavior of WC based HVOF coatings. Three kinds of coatings, each with a different binder, were prepared using commercial feedstock powders, i.e. WC-12Co, WC-10Co4Cr and WC-12Ni. Micro Vickers hardness tester, XRD and SEM were used. The corrosion performance was evaluated using a salt spray tester. It was found that the WC-10Co4Cr coating showed the highest corrosion resistance and superior hardness comparable to the WC-12Co coating.

Abstract: The 5083 aluminum alloy was prepared and subjected to cryogenic rolling (CR) after heat treatment. The samples were reduced from 15mm to 1.5 mm in the thickness direction and the amount of deformation was 90%. For comparison, samples with the same deformation amount were obtained by room temperature rolling (RTR). The corrosion behavior of CR and RTR samples was measured by electrochemical test, and their microstructures before and after corrosion had been studied through electron scanning microscopy (SEM) and optical microscope (OM). The influence of cryogenic rolling on the corrosion behavior of 5083 aluminum alloys was explored. The experiment results suggested that anti-corrosion ability of 5083 aluminum alloys could be enhanced through cryogenic rolling. The corrosion potential elevated and the corrosion current density reduced according to the electrochemical test. The primary reasons and corresponding mechanism were also discussed.