Papers by Keyword: Corrosion

Abstract: The microstructure of Al-6Mg-0.9Mn-0.07Zr-0.2Er (wt.%), registered as 5E61 alloy, were investigated using optical microscopy, scanning electron microscopy and transmission electron microscopy. The results showed that the addition of 0.2 wt.% Er can refine the dendritic structure and form fine and coherent L1₂ structured Al₃(Er_xZr_1-x) precipitates in the alloy. After a two-stage homogenization (280°C/10h, 460°C/36h), the recrystallization temperature of the alloy with 0.2 wt.% Er is about 15°C higher than that of the alloy without Er. The better recrystallization resistance may be related to the Al₃(Er_xZr_1-x) precipitates, which can pin on dislocations and sub-grain boundaries. The hardness of the cold-rolled alloy with 0.2 wt.% Er is 143HV, which is 5% higher than the alloy without Er. The exfoliation corrosion and nitric acid mass loss test were also performed. The exfoliation corrosion of the alloy is N grade, and the mass loss is only 9.84mg/cm².

Abstract: Crevice corrosion of 3.5NiCrMoV and 13Cr steels, which are used as low-pressure (LP) steam turbine materials, was investigated by electrochemical corrosion tests in the simulated boiler water contained chloride and sulfate ions. For 3.5NiCrMoV steel, by comparison with the surfaces outside crevice, the surfaces inside crevice of the specimens coupled with both of the same steel and 13Cr steel showed no remarkably corroded pattern even though pitting corrosion was observed. The specimen of 13Cr steel coupled with the same steel plate exhibited pitting corrosion inside the crevice, and a lower open cycle potential (Ocp) than the single plate of 13Cr steel. On the other hand, the specimen of 13Cr steel coupled with 3.5NiCrMoV steel plate showed the lowest Ocp, as the anodic dissolutions of 3.5NiCrMoV steel became the dominate corrosion mechanism.

Abstract: Permanent mold cast (PMC) AJ62 magnesium alloy exhibits a fine-grained microstructure in the thin section and a coarse-grained microstructure in the thick section. Microstructure of the PMC AJ 62 alloy was analyzed by using the Scanning Electron Microscopy (SEM). Potentiodynamic polarization experiments were performed to investigate the corrosion resistances of the PMC AJ62 alloys in salt solutions and engine coolant. The corrosion behaviors in the fine- and coarse-grained AJ62 alloys were compared. The results show that the AJ62 alloy with fine microstructure presents enhanced corrosion resistance.

Abstract: The nickel-iron-chromium-based alloy, Incoloy alloy 800, was corroded at 600, 700 and 800 °C for 10-70 h under 1 atm of total pressure in three different atmospheres, viz., 1 atm of N₂, N₂/H₂O, and N₂/H₂O/H₂S-mixed gases. The corrosion rates always increased with addition of H₂O and, much more seriously, with the addition of H₂S gas. In N₂ and N₂/H₂O gases, oxidation prevailed. In N₂/H₂O/H₂S gases, sulfidation dominated. The corrosion resistance increased in the T22 steel displayed better resistance to oxidation and sulfidation than Fe-2Mn-0.5Si steel, owing to the presence of Cr. Strong enrichment of Cr and the presence of Ni and Fe were noticeable in the inner scale. Chromium sulfidized to FeCr₂S₄ in N₂/H₂O/H₂S gases, which was responsible for the enhanced sulfidation resistance of T22 compared with Fe-2.0Mn-0.5Si steel.

Abstract: Due to their specific properties magnesium and magnesium alloys find huge application possibilities mainly in automotive, engineering, transport and space industry. Important properties of magnesium alloys for engineering applications are high specific strength and high internal dumping values, while biocompatibility, biotoxicity and biodegradability open them the possibility to be used for biomedical applications. Development of new biodegradable magnesium alloys, investigation of new production and processing technologies on their properties and evaluation of corrosion degradation in simulated body fluids solutions are the main topics of the last decades.The paper offers a method simulating in-vivo tests for description of the corrosion process of potential biomedical materials in time using atomic force microscopy (AFM). To prove the proposed methodology detailed analysis of the corrosion degradation of AZ31 cast magnesium alloy in flowing Hanks’ balanced salt solution (HBSS) was performed. Corrosion degradation process of the examined alloy was influenced by different microstructural features and their interfaces. Results of the created corrosion galvanic cells and the corrosion attack evolution on the interface of the present intermetallic phases and the matrix led to profile changes detected by AFM.

Abstract: This work is focused on the austenite decomposition in Cr-Mn-N austenitic stainless steels. The experimental steels was solution heat treated (1100°C/30 min. followed by water quenching) and then annealed in the temperature range from 650 to 900°C for holding time 5 min. to 100 hours for the study of precipitation. The precipitation behaviour during isothermal aging was investigated using light optical microscopy, transmission electron microscopy, selected area diffraction and energy-dispersive X-ray spectroscopy. The results show that the phase composition of the precipitates depends on the chemical composition of the experimental steel. The critical temperature of precipitation is 825°C with the corresponding time 100 s.

Abstract: The Late Bronze Age copper mining site “Gasteil Cu I” (ca 1050–850 BC) is located in the district of Neunkirchen, Lower Austria. Since 2010 five excavation campaigns took place and many artifacts as well as corroded metallic droplets were discovered. Two of these droplets were investigated by metallography. At the droplet ́s surface tin was measured, indicating that these droplets are formed during bronze casting. The small droplet is severely corroded but in its core the original bronze alloy is still present. The analysis showed about 10 wt.% Sn. The microstructure is characterized by a Cu-Sn solid solution and a Cu-Sn intermetallic phase. Additionally small amounts of Cu₂S were observed in the metallic core. The corroded rim contains oxides and hydroxides of Cu and Sn and other impurities like Ca, P, Si, S and Fe. Analyzing the corrosion products, Sn concentrations up to 40 wt.% were measured. This enrichment can be explained by a simultaneous formation of insoluble SnO₂ and Cu ions, which were transported to the surface. Surprisingly, the other large droplet has a corroded core and metallic phases are remaining at the rim. The microstructures of the corrosion products reflect the original casting microstructures of the bronze.

Abstract: The exploitation durability of Kaplan hydraulic turbines blades is first of all determined by their structure, by the steel elaboration technology, respectively by the content of non-metallic inclusions and later by the physical-chemical parameters of the exploitation environment.This paper presents a study regarding the situations in which the elaboration-casting technology of Kaplan blades using alloyed austenitic stainless steel, X5CrNiMo17-13-3 which has an important role in the quality of castings. Thus, the authors verify the formation of sulfides and of oxi-sufides during the steel elaboration process, treatment during a liquid state and their influence in the castings behavior to wearing. It is a well known fact that the presence of sulfides and oxi-sufides in the cast blades structure accelerates the corrosion process in contact with river waters.

Abstract: Corrosion properties of Sn-0.7Cu solder were investigated in 1 M HCl. The scanning rates used were 0.5, 1.0, 1.5 and 2.0 mVs^-1 to study the aggressiveness level of HCl electrolyte in various environment. The morphological, elemental and structural of the samples were compared before and after the corrosion. Scan rate 1.0 mVs^-1 was chosen as the most optimum scan rate during corrosion analysis. The morphological analysis observed two types of corrosion product which is compacted and loosely-compacted corrosion product after the samples was polarized in 1 M HCl.

Abstract: The corrosion properties of Sn-9Zn lead-free solder was studied through potentiodynamic polarization in different concentration of hydrochloric acid (0.5, 1.0, 1.5, 2.0 M). Two types of polarization profile were observed for Sn-9Zn solder at lower concentration acid (0.5 to 1.0 M) and one at higher concentration acids (1.5 to 2.0 M). The morphological analysis showed that two distinctive structures of lamellar-like groove and irregular shaped of the corrosion product compounds formed on the solder surface after being polarized at different concentrations. Phase and elemental analyses revealed the formation of mixed corrosion product such as SnO, SnO₂, ZnO, ZnO₂, and Zn(OH)₂ on the surface after polarization.