S.E. Kuri

Corrosion resistance of amorphous and nanocrystalline Fe–M–B (MZr, Nb) alloys

Amorphous Fe‐M‐B (M‚Zr, Nb) based alloys with nanometer-sized crystallites have attracted attention due to their magnetic properties. Although corrosion resistance is a desirable property in such alloys, no study concerning this aspect has been reported. The eAect of metalloid content and partial crystallization on corrosion resistance of Fe‐M‐B (M‚Zr, Nb) amorphous alloys, Fe84Nb7B9 ,F e 84Zr7B9 and Fe83Zr3:5Nb3:5B9Cu1, was investigated. Corrosion resistance measurements were carried out by mass loss, potentiodynamic polarization, and thermogravimetric mass gain measurements. The partial crystallization of the amorphous alloy results in a decrease of the corrosion resistance for all the compositions analyzed. We also observed a greater corrosion resistance when Nb was present in comparison to the case when Zr was present. These results are an eAect of the superficial passive film protector formed. ” 2000 Published by Elsevier Science B.V. All rights reserved.

Corrosion resistance of amorphous and polycrystalline FeCuNbSiB alloys in sulphuric acid solution

Abstract The influence of structural changes such as structural relaxation and crystallization on the corrosion resistance of the amorphous Fe74Cu1Nb3Si13.5B8.5 alloy in 0.1M sulphuric acid was investigated. A controlled crystallization of such amorphous alloy leads to nanocrystalline microstructure which increases the corrosion resistance, whereas structural relaxation of amorphous alloy results in reduced corrosion resistance. Different conditions of relaxation (330°C and 380°C) and structural crystallization (554°C and 610°C) were analyzed.

Influence of Nb content on the corrosion resistance and saturation magnetic density of FeCuNbSiB alloys

Abstract Nanocrystalline FeCuNbSiB alloys obtained from the partial crystallization of amorphous alloys have attracted technological attention due to their excellent magnetic properties, but the relationship between corrosion resistance and magnetic properties is not well established. The influence of Nb as an alloying element and effect of partial crystallization on the corrosion resistance of Fe73.5Si13.5B10Cu1, Fe73.5Si13.5B7Nb3Cu1 and Fe73.5Si13.5B5Nb5Cu1 amorphous alloys were studied and the effect of corrosion on magnetization saturation flux density, Bs, was investigated. The addition of niobium on amorphous alloys increases the corrosion resistance. The raise of Nb content from 3 to 5% increases the corrosion resistance also. A partial crystallization increases the corrosion resistance of the samples with Nb. However, in the samples without Nb, the partial crystallization diminishes the corrosion resistance. The values of Bs depend on the alloy corrosion resistance.

Influence of the corrosion on the saturation magnetic density of amorphous and nanocrystalline Fe73Nb3Si15.5B7.5Cu1 and Fe80Zr3.5Nb3.5B12Cu1 alloys

Abstract Amorphous FeMBCu (M=Nb, Zr) and FeNbSiBCu alloys with nanometer size crystallites have attracted attention due to their soft magnetic properties. The mechanism through which crystallization affects the corrosion and the comparative effect of corrosion on magnetic properties of FeMBCu (M=Nb, Zr) and FeNbSiBCu alloys has not yet been evaluated. In this paper the effect of partial crystallization on corrosion resistance of amorphous Fe 73 Nb 3 Si 15.5 B 7.5 Cu 1 and Fe 80 Zr 3.5 Nb 3.5 B 12 Cu 1 alloy ribbons and the comparative effect of corrosion on saturation magnetic flux density, Bs, of these alloys were investigated. The samples were characterized by X-ray diffraction, differential scanning calorimetry and X-ray photoelectron spectroscopy. Corrosion resistance evaluation was carried out by measuring mass loss of samples immersed in 0.1 M H 2 SO 4 solution, and by measuring potentiodynamic polarization curves (potential vs. current). Saturation magnetic flux density, Bs, of the samples were measured. After partial crystallization of Fe 80 Zr 3.5 Nb 3.5 B 12 Cu 1 amorphous sample the corrosion resistance decreased, while for the Fe 73 Nb 3 Si 15.5 B 7.5 Cu 1 the corrosion resistance increased. The decrease of Bs after treatment in the corrosion solution as observed in the nanocrystalline Fe 80 Zr 3.5 Nb 3.5 B 12 Cu 1 sample was larger than that observed for both amorphous and the nanocrystalline Fe 73 Nb 3 Si 15.5 B 7.5 Cu 1 samples after the same treatment.

Corrosão metálica associada ao uso de combustíveis minerais e biocombustíveis

Fuels and biofuels have a major importance in the transportation sector of any country, contributing to their economic development. The utilization of these fuels implies their closer contact to metallic materials, which comprise vehicle, storage, and transportation systems. Thus, metallic corrosion could be related to fuels and biofuels utilization. Specially, the corrosion associated to gasoline, ethanol, diesel, biodiesel, and their mixtures is discussed in this article. Briefly, the ethanol is the most corrosive and gasoline the least. Few investigations about the effect of biodiesel indicate that the corrosion is associated to their unsaturation degree and the corrosion of diesel is related to its acidity.

Effect of thermal aging conditions on the corrosion properties and hardness of a duplex stainless steel

The corrosion properties of a 22.5 wt. (%) Cr duplex stainless steel were investigated after long-term aging of 3000, 5000 and 7000 hours at 300 and 400 oC. The corrosion resistance was measured based on mass loss in a FeCl3 10 wt. (%) solution and electrochemical measurements in a 0.1 M H2SO4 solution. The results indicate that the corrosion resistance decreased steadily up to 5000 hours of aging. However, the samples subjected to 7000 hours of aging showed better corrosion resistance than those aged for 3000 and 5000 hours. This effect is attributed to the phase transformation that occurs during aging, a finding which was confirmed by hardness, transmission electron microscopy and X-ray photoelectron spectroscopy measurements.

Localized Corrosion Susceptibility of Supermartensitic Stainless Steel in Welded Joints

Abstract Supermartensitic stainless steels is known for its better weld-ability and corrosion resistance compared to the conventional martensitic, mainly due to its lower carbon content. This enables the production of welded joints with superior resistance to hydrogen embrittlement and to sensitization, particularly in the heat-affected zone. These characteristics can be optimized with the production of weldments using high-power density processes, such as electron beam welding. This process creates a narrow heat-affected zone with a high thermal gradient, which makes it less susceptible to precipitation, particularly to chromium carbides. Thus, its pitting potential is improved.

Probing the duplex stainless steel phases via magnetic force microscopy

Duplex stainless steels are austenitic-ferritic alloys used in many applications, thanks to their excellent mechanical properties and high corrosion resistance. In this work, chemical analyses, x-ray diffraction, and magnetic force microscopy (MFM) were employed to characterize the solution annealed and aged duplex stainless steel. The samples exhibited no changes in lattice parameters and the MFM technique proved successful in clearly imaging the magnetic domain structure of the ferrite phase.

Influence of composition and partial crystallization on corrosion resistance of amorphous Fe–M–B–Cu (M=Zr, Nb, Mo) alloys

Abstract The corrosion resistance of Fe–M–B–Cu alloys in which M is a transition metal of two first series, particularly concerning the effect of composition and also concerning the affect of corrosion on magnetic properties have not been evaluated. In this paper, the effect of composition and partial crystallization on corrosion resistance of Fe 80 Nb 3.5 Zr 3.5 B 12 Cu 1 , Fe 80 Nb 3.5 Mo 3.5 B 12 Cu 1 , Fe 80 Zr 3.5 Mo 3.5 B 12 Cu 1 and Fe 80 Mo 7 B 12 Cu 1 amorphous alloys and its effect on saturation magnetic flux density, B s , were investigated using 0.1 M H 2 SO 4 solutions. Corrosion resistance measurements were carried out by mass loss, potentiodynamic polarization, and potentiostatic polarization. Greater corrosion resistance is observed in alloys with Nb addition and the smaller resistance in alloys containing only Mo. The alloy with Zr and Mo has an intermediate corrosion resistance. This result was related to the protective passive film of the alloys. Crystallization decreases the corrosion resistance of the amorphous alloys for every composition analyzed. The decrease in saturation magnetic flux density, B s , with immersion in a corrosive solution and a dependence of this decrease as corrosion resistance of alloys analyzed, show that control of the corrosion phenomena in these alloys is necessary for applications in which the magnitude of B s is important.

Evaluation of Metallic Corrosion Caused by Alcohol Fuel and Some Contaminants

In the present work, it is evaluated the effect of water and other contaminants of alcohol fuel on the corrosion behavior of different materials, which can constitute vehicles, storage and transportation fuels systems. For such, 5 metallic materials (zamak, low-carbon steel, stainless steel, and two Al alloys) were chosen and 5 alcoholic solutions were prepared: anhydrous ethanol (AEAC; solution 1); hydrated ethanol (AEHC; solution 2); AEAC and water with some impurities (AEAC + 6 % “corrosive” water; solution 3); AEHC and water with some impurities (AEHC + 6 % “corrosive” water; solution 4); and, AEAC and tap water (AEAC + 6 % tap water; solution 5). The crevice corrosion was investigated in static immersion tests, which were carried out at 50 °C for 2 months. The evaluation of the corrosive process was carried out by visual inspection, weight loss, optic microscopy, and scanning electron microscopy (SEM). Also, some quality parameters of the alcoholic solutions (specific mass, alcoholic content, pH, and conductivity) was analyzed in order to determine the influence of corrosion of the materials on them. The results have shown that crevice corrosion of all materials mostly occurred in solutions 3-5, which had a high amount of water and impurities. Some corrosion rates in such solutions were 90-400 times higher than those obtained in AEAC and AEHC. Among the materials, zamak and carbon steel suffered severe corrosive attack. The physicochemical properties of alcoholic solutions employed in the tests also changed, mainly the increase of pH and conductivity was observed. Therefore, the results demonstrate that the quality control of alcohol fuel is essential in order to avoid the damage of engine parts and storage and transportation systems. Specially, water, sulphate, chloride and acetate content must be monitored.