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R Balasubramaniam - One of the best experts on this subject based on the ideXlab platform.
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Effect of cerium addition on the corrosion behaviour of carbon-alloyed iron Aluminides
Corrosion Science, 2006Co-Authors: S. Sriram, R Balasubramaniam, M. N. Mungole, S. Bharagava, R G BaligidadAbstract:Abstract The effect of Ce addition on the microstructure and corrosion behavior of carbon-alloyed iron Aluminides Fe–20.0Al–2.0C, Fe–18.5Al–3.6C and Fe–19.2Al–3.3C–0.07Ce (in at.%) has been studied. The potentiodynamic polarization behaviour of the alloys was evaluated in freely aerated 0.25 mol/l H 2 SO 4 . A 0.05% C steel was used for comparison purposes. All the alloys exhibited active–passive behaviour in the acidic solution. The addition of Ce destroyed passivity as indicated by lower breakdown potentials in polarization studies. This has been related to the finer distribution of the carbides in the microstructure. Corrosion rates were evaluated by immersion testing. The iron Aluminide with Ce addition exhibited a lower corrosion rate compared to the Aluminides without Ce addition. This has been attributed to modifications in surface film with Ce addition. Scanning electron microscopy of corroded surfaces indicated that the carbon-alloyed intermetallics were susceptible to localized galvanic corrosion due to the presence of carbides in the microstructure.
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Hot corrosion of carbon-alloyed Fe3Al-based iron Aluminides
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: R Balasubramaniam, M. N. MungoleAbstract:Abstract The oxidation and hot corrosion behavior of two Fe 3 Al-based iron Aluminides, Fe–25Al and Fe–27.5Al–3.7C (at.%) have been studied at 1100, 1225 and 1330 K. Hot corrosion studies were conducted by coating the specimen surfaces with 2.5±0.2 mg cm −2 of Na 2 SO 4 prior to exposure in pure oxygen. The oxidation kinetics of the carbon-alloyed iron Aluminide were generally slower than that of the binary alloy. Alumina was identified in the scale after oxidation of both the alloys. The rates of hot corrosion were generally higher than the rates of oxidation for both the alloys. The presence of α-Fe 2 O 3 in addition to alumina was indicated by X-ray diffraction analysis of the scales present on the surface of the samples after hot corrosion. Fourier transform infrared spectra from the spalled scales in hot corrosion divulged the presence of α-Al 2 O 3 , α-Fe 2 O 3 and sulfate. Cross-sectional microscopy revealed that the scale–metal interfaces were pitted under hot corrosion conditions and the pits contained aluminum sulfide. Aluminum sulfide was also identified along the grain boundaries in the binary Aluminide matrix below the scale–metal interface. The hot corrosion process has been explained based on sulfide formation and its subsequent oxidation. The lower rate of hot corrosion in the carbon-alloyed iron Aluminide has been related to the blocking effect of carbides, present along the grain boundaries, for the penetrating sulfur.
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hydrogen diffusivity in iron Aluminides determined by subscale microhardness profiling
Scripta Materialia, 1998Co-Authors: P Banerjee, R BalasubramaniamAbstract:It has been well established that the poor ductility of iron Aluminides at ambient temperatures is due to hydrogen embrittlement. Hydrogen is produced by the reaction of moisture with the iron Aluminide and enters the lattice to cause embrittlement. Therefore, one of the important factors that needs to be understood is the diffusion of hydrogen in iron Aluminides. There are relatively few studies that have determined the diffusivity of hydrogen in iron Aluminides. The apparent hydrogen diffusion coefficient can be easily measured by the technique of subsurface microhardness profiling after cathodic hydrogen charging. This technique has been utilized to determine room temperature hydrogen diffusivity in Al-Li alloys and several austenitic stainless steels. A similar technique was also used to determine high temperature oxygen and nitrogen diffusivities in titanium Aluminides. The aim of the present paper is to determine the diffusivity of hydrogen, in stoichiometric Fe{sub 3}Al and iron Aluminides alloyed with Cr nd Ti, by this technique.
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deciphering the potentiodynamic polarization curves of iron Aluminides fe3al and fe3al cr
Bulletin of Materials Science, 1996Co-Authors: Sagato Mukherjee, R BalasubramaniamAbstract:The potentiodynamic polarization curves of Fe3Al and Fe3Al + Cr intermetallics obtained in aerated pH 4 H2SO4 acidic solution have been theoretically analyzed. The role of chromium in minimizing the hydrogen embrittlement (HE) of the intermetallic Fe3Al (resulting in its poor ductility) has been addressed based on the analysis. In the case of the chromium-alloyed iron Aluminide, calculations indicate that hydrogen liberation does not occur on the surface due to the shift of the corrosion mixed potential to a value nobler than the electrode potential for the hydrogen evolution reaction. This shift occurs due to the induction of passivity on alloying with Cr resulting in the formation of a passive film. The minimization of HE of iron Aluminides on alloying with Cr can thus be understood.
Christoph Kenel - One of the best experts on this subject based on the ideXlab platform.
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microstructure and oxide particle stability in a novel ods γ tial alloy processed by spark plasma sintering and laser additive manufacturing
Intermetallics, 2017Co-Authors: Christoph Kenel, Karl Dawson, Josh Barras, Carl Hauser, Georgia Dasargyri, Thomas Bauer, Alberto Colella, Adriaan B Spierings, G J TatlockAbstract:Abstract In this work, a novel oxide dispersion strengthened titanium Aluminide alloy (Ti-45Al-3Nb- 2 O 3 at.%) was developed for powder-based processing technologies with a focus on spark plasma sintering and additive manufacturing. Titanium Aluminides are promising structural intermetallics for weight reduction and an increased performance of high temperature components. The alloy design and selection process was supported by computational thermodynamics based on the CALPHAD approach, taking into account requirements for processing as well as long term alloy behavior under service conditions. Processing trials using spark plasma sintering, direct metal deposition and selective laser melting were conducted to study the alloy behavior, microstructure formation and introduction as well as stability of the ODS particles. Additionally, thermal annealing on the sintered and laser consolidated material was performed. Conventional dual phase α 2 -Ti 3 Al and γ-TiAl duplex and near-lamellar microstructures were obtained from the processed material. The ODS particles were homogeneously distributed in the alloy matrix after processing in the liquid state. For the direct metal deposition process, the novel alloy was compared to the established GE48-2-2 alloy (Ti-48Al-2Cr-2Nb) in terms of phases, microstructure and texture after processing. A significantly reduced texture formation was observed with the novel alloy. The hardness of the consolidated material shows superior properties for ODS-containing TiAl compared to ODS-free material. This work provides a first step towards tailored alloys for AM and the production of ODS TiAl alloys.
M. N. Mungole - One of the best experts on this subject based on the ideXlab platform.
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Effect of cerium addition on the corrosion behaviour of carbon-alloyed iron Aluminides
Corrosion Science, 2006Co-Authors: S. Sriram, R Balasubramaniam, M. N. Mungole, S. Bharagava, R G BaligidadAbstract:Abstract The effect of Ce addition on the microstructure and corrosion behavior of carbon-alloyed iron Aluminides Fe–20.0Al–2.0C, Fe–18.5Al–3.6C and Fe–19.2Al–3.3C–0.07Ce (in at.%) has been studied. The potentiodynamic polarization behaviour of the alloys was evaluated in freely aerated 0.25 mol/l H 2 SO 4 . A 0.05% C steel was used for comparison purposes. All the alloys exhibited active–passive behaviour in the acidic solution. The addition of Ce destroyed passivity as indicated by lower breakdown potentials in polarization studies. This has been related to the finer distribution of the carbides in the microstructure. Corrosion rates were evaluated by immersion testing. The iron Aluminide with Ce addition exhibited a lower corrosion rate compared to the Aluminides without Ce addition. This has been attributed to modifications in surface film with Ce addition. Scanning electron microscopy of corroded surfaces indicated that the carbon-alloyed intermetallics were susceptible to localized galvanic corrosion due to the presence of carbides in the microstructure.
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Hot corrosion of carbon-alloyed Fe3Al-based iron Aluminides
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: R Balasubramaniam, M. N. MungoleAbstract:Abstract The oxidation and hot corrosion behavior of two Fe 3 Al-based iron Aluminides, Fe–25Al and Fe–27.5Al–3.7C (at.%) have been studied at 1100, 1225 and 1330 K. Hot corrosion studies were conducted by coating the specimen surfaces with 2.5±0.2 mg cm −2 of Na 2 SO 4 prior to exposure in pure oxygen. The oxidation kinetics of the carbon-alloyed iron Aluminide were generally slower than that of the binary alloy. Alumina was identified in the scale after oxidation of both the alloys. The rates of hot corrosion were generally higher than the rates of oxidation for both the alloys. The presence of α-Fe 2 O 3 in addition to alumina was indicated by X-ray diffraction analysis of the scales present on the surface of the samples after hot corrosion. Fourier transform infrared spectra from the spalled scales in hot corrosion divulged the presence of α-Al 2 O 3 , α-Fe 2 O 3 and sulfate. Cross-sectional microscopy revealed that the scale–metal interfaces were pitted under hot corrosion conditions and the pits contained aluminum sulfide. Aluminum sulfide was also identified along the grain boundaries in the binary Aluminide matrix below the scale–metal interface. The hot corrosion process has been explained based on sulfide formation and its subsequent oxidation. The lower rate of hot corrosion in the carbon-alloyed iron Aluminide has been related to the blocking effect of carbides, present along the grain boundaries, for the penetrating sulfur.
Pibo Liao - One of the best experts on this subject based on the ideXlab platform.
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microstructure and high temperature corrosion behaviors of Aluminide coatings by low temperature pack aluminizing process
Applied Surface Science, 2010Co-Authors: Zhaolin Zhan, Zhong Liu, Jianxiong Liu, Pibo LiaoAbstract:Abstract Aluminide coatings were produced on carbon steel and Fe–5Cr–Mo alloy at a relatively lower temperature below 600 °C in shorter treatment time by a combination of surface refinement process and pack aluminizing process. Repetitive ball impact, generated by mechanical vibration, caused the top-layer refinement of substrates in a conventional pack aluminizing process. The effects of temperature and treatment time on the formation of Aluminide coatings were analyzed. The microstructure of the coatings was investigated by SEM, AFM and XRD. The Aluminide coatings were one-layer, compacted structure with ultrafine grains and uniform elemental distribution. High-temperature oxidation and sulphidation tests were carried out at 600 °C in air for 200 h and 10% SO 2 + Ar gas mixture atmosphere for 50 h, respectively. The mass gains and spallation indicated that the Aluminide coatings significantly improved the high-temperature oxidation and sulphidation resistance.
Ramesh Balasubramaniam - One of the best experts on this subject based on the ideXlab platform.
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hydrogen in iron Aluminides
Journal of Alloys and Compounds, 2002Co-Authors: Ramesh BalasubramaniamAbstract:Abstract Ordered intermetallic alloys based on the stoichiometric iron Aluminide compositions of Fe3Al and FeAl are being actively considered for high-temperature structural applications. They exhibit poor room temperature ductilities due to hydrogen embrittlement. Surface passive films reduce embrittlement by lowering the rate of hydrogen liberation on the surface. This has been explained by the mixed potential theory. The mechanism of hydrogen embrittlement in iron Aluminides (namely, decohesion) has been addressed. Methods to minimize the degree of embrittlement have been discussed. These include passivity induction, addition of oxygen active elements, recrystallization inhibition and addition of irreversible hydrogen traps. The diffusion of hydrogen in iron Aluminides has also been reviewed.
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Role of surface passive films in the hydrogen embrittlement of iron Aluminides
Bulletin of Materials Science, 1996Co-Authors: Arvind Agarwal, Ramesh BalasubramaniamAbstract:The room temperature hydrogen embrittlement problem in iron Aluminides has restricted their use as high temperature structural materials. Previous studies have established that surface films affect hydrogen embrittlement (HE). The effect of surface passive layer on the hydrogen embrittlement behaviour of iron Aluminides has been critically reviewed in this presentation. The role of thermomechanical treatments in affecting the mechanical properties has been discussed from a processing-structure-properties correlation view point. The alloy development philosophy to yield ductile iron Aluminides has been outlined based on this review. Novel iron Aluminide intermetallics that are being currently synthesized and characterized along these lines at IIT Kanpur are finally introduced.