• R Balasubramaniam

      Articles written in Bulletin of Materials Science

    • Corrosion of carbon-alloyed iron aluminides

      M Sen R Balasubramaniam A V Ramesh Kumar

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      The corrosion behaviour of two carbon-alloyed intermetallics of composition Fe-28.1Al-2.1C and Fe-27.5Al-3.7C has been studied and compared with that of binary intermetallics. Potentiodynamic polarization studies indicated that the intermetallics exhibited active-passive behaviour in an acidic solution of pH = 1, whereas they exhibited stable passivity in a buffer solution of pH 8.4. Corrosion rates were also obtained by immersion testing. The variation of corrosion rate as a function of time was similar for both the intermetallics. The variation in corrosion rate as a function of time has been explained based on the observed potentiodynamic polarization behaviour. Scanning electron microscopy of corroded surfaces indicated that the carbon-alloyed intermetallics were susceptible to galvanic corrosion, due to the presence of carbides.

    • Characterization of ancient Indian iron and entrapped slag inclusions using electron, photon and nuclear microprobes

      P Dillmann R Balasubramaniam

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      Compositional and structural information were obtained from an ancient 1600-year old Indian iron using microprobe techniques (EDS, 𝜇XRD and 𝜇PIXE). Several different local locations in the iron matrix and in the entrapped slag inclusions were analyzed. The P content of the metallic iron matrix was very heterogeneous. Lower P contents were observed in the regions near slag inclusions. This was correlated to the dephosphorization capacity of the slag. The crystallized phases identified in the slag inclusions were wüstite and fayalite. The compositions of the slag inclusions were relatively homogeneous.

    • On critical hydrogen concentration for hydrogen embrittlement of Fe3Al

      A Priyadarshi R Balasubramaniam

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      The critical hydrogen concentration for hydrogen embrittlement in iron aluminide, Fe3Al has been estimated (0.42 wppm). The estimated critical hydrogen content has been correlated to structural aspects of the decohesion mechanism of hydrogen embrittlement.

    • Effect of hydrogen on the mechanical behaviour of carbon-alloyed Fe3Al-based iron aluminides

      M Sen R Balasubramaniam

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      The effect of hydrogen on the mechanical behaviour of two carbon-alloyed iron aluminides was studied. Weakening of some carbide–metal interfaces in the presence of hydrogen was indicated. The effect of cathodic hydrogen charging on the microstructure has also been addressed.

    • Alloy design of ductile phosphoric iron: Ideas from archaeometallurgy

      Gouthama R Balasubramaniam

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      Alloy design criteria to produce ductile phosphoric irons have been proposed based on a detailed microstructural study of ancient Indian irons. The alloy design aims at avoiding phosphorus segregation to the grain boundaries by

      soaking the phosphoric iron at high temperatures within the ferrite + austenite region to precipitate austenite allotriomorphs,

      utilizing a critical amount of carbon to segregate to grain boundaries, and

      precipitation of some of the phosphorus in solid solution in the ferrite matrix as fine coherent phosphide precipitates.

    • Material characterization of ancient Indian copper

      A Srivastava R Balasubramaniam

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      A chalcolithic (2350–1800 BC) copper chisel from Balathal has been characterized by X-ray diffraction, microstructural and electrochemical methods. The surface patina was composed of sulfates and oxysulfates in the outer layers while the inner layers were rich in copper oxides. The chisel exhibited smaller grain sizes near two of the surfaces while the structure in the interior was equiaxed. The deformed grains and inclusions near the surfaces and variation in the microhardness of the sample from different faces proved that the copper chisel was processed by cold deformation after initial casting of the square cross-section chisel. The electrochemical behaviour of chalcolithic Cu has been compared with that of a modern Cu sample by potentiodynamic polarization studies. The corrosion rate of chalcolithic Cu in aerated 3.5% NaCl solution was only marginally higher than that of modern Cu. The higher rate of corrosion has been attributed to the presence of second phase sulfide inclusions. The excellent condition of preservation of the 3800-year-old copper object, with no indications of stress corrosion cracking, suggests that pure copper or copper-based materials can be seriously considered as candidate canister materials for long-term underground storage of nuclear wastes in underground repositories.

    • Effect of cerium addition on microstructures of carbon-alloyed iron aluminides

      S Sriram R Balasubramaniam M N Mungole S Bharagava R G Baligidad

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      The effect of Ce addition on the microstructure of carbon-alloyed Fe3Al-based intermetallic has been studied. Three different alloys of composition, Fe–18.5Al–3.6C, Fe–20.0Al–2.0C and Fe–19.2Al–3.3C–0.07Ce (in at%), were prepared by electroslag remelting process. Their microstructures were characterized using optical and scanning electron microscopies. Stereological methods were utilized to understand the observed microstructures. All the alloys exhibited a typical two-phase microstructure consisting of Fe3AlC carbides in an iron aluminide matrix. In the alloy without Ce addition, large bulky carbides were equally distributed throughout the matrix with many smaller precipitates interspersed in between. In the alloy with Ce addition, the carbide grain sizes were finer and uniformly distributed throughout the matrix. The effect of Ce addition on the carbide morphology has been explained based on the known effect of Ce in modifying carbide morphology in cast irons.

    • Effect of surface morphology on atmospheric corrosion behaviour of Fe-based metallic glass, Fe67Co18Si14B1

      B Vishwanadh R Balasubramaniam D Srivastava G K Dey

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      The nature of atmospheric corrosion behaviour of an as-cast metallic glass, Fe67Co18Si1B14 ribbon, was evaluated. The wheel side surface of the ribbon was more corroded than the air side surface, due to the higher density of air pockets present. The phases present in atmospheric rust were analysed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to be goethite, lepidocrocite, magnetite, cobalt oxide and cobalt hydroxide phases. Goethite and lepidocrocite were in amorphous form. The nature of rusting was understood by scanning electron microscopy (SEM). Nucleation of rust started at preferred locations on the surface and grew along the surface in certain directions.

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