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Mannava V.,Indian Institute of Technology Madras | Rao A.S.,Structural Failure Analysis Group | Paulose N.,Gas Turbine Research Establishment | Kamaraj M.,Indian Institute of Technology Madras | Kottada R.S.,Indian Institute of Technology Madras
Corrosion Science | Year: 2016

The oxidation behavior of GTMSU718 alloy with 87.5 wt.% Na2SO4 + 5 wt.% NaCl + 7.5 wt.% NaVO3 (3SM) was studied at 650 °C. Cyclic oxidation studies with 3SM show more weight gain than 2SM (90 wt.% Na2SO4 + 10 wt.% NaCl). It indicates that NaVO3 accelerates the oxidation behavior. Isothermal studies show a repetitive NaVO3 formation by combination of V2O5 and Na2SO4 until Na2SO4 is exhausted. Cr depletion layer occurs due to formation of Cr-sulphides, CrVO4 and liberation of Na2Cr2O7. Based on the detailed critical analysis, a plausible hot corrosion mechanism with 3SM was analysed to be basic fluxing mechanism, in parallel with sulphidation followed by oxidation. © 2016 Elsevier Ltd.

Palit M.,Advanced Magnetics Group | Banumathy S.,Structural Failure Analysis Group | Singh A.K.,Structural Failure Analysis Group | Pandian S.,Advanced Magnetics Group | Chattopadhyay K.,Indian Institute of Science
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2016

Tb0.3Dy0.7Fe1.95 alloy was directionally solidified by using a modified Bridgman technique at a wide range of growth rates of 5 to 100 cm/h. The directionally grown samples exhibited plane front solidification morphology up to a growth rate of 90 cm/h. Typical island banding feature was observed closer to the chilled end, which eventually gave rise to irregular peritectic coupled growth (PCG). The PCG gained prominence with an increase in the growth rate. The texture study revealed formation of strong 〈311〉 texture in a lower growth rate regime, 〈110〉 and “rotated 〈110〉” in an intermediate growth regime, and 〈112〉 in a higher growth rate regime. In-depth analysis of the atomic configuration of a solid–liquid interface revealed that the growth texture is influenced by the kinetics of atomic attachment to the solid–liquid interface, which is intimately related to a planar packing fraction and an atomic stacking sequence of the interfacial plane. The mechanism proposed in this article is novel and will be useful in addressing the orientation selection mechanism of topologically closed packed intermetallic systems. The samples grown at a higher growth rate exhibit larger magnetostriction (λ) and dλ/dH owing to the absence of pro-peritectic (Tb,Dy)Fe3 and formation of 〈112〉 texture, which lies closer to the easy magnetization direction (EMD). © 2016, The Minerals, Metals & Materials Society and ASM International.

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