Browsing by Author "T.K.G. Namboodhiri"

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CORROSION IN METALLIC GLASSES.
(1986) T.K.G. Namboodhiri
Metallic glasses have many beneficial properties, an important one of which is corrosion resistance. Here an overview of the field is given. Metal-metalloid glasses based on Fe, Ni and Co and metal-metal glasses like Cu-Ti, Cu-Zr and Zr-Ni have been evaluated for their general corrosion behavior, localized corrosion, and environment assisted fracture susceptibilities. Fe, Ni and Co base glasses containing Cr, P and C were found to be extremely corrosion resistant.
CORROSION RESISTANCE OF TWO MAGNETIC METALLIC GLASSES IN ACIDIC AND NEUTRAL AQUEOUS SOLUTIONS.
(1986) I.B. Singh; R.S. Chaudhary; T.K.G. Namboodhiri
The corrosion resistance of two magnetic metallic glasses, viz. Fe//4//0Ni//4//0B//2//0 and Fe//3//9Ni//3//9Mo//2 (SiB)//2//0 was evaluated in H//2SO//4 and NaCl solutions by weight loss measurement and electrochemical techniques. In exposures up to six days the corrosion rate of Fe//4//0Ni//4//0B//2//0 was about 5 mpy while Fe//3//0Ni//3//9Mo//2 (SiB)//2//0 corroded about two times faster in 0. 1 M H//2SO//4 solution. In 3. 5% NaCl both alloys corroded at about the same rate, nearly 2 mpy. In potentiostatic polarization measurements the Mo bearing alloy passivated in the potential range plus 0. 45 V to plus 1. 45 V with respect to saturated calomel electrode in H//2SO//4 solutions of concentration 0. 001 M to 0. 1 M, but both alloys failed to passivate in NaCl solutions.
Effect of alloying on the corrosion behaviour of FeB metallic glasses in sulphuric acid
(1986) I.B. Singh; R.S. Chaudhary; T.K.G. Namboodhiri
The corrosion behaviour of seven metallic glasses based on the FeB system, namely (i) Fe40Ni40B20 (Vitrovac 0040), (ii) Fe40Ni38Mo4B18 (Metglas 2826MB), (iii) Fe39Ni39Mo2(SiB)20 (Vitrovac 4040), (iv) Fe40Ni40P14B6 (Metglas 2826), (v) Fe32Ni36Cr14P12B6 (Metglas 2826A), (vi) Fe78B13Si9 (Metglas 2605-S-2) and (vii) Fe67Co18B14Si1 (Metglas 2605Co), was investigated in H2SO4 solutions of various concentrations (0.001-0.1 M) using mass loss and electrochemical techniques. In exposures of up to 6 days the corrosion rate in 0.1 M H2SO4 changed in the following order: 2826A < 2826 < 0040 < 2826MB < 4040 < 2605Co < 2605-S-2. During anodic polarization the alloys 2605-S-2, 2605Co and 0040 did not exhibit passivation whereas the remaining four alloys passivated in all the H2SO4 solutions used. Icorr, Icrit and Ipass for these metallic glasses were found to be dependent on the concentration of the corrodent. Icorr and Icrit for all the alloys decreased with decreasing H2SO4 concentration. Ipass for Metglas 2826 and 2826MB increased with decreasing acid concentration while the opposite effect was found for the other two passivating alloys. The present results showed that the corrosion resistance of FB-based metallic glasses depends on the alloying elements present in them. Their corrosion resistance increased by alloying with metals whose effectiveness increased in the following order: cobalt, molybdenum, nickel and chromium. Similarly, metalloids were effective in increasing corrosion resistance in the following order: silicon, boron and phosphorus. The passive film formed on Metglas 2826A alloy was found to be more stable than those on alloys 2826, 2826MB and 4040. © 1986.
Effect of cold rolling on the hydrogen induced delayed failure of API X-52 line-pipe steel
(2002) Amarnath; T.K.G. Namboodhiri
Hydrogen induced delayed failure of the commercial line pipe steel API X-52 was investigated by static loading tests on cathodically hydrogen charged sheet specimens. Annealed specimens were cold rolled to 10, 30 and 50% reductions in thickness and delayed failure characteristics evaluated. The annealed steel exhibited typical delayed failure behaviour. Cold work alters this behaviour in a complex fashion. The incubation period is reduced or eliminated. The upper critical stress and static fatigue limits were lowered with increasing cold work up to 30 % beyond which they were raised. Scanning electron fractography revealed a micro void coalescence fracture mode in all cases.
EFFECT OF COLD WORK ON CORROSION AND DEZINCIFICATION OF MUNTZ METAL IN AMMONIA.
(Natl Research Council of Canada, 1984) R.S. Tripathi; T.K.G. Namboodhiri
Effect of cold work on the corrosion and dezincification behaviour of 60/40 brass was evaluated by weight loss measurements, solution analysis and electrochemical polarization measurements. Weight loss from the brass increased with cold reductions upto 40% but decreased at higher reductions. Dezincification factor was lowered by cold work. Both the corrosion rate and the dezincification factor decreased with exposure time. These results were supported by potentiostatic polarization curves and open circuit potential measurements.
Effect of heat treatments on the hydrogen embrittlement susceptibility of API X-65 grade line-pipe steel
(Indian Academy of Sciences, 2003) G. Ananta; Nagu Amarnath; T.K.G. Namboodhiri
Delayed failure tests were carried out on hydrogen charged API X-65 grade line-pipe steel in as received (controlled rolled), normalized, and quenched and tempered conditions. The resistance to hydrogen embrittlement was found in the order of controlled rolled > quenched and tempered > normalized. The fracture mode in the hydrogen embrittled steel was ductile.
Effect of molybdenum on the resistance to H2S of high sulphur microalloyed steels
(1993) K. Ravi; V. Ramaswamy; T.K.G. Namboodhiri
The resistance to hydrogen sulphide of microalloyed steels with sulphur levels around 0.02% and containing copper, chromium, nickel and molybdenum was studied. The sulphide stress cracking (SSC), hydrogen induced blister cracking (HIBC), hydrogen embrittlement (HE) and corrosion rates of the steels were evaluated. The threshold stress during SSC testing was found to increase with an improvement in HE resistance. Molybdenum was found to improve the HE resistance which increases the SSC resistance. HIBC and corrosion rates were lowest at 0.3% molybdenum content in the steel. Additions of copper, chromium and nickel to a 0.3% molybdenum bearing steel enhance the resistance to SSC, HIBC and HE and corrosion rates. Fine precipitates 10-25 nm in size, containing molybdenum, titanium, vanadium, chromium and sulphur, uniformly distributed in the matrix were found to improve the sour gas resistance. Without molybdenum coarser precipitates 150 nm in size were observed and HIBC was found to initiate at such precipitates. Steel with low sulphur content (0.015%) but with coarser precipitates did not show any improvement to sour gas resistance when compared with a steel with high sulphur (0.028%) content, but possessing fine precipitates. © 1993.
EFFECT OF SOME ANIONS ON THE CORROSION CHARACTERISTICS OF Fe//4//0Ni//4//0B//2//0 METALLIC GLASS.
(1986) I.B. Singh; T.K.G. Namboodhiri; R.S. Chaudhary
The corrosion behavior of Fe//4//0Ni//4//0B//2//0(0040) metallic glass in the presence of sodium salts of Na//2SO//4, Na//2CO//3, Na//2HPO//4, NaNO//3, Na//2MoO//4, Na//2WO//4 and Na//2CrO//4 was investigated. The open circuit potential (OCP) variation in solutions containing these salts in concentration from 0. 1 M to 0. 001 M were measured up to 2 hours. The anodic polarization curves of the alloy have been recorded under potentiostatic condition. The OCP shifted towards the noble direction in presence of chromate and tungstate while towards the active direction in the case of the other anions in ennobling the alloy under OCP conditions.
ELECTROCHEMICAL AND AES INVESTIGATIONS OF SOME METALLIC GLASSES IN SULPHURIC ACID SOLUTION.
(1987) I.B. Singh; R.D.K. Misra; T.K.G. Namboodhiri; R.S. Chaudhary
No passivation is observed for 0040 alloy whereas all the other alloys passivated in sulphuric acid solutions. Initial dissolution of the alloy in the active region is essential for passivation in molybdenum containing alloys and the concentration of Mo in the passive film is less than that of in the bulk of the alloys. Better passivation is observed in 2826 alloy when the dissolution rate is high in the active region. Prepassive film on 2826MB and 2826 alloys is nickel rich which changes to iron rich passive film at higher anodic potentials. In 2826A alloy, chromium and phosphorous concentrations are higher in the passive film.
ELECTROCHEMICAL AND AES INVESTIGATIONS OF SOME METALLIC GLASSES IN SULPHURIC ACID SOLUTION.
(1987) I.B. Singh; R.D.K. Misra; T.K.G. Namboodhiri; R.S. Chaudhary
No passivation is observed for 0040 alloy whereas all the other alloys passivated in sulphuric acid solutions. Initial dissolution of the alloy in the active region is essential for passivation in molybdenum containing alloys and the concentration of Mo in the passive film is less than that of in the bulk of the alloys. Better passivation is observed in 2826 alloy when the dissolution rate is high in the active region. Prepassive film on 2826MB and 2826 alloys is nickel rich which changes to iron rich passive film at higher anodic potentials. In 2826A alloy, chromium and phosphorous concentrations are higher in the passive film.
ENGINEERING EDUCATION IN INDIA.
(1986) T.K.G. Namboodhiri
Some of the problems in engineering education are analyzed in the light of the Government's policy statement. Non-uniformity of curriculum and standards, lack of proper training facilities and good teachers, absence of intelligent students to do post-graduate studies and research and irrelevance of research carried out to the national need are some of the drawbacks of the present engineering education. Proper allocation of funds, identification of industrial needs, insistence on indigenous technology development and above all acceptance of the dignity of labor are some of the measures which may improve the system.
ENVIRONMENT ASSISTED FRACTURE OF METALLIC GLASSES.
(Pergamon Press, 1984) T.K.G. Namboodhiri
Hydrogen embrittlement and stress corrosion cracking of three metal-metalloid glasses based on iron and nickel were studied in sulfuric and hydrochloric acid media using slow strain rate tensile testing and scanning electron microscopy. All the three alloys were found to be susceptible to hydrogen embrittlement which results in a drastic reduction in fracture stress and a brittle fracture morphology. Only one of the alloys was found to be susceptible to stress corrosion cracking. From fractographic observations of voids at the hydrogen embrittled fracture surfaces it is suggested that hydrogen may collect at localized shear bands and cause the premature brittle failure of these materials.
FRONTIER AREAS IN THE ELECTROCHEMISTRY OF STRESS CORROSION CRACKING.
(1984) T.K.G. Namboodhiri
The author briefly discusses the mechanism of hydrogen entry at the metal surface; influence of mobile dislocations, grain boundaries and other structural defects; kinetics of breaking and reforming of passive layers in material/environment systems; accurate definition of crack tip conditions; computer modelling of environmental effects on crack initiation and propagation; electrodics of elastically and plastically deformed materials.
HYDROGEN EMBRITTLEMENT OF METALLIC MATERIALS.
(1984) T.K.G. Namboodhiri
Hydrogen may be introduced during melting, working, finishing, fabrication, and throughout their service life from the surroundings. The various forms of hydrogen damage are indicated. Experimental techniques useds to measure hydrogen in metals and evaluation of hydrogen embrittlement are pointed out. The phenomenological characteristics of hydrogen embrittlement is proposed. Important metallurgical variables controlling embrittlement are described and some guidelines for developing alloys with good resistance to hydrogen damage are suggested. The inadequacy of the present state of knowledge on the atomistic mechanism of hydrogen embrittlement is pointed out and several frontier areas of research are indicated.
Hydrogen embrittlement of three metallic glasses
(1983) T.K.G. Namboodhiri; T.A. Ramesh; G. Singh; S. Sehgal
Slow strain rate tensile tests and scanning electron fractography were used to evaluate the hydrogen embrittlement of three metallic glasses, Ni40Fe40B20,Ni39Fe39Mo4Si6B12 and Ni40Fe6Co20Cr12Mo6B16. The cathodic polarization in 0.1 N H2SO4 of these alloys reduced their fracture strengths and produced brittle fracture. With increasing cathodic current density the fracture stress decreased and reached a plateau value of 20%-40% of the fracture stress in air. Fractography revealed the presence of a translucent film on the ductile fracture surfaces which was probably formed by incipient melting of the shear band during the final fracture stage. A large number of microvoids of various sizes were observed on the hydrogen-embrittled fracture surfaces which may have nucleated because of hydrogen. The present results support the mechanism of ductile fracture proposed by Takayama and Maddin for metallic glasses. © 1983.
Hydrogen sulphide resistance of high sulphur microalloyed steels
(1990) K. Ravi; V. Ramaswamy; T.K.G. Namboodhiri
Sulphide stress cracking (SSC) and hydrogen-induced blister cracking (HIBC) studies were conducted on a set of seven microalloyed steels to determine the effects of alloy additions and sulphide shape control on their H2S resistance. Two commercial steels with a sulphur level of 0.025% exhibited poor SSC and HIBC resistance when tested in H2S-containing acidic environments. A laboratory steel with 0.006% S (sulphide shape controlled) gave good SSC and HIBC resistance. High sulphur (0.025%) laboratory steels alloyed with copper, chromium, nickel, aluminium and molybdenum, and rare earth metal (REM) treated for sulphide shape control, gave an H2S resistance equal to or better than the low sulphur steel. Addition of copper, chromium and nickel lowered the corrosion rate and improved both the SSC and HIBC resistance. Further addition of 0.5% Al improved the SSC resistance, while addition of 0.3% Mo improved both the SSC and HIBC properties. The low sulphur steel had the lowest hydrogen concentration after exposure to H2S environments, while alloy additions and REM treatment lowered the amount of hydrogen absorbed by the high sulphur steels. Molybdenum addition seems to be a suitable method to make high sulphur microalloyed steels resistant to H2S environments. © 1990.
INHIBITIVE ACTION OF PIPERIDINE ON HSLA STEEL CORROSION AND HYDROGEN EVOLUTION REACTION IN H//2SO//4 MEDIA.
(1987) Reeta Agrawal; R.S. Chaudhary; T.K.G. Namboodhiri
A study of the corrosion behavior of HSLA steel in 1N-H//2SO//4 solution suggest that piperidine acts as a good inhibitor for corrosion and hydrogen evolution reaction (h. e. r. ). The rate of h. e. r. on HSLA steel was found to be of first order with respect to left bracket H** plus right bracket . The corrosion current decreases with increasing concentration of piperidine. The adsorption of piperidine on the surface of the steel follows Langmuir adsorption isotherm.
INHIBITIVE ACTION OF SOME MERCAPTANS TOWARDS THE CORROSION AND DEZINCIFICATION OF 60/40, 63/37 & 70/30 BRASSES IN 13. 4 N NH4OH.
(Natl Research Council of Canada, 1984) Pushpa Gupta; R.S. Chaudhary; T.K.G. Namboodhiri; B. Prakash
The inhibitory action of benzyl, n-butyl, sec. butyl mercaptans and 2-mercapto ethanol towards the corrosion and dezincification has been investigated, using weight loss, solution analysis and potentiostatic techniques. All the inhibitors are effective to reduce the corrosion of brasses, only benzyl mercaptan and 2-mercapto ethanol are effective to minimize the dezincification in brasses. These chemicals inhibit both anodic as well as cathodic reactions, indicating a mixed type of inhibition.
MECHANICALLY ASSISTED DEZINCIFICATION AND STRESS CORROSION CRACKING OF 60/40 BRASS.
(1986) R.S. Tripathi; T.K.G. Namboodhiri
Dezincification studies and slow strain rate tensile testing of annealed and cold rolled 60/40 brass were carried out in 10 N NH//4 OH. Applied elastic stresses increase dezincification from the brass, and pre-exposure to elastic stresses causes greater susceptibility to stress corrosion cracking. Plastic deformation by cold rolling increases the corrosion of the brass at low percentage reductions but the effect is reversed at higher reductions. A similar trend was found in the loss in ductility of the brass during slow strain rate tensile testing. Fracture occurs by a predominantly ductile mode.
Precipitation hardening and hydrogen embrittlement of aluminum alloy AA7020
(2011) Santosh Kumar; T.K.G. Namboodhiri
AA7020 Al-Mg-Zn, a medium strength aluminium alloy, is used in welded structures in military and aerospace applications. As it may be subjected to extremes of environmental exposures, including high pressure liquid hydrogen, it could suffer hydrogen embrittlement. Hydrogen susceptibility of alloy AA7020 was evaluated by slow strain-rate tensile testing, and delayed failure testing of hydrogen-charged specimens of air-cooled, duplexaged, and water-quenched duplex agedmaterials. The resistance to hydrogen embrittlement of the alloy was found to be in the order of air-cooled duplex aged alloy > as-received (T6 condition) > water quenched duplex aged material. © Indian Academy of Sciences.