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Item Corrosion inhibition of T-6 treated 6061 Al-SiC(p) composite in hydrochloric acid(Indian Institute of Metals, 2008) Nayak, J.; Hebbar, K.R.Addition of reinforcements like SiC to aluminium matrix has been reported to decrease the corrosion resistance of the matrix due to several reasons, one of them being the galvanic action between the reinforcement and the matrix. Aging of aluminium alloys can also have similar effects as aging results in precipitation of intermetallics. The work deals with effect of aging (T-6 treatment) on the corrosion behaviour as well as corrosion inhibition of 6061Al-SiC composite. Corrosion behaviour of 6061 Al-SiC(p) composite were determined in HCl by Tafel extrapolation technique in the temperature range of 30°C-50°G. Further, the inhibition studies were made using two inhibitors viz. (i) Allyl Thiourea and (ii) Glycyl Glycine. The results indicate that both the organic compounds act as anodic inhibitors and are moderately effective in inhibiting the corrosion of 6061Al-SiC(p) composite. The inhibition efficiency increases with increase in inhibitor concentration. Similar inhibition studies were made on the aged samples. However, in the case of T-6 treated samples, the inhibition efficiency was found to be poor compared to the non-heat treated samples.Item The stress corrosion cracking (SCC) characteristics of Zircaloy?2 sheets in methanol?0.4 vol. pct. hydrochloric acid have been studied in the annealed and cold?rolled conditions using longitudinal and transverse specimens. The times to failure for annealed longitudinal specimens were longer than those for similarly tested transverse specimens at stress levels below ?45% UTS. The cold?rolled specimens developed resistance to SCC, but failed totally by cleavage when notched, unlike annealed specimens which failed by intergranular initiation followed by cleavage. The crystallographic texture developed by cold rolling is such that the crack initiation is difficult because of quicker passivation characteristics of the crack initiating plane. The texture also gives unfavourable orientation of slip and twinning planes with respect to tensile axis. The crack initiating planes are identified with the help of X?ray pole figures. The apparent activation energy is found to be texture dependent at a given stress level. On the basis of apparent activation energy measurements, dynamic tests at constant cross?head speeds and electrochemical measurements, the mechanism of SCC is identified to be the one involving stress?aided anodic dissolution. Copyright © 1982 Verlag GmbH & Co. KGaA, Weinheim(Stress corrosion failure of Zircaloy?2 sheets in methanolic HCl solution: Role of crystallographic texture) Hebbar, K.R.; Sudhaker Nayak, H.V.; Ramchandran, T.1982Item The use of electrochemical methods to characterize materials for their corrosion behaviour is well known. Both linear polarisation and Tafel extrapolation techniques are made use of to study the corrosion behaviour of ductile iron (DI) in natural sea water, 5 v/o H2SO4 and 5 w/o NaOH. Samples were tested in the as cast, annealed and cold worked conditions at 300 K, 325 K and 340 K. It was found that annealed material had the least corrosion rate. This is explained on the basis of the proportion of phases in the microstructure, the DI has on annealing. On annealing as cast DI, certain amount of cementite in the pearlite is converted into ferrite. Since a single phase material is always more corrosion resistant than a multiphase one, ferrite phase increases corrosion resistance. High degree of cold working is detrimental with respect to corrosion resistance as it increases the stored energy and dislocation density in the material thereby enhancing the kinetics of corrosion reactions. The activation energy for DI was found to be lowest in sulphuric acid medium and highest in sodium hydroxide medium. The corrosion rates for DI in H2SO4 medium were the highest while in NaOH they were the lowest irrespective of material condition and technique of rate measurement.(Study of corrosion behaviour of ductile iron by electrochemical polarisation techniques) Surendranathan, A.O.; Hebbar, K.R.; Sudhaker Nayak, H.V.1998Item Weldments of AISI grade 316 stainless steel, having a ferrite content of 4-6% and a variety of nitrogen concentrations were prepared using a modified element implant technique. Charpy impact specimens prepared from these weldments were subjected to a variety of aging treatments. Impact toughness decreases with aging time at all aging temperatures. Nitrogen is found to be beneficial to toughness. An empirical relation connecting the aging temperature, aging time and nitrogen content with toughness has been developed which can be used to estimate the time for embrittlement.(Indian Academy of Sciences, Estimation of embrittlement during aging of AISI 316 stainless steel TIG welds) Nayak, J.; Udupa, K.R.; Hebbar, K.R.; Nayak, H.V.S.2004Item Simulated weldments of AISI grade 304 stainless steel having a ferrite content of 4-6% with three levels of nitrogen (0.03, 0.08, and 0.11 wt-%) were prepared using a modified elemental implant technique. From these weldments, subsize Charpy impact specimens were prepared and subjected to aging treatment at different temperatures, 623-748 K, and for different times, 1000-5000 h. Impact toughness curves for these aged samples were generated by testing at various temperatures from 77 K to 300 K. From the impact curves the upper shelf energy (USE) and lower shelf energy (LSE) were determined. It was observed that both USE and LSE decreased with aging time at all temperatures. Nitrogen seems to offer a beneficial effect as far as impact toughness is concerned, as both USE and LSE values increased with increasing nitrogen content. The worst aging conditions were identified as 748 K, 2000 h at the lowest nitrogen level of 0.03 wt-%. An empirical relation connecting the aging temperature, aging time, and nitrogen content to the LSE was developed, which can be used to predict the time for embrittlement at a given nitrogen level and aging temperature. © 2005 Institute of Materials, Minerals and Mining.(Prediction of embrittlement during aging of nuclear grade AISI 304 stainless steel TIG welds) Nayak, J.; Udupa, K.R.; Hebbar, K.R.; Nayak, H.V.S.2005