Browsing by Author "Sudhaker Nayak, H.V."

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A commercial (?+?) titanium alloy Ti-6Al-1.6Zr-3Mo-0.3Si (designated as VT9) of Russian origin is used for compressor discs and blades in jet engines up to temperatures of 773K. The ? transus for this alloy is ?1233K. The alloy blanks were subjected to ? solution treatment at ?1293K for 0.5 hours and cooled at different rates namely water quenching (WQ), air cooling (AC) and furnace cooling (FC). The blanks WQ, AC and FC were aged at 973K for 12 hours and these were designated as WQA, ACA and FCA respectively. Low cycle Fatigue (LCF) testing was carried out for all the conditions namely WQ, WQA, AC, ACA and FC, FCA at room temperature in the total strain amplitude range of 0.70% ± 1.7% at a frequency of 0.2Hz using triangular wave form. While Coffin-Manson (C-M) plots between plastic strain amplitude versus number of reversals to failure showed dual slopes in WQA, AC, ACA and FC conditions, single slope was observed in WQ and FCA conditions. Study of the slip activity on the surface close to the fracture end of the specimen failed in LCF for the AC and ACA conditions using scanning electron microscopy (SEM) clearly correlated with the results of TEM study. For other thermally treated conditions namely WQ, WQA and FC, FCA, SEM technique was used to study the slip band activity close to the fracture ends of the specimens failed under fatigue conditions from lower and higher strain amplitude regions. In the case of WQ and FCA where single slope is seen in C-M plots, there is no difference in the slip band activity and thus it indicates no change in deformation mode. However, distinct differences in slip band activity in specimens from lower and higher strain amplitude regions conform to the dual slope behavior in C-M plots in WQA and FC conditions.
(A study of the change in deformation mode under low cycle fatigue conditions of a commercial (?+?) titanium alloy) Ramachandra, C.; Kashyap, K.T.; Nanjundaswamy, G.S.; Chatterji, B.; Sudhaker Nayak, H.V.; Ramakanth Hebbar, K.
2000
Assessment of corrosion behavior of ductile irons by factorial experiments
(2009) Surendranathan, A.O.; Prabhu, K.N.; Sudhaker Nayak, H.V.
The corrosion behavior of unalloyed and alloyed ductile irons (as cast, annealed, and cold worked) in sea water, dilute sulfuric acid, and dilute sodium hydroxide solutions was assessed. Specimen history had a significant effect on the corrosion potential except in ductile iron alloyed with Ni. When the specimens were subjected to different levels of cold working, the corrosion rate was influenced by both the history and the medium. Temperature had a significant effect on the corrosion rate except in the case of unalloyed ductile iron. Factorial experiments indicated that the cold-worked samples were more sensitive to the effect of temperature and composition on the corrosion rate as compared to annealed and as-cast samples. The medium had a significant effect on the corrosion rate in all the cases. © 2009 ASM International.
ELECTRO-CHEMICAL BEHAVIOUR OF COATED REINFORCEMENT IN CEMENT CONCRETE.
(1987) Patil, B.T.; Gajendragad, M.R.; Ramchandran, T.; Ranganna, G.; Sudhaker Nayak, H.V.
Concrete constructions exposed to marine environments eventually suffer from corrosion of embedded steel rods, in its advanced state, this corrosion can crack the concrete and weaken the structure. The behaviour of paint coated reinforcements in cement concrete containing different amounts of chloride through an electrode polarization technique. Coated steel rods perform better as far as corrosion of rebar is concerned.
The inhibiting effect of N - cyclohexyl - N?- phcnyl thiourea (CPTU) and N-naphthyl-N?- phenyl thiourea (NPTU) on the corrosion of mild steel in aqueous solution of 0.1 N H2SO4 have been demonstrated using potentiodynamic polarization technique. The polarization data have shown that these compounds act as efficient anodic inhibitors for mild steel. Adsorption of these compounds on the mild steel surface was found to obey Temkin's adsorption isotherm. Good inhibition efficiency (IE) was evidenced in both the compounds and it was found to vary with concentration of the inhibitors. The kinetic parameters of adsorption obtained reveal spontaneous adsorption and a strong interaction of the compounds on the mild steel surface. © 2006 SAEST.
(Inhibition of mild steel corrosion in sulphuric acid solution) Divakara Shetty, S.; Shetty, P.; Sudhaker Nayak, H.V.
2006
The stress corrosion cracking (SCC) characteristics of ?-titanium sheets in a bromine-methanol solution 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. The cold-rolled specimens developed resistance to SCC, but failed by cleavage when notched, unlike the intergranular separation in annealed titanium. The apparent activation energy was found to be texture dependent and was in the range 30 to 51 kJ mol-1 for annealed titanium, and 15kJ mol-1 for cold-rolled titanium. The dependence of SCC behaviour on the texture is related to the changes in the crack initiation times. These are caused by changes in the passivation and repassivation characteristics of the particular thickness plane. The thickness planes are identified with the help of X-ray pole figures obtained on annealed and cold-rolled material. On the basis of the activation energy and the electrochemical measurements, the mechanism of SCC in annealed titanium is identified to be the one involving stress-aided anodic dissolution. On the other hand, the results on the cold-rolled titanium are in support of the hydrogen embrittlement mechanism consisting of hydride precipitation. The cleavage planes identified from the texture data match with the reported habit planes for hydride formation. © 1980 Chapman and Hall Ltd.
(Kluwer Academic Publishers, Texture dependent stress corrosion failure of commercial titanium sheets in bromine-methanol solution) Sudhaker Nayak, H.V.; Vasu, K.I.; Prasad, Y.V.R.K.
1980
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.
1982
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.
1998