Papers by Indranil Chattoraj
Journal of Materials Engineering and Performance
Materials Science Forum
The pipeline steels which are used for transportation of natural gas and crude oil suffer from hy... more The pipeline steels which are used for transportation of natural gas and crude oil suffer from hydrogen damage at their internal as well as external surfaces. The internal surfaces of pipelines are generally affected due to hydrogen induced cracking and the external surfaces due to the soil environmental conditions which cause stress corrosion cracking. In the present investigation, the electrochemical corrosion behavior of X70 pipeline steel was studied in sour environment and near neutral soil environment. To assess the mechanism of hydrogen damage in steel, electrochemical hydrogen charging and permeation techniques were used to characterize the hydrogen distribution, trapping and its diffusion in X70 pipeline steel. It has been found that corrosion behavior of pipeline steel in the sour environment is higher than the near neutral soil solution. From the hydrogen permeation study it is established that the hydrogen permeation rate increases with the square root of the charging cu...
The saturation magnetization and switching characteristics of amorphous Fe77.5Si7.5B15 fibres wer... more The saturation magnetization and switching characteristics of amorphous Fe77.5Si7.5B15 fibres were investigated after hydrogen incorporating by the electrochemical method. The switching field (H*) increased from its as-received value (5.57 Am−1 to 18.62 Am−1 after charging with a current density (Ich) of 30 mA cm−2 for 2 h. The saturation magnetization (Ms) decreased with hydrogen content up to a critical concentration corresponding to Ich = 60 mA cm−2 after 2 h of charging. At this critical current density, Ms decreased from 1.57 T, its as-received value, to 0.89 T. The results are explained by considering various kinds of interaction of hydrogen with metals, such as electron exchange, volume dilation, etc.
The electrical, magnetic and electrochemical behaviour of Fe70.5Nb..5CuiSi,638 has been studied i... more The electrical, magnetic and electrochemical behaviour of Fe70.5Nb..5CuiSi,638 has been studied in the as-received and heat treated conditions. The as-received material was amorphous which crystallized in two different stages at 780K and 940K when heated continuously. At the primary crystallization stage, nanometre sized grain of ordered FesoSi20 phase was formed. The superior soft magnetic properties were achieved after primary crystall-ization which were attributed to the averaging out of magnetocrystalline anisotropy due to the nanocrystalline structure and the reduction of magnetoelastic anisotropy energy due to the negative magnetosirictive nature of Fe8oSi20 phase and positive magnetosirictive value of the rest amorphous phase. After primary crystallization spon-taneous passivating nature of the alloy is also observed in electrochemical study.
Failure of a component indicates it has become completely or partially unusable or has deteriorat... more Failure of a component indicates it has become completely or partially unusable or has deteriorated to the point that it is undependable or unsafe for normal sustained service. Failure analysis is an engineering approach to determining how and why an equipment or a component has failed. Some general causes for failure are structural loading, wear, corrosion and latent defects. The goal of a failure analysis is to understand the cause of the failure so as to prevent similar failures in the future. In addition to verifying the failure mode it is important to determine the factors that explain the how and why of the failure event. There are specific successions of events that lead to a failure. A failure analysis investigation follows the cause and effect path from the final failure back to the cause.
Materials Science and Engineering: A, 2016
The effect of hydrogen on the mechanical properties of AA 7075-T6 was studied by in-situ hydrogen... more The effect of hydrogen on the mechanical properties of AA 7075-T6 was studied by in-situ hydrogen charging with slow strain rate technique in two aqueous media. A comparative study has been made on the stress-strain curve, time to failure at different strain rates (10 À 4-10 À 6 s À 1) in the air and by in-situ hydrogen charging. A variable effect of strain rate on embrittlement was observed. The alloy developed a surface film of oxide or hydroxide in the environments tested in spite of cathodic charging. This oxide film interferes with hydrogen embrittlement in the alloy. The kinetics of film formation and consistency of the film were dependent on the environment. At intermediate strain rates the film interfered and reduced hydrogen entry, while at the slowest strain rates hydrogen embrittlement was significant.
Procedia Engineering, 2015
Scripta Metallurgica et Materialia, 1992
Scripta Metallurgica et Materialia, 1993
ABSTRACT
Pitting corrosion is considered to be one of the principal degradation mechanisms for highstrengt... more Pitting corrosion is considered to be one of the principal degradation mechanisms for highstrength aluminum alloys. The aircraft airframe has been the most demanding application for aluminum alloys. The combined effects of corrosion and cyclic loading have been shown to produce cracks from corrosion pits and pits have frequently been the source of cracks on aircraft components operating in fleets. Once the pit or group of pits form, the rate of pit growth is dependent mainly on the material, environmental conditions and type and state of stress. Therefore, to estimate the total corrosion fatigue life of a component, it is of great importance to develop realistic models to establish the component life in these situations and to formulate methods by which designers and operators know likely sources of pitting early in the design and fleet operation. There are certain gaps in knowledge with regards to life prediction for pitting initiated fatigue. The need is to gauge the extent of pitting damage of a component or material non-destructively and predict the remaining life through superimposition of the pertinent operational, environmental and material parameters. However, a foolproof non-destructive means to characterize and three-dimensionally map pits is not available. The pitting phenomenon has to be analyzed statistically and the kinetics of pitting assessed through a change in the statistical distribution parameter of pits rather than deterministic equations relating pit dimensions to time. In this work we have applied high frequency ultrasonic and non-linear ultrasonic to assess the damage due to pitting and attempt has been made to establish correlations between this non-destructive tools and pit stochastic.
Intergranuular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC) of commercial ... more Intergranuular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC) of commercial stainless steels e.g. type 304 and 316 are frequently observed in several process environments. These localized attacks are normally attributed to the carbide precipitation and concomitant depletion of chromium near grain boundary due to alloy exposure to sensitization temperature. Such undesirable microchemistry is expected to be changed further if the material undergoes deformation prior to sensitization. Present paper deals with the influence of a wide range of cold rolling on the sensitization kinetics and consequently on intergranular corrosion. The plates of SS304 were cold rolled and coupons cut from these were sensitized at various temperatures for different periods. The consequences of deformation on IGC have been investigated by using ASTM A262 methods. Intergranular corrosion of solution-annealed samples was found to increase with sensitization temperature and time. Introducing deformation to the stainless steel seems to change the kinetics and thereby changes its resistance to IGC. Low level of cold rolling increases the IGC while severe rolling enhances the resistance. This critical level of rolling may depends upon the time and temperature of sensitization. Overall, effect of deformation is found to reduce the aggressiveness of IGC.
In this investigation we report the fractal characteri-stics of the fracture surfaces and microst... more In this investigation we report the fractal characteri-stics of the fracture surfaces and microstructure of HSLA steel using the fractal dimensional D computed from the fractographs and microstructural images of HSLA-100 steel at variously tempered conditions. Digital images of fract-ographs and microstructure obtained by the Scanning Electron Microscope (SEM) were analysed to compute fractal dimensions.
Sensitization behavior of thermo-mechanically processed stainless steel AISI 304L has been invest... more Sensitization behavior of thermo-mechanically processed stainless steel AISI 304L has been investigated. The thermo-mechanical processing was carried out at defor-mations 0-90%(reduction in thickness), annealed subse-quently at temperature ranging from 800-950oC for 15-60 minutes. Stainless steel was then sensitized at 675oC both for short (2 hours) and long and (53 hours) durations. The treated specimens were characterized for grain boundary character distribution, grain size and degree of sensiti-zation. The increase in annealing temperature and time during thermo-mechanical processing showed to increase grain size (upto 37 um) and the degree of sensitization. The ....(3-29) were also noticed to increase with the annealing temperature. The increasing fraction of coin-cident site lattice boundaries.... ...however did not decrease the degree of sensitization. The grain size through its effect on grain boundary surface area and effective grain boundary energy correlated well with the sensitization. Grain growth reduces the grain boundary surface area and the effective grain boundary energy as well which, in turn, enhanced the degree of sensitization. The degree of sensitization below a critical grain size(- 0.05) is effective in minimizing the sensitization to the insignigicant level.
Materials Science Forum, 2011
Attempt has been made to correlate the cold rolling (CR) texture with the degree of sensitization... more Attempt has been made to correlate the cold rolling (CR) texture with the degree of sensitization (DOS) in rolled 304LN after ageing at 500-600oC for various durations. The susceptibility of sensitization is observed to increase with %CR cold rolling from 5-25% and aged at 500-600oC. No one to one correlation between texture and DOS is observed. Brass component, overall, seems better for lower DOS while Goss component led to relatively higher DOS values. It is observed that the ratio of Brass to Copper may have a critical value for lower DOS.
Advanced Materials Research, 2010
Pitting corrosion of two tempers (T6 and T73) of 7075 Aluminium alloy were quantified by digital ... more Pitting corrosion of two tempers (T6 and T73) of 7075 Aluminium alloy were quantified by digital image processing. The effect of pitting corrosion on fatigue life in 7075 Aluminium alloy in two aging conditions was studied. Pitting was found to be slightly more severe for T6 tempers compared to T73 tempers for different time of exposures. The fatigue lives of two tempers of 7075 Aluminium alloy at high peak stresses were compared in the uncorroded and pre-corroded (pitted) states. Absolute fatigue lives of T73 samples were much higher than that of T6 in the uncorroded as well as pre-corroded condition. The various crack initiation methodologies observed through fractographic analysis is discussed.
Materials Science and Technology, 2009
This paper reports a procedure based on discrete Fourier transformation adopted for verifying sta... more This paper reports a procedure based on discrete Fourier transformation adopted for verifying statistical self-affinity and self-similarity in microstructural images of high strength low alloy steel. The procedure is first applied on synthetic images based on fractional Brownian motion to show the degree of self-similarity in them and finally, applied on microstructural images of three different magnifications. Effects of length scales on power spectral estimates of the microstructural images captured by scanning electron microscopy have been discussed. Importance of appropriate image resolutions and characteristic length for fractal based quantification of microstructural images is highlighted.
Journal of Materials Science - J MATER SCI, 2003
The effect of low dosage plasma ion implantation on hydrogen embrittlement was studied for an HSL... more The effect of low dosage plasma ion implantation on hydrogen embrittlement was studied for an HSLA steel using notched tensile samples. The plasma treatment caused an enhancement in the linear strain to failure under embrittling conditions. This was however not reflected in the fracture surfaces of the treated samples which had similar fractographic features as those of untreated samples. The plasma treatment delayed the process of embrittlement without causing any alteration in the basic mechanism of embrittlement. This was due to introduction of residual compressive stresses as well as reduction in the hydrogen permeation flux. Implantation in pure nitrogen seemed most beneficial while implantation in pure argon caused very little improvement.
Scripta Materialia, 2007
Austenitic stainless steels sensitize in the temperature range 550800 °C and consequently suffer... more Austenitic stainless steels sensitize in the temperature range 550800 °C and consequently suffer from intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC) in corrosive environments. These typical failure modes have been identified as common ...
Scripta Materialia, 2010
A model to compute an effective microstructural length scale by fractal analysis of self-affine t... more A model to compute an effective microstructural length scale by fractal analysis of self-affine tensile fractographic images has been proposed. Good correlation between the characteristic microstructural length scale and the average circular diameter of voids as well as yield strength is demonstrated for a Cu-strengthened HSLA steel. Using the fractal-based model, fracture toughness is computed, which agrees well with that determined experimentally.
Uploads
Papers by Indranil Chattoraj