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July 2000 - November 2017
July 2000 - present
Publications
Publications (71)
Influence of grain size and grain boundary character distribution on the short-term oxidation behavior of IN740H was evaluated using thermogravimetric analysis test at 760 °C for 50 h. The oxidized specimens were critically examined through electron microscopy. Specimen with fine grain size recorded the lowest mass gain. This is attributed to highe...
A physically‐based constitutive modeling framework is proposed for the cyclic deformation and softening of Ni‐based superalloys. The constitutive model accounts for underlying mechanisms of grain size strengthening, dislocation strengthening, solid solution strengthening, and precipitate strengthening, commonly observed in these alloys. A constitut...
High-temperature tensile deformation behavior of polycrystalline nickel based superalloy 720Li used for manufacturing aero engine disks was studied by conducting uniaxial tensile tests in the temperature range of 25-800oC and subsequent transmission and scanning electron microscopic examinations to decipher strain hardening/softening behavior. The...
This study explores the dual‐slope Coffin–Manson (C–M) behavior of a polycrystalline nickel‐based superalloy, EA, used in turbine engine applications with an emphasis on discerning the micro‐mechanisms responsible for it. The motivation for distinguishing the micro‐mechanisms responsible for bi‐linear C–M behavior stemmed from the earlier evolved c...
The tensile flow behavior of nickel base super alloy 720Li is investigated in the temperature range of 25 to 720 °C. At 350 and 450 °C, 720Li alloy exhibits serrated flow and the cause for the same is solute segregation at the dislocation core. From the energy filter transmission electron microscopy (EF-TEM) examination, it is evident that chromium...
The ratcheting phenomenon leads to plastic strain accumulation in structural materials, specifically under variable load or pressure. This investigation focuses on the effect of accumulated plastic strain due to asymmetric cyclic loading (ratcheting) up to 200 cycles on tensile behavior of the micro-alloyed 2.25Cr–Mo steel, at ambient temperature (...
Strain ratio (Rε) is varied during isothermal strain-controlled fatigue tests of nickel-base superalloy IN740H at 760 °C; Rε = −1, 0, 0.5. Unlike most alloys, highest fatigue life is observed under Rε = 0 test condition compare to Rε = 0.5 and −1. From extensive electron microscopy, i.e. energy-filtered TEM (EF-TEM), WDS and EDS studies, it is conf...
The aim of the present investigation is to study the tensile creep behavior of nickel-based disk superalloy, which is widely used in the manufacturing of turbine disks for the aero engines. Tensile creep tests were performed over a wide range of stresses (100–900 MPa) and temperatures (625–850 °C) and rupture time varies from 93.1 to 9473 h. Furthe...
Ratcheting fatigue tests were carried out on the micro-alloyed 2.25Cr–Mo steel with variable mean stress (σm), stress amplitude (σa) and stress rate (σ˙) at room temperature. Increase in the σm and σa resulted in higher plastic strain accumulation and caused a reduction in fatigue life; however, rise in the σ˙ enhanced the fatigue life. Hysteresis...
In this study, efforts were made to elucidate the tensile deformation micro-mechanisms of a polycrystalline nickel-base superalloy used for the fabrication of critical rotating and stationary components of the gas turbine engine under relevant service conditions. The microstructural evolutions during the investigated temperatures and strain-rates a...
The evolution of geometrically necessary dislocation density (GND) at the γ and primary γ′ interface during tensile deformation of turbine disk alloy was studied. Extensive electron microscopy analysis (i.e. EBSD and TEM) was carried out to explore the structure and GND evolution at the γ-γ′ interfaces. It is found that GND value is highest for ten...
The influence of stress rate (σ˙) on load/strain partitioning between different phases of a micro-alloyed 2.25Cr–Mo steel during stress-controlled fatigue deformation at room temperature (RT) was studied by conducting asymmetrical ratcheting fatigue tests employing σ˙ values of 50–450 MPa/s. Fatigue life (Nf) significantly reduced for tests conduct...
In the present research, efforts were made to understand the mechanistic and microstructural aspects of the low cycle fatigue failure of a directionally solidified (DS) nickel-based superalloy under relevant operating conditions. The differences between the dislocation structures observed during different temperatures and strain amplitudes are clea...
Using in situ transmission-electron-microscopy (TEM) heating and subsequent energy-filtered TEM (EF-TEM) and high-resolution-TEM (HR-TEM) analysis on a newly developed 3Co-3W-9Cr steel, enrichment of boron at the Fe 2 W and matrix interface has been studied for the first time. The heat treatment has been carried out at a temperature of 770°C. From...
During present investigations, an attempt was made to understand the effect of mean stress and oxidation on low cycle fatigue (LCF) behaviour of CM 247 DS LC alloy at T = 850°C. A significant reduction in fatigue life was observed during LCF tests conducted at strain ratio (R) of 0 as compared to R = −1. Reduction in fatigue life is attributed to t...
In order to meet the 21st century challenges, the need to improve the high temperature load bearing capabilities or creep properties of nickel base superalloys is more important than ever. Thorough understandings of creep deformation micro-mechanisms are essential for improving high temperature performance of these alloys. Therefore, in the present...
The superimposition of time-dependent damage on fatigue, otherwise, known as creep-fatigue interaction (CFI), significantly affect the fatigue life of power plant boiler components. IN740H is a candidate material for advanced ultra-supercritical (A-USC) boilers components. The creep-fatigue interaction of alloy IN740H was studied at 760°C, by condu...
In the present study, an effort is made to understand the effect of the initial loading path on low cycle fatigue behavior of nickel-base superalloy IN 740H at 760oC employing a strain rate of 1x10 -3 s -1. The evaluation of back stress vis-a-vis the Bauschinger effect due to cyclic deformation was investigated. It is observed that reverse yield st...
The yield strength anomaly (YSA) and dynamic strain ageing (DSA) behaviour of advanced ultra-supercritical boiler grade wrought nickel-based superalloy IN 740H is studied by conducting tensile tests in temperature range 28–930°C and by employing strain rates 1 × 10⁻², 1 × 10⁻³, 1 × 10⁻⁴ and 1 × 10⁻⁵ s⁻¹ followed by extensive electron microscopic ex...
This paper critically assesses phase transformations occurring after welding and subsequent post weld heat treatments in simulated sub-heat affected zones (HAZ) of P91B steel. Samples for weld-HAZ simulation were produced corresponding to grain-coarsened HAZ, grain-refined HAZ and inter-critical HAZ. Analyses revealed diverse phase transformation m...
This paper reports new dislocation configurations responsible for cyclic hardening/softening behaviour of a directionally solidified nickel base superalloy after relaxation fatigue tests at 850 °C with hold durations of 1 and 5 min. Dislocation interactions in the gamma (γ)-matrix and the formation of new dislocation configurations during relaxatio...
Wear resistance of white cast iron is known to be sacrificed when it is attempted to enhance the impact
toughness. In the present study, it is shown that a suitably engineered microstructure can retain/enhance the wear resistance between 2.5 and 3.5 times even when impact energy value is increased from 4 J/cm2 to 13 J/
cm2. A novel microstructure i...
Dislocation based deformation micromechanisms during low cycle fatigue deformation of nickel base superalloy CM 247 DS LC at 850 °C was investigated by conducting fatigue tests employing constant strain amplitudes for strain ratio (R) values of 0, −1 and carrying out extensive SEM and TEM examinations. Cyclic life of the alloy reduces for all fatig...
In contrast to other structural alloys, yield strength of nickel base superalloys either remains constant or increases with temperature up to 700–800 °C making them more suitable for high temperature structural applications. However, the increase in yield strength is usually accompanied by a decrease in ductility. The results of the present investi...
High-temperature tensile deformation behavior of directionally solidified nickel base superalloy CM 247 DS is studied by conducting tensile tests in temperature range RT-955 °C employing a constant strain rate of 10⁻³ s⁻¹ and carrying out extensive electron microscopic examinations to understand the concomitant substructural evolution. The alloy ex...
Alloy IN 718 is used for manufacturing many critical components of gas turbine engine such as compressor blades, discs, and shafts. During engine operation, these components are subjected to cyclic loading along with steady-state operation at high temperatures. These operating conditions induce damage resulting from interaction of creep and fatigue...
It is attempted to enhance the impact toughness of industrially used high chromium white cast iron (WCI) without sacrificing wear resistance. The microstructure is engineered by cyclic anneal-ing to obtain features such as duplex grain matrix, where austenite envelops ferrite grain, refined M 7 C 3 carbide. The newly cast and heat-treated alloy sho...
Mechanism of serrated plastic flow in a cast nickel base superalloy was investigated in the temperature range of 25–850 °C by conducting tensile tests employing strain rates of 1 × 10⁻³, 1 × 10⁻⁴ and 1 × 10⁻⁵ s⁻¹ and subsequent TEM studies. Shearing of γ′ precipitates by superpartials a/2[1 1 0] bounded by anti- phase boundaries are found to be res...
High temperature tensile deformation behaviour of directionally solidified nickel base superalloy CM 247 DS was studied by conducting tensile tests in the temperature range 25–955 °C and extensive electron microscopic examinations to understand the influence of different phases on tensile behaviour. Micro-constituents, especially carbides and γ−γ′...
To understand the cause of discrepancy between predicted creep life through parametric
methods using short term creep test data and creep life obtained from long term experiments,
1000 and 10,000 h duration creep tests were conducted on a 9Cr-1Mo grade steel at 550 and
650 °C and the oxide scale, fracture surface and microstructure of the crept...
To understand the cause of discrepancy between predicted creep life through parametric methods using short term creep test data and creep life obtained from long term experiments, 1000 and 10,000 h duration creep tests were conducted on a 9Cr-1Mo grade steel at 550 and 650 °C and the oxide scale, fracture surface and microstructure of the crept spe...
The alloy IN740H is ASME code approved vide Case 2702 for manufacturing of superheater and reheater tubes, headers and steam pipes. In order to understand the growth kinetics of γ' precipitates in alloy IN740H, specimens were aged at 800◦C for 100, 500, 1000, 5000 and 10000 hours. The size of the precipitate increased and shape changed from spheric...
In order to understand the simultaneous operation of fatigue and creep mechanisms, strain rate ( ) effect on low cycle fatigue (LCF) behaviour of recently developed power plant grade wrought Ni-based superalloy IN740H was studied. Fatigue experiments were conducted in air, at 760 °C at values 10−2, 10−3 and 10−4 s−1. The fatigue life significantly...
In the present investigation, an attempt was made to understand the cyclic deformation micromechanism of gas turbine alloy Inconel 718 at 600 °C (i) by conducting low cycle fatigue and creep–fatigue interaction tests and (ii) by studying the microstructure evolution in the material during fatigue tests through extensive electron microscopy. Bilinea...
The strain rate (ε ̇) effect on high temperature, low cycle fatigue (LCF) behavior of nickel-base superalloy IN740H was studied by (i) conducting total strain amplitude controlled complete reversal fatigue tests with different values of strain amplitude at 760oC at ε ̇ values 1x10-2, 1x10-3, 1x10-4 s-1; (ii) studying concomitant microstructural cha...
Low cycle fatigue(LCF) behavior of precipitation-strengthened nickel-based superalloy IN740H was investigated systematically by conducting fatigue tests under fully reversed total strain amplitude control conditions at 760oC employing different values of strain amplitude at constant strain rate 1x10-3 s-1. The deformation curves exhibited the initi...
Accelerated oxidation and corrosion of aero engine components due to the presence of hot salt mixture in the operating condition is known as hot corrosion. Hot corrosion degrades life of aero engine components and is broadly divided as type I and type II based on the prevailing temperature and type of salt present in the salt mixture and accordingl...
INCONEL alloy 740H is a candidate material for the boiler tubes and headers to be used in Advance Ultra Supercritical (A-USC) power plants approved via ASME code 2702. The isothermal high temperature oxidation and hot corrosion behavior of IN 740H were studied by; (i) conducting Thermogravimetric analysis (TGA) in air and flue gas (0.25% SO2 + 15%C...
Inconel alloy 740H is a candidate material for use in Advanced Ultra Super Critical boilers at operating steam temperature of 760oC and steam pressure of 37.5 MPa. The alloy 740H is ASME code approved vide Case 2702 for manufacturing of tubes and pipes for superheaters, reheaters, and headers. Nickel base superalloys containing a higher volume frac...
The influence of hot corrosion on low cycle fatigue behavior is studied by conducting fatigue tests at 800 °C in air on bare and salt-coated (90%Na2SO4 + 10%NaCl) specimens. This was followed by extensive scanning electron microscopic (SEM) examinations. Significant reduction in fatigue life is observed across all values of Δεt/2 for the salt-coate...
![Fig. 5. SEM fractograph of bare [(a) and (b)] and salt deposited [(c),...](profile/Jitendra-Sahu-6/publication/257339848/figure/fig4/AS:552873714032640@1508826773704/SEM-fractograph-of-bare-a-and-b-and-salt-deposited-c-d-and-e-sample-crept_Q320.jpg)
The present paper highlights the effect of Na2SO4 and NaCl salt mixture on creep rupture properties of Nimonic-263 alloy at 800 and 850 °C. Results revealed that for short duration tests, the rupture life is not much affected by the corrosive action of the salt mixture at both the temperatures. Whereas for long term creep tests, salt mixture affect...
This paper deals with damage assessment of 17 years service-exposed P-22 grade of steel used in main steam pipe of a boiler in a thermal power plant. Experimentally determined conventional creep data under identical testing condition were used in the present investigation. The value of (ratio of rupture strain to Monkman Grant constant) infers that...
Fatigue crack initiation behavior in duplex stainless steel was studied in the embrittled condition (aging at 475 °C for 100 h) by interrupting fatigue tests conducted at different Δσ/2 values, identifying the crack initiation sites and relating them to the crystallographic parameters obtained from electron back scattered diffraction scans. From th...
The excellent combination of mechanical properties and corrosion resistance of duplex stainless steel is obtained from balanced amount of ferrite and austenite in the microstructure. However, this grade of steel embrittles when exposed in the temperature range of 280-500°C limiting its application to temperatures below 280°C. To study the effect of...
AISI 304L austenitic stainless steel was cold rolled to 90% with and no inter-pass cooling to produced 89% and 43% of deformation induced martensite respectively. The cold rolled specimens were annealed by isothermal and cyclic thermal process. The microstructures of the cold rolled and annealed specimens were studied by the electron microscope. Th...
The low-cycle fatigue behaviour of titanium alloy IMI 834 was comparatively studied in bare condition and with titanium aluminide (Al2Ti) coating at 600 °C in air. Results revealed that at higher values of total strain amplitudes (Δε t/2), Al2Ti-coated IMI 834 alloy has longer fatigue life (N f) compared to the bare IMI 834 alloy, which appears to...
The low cycle fatigue behaviour of titanium alloy IMI 834 was comparatively studied in bare
condition and with titanium aluminide coating, at 600° C in air, for compressor disc of aero
engines. At higher values of total strain amplitudes (Δɛt/2), coated alloy has longer fatigue
life as compared to the bare alloy which appears to be due to load shif...
The elastic, inelastic deformation and stress distribution pattern of a seventeen years service exposed primary superheater tube in a 120 MW boiler of a thermal power plant have been evaluated by using both analytical and numerical techniques. The commercial finite element computer code ANSYS was used for stress analysis. The methodology is a valua...
The solution treated commercial grade AISI 304L austenitic stainless steel plate was heavily cold rolled to 90% of thickness reduction. Cold rolled specimens were annealed at various temperatures by thermal cycles and isothermal annealing. Strain-induced phase transformations and microstructure studies were carried out both in the cold rolled and a...
Duplex stainless steels (DSSs) are two-phase materials consisting of both the ferritic and the austenitic phase. The alloys are prone to embrittlement particularly in the temperature range between 280°C and 512°C. This so-called 475°C embrittlement is caused by a decomposition of the ferritic phase into a chromium-rich α' and an iron-rich α phase....
The low-cycle fatigue behaviour of a duplex stainless steel was comparatively studied in standard heat-treated and isothermally aged (at 475 °C for 100 h) conditions by mechanical testing, scanning and transmission electron microscopy. It was established that fatigue life is longer in the aged condition as compared to the annealed condition at lowe...
As-received hot-rolled commercial grade AISI 304L austenitic stainless steel plates were solution treated at 1060°C to achieve
chemical homogeneity. Microstructural characterization of the solution-treated material revealed polygonal grains of about
85-μm size along with annealing twins. The solution-treated plates were heavily cold rolled to about...
The binary iron–chromium alloy embrittles in the temperature range of 280–500 °C limiting its applications to temperatures below 280 °C. The embrittlement is caused by the decomposition of the alloy to chromium-rich phase, α′ and iron-rich phase, α. This phenomenon is termed 475 °C embrittlement as the rate of embrittlement is highest at 475 °C. Pr...
This paper highlights some of the results obtained while studying Ni20Co18Cr12.5Al0.6Y (NiCoCrAlY) type metallic bond-coat properties of a thermal-barrier coated (TBC), AE-437A Ni base superalloy mostly employed for manufacturing compressor and stationary stator blades in aero turbines. Experiments were mainly focused in the area of evaluation of m...
The elastic, inelastic deformation and stress distribution pattern of a seventeen year service-exposed primary super heater tube in a 120 MW boiler of a thermal power plant have been evaluated by using both analytical and numerical techniques. The commercial finite element computer code ANSYS® was used for stress analysis. The methodology is a valu...
![Fig. 2.17: Cyclic deformation curves [73].](profile/Jitendra-Sahu-6/publication/321573122/figure/fig13/AS:568438004826112@1512537589049/Cyclic-deformation-curves-73_Q320.jpg)
![Fig. 2.3: A schematic diagram of dislocation dipole [46].](profile/Jitendra-Sahu-6/publication/278000832/figure/fig3/AS:669485019176973@1536629075742/A-schematic-diagram-of-dislocation-dipole-46_Q320.jpg)
![Fig. 2.5: PSB and channel-vein structure [9].](profile/Jitendra-Sahu-6/publication/278000832/figure/fig5/AS:669485019193378@1536629075777/PSB-and-channel-vein-structure-9_Q320.jpg)
The low cycle fatigue behaviour of a duplex stainless steel was studied in standard heat treated and embrittled (by aging at 475oC for 100 hours) condition by mechanical testing, scanning and transmission electron microscopy. The fatigue crack initiation behaviour was studied in the embrittled condition by interrupting stress-controlled fatigue tes...
Fatigue testing of thermal barrier coated (TBC), bond coated only and bare Superni C263 superalloy was conducted at 800°C in air. Results reveal that the endurance limits for the TBC and bond coated substrate was substantially higher than that of the base alloy, while the opposite was found for high stress, low cyclic life times. It appears that th...
![Fig. 2.3: A schematic diagram of dislocation dipole [46].](profile/Jitendra-Sahu-6/publication/264840394/figure/fig3/AS:643549301309447@1530445518877/A-schematic-diagram-of-dislocation-dipole-46_Q320.jpg)
![Fig. 2.5: PSB and channel-vein structure [9].](profile/Jitendra-Sahu-6/publication/264840394/figure/fig5/AS:643549301329928@1530445518957/PSB-and-channel-vein-structure-9_Q320.jpg)
