The gas metal arc welding (GMAW) process, prevalent in construction and fabrication sectors, traditionally relies on postproduction evaluations, which are both costly and time-consuming. This study proposes a more efficient, real-time monitoring approach utilizing high-speed data acquisition and analysis systems to record and scrutinize voltage and current fluctuations during welding. Various decomposition techniques, including EMD (empirical mode decomposition), EEMD (ensemble empirical mode decomposition with noise), CEEMDAN (complete ensemble empirical mode decomposition with adaptive noise), and ICEEMDAN (improved complete ensemble empirical mode decomposition with adaptive noise), were analyzed to assess arc variations and thereby evaluate GMAW process quality. The research identified an optimal technique for analyzing non-stationary welding signals, further applied to real-time signals using decomposition and time–frequency representation (TFR) techniques. Findings indicate that key GMAW parameters, such as metal transfer mode and penetration depth, correlate significantly with the intrinsic mode functions (IMFs) and TFRs of decomposed signals. The study suggests that the introduced techniques can effectively analyze the influence of different shielding gases and arc currents on the GMAW process, presenting a promising method for real-time GMAW process monitoring.

Fretting-induced damage is an important failure mechanism in steam generator (SG) tubes in which there will be continuous contact and relative motion between tube and tube-support structures. In this work, the influence of various contact-materials on the fretting fatigue (FF) behavior of modified 9Cr-1Mo (P91) steel, a widely used SG material has been studied. The test setup has been configured as a flat-on-flat contact between the fatigue specimen made of P91-steel and contact-pad. The three different bridge type contact-pads namely, P91-steel, Inconel-718 (IN-718) and aluminized IN-718 were employed. The contact-pad applies constant pressure on the specimen while it is undergoing fatigue cycle. All the tests were carried out at a frequency of 10 Hz, with maximum cyclic stresses ranging from 250 to 525 MPa and a stress ratio of R = 0.1 at a constant contact pressure of 100 MPa. The FF life of the alloy with the contact material made of aluminized IN-718 alloy was observed to be lower in comparison with the IN-718 and P91 contact-materials. The life reduction in the former case was investigated through a comparative analysis of the formation and distribution of debris on fretted surfaces, surface roughness, and the fracture surface of the steel. The formation of the oxide phase such as Fe2O3 (hematite) and Fe3O4 (magnetite) was found on the fretted surface of the specimens.

Proof for distribution of boron in M23C6 precipitates and prior austenite grain boundaries, and role of boron in reducing the coarsening kinetics of the precipitates and thereby improving the creep strength, are established and quantified in modified 9Cr1Mo steels using AES, APT, and TEM. The average atomic concentration of B estimated using APT found to be similar to 80 times more in the precipitate than its nominal composition in the 100 ppm B containing steel. The necessity to have a small quantity of nitrogen in the steel to take advantage of strengthening by carbo-nitrides along with boron-carbides is also proven from the characterization performed on three different steels after creep tests, one with 500 ppm N with no intentional addition of B (rupture life-44 h for creep test at 650 degrees C/120 MPa), another with 70 ppm B and 108 ppm N (rupture life-770 h) and the third steel with 100 ppm of B and 20 ppm of N (rupture life-282 h). Based on the results of characterization and the creep tests, maintaining an optimal concentration of around 70-120 ppm B and 90-120 ppm N are recommended for the maximum advantage of the presence of these two micro-alloying elements in this class of steel.

The fracture behavior of bi-material made of Ni-Cr-B-Si hardfacing alloy deposited over SS316LN substrate was evaluated under quasi-static and dynamic loads. The crack growth started from notch made on the deposit side and progress toward the substrate deposit interface under both loading conditions was monitored. The displacement rate in quasi-static loading and the loading rate for dynamic loading varied and crack propagation was studied. It was observed that the crack was deflected at the interface and not penetrated to the substrate, irrespective of loading conditions. The reason for crack deflection at the interface was analyzed using the energy-based method. It is shown that the ratio of fracture toughness of the interface to that of the substrate (0.044) is lower than the ratio of energy release rate for the deflecting crack to that of the penetrating crack (0.235). Thus, this material combination satisfies the condition for crack deflection rather than penetration. The fracture toughness of the interface was estimated as 68 MPa m1/2 and it falls between that of hardfacing alloy and SS316LN base metal. Optical and SEM examinations were conducted to corroborate the crack path deviations during crack growth. Results suggest that isolated cracks might be present on hardfaced coatings on critical components for which such cracks are usually not permitted. It may be allowed in preference to repair of these cracks, which is difficult and significantly increases the risk of additional cracks forming on the deposits because of the high susceptibility of the hardfacing alloy to cracking.

Surfaces of numerous sodium-cooled fast breeder reactor components are hardfaced with galling-resistant alloys (Ni–Cr–B–Si–C). Coatings are susceptible to cracking during hardfacing. From a fabrication standpoint, it is preferable to avoid repair if the cracks are few and isolated. On the other hand, there is a risk that a pre-existing crack in the coating, if left without repair, may grow into the substrate material, making the components prone to failure. The path of a growing crack in the coating is examined using cohesive zone simulation. Three-point bend tests were done to validate the simulation results. It is shown that an advancing crack deflects at the interface between hardfacing alloy and stainless steel, preventing cracks from traversing the interface and causing catastrophic component failure. The findings of this study give designers an option of accepting reactor components that have isolated cracks on the hardfaced coating without repair.

Ni-Cr-B-Si hardface coating plays an important role in the mating components of nuclear power plants. Obtaining a crack-free coating with low dilution and optimum hardness is essential for reactor applications. In general, it is difficult to achieve this through conventional high heat input processes. In this work, Ni-Cr-B-Si hardface coating was successfully developed on 316LN stainless steel substrate by Cold Metal Transfer (CMT) welding process using metal-cored filler wire. Moreover, for comparative analysis, Ni-Cr-B-Si hardface coating was deposited using Plasma Transferred Arc (PTA) process. The obtained coatings were characterised for their microstructure, hardness, and wear behaviour. Results revealed higher hardness and lower specific wear rate of hardface coating made by the CMT process compared to the coating made by the PTA process. The superior behaviour of the CMT coating obtained may be due to its low dilution compared to the coating made using the PTA process. Confocal microscopy on the worn pins revealed abrasive and adhesive wear as a dominant mechanism in the CMT and PTA coatings, respectively. This study concluded that CMT could be used as an alternate potential process for depositing a crack-free hardface coating with superior wear behaviour.

To comprehend the combined impact of B and N concentrations on modified 9Cr-1Mo steel's heat affected zone (HAZ) creep resistance, five different steels with varying B (0-100 ppm) and N (20-500 ppm) concentrations were subjected to two types of weld thermal cycles (WTC), namely coarse-grained HAZ simulation and inter-critical HAZ simulation with peak temperatures of 1175 degrees C and 850 degrees C, respectively. Prior to and after creep testing (at 650 degrees C, 120 MPa stress), the microstructures and precipitates in the WTC simulated samples were studied using optical and electron microscopy, electron backscattered diffraction, and auger electron spectroscopy techniques. As expected, simulated HAZs of high B-containing steels (70-100 ppm B) showed superior creep resistance compared to low B steels (0-25 ppm B) due to the B stabilizing effect of M23C6 precipitates (primarily (Fe,Cr)23(B,C)6) though the rupture time for the simulated HAZs are lower than that of the base metals tested at the same test temperatures and stress levels. An interesting finding is that, despite the fact that 70 ppm B steel (with 108 ppm N) demonstrated the best creep resistance in normalized and tempered condition, 100 ppm B steel (with just 20 ppm N) obtained the best creep resistance of simulated HAZ. Large difference in the rupture lives between simulated ICHAZ and simulated CGHAZ specimens reveals the effect of triaxility in reducing the rupture lives in simulated CGHAZ specimens. This is also applicable to actual weld joints.

The combined effect of grain size variation and plastic deformation on the acoustic nonlinearity parameter has been investigated in an austenitic stainless-steel material of grade 304. The nonlinear behavior of this parameter with grain growth has deviated to linear fit with deformation. This is due to the interaction of elastic waves with the strain-induced dislocation substructure in the grains. The normalized mean square strain of the deformed specimens has been estimated through angle dispersive x-ray diffraction studies using a synchrotron source, and this has been correlated with the change in the acoustic non-linearity parameter with deformation. The nonlinearity parameter is found to be very sensitive to the plastic deformation even in the presence of grain size variations. The results infer that the variations in the nonlinearity parameter can be used to have an estimate of the extent of localized deformations often occurring during the fabrication of metallic components.

Influence of dilution on high-temperature–high-vacuum-friction behaviour of Ni-Cr-B-Si coating made on AISI 316L (N) stainless steel using plasma transferred arc welding process is studied. Two coatings with different dilution levels are made by using two different welding currents. With increase in dilution (Ni/Fe change from 4.4 to 2.5 and hardness from 46 ± 3 to 30 ± 5 R C ), microstructure changed from hypereutectic to eutectic with variations in the distribution of borides and carbides as well as their relative contents. Sliding wear tests were conducted for coatings using SiC ball as the counterbody, at 823 K under vacuum of 10 –5 mbar. Friction coefficient increased from 0.17 ± 0.04 to 0.42 ± 0.12 with increase in dilution, with the change of wear coefficient from 0.60 × 10 −14 to 0.92 × 10 −14 (m 3 /Nm). Results revealed the dependence of friction on dilution, the effect of which influences the nature of the triboinduced film which in turn controls wear.

Integrity assessment of 10Cr ferritic steel/alloy 617M dissimilar metal weld joint (DMWJ) fabricated from hot-wire narrow-gap TIG (NG-TIG) welding process using alloy 617 filler wire (ERNiCrCoMo-1) was carried out under creep testing at 888 K. Microstructural constituents and hardness across the weld joint (10Cr steel-alloy 617 butter layer-alloy 617 weld metal-alloy 617 M) were found to vary significantly. Alloy 617 weld metal and butter layer have possessed higher hardness as compared to base metals of alloy 617M and 10Cr steel. However, lower hardness was observed in the alloy 617 butter layer, which is adjacent to 10Cr steel, and in the outer edge of HAZ in the 10Cr steel. The carbon migration was predominantly observed across the interface between 10Cr steel and alloy 617 butter layer. Creep tests performed on 10Cr steel and DMWJ at 888 K have revealed the lower creep strain accumulation in DMWJ than the 10Cr steel base metal. An early onset of tertiary creep deformation and consequent premature failure of DMWJ were noticed as compared to the 10Cr steel. Creep rupture strength of the DMWJ was about 31% lower than the 10Cr steel. Fracture in the weld joint has occurred at the interface between 10Cr steel and alloy 617 buttered layer with significant reduction in ductility. The formation of coarse M23C6 precipitates and Laves phase (enriched by Mo and W), oxidation, heterogeneity in strength across the interface have facilitated the extensive cavitation at the interface, thereby leading to premature failure of the DMWJ. Weld strength reduction factor of about 0.69 at 888 K for 10(4) h has been obtained for the DMWJ.

A chemistry-controlled variant of nickel-based Alloy 617 (UNS N06617) designated as Alloy 617M is the candidate structural material for superheater header and tubing and high pressure and intermediate pressure steam turbines for Indian advanced ultra-supercritical (AUSC) coal-fired thermal power plant mission program. This study evaluates the effect of ageing due to service exposure on microstructure, mechanical properties and repair welding behaviour of Alloy 617M boiler tube material. Initially, Alloy 617M tube weld joints (52 mm diameter and 11.9 mm thick) were fabricated by multi-pass manual gas tungsten arc welding (GTAW) process using ERNiCrCoMo-1 welding wire. Service-exposed material is simulated by subjecting the base metal and welded tubes to ageing heat treatment at 700 °C and 750 °C for 1000 h and 4000 h. Extensive carbide precipitation along the grain boundaries and γ′-Ni 3 (Al, Ti) within the grains were observed in the aged base metal and weld metal. The yield strength and tensile strength of Alloy 617M base metal and weld metal after ageing heat treatment increased by 150–200 MPa in comparison to as-received/as-welded condition. In contrast, the Charpy V-notch toughness showed significant reduction after ageing, viz. weld metal toughness reduced from 125 J in the as-welded condition to 50 J after ageing. Partial penetration repair weld joints fabricated from the aged welded tubes showed presence of micro-fissures in the heat-affected zone (HAZ) and are intergranular in nature. However, the application of solution annealing heat treatment at 1160 °C for 1 h to aged Alloy 617M before repair welding could help in producing repair welds without micro-fissures.

In the present study, the lattice misfit and lattice strain of aged Alloy 617 (aged at 700°C for 100h, 1000h and 4000h) has been studied using X-ray diffraction Rietveld analysis and compared with observed microstructure characterized using FESEM. Aged Alloy 617 showed presence of fine uniformly distributed g¢-Ni3(Al, Ti) precipitates within the grains (g-matrix) along with Cr-rich precipitates along the grain boundaries. The size and volume fraction of g¢ precipitates increased with increase in ageing time. Peaks corresponding to Cr-rich precipitates are absent in the XRD pattern and γ΄- peaks overlapped with γ-matrix peaks. The lattice parameters of γ and γ¢ calculated from de-convoluted peaks by Rietveld method varied from 3.5806 Å to 3.58211 Å and 3.5744 Å to 3.5877 Å respectively. Lattice misfit of γ/γ΄ calculated in aged specimens revealed that misfit transitioned from negative for 100h and 1000h ageing to positive for 4000h of ageing time. Williamson-Hall size-strain analysis for lattice strain evaluation couldn’t be applied in the present study due to anisotropic peak broadening. The lattice strain was evaluated by phenomenological method and the strain decreased in 100h aged sample compared to as-received solution annealed sample, and the lattice strain increased with increasing ageing time. The evolution of lattice misfit and lattice strain as a function of aging time associated with microstructural changes are correlated with their mechanical properties.

In this paper investigation of FEM based thermal analysis of Gas Tungsten Arc welding of 2 mm thick plate ferritic martensitic steel plate was carried out. Three dimensional thermo-elastic model based on FEA was carried using two different softwares SYSWELD and FlexPDE. In the initial part of the work, heat source fitting (HSF) was carried out using Grade 91 steel bead on plate welding. Predicted weld profile using heat source fitting tool was compared with predicted models. In both the softwares step-by-step modeling has been carried out using HSF analysis tool. In the second step square butt joint welding of Grade 91 steel was carried.

The present study investigates the relative effect of B and N concentrations and the austenitization temperature on the microstructure and mechanical properties (tensile and Charpy impact) of modified 9Cr-1Mo (P91) steels. Initially, a B-free P91 steel (with 500 ppm N) and four different B-containing steels (25–100 ppm) with varying N concentrations (20–108 ppm) were hot-rolled, normalized from different austenitization temperatures (1000–1100 °C/1 h) and finally tempered at 760 °C for 1 h. A Charpy impact test shows that the ductile–brittle transition temperature (DBTT) of all the B-added steels decreases with an increase in the austenitization temperature, where the 100 ppm B steel offers the lowest DBTT (−85 °C). Similarly, the strength increases with the increase in the austenitization temperature (1100 °C), with a slight drop in ductility. The influence of precipitates on the microstructure and mechanical properties is explained considering the B enrichment at the precipitates and the thermodynamic stability of the precipitates. The 100 ppm B steel (containing the maximum B and minimum N), normalized from 1100 °C austenitization, shows the best combination of tensile and Charpy impact properties, owing to the effective dissolution of coarse M23C6 and MX precipitates during the normalization treatment and the formation of fine B-rich (Fe,Cr)23(B,C)6 precipitates during the subsequent tempering.

The use of blended green concrete with improved performance has significantly increased in the industrial sector owing to the CO2 gas emissions and carbon footprint caused by the production of ordinary Portland cement. Although improvements have been continuously made, the deterioration of concrete structures in seawater poses a serious concern. The long term performance of green concretes in seawater environment are scarcely studied. Here we report the long-term strength, durability and anti-fouling properties of a novel blended eco-friendly concrete made with ordinary Portland cement, fly ash, nanoparticles, and corrosion inhibitor in natural seawater for one year. The mechanical strength, alkalinity, free chloride concentrations, biofouling attachment, and total viability count are studied. After a year of exposure to seawater, the ternary blended green concrete showed improved mechanical strength, a significantly lower chloride penetration and water penetration depth, a 70% reduction in free chloride content, a high calcium silicate hydrate content, and a four-order reduction in the total biomass. Our results suggest that the new concrete mix is promising for applications in seawater environments because of its improved mechanical properties, durability, and biofouling resistance.

SMAW (Shielded Metal Arc Welding) and GMAW (Gas Metal Arc Welding) are two of the most prominent welding processes commonly utilized in almost all types of modern industries. Among various aspects of these processes, some of the important parameters that govern the quality of the final weld product are the skill level of welders, welding consumables, and the role of shielding gases (in GMAW). Currently, the role of these parameters in determining the quality of the welded product is examined by evaluating the final weld produced and not by investigating how these factors affect the welding process. This is an indirect way to evaluate such welding parameters, which are both time-consuming and expensive. During the actual welding process, random variations in arc signals (voltage and current) take place. These dynamic variations are so short and rapid that ordinary ammeters and voltmeters cannot monitor the rate of such variations. However, the reliable acquisition of such variations and its subsequent analysis can provide very useful information in determining the quality of the final weld product. In this study, arc voltage and current were acquired at 100,000 samples/sec, filtered and subsequently analyzed using Continuous Wavelet Transform based on Fast Fourier Transform (CWT-FFT) technique to evaluate welding skill, welding electrodes (in SMAW process), and the effect of shielding gases (in GMAW process). Results thus obtained clearly differentiated the skill level of different trainee welders and welding electrodes in the SMAW process and the effect of shielding gases and arc current in the GMAW process. Very good correlation among the obtained results, its weld bead and its weld pool images were observed. Hence, this research proposes a simple yet effective methodology to evaluate the arc welding process parameters using CWT-FFT analysis of the welding signals.

AM350 is a candidate material for welded disc bellows in nuclear applications. The assessment of tensile deformation behavior of AM350 stainless steel in two different heat treatment conditions, solution annealed (SA) and sub-cooling and tempered (SCT), has been carried out in this investigation. Microstructure in the former heat treatment condition was predominantly austenitic while in the latter, it was martensitic. The material in SCT condition was found to have higher yield and tensile strengths and lower ductility at room temperature and 530 °C than in the SA condition. During tensile deformation, it was found that the material exhibited strain-induced martensite, which was estimated by volume fraction in XRD and ferritescope measurements. However, at 530 °C, the same was absent as the testing temperature was more than Md temperature. The results of the work are useful in understanding the response of AM350 during manufacturing and in service.

Boron-added modified 9Cr-1Mo (P91B) steel is being considered as an alternate candidate material for steam generators of sodium cooled fast reactors. As components in service consist of discontinuities in geometry, the creep behaviour of P91B steel was investigated by including discontinuity in the form of U-notch. The notch root radius (r) of notched specimens was varied as 0.25, 1.25 and 2.5 mm, while keeping the notch diameter and depth (h) as the same. The corresponding notch acuity ratios (h/r) are 6.7, 1.34 and 0.67 respectively. The creep tests were conducted on notched specimens at 923 K and at 240 and 260 MPa. A non-contact type video extensometer was used to measure the elongation in the different regions of the notched specimen. The creep strain in both the plain as well as notch regions were measured individually. It has been observed that the response of material to applied load was not uniform along the specimen length, due to existence of stress gradient in the presence of notch and was manifested as compressive strain in the plain region between the double U-notches in some tests. At the stress level of 240 MPa, the creep rupture life increased upto 1.5 times with increase in notch acuity ratio from 0.67 to 6.7.

Laser-welded fully austenitic stainless steel (AISI 316LN) weldments revealed the presence of micro-fissures. They appeared at the grain boundaries, near the center of the welds. The grain boundaries, however, did not contain second phase or micro-segregation. The relative presence of micro-fissures decreased with increasing weld heat input. Spatial locations of the micro-fissures and their relative presence were associated with local misorientations and, in particular, with grain reference orientation deviation. Microstructural and microtextural studies indicated that solidification shrinkage was the origin of the micro-fissures in the laser welds. The use of sub-size tensile specimens (of 5- and 1-mm gauge length) with digital image correlation (DIC) related the presence of micro-fissures with mechanical property degradation by the appearance of strain localizations. This was further confirmed by analytical solutions and finite element analysis of critical flaw size and critical stress for fracture.

Molten salt reactors (MSR) are Generation-IV fission reactors. MSR is a class of nuclear fission reactors in which the coolant is a mixture of molten salts. They are very compact design of nuclear reactors. Many agencies working on this conclude that MSR can deliver a safe, economical, sustainable energy, without generation of CO2 gas. As MSRs operate at very high temperatures compared to water cooled reactors, they have high thermodynamic efficiency. The molten salts are more efficient than compressed helium as it can remove more heat from core, hence making the system more compact. However, many constraints have been identified which could create setbacks in MSR. Many of these have been addressed to a large extent by various research works that were carried out throughout the world. This paper reviews the evolution of molten salts as coolant and since the Indian nuclear program has identified FLiNaK as one of the candidate coolants for the Indian MSR, a review on the degradation of structural materials in FLiNaK medium is also presented and discussed.