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Heat treatable nickel-based super alloys have appropriate wear resistance to sweet and sour wear environments. Therefore, they are used in disparate industries such as petroleum, gas, and transportation. These super alloys have appropriate hardness, however, sometimes in the oil, gas, and military of this super alloy, more hardness is required to increase erosion resistance. Hence, it is efficient to apply cladding on the super alloy by cobalt-based super alloys.Surface cladding is one of the appropriate methods for increasing the service life of this class of cobalt-based super alloys is used. In the present research, Incoloy 718 were coated with stellite6 cobalt-based super alloys through GTAW method and examined the effect of TIG welding process parameters were examined on hardness and erosion resistance by conducting investigations such as Metallography, microhardness testing, SEM microscope analysis and erosion experiments.The results demonstrated that hardness and erosion resistance of the weld metal from surface to the depth of weld toes increased gradually. The gradual decrease of hardness of weld metal is pertinent to the reduction of the size and quantity of NbC and cobalt. Besides, by increasing the welding current (heat input) preheating temperature, the hardness and resistance to erosion in weld metal was decreased and increased, respectively. Upon increasing the intensity of the welding current and the number of coating layers the dilution value of the base metal in weld metal increases and decreased, receptively. By increasing of preheat temperature, the input value of the basic metal element decreased in coating layer.Finally, the highest erosion resistance is pertinent to the coated samples in 1. triple layer coating, 2. coated sample in the lowest welding current, 3. coated sample in the at 200 and 300 degrees centigrade preheating temperature.

Some shortages in conventional flood cooling technique under heavy cutting settings were noted while machining. Therefore, nanofluids (NF’s) that have elevated thermal conductivity than traditional...

In the present study, effect of prolonged exposure of Incoloy-800HT to molten FLiNaK salt (Fluorides of Li, Na and K) at 923 K on its tensile properties at 300 K (ambient temperature) was investigated. For this purpose tensile tests were conducted using specimens prepared from as-received material (annealed condition), specimens aged at 923 K for 1000 h and those exposed for 1000 h to molten FLiNaK salt at 923 K. Tests were conducted using both standard round bar specimens and miniature flat specimens with an objective to reveal the effect of exposure to molten salt on tensile properties. Results indicated that thermal aging at 923 K has a marginal strengthening effect on the material and exposure to molten salt leads to reduction in specimen thickness which in turn is reflected in the results of the tension test. However, re-estimation of the stress, considering the reduction in the area arising out of the molten salt, revealed that reduction in YS and UTS observed in the testing of miniature specimens exposed to molten salt is only due to early necking arising out of instability generated on the surface of specimens due to molten salt corrosion. A separate study carried out using corrosion test specimens exposed to different duration in molten salt at 923 K revealed that depth of attack saturate beyond 500 h of exposure. Corrosion degradation is uniform throughout the specimen with no evidence of preferential degradation of varying depth, making it possible to have a reasonable prediction of loss of thickness from molten FLiNaK salt corrosion. This provides the option of using Incoloy-800HT as a structural material for applications involving use of molten FLiNaK salt in static condition with sufficient allowance on thickness for molten salt corrosion and further studies are recommended to be conducted in molten salt flow loops.

In this study, the cause of a severe failure and degradation of a nozzle in a secondary reformer unit in an ammonia plant was investigated. The nozzle was made of Incoloy 800H and exposed to harsh atmospheres containing H2, CO, and H2O vapor at a temperature close to 800 °C. Service life of this nozzle is approximately 20,000 h which is much less than its expected design lifetime (80,000 h). Visual inspections indicated that parts of the nozzle’s surface have been degraded into fine black powders/dust. According to the X-ray diffraction (XRD) result, the dust formed on the surface mainly consisted of carbon, Cr7C3, MnCr2O4, MnFeCrO4, Cr23C6, Mn23C6, and Fe3O4 phases. SEM images from the nozzle’s cross section showed that there are some pits on the surface which are filled with metal, oxide, and carbide particles. Micro-hardness test results showed that in areas adjacent to the surface of the pits, the hardness has decreased from 145 to 89 HV due to the depletion of alloying elements and formation of spinel oxide layers over these areas. Overall, metal dusting was diagnosed as the main cause of premature degradation of nozzles in this plant. A failure scenario and some mitigation strategies were proposed, based on the obtained results.

We explore the effects of thermo-chemical aluminization on wear resistance of candidate alloys Incoloy 800HT and Inconel 617 for high-temperature gas-cooled reactor (HTGR) components. Aluminized samples were conditioned for 22 days in a once-through helium loop to simulate oxidizing conditions of HTGRs. The tribological performance of unconditioned and conditioned samples was tested using pin-on-disk tribometer in an air environment at 750 °C for 800HT and 900 °C for 617. Aluminized 800HT exhibited superior wear resistance compared to that of the as-received 800HT due to harder Fe-Al intermetallic compounds that formed at the surface of the alloy. Aluminized 617 exhibited wear resistance superior to that of the as-received 617 at higher loads but inferior resistance at lower loads. Conditioned 800HT as well as aluminized and then conditioned 800HT exhibited negligible wear when the protective oxide remained intact during tribotesting. When the oxide wore through, aluminized and then conditioned 800HT exhibited superior wear resistance compared to that of conditioned 800HT due to the increased hardness of intermetallic zones. Aluminized and then conditioned 617 exhibited inferior wear resistance compared to that of conditioned 617 due to significant ceramic wear of the aluminum oxide. Connections between surface hardness, chemical composition, initial friction coefficients, and wear resistance are established.

The aim of the current research work is to enhance the surface integrity of EDMed (electro-discharge machined) Incoloy 825 by suspending graphite powder particles in dielectric during electro-discharge machining (EDM). For this purpose, a specially designed and fabricated re-circulation dielectric tank was integrated with the existing EDM setup. The effect of three process variables, i.e., peak current, pulse-on time, and duty cycle was studied on EDM characteristics such as material removal rate, surface roughness (Ra), radial overcut, surface microhardness, microhardness in sub-surface regions, recast layer, phase changes and residual stress. Results showed that the machining rate increased up to 23% using powder-mixed EDM compared to conventional EDM. Significant reduction in surface roughness, white layer thickness, surface cracks and residual stress was observed while machining with graphite mixed dielectric. The addition of powder resulted in the formation of carbides and other alloy compounds on the machined surface which enhances the microhardness of surface and subsurface region.

This work mainly studies the microstructure and mechanical properties of Incoloy 825 electron beam welded joints at different temperatures along with their electrochemical corrosion behavior. Two thick Incoloy 825 plates are joined by electron beam welding. The microstructure of the welded joints is analyzed by optical microscopy, scanning electron microscopy and energy-dispersive spectroscopy. The welded joints primarily consist of equiaxed crystals and columnar crystals. Compared with the base metal, there is no obvious variation in the elemental distribution in the weld zone. Microhardness tests are conducted in different regions of the welded joints and base metal, and the results show that the microhardness value of the weld zone is approximately the same as that of the base metal (approximately 180–210 Hv). Thus, the microhardness of the weld zone and the base metal is almost the same. Moreover, tensile tests at 25 °C and 600 °C are conducted in the weld zone, and the results show that the tensile strength and yield strength of the weld joints are roughly similar under the two different conditions. The electrochemical test in an acidic solution at pH = 3 shows that the weld zone has good corrosion resistance.

Anti-fatigue performance is vital for components used in aerospace industry, and cutting processes were widely considered to modify the workpiece anti-fatigue performance. However, most of the existing researches only associated the anti-fatigue performance to the cutting condition and surface integrity, without revealing the effect of material microstructure. In this work, the Incoloy A286 and titanium alloy TC17, two kinds of commonly used material in aerospace industry, were adopted as samples to reveal the influence mechanism of material microstructure on the high-speed cutting modified anti-fatigue performance. It was found that, due to the different microstructure, especially the grain structure and size, the effects of cutting process on the machined surface integrity and anti-fatigue performance of these two materials were different. For Incoloy A286, the large size and cubic structure increased the difficulty in deformation and breaking of grains, making the cutting parameters have limited effect on grain refinement. Hence, the fracture toughness of machined surfaces decreased on the whole with an increased feed rate and depth of cut, which reduced the fatigue life. For titanium alloy TC17, the small lath-shaped grains were easy to deform and break, resulting in the notably grain refinement of machined surfaces, which contributed to the prolonged fatigue life when the feed rate and depth of cut increased. All in all, the material microstructure may change the effect rule of cutting process on the machined workpiece anti-fatigue performance, and thus the cutting condition should be designed by considering the material microstructure.

Radiation fields occur in nuclear power plant primary circuits, and decontamination is needed before the permanent shutdown of a reactor. Radiation field reduction in the primary coolant system of water-cooled reactors can be achieved by using a decontamination solution. As part of this, the corrosion behavior and characterization of oxide layers formed on different kinds of metal should be examined. In this study, NiFe2O4 thin film was deposited on substrates of stainless steel, inconel and carbon steel via electron beam evaporation. The reaction between nickel ferrite and different metal ions results in varying compositions of oxide layers. The phase, structure and morphology of materials were confirmed by SEM, XRD and XPS analysis, and the magnetic properties of each deposited sample were observed by using vibrating sample magnetometer (VSM). The characteristics of the surface-coated metals are the main focus of this work.

Wire Electric Discharge Machining is one of the non-conventional machining processes, used to machine alloy materials with high mechanical strength and also cuts intricate shapes. This paper presents a study in multi performance optimization of machining parameters of Wire electric discharge machining of Incoloy 800 alloy using Taguchi method and grey relational analysis. Incoloy 800 alloy is a nickel, iron and chromium based alloy. The variation in process parameters affects the response variables such as Surface roughness and Material removal rate. Taguchi L27 Orthogonal array is used to perform the experiments. Experiments are performed by considering machining parameters such as Pulse on time, Pulse off time, Gap Voltage, Peak current. By varying the machining parameters accordingly the optimum values are obtained for performance characteristics. The optimization is performed in order to obtain best Surface Roughness and maximum Material Removal Rate. By Grey relational analysis the optimal combination of machining parameters is obtained. ANOVA reveals the most influential factor for Surface roughness and MRR. The results show that the machining parameter Pulse ON time has the greater impact on the performance characteristics.

Incoloy 800 is one among the difficult to machine nickel based superalloy and comprehensively used in high temperature environments. It has better strength and lower thermal diffusion that leads to deprived machining by traditional methods of machining. To overcome such kind of shortcomings, nontraditional approach of material removal processes have been developed and expected to be a suitable substitute method for traditional methods of machining. Wire Electrical Discharge Machining (WEDM) is one of the variant evolved from the perception of Electrical Discharge Machining process that is predominantly employed for machining of hard materials and also for making complex shaped components. In this study, an experimental study has been done on WEDM of nickel based superalloy and primarily focusing on optimizing the process variables for machining of Incoloy 800 by using Taguchi’s analysis. The experimental runs are planned by Taguchi’s DoE approach. The experiments have been performed by considering the process parameters such as pulse on time, pulse off time and peak current at three various levels. Material Removal Rate (MRR), Surface Roughness (SR) and Overcut (OC) are the desired performance measures considered in this present analysis. Taguchi’s analysis and Analysis of Variance (ANOVA) has been used to determine the significance and influence of independent variables on the desired dependent variables. Taguchi - Grey methodology has been adopted for the WEDM process and combination of process parameters are determined for obtaining improved multi performance characteristics. The performance of the selected machining processes has been improved by proposed approach.

Microstructural and mechanical properties of Incoloy 20 were investigated in the as-received (hot rolled and solution annealed) and various heat-treated conditions. Particular interest has been shown to identify the characterization of primary and secondary precipitates at elevated temperatures. As-received Incoloy 20 microstructures revealed fine and twin-annealed grain structures. Incoloy 20 is heat-treated with three different temperatures (700°, 900°, and 1100 °C) at duration of 5 and 10 h. Reduction of segregation and coarsened grain structures is noticed while increasing the homogenization temperature. However, the grain structure remained same with diminution of strength and increased ductility. After the heat treatment, the tensile strength reduced gradually while increasing the temperature for Incoloy 20. The microstructures of the heat-treated specimens revealed the porous structure at grain boundary regions majorly at 900 °C with both durations. In this study, optimal operating temperature for Incoloy 20 is 700 °C where strength remain similar to base metal and also similar microstructure noticed.

In this research the microstructure evolution and mechanical behavior of dissimilar weld between AISI 321 stainless steel (SS) and INCOLOY 825 using ERNiCrMo-3 (Inconel 625) filler wire were investigated. Electron back scattered diffraction (EBSD) analysis was used to characterize the weld substructure. The microstructural examination exhibited an austenitic matrix in either of the two base materials in which formation of Ti-bearing precipitates, more often with cubic morphology, were unveiled. An incomplete transformation of ferrite to austenite led to a significant accumulation of δ-ferrite at the heat affected zone (HAZ) of AISI 321 SS. An entirely austenitic structure accompanied by evidences of secondary phases, rich in Mo and Nb, at the inter-dendritic spaces in the weld metal were observed. Some columnar grains showed the direction parallel to the normal direction relationship. The grain orientation spread map indicated that misorientation variations within the weld metal grains were significantly higher than those of the base metals and HAZs. Texture intensities of HAZs were relatively low. The abnormal grain growth observed in INCOLOY 825 HAZ had a significant effect on orientations of the austenite grains. However, it did not weaken the tensile strength of the weldment. Tensile specimen failure from SS side indicated that this material was more feeble comparing to the INCOLOY one and the weld area. Presence of brittle phases at the inter-dendritic spaces led to a fall in the weld impact toughness in comparison with the parent materials.

Machinability comparisons have been made between superalloys such as Incoloy 825, Inconel 603 XL, Monel K400, and Inconel 600 using wire cut electrical discharge machining based on straightness, surface roughness and perpendicularity. The squared holes have been cut out on different superalloys as per the orthogonal array. Pulse duration, voltage, pulse interval, wire feed and mean current consisting of five levels have been selected as inputs tuning factors for wire cut electrical discharge machining. The scanning electron microscope analysis have been employed to study the machined surface defects of superalloys and unique optimum process parameters respectively. Monel K400 produced better results than other superalloys.

Austenitic alloys such as austenitic stainless steels and Ni-based alloys have been specified as container materials for molten salt reactors (MSRs). In MSR environments, these alloys are susceptib...

Incoloy 925 joints of 5 mm thick were accomplished by adopting high energy density, electron beam welding (EBW) process. Although the weld seam microstructure was completely austenitic and free from solidification cracking, the heat-affected zone (HAZ) of EBW joints experienced liquation cracking. The mechanical behaviour of the EB weld seams in the as-welded and direct aged (DA) at 732 °C for 4 h and air-cooled conditions were compared. Electron backscattered X-ray diffraction (EBSD) analysis revealed the formation of strengthening precipitate γ′ in the matrix and the precipitation of sigma (σ) phase, M7C3, M23C6 and Ti-rich carbides formed along the crystallite boundaries in the DA condition. The tensile property outcomes opined that the joint efficiency of the weld seams in the DA condition (99.32 %) was found to be better than the ones in the as-welded condition (71.32 %). Also, the yield strength has been considerably improved in the EB weld seams subjected to DA conditions. The carbide precipitation along the grain boundaries is discontinuous and also not effective in pinning the dislocations under impact loads.

Elemental segregation leads to hot fissuring in the Incoloy 20. The present investigation examines the possibility of lessening the elemental segregation in the conventional arc welding techniques. In the present investigation, Incoloy 20 plates were fused by continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) with two different nickel-based filler wires (ERNiCrMo-2 and ERNiCrMo-3). The result of the macroexamination shows that steady fluid flow with crack-free welding was succeeded in all the weldments. Optical and scanning electron microscope proves the columnar and cellular structure in CCGTAW specimens and fine equiaxed dendritic structure in PCGTAW specimens. Energy-dispersive spectroscopy (EDS) and X-ray diffraction results exhibit that the weld joint produced by CCGTAW ERNiCrMo-2 shows Cr segregation that leads to the formation of M23C6 phases in the interdendritic regions, whereas ERNiCrMo-3 shows the presence of NbC instead of M23C6. The elemental segregation is suppressed when it comes to PCGTA weldments in both filler wires. Electron backscatter diffraction analysis shows that the CCGTA weldments show coarser grain structure in the heat-affected zone (HAZ). In all the cases, the formation of secondary phases affects the strength of the weld joints at HAZ. Refined microstructure obtained in the PCGTAW in both filler wires shows the marginally higher ultimate tensile strength and toughness compared to the corresponding CCGTA weldments. From the corrosion study, PCGTAW specimens exhibit higher corrosion resistance than the CCGTAW specimens for both filler wires.

Dynamic recrystallization (DRX) plays significant roles in manipulating of microstructures during hot deformation and the result mechanical properties; however, the underling mechanism leading to multi scale–microstructures remains poorly understood. Here, the DRX mechanism under wide processing conditions (i.e. 950–1200 °C, 0.001–10 s−1) in Incoloy 028 alloy was investigated, where the relationships among flow stress, Z parameter and grain size, as well as the evolution of characteristic microstructures (grain size, sub–grain boundaries, and high angle grain boundaries), are established. As the values of Z parameters decrease (corresponding to decreased flow stresses), three typical softening mechanisms successively occur, ranging from continuous DRX controlled by dislocation glide, discontinuous DRX dominated by dislocation motion (climb and cross/multiple slip) and grain boundary migration, to dynamic normal/abnormal grain growth resulting from grain boundary migration, with transition regions where two adjacent mechanisms occur simultaneously. Correspondingly, these above three softening mechanisms result in ultrafine, fine and coarse grains, respectively. The present findings demonstrate a comprehensive understanding of DRX mechanism over a wide range of processing conditions, and further provide a new guideline for preparing single crystals.

This paper studies the stress corrosion cracking (SCC) behaviour of Incoloy 800 in pure 10%NaOH and, respectively, 10%NaOH+0.33g/l NaCl solutions. Notched and un-notched C-ring specimens were tested in a static autoclave at 2600C and 50 bars. To evaluate the electrochemical behaviour of different metal/environment systems, the most important electrochemical parameters were calculated from polarization curves recorded between (�800)mVvsSCE and (+1200)mVvsSCE (scan rate 1mV/s), at 850C. It was emphasised that the presence of Cl- in caustic environment conducts to the decreasing of corrosion rate and corrosion current. Optical microscopy (OM) and scanning electron microscopy (SEM) revealed that the initiation mechanism and penetration depth of SCC cracks depend on the composition of the testing solution: in pure caustic solution, the SCC initiation is transgranular the SCC cracks propagated up to 120m, while in the presence of the Cl-, the SCC cracks started from the pits formed on the samples surface and the SCC depth is shorter than in the pure caustic solution (only up to 20m). X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) analyses were used to identify the composition of the oxide layer build-up on the surface of the specimens exposed in autoclaves. The results indicate that, in the presence of the Cl- anions, the spinel oxide NiCr2O4 is formed in a bigger amount. Due to this compound formation, a greater SCC resistance of Incoloy 800 was observed.

Grain size variations are common in thermomechanically processed alloys with non-uniform cold work. A method to produce samples with grain size gradients was developed using Incoloy 800H. Two tensile samples with non-uniform gages were designed with finite element analysis and manufactured. Measured strain profiles were consistent with designs, and maximum von Mises strains of $$({18.6 \pm 6.1})$$ and $$({13.6 \pm 4.6})$$ pct were obtained. After annealing, an area $${40 \, {\hbox {mm}} \times 5}\, {\hbox {mm}}$$ was mapped by electron backscatter diffraction. Totals of 2849 and 2569 grains were identified after merging twins. Both samples had duplex grain structures as defined in ASTM E1181. Grains were binned into 4 mm strips to evaluate the spatial grain size distribution. Grain size gradients of 0.0081 and 0.0112 $${\hbox {mm}^2/\hbox {mm}}$$ were obtained. Simulated grain growth of the linear gradient microstructure was consistent with accelerated growth predictions. This new method of making samples will enable laboratory studies of gradient grain size effects in realistic industrial alloy microstructures. Further, samples could be used for parallel, single specimen experiments on phenomena that depend on grain size such as complexion transitions and fatigue. Most importantly, high-throughput parallel testing of microstructures enabled by our method could accelerate materials discovery and qualification in fields such as high-entropy and nuclear alloys.

A manifold pipe made of the wrought Incoloy 800H and handling gaseous hydrocarbons at 820 °C has developed longitudinal cracks leading to unscheduled plant shutdown short of about 17% of the expected service life. The respective hydrocarbons result from steam reforming of methane to produce hydrogen in a series of furnace tubes attached to the pipe and externally heated by outside burners. It is shown that the cracks are of intergranular nature and have resulted from massive precipitation of grain boundary carbides particularly the extremely hard and brittle M7C3-type. This is correlated with substantial absorption of elemental carbon released by chemical reactions among carbonaceous gases and subjecting the pipe to carburization attack. However, the role of possible higher than normal external firing temperature in accelerating the carburization and creep rates could not be ruled out. This can occur to compensate for the insulating effect of coke deposited at the inner surface.

In this paper, metallurgical and mechanical properties are assessed for Incoloy 20 weldment made using traditional arc welding methods with ERNiCrMo-4 filler metal. High magnification microscopes (optical and scanning electron microscopes) are utilized to observe the microstructure of welded specimens. Energy dispersive X-ray spectroscopy is utilized to explore the elemental segregation of welded specimens. Secondary precipitates formed during welding are identified through X-ray diffraction method. It is explored that crack-free weldments are achieved from both continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) processes. Hardness, impact and tensile tests are conducted to identify the mechanical properties for welded specimens. Results of CCGTAW and PCGTAW specimens are compared and analyzed in detail. Comparatively, PCGTAW specimens offered better results than that of CCGTAW.

The keyhole mode of plasma arc welding (K-PAW) was employed to weld Incoloy 800H plates of 6 mm thickness. A nickel–chromium-based superalloy, Incoloy 800H is a fully austenitic face-centered cubic structure and imparts better tensile strength, fatigue strength, and creep properties at higher temperatures. Full-penetration weld was achieved by a single-pass welding, and no defects were observed in X-ray radiography testing. Microstructural studies revealed fine equiaxed dendritic structure present in the weld metals due to the steep temperature gradient induced by the K-PAW. Due to fine grain structure, no solidification cracking was observed in the weldment. Mechanical properties studies confirmed that weldments attained the minimal requirements of tensile strength, hardness, ductility, and toughness as per the boiler pressure vessel fabrication requirement norms.

This investigation attempts to explore the weld characteristics of a laser welded dissimilar joint of ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel and Incoloy 800HT austenitic nickel alloy. This dissimilar joint is essential in power generating nuclear and thermal plants operating at 600–650 °C. In such critical operating conditions, it is essential for a dissimilar joint to preserve its characteristics and be free from any kind of defect. The difference between the physical properties of P91 and Incoloy 800HT makes their weldability challenging. Thus, the need for detailed characterization of this dissimilar weld arises. The present work intends to explore the usage of an unconventional welding process (i.e., laser beam welding) and its effect on the joint’s characteristics. The single-pass laser welding technique was employed to obtain maximum penetration through the keyhole mode. The welded joint morphology and mechanical properties were studied in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The macro-optical examination shows the complete penetrations with no inclusion and porosities in the weld. The microstructural study was done in order to observe the precipitation and segregation of elements in dendritic and interface regions. Solidification cracks were observed in the weld fusion zone, confirming the susceptibility of Incoloy 800HT to such cracks due to a mismatch between the melting point and thermal conductivity of the base metals. Failure from base metal was observed in tensile test results of standard AW specimen with a yield stress of 265 MPa, and after PWHT, the value increased to 297 MPa. The peak hardness of 391 HV was observed in the P91 coarse grain heat-affected zone (CGHAZ), and PWHT confirmed the reduction in hardness. The impact toughness results that were obtained were inadequate, as the maximum value of impact toughness was obtained for AW P91 heat-affected zone (HAZ) 108 J and the minimum for PWHT Incoloy 800HT HAZ 45 J. Thus, difficulty in obtaining a dissimilar joint with Incoloy 800HT using the laser beam welding technique was observed due to its susceptibility to solidification cracking.

For the long-term service of X65/Incoloy 825 bimetallic composite pipe girth welds in the H2S environment, the corrosion damage behavior was investigated. Characterizations of welded joints were conducted by OM, SEM, XRD, and EDS. The pitting corrosion’s 3D surface morphology of welded joints in NACE-B solution saturated with H2S was investigated. The results show that composition segregation occurs in the welding process, and the Laves phase appears between dendrites, which lead to the decrease in corrosion resistance. The maximum depth of the corrosion pit is 2.46 μm after 30 days, 4.54 μm after 60 days, and 10.94 μm after 180 days. The cell automata (CA) model of corrosion damage was established based on the MATLAB program, and the basic elements of the cell automata model were determined. Through the simulation of the electrochemical reaction and diffusion process, the influence of different parameters of the pitting corrosion morphology was determined. The simulation results were compared with experimental data, which are available for the prediction of the morphology and size of the corrosion pits on the sample surface after 300 days. The results will be beneficial for the long-term service of the bimetallic composite pipe.

Accomplishment of good dimensional accuracy and acceptable surface integrity in micro drilling of Ni-based superalloys has always been a challenge. The current study seeks to explore these aspects and correlate the same with spindle speed, feed and forces in micro drilling of Incoloy 825 under flood cooling condition. Spindle speeds of 10,000, 20,000 and 30,000 rpm along with four different feeds of 1, 4, 8, 12 μm/rev were considered in the present work. Thrust force exhibited increasing trend with cutting parameters. The dynamic fluctuation (%) for radial forces was considerably higher compared to that of thrust force. A gradual transition from ploughing to shearing was discernible when feed was increased from 1 to 4 μm/rev. Oversize error was found to be closely related with radial forces. Circumferential deformation layer, white layer and plastic deformation zone at sub-surface region along hoop direction showed distinct relationship with spindle speed and feed. However, spindle speed has more pronounced influence on white layer formation than feed. After careful analysis of results, it was observed that optimal results in the form of superior dimensional accuracy, minimum circumferential damage, burr formation, minimum radial force, and reasonably less value of thrust force were achieved under the feed of 4 μm/rev and spindle speed of 10,000 rpm.

The objective of the study is to investigate the phase evolution of the aluminized surface of iron-concentrated nickel-based superalloys. Aluminization is carried out via pack cementation at constant temperature of 900 °C at three processing times of 1, 2.25 and 4 h. Backscattered images and X-ray diffractions are used for phase identification. Small incident angle X-ray diffraction applied on the surface and subjected to repetitive polishing elucidate a formation sequence of iron aluminides. The overall thickness of the aluminized layers is proportional to the processing time squared. The samples are composed of 4 zones, identified by elemental concentration profiles. Only iron aluminides are observed which is in agreement with thermodynamic- and atomic diffusion. The results conclude that aluminization on alloys is similar to oxidation and that nickel aluminide forms with great difficulty on the surface of an aluminized Incoloy 825 alloy.

The oxidation behaviour of Incoloy 909 superalloy subjected to diffusion boronizing treatments was studied at 750 and 850°C in atmospheres of dry air and a mixture of dry air + water vapour for tim...

Advanced power plant alloys must endure high temperatures and pressures for durations at which creep data are often not available, necessitating the extrapolation of creep life. A recently develope...

The feasibility of dissimilar friction stir welding (FSW) between the SAF 2507 super duplex stainless steel and the Incoloy 825 Ni-based superalloy was evaluated. The microstructure and mechanical behavior of the weldments were examined too. The results showed that the alloys were successfully welded together by positioning the SAF 2507 on the advancing side. The nuggets displayed higher hardness than the base metals, due to the occurrence of dynamic recrystallization and the subsequent refinement of the microstructures. The welded sample obtained the similar strength to the Incoloy 825 parent metal, showing the ductile fracture mode after the tensile tests by SEM. Moreover, the weld zone (31 J) exhibited higher and lower toughness than the Incoloy 825 (23 J) and SAF 2507 (42 J) parent metals, respectively. Based on the obtained results, the FSW method could be recommended to weld the super duplex stainless steel/Ni-based superalloy joints.

Incoloy 800HT and Inconel 617 have been selected as candidate structural alloys for the high-temperature gas-cooled reactor (HTGR) concept. Helium, the primary coolant, contains impurities (e.g., H2O and CH4) that can induce corrosion reactions at high temperatures, which in turn can affect the tribological behavior of components in sliding contact such as valves and control-rod drive systems. This paper presents results from the study of the tribological behavior of both alloys before and after conditioning them in either an impure-helium oxidizing environment or in an air environment. Both alloys were conditioned for 22 days at elevated temperatures in a once-through helium loop with 4 ppmv H2O and tested subsequently at elevated temperatures with a pin-on-disk tribometer in an air environment - 650 °C and 750 °C for 800HT; 850 °C and 900 °C for 617 – with various applied loads - 1 N, 2 N and 5 N. SEM-EDS analysis revealed that conditioning the samples in an oxidizing environment leads to the formation of a mixed Fe/Cr-oxide on alloy 800HT and a Cr-oxide on alloy 617, both increasing the wear resistance compared to that of as-received samples. Alloy 617 exhibited lower steady-state friction coefficients compared to those of alloy 800HT. There was a significant decrease in the scatter of the steady-state friction coefficient of the conditioned samples compared to that of the unconditioned samples. The steady-state friction coefficient for alloy 800HT and 617 were found to be 0.53 ± 0.07 and 0.25 ± 0.04, respectively. The wear resistance of alloy 800HT is approximately one order of magnitude lower than that of alloy 617 in all cases that exhibited measurable wear. After sample conditioning, the wear volumes measured at low loads were undistinguishable from the unworn background, a result attributed to the formation of a compacted glaze layer under high temperatures and high contact stresses.

A total of fifty-eight Incoloy 800H samples were creep tested between temperatures of 1023 K and 1293 K, stresses of 14.1 to 105 MPa, and average grain sizes of 87.7 to 315 µm. Combined with data obtained by the National Institute for Materials Science (NIMS), a deformation mechanism map (DMM) for Incoloy 800H was produced. Optimization of the fit of the constitutive creep equations to the experimental data was performed using a global search iterative numerical optimization tool called a genetic algorithm (GA). It was found that the data were well represented by both high-temperature and low-temperature power-law creep mechanisms, but the extent of the influence of diffusion-based creep mechanisms, most specifically Coble creep, will require further investigation. A training and test method was performed to validate the solution and to test the extrapolability of the dataset. It was determined that the extrapolability of the data in all directions of the DMM was generally low.

Running Condition and Material Response Fretting Maps of Incoloy 800 steam generator tubes against AISI 304 L were determined in air at room temperature. Tests were performed up to 106 cycles using displacement amplitudes between 5 and 50 μm and normal contact loads in the range 5–20 N. The regimes identified were Partial Slip (PSR), Gross Slip (GSR) and Mixed Fretting (MFR). In PSR only slight surface damage corresponding to a false brinelling effect of the contacting surfaces was detected. In MFR, fretting wear associated with particle detachment was identified as the main damage mechanism, while the formation of cracks was not detected. In GSR, fretting wear was predominant. Detached debris in GSR were agglomerates of (Ni,Fe)(Fe,Cr)2O4 with sizes between 5 and 20 nm.

The current work employs a two-dimensional plane strain finite element analysis to investigate the unidirectional sliding contact between a deformable half-cylinder and a deformable flat block. The unidirectional sliding is governed by a displacement-controlled action where the materials of the two contacting bodies are first set to identical steels at 20 ℃ and then to Inconel 617 and Incoloy 800H at 800 ℃. First, a normal interference (indentation) is applied, which is followed by unidirectional sliding. The von Mises stress distribution, plastic strain distribution, junction growth, normal force, tangential force, effective coefficient of friction, and scars on the surface of the block are obtained during the sliding motion. The leading edge of the contacting area and the bulk material under the leading edge experience large von Mises stresses. The large plastic strain is found on the surface of the block, and forms a “pocket” shape under the surface. The junction growth is also investigated, showing the direction of the growth is in the same direction of the tangential force that the weaker material experiences. The forces and the effective coefficient of friction are found to stabilize after a certain sliding distance, and the effective coefficient of friction converges to the coefficient of friction used in the model. Pileup is found on the surface of the block after a sufficient unidirectional sliding distance.

Dissimilar joints are commonly encountered in the fabrication of high-temperature power plant components. In this current work, dissimilar joints between P91 and Incoloy 800HT have been produced using two different types of filler materials like ER505 and ERNiCr-3 with the GTAW welding process. Microstructure characterization of the weld metal reveals the presence of columnar dendritic structures. The microhardness value is higher in ER 505 filler-based weldment due to the formation of δ ferrite, M23C6 and MX precipitates. Impression creep test of dissimilar weldments has been conducted with the help of flat bottom cylindrical punch. The impression creep test has been carried out at the temperature of 873.15 K and 923.15 K with a constant load of 135 Mpa with 7200 s of holding time by using a vacuum of the order of 1 × 10−6 mbar in the heating chamber. The impression creep test result has revealed that the depth of penetration of weld with ER505 filler metal has a higher value compared to other weldments. The creep strength of the specimen is compared by the calculated activation energy of each specimen. The creep strength of the weld with ER505 filler metal (Exp No 4) is higher than that of all the other weld’s specimens. Hence, the dissimilar weld with ER505 as a filler material by GTAW process will produce better results.

This research investigated the microtexture and boundaries characteristics of the Incoloy 825 Ni-based superalloy/UNS S32750 super duplex stainless steel (SDSS) dissimilar welds using electron back scattered diffraction analysis. The results indicated that the weld metal was textured; thus, {293} and {348} texture components were observed. As a result of the grain growth and the changes in the morphologies of the phases in the heat affected zones (HAZs), the primary texture components of the alloys were replaced by the new components. In addition, the maximum texture intensities of the generated components in the HAZs were higher than those of the related base metals. The grain growth as well as the changes in the phase morphologies also resulted in a decrease in the proportion of coincident site lattice (CSL) boundaries in the HAZs, in comparison with the base metals. Absence of CSL boundaries in the weld metal was observed too.

This work addressed the effect of pulsed current (PC) and pass number on the microstructure, mechanical properties and corrosion behavior of Incoloy 825/UNS S32750 welds. The alloys were welded using PC and continuous current techniques. Mechanical properties of the weldments were examined using hardness, Charpy and transverse tensile tests. General corrosion and pitting corrosion behavior of the weld metals were studied using potentiodynamic polarization and electrochemical impedance spectroscopy tests. The weld metals had a dual-phase microstructure including ferrite and austenite phases. Employing the PC mode resulted in an increase in the ferrite content of the weld metals, which led to the improvement in impact resistance. Based on the results of tensile tests, the weakest part of the weldments was Incoloy 825 base. The weld metals at the root pass showed the weakest corrosion behavior. Overall, use of the PC mode improved the properties of the weldments.

The main causes of creep failure in the pigtails and tubes made of high-temperature Incoloy 800HT and HP-modified alloy materials of two natural gas primary reformers operating at a petrochemical plant complex were studied. Optical emission spectroscopy, high-resolution optical microscopy, scanning electron microscopy, and energy-dispersive x-ray spectroscopy were performed to verify that creep was the prevailing failure mechanism in both cases. Creep was confirmed in both cases by the (massive) presence of intergranular voids (aligned in some cases) at the grain boundaries and cracks originating from the edge and longitudinal to the edge in some areas. Localized overheating due to burner flame impingement most likely accelerated the creep rate deformation for the HP-modified reformer tube material though the material surpassed its design life of 100,000 h. The findings substantiate that high priority should be placed on reformer burner management and ensuring the catalyst in the reformer tubes is packed optimally to avoid downstream flows issues in the outlet pigtails. These measures can serve to mitigate the effects of localized heating that can contribute to the failure of these components.

The results of this study show that Incoloy 945X is 19.36% harder and 10.91% stronger than Incoloy 945. Of particular interest is the morphology of precipitates responsible for precipitation hardening in both alloys. To identify and understand the physical mechanisms that lead to these results, this study undertook an extensive microstructural study in which γ’ size, shape and elemental constitution was investigated and correlated to the aging conditions. The main strengthening phase for both alloys is identified by transmission electron microscopy to be the main population of γ’ precipitates, which are between 10 and 25 nm in size. Scanning transmission electron microscopy line scans across the γ' precipitate reveal more Nb and Ti deflection in Incoloy 945X than in Incoloy 945. This is further supported by the results of transmission electron microscopy, in which γ’ in 945X appear bright (because of Nb) with faceted growth, resulting in a higher value of 0.2% yield strength (1100 MPa) and hardness (430 HV5) than Incoloy 945.

Incology825 is a nickel-based alloy with good corrosion resistance as well as heat resistance. For effective application of Incoloy825, the flow behavior of the Incoloy 825 during hot deformation needs to be studied and the efficient flow model developed. In this study, hot deformation test was carried out under the temperature of 925℃, 1050℃ and 1150℃ and strain rate of 0.003/s and 3/s. Deep neural network and support vector regression algorithm was thereafter used to model the flow behavior of Incoloy825. The research found that both algorithms describes the flow stress of incoloy825 well. Comparison between deep neural network and support vector regression was done.

The joints of Incoloy 925 obtained from gas tungsten arc welding (GTAW) with pulsating current utilizing ERNiCrMo-3 and ERNiCrMo-10 were investigated under as-welded and direct aged conditions. The microstructure showed the microsegregation of Nb-Mo-, Ti-rich phases in the weld zone of ERNiCrMo-3 in the as-welded condition. Post-weld heat treatment (PWHT) involving direct aging was carried out on the weldments at 732 °C for 4 h followed by air cooling. On direct aging, the tensile strength of the base metal increases by 40% when compared to the as-received ones. The failures were experienced in the parent metal of Incoloy 925 upon tension testing in as-welded conditions. Although the tensile strength was improved considerably, the failures occurred at the fusion zones, for both the fillers in the direct aged conditions. The joint efficiencies of Incoloy 925 welds employing ERNiCrMo-3 and ERNiCrMo-10 were reported as 95 and 86%, respectively. The impact toughness of the weldments in both the as-welded and PWHT conditions was considerably greater compared to that of the candidate metal.