Hastelloy C-276 Research Articles

Optimization of Process Parameters of EDM of Inconel 617 by Taguchi Based PCA and GRA Technique and Effect of Recast Layer Formation

Inconel materials are manufactured in various series which have differences in their chemical composition and hence in its physical and chemical properties. These alloy materials are known for their high strength, corrosion resistance and oxidation resistance. They are not easily machine-able through conventional machining, due to rapid work hardening tendency, high toughness and hardness, tendency to form built up edges, hence for their machining, non conventional machining equipments like EDM are used. A number of experiments has been performed to optimize process parameters of EDM on different series of Inconel material like Inconel 625, Inconel 718, Inconel 601, Inconel hastelloy C-276, Inconel 690 etc. by different optimization technique Taguchi, PCA, GRA etc however there is a lack of data available for optimization of process parameters of EDM machining for Inconel 617. So in this paper optimization of process parameters like Pulse on time, peak current, gap voltage have been done by taking Material Removal Rate and Tool Wear Rate as response variables. Other process parameters have been kept constant during EDM process. It is found that for different values of process parameters pattern of variation of MRR and TWR is different. Also the effect of recast layer formation on MRR and TWR has been analyzed and it is found that at high Peak Current and high Pulse on Time, tendency of formation of recast layer is high. Formation of recast layer adversely affects MRR and TWR i.e. it reduces MRR and TWR. Also Results obtained from PCA and GRA has been compared and it is found that both methods give same optimum set of process parameters but they have differences in pattern of variation of MRR and TWR.

Adjust dilution level to suppress the precipitated phase by dilution level model of dissimilar metal laser welding with filler wire

To suppress the precipitated phase by adjusting the dilution level of 304 in the dissimilar metal (Hastelloy C-276/SUS 304) laser welding with filler wire, a mathematical model was established between laser parameters and the dilution level of 304 through energy conservation and mass conservation. And the model was verified by the corresponding experiment. The dilution level of 304 is linear with the single pulse energy E and inverse of wire feeding speed (1/VF), and it is also affected by energy melting efficiency and the ratio of two base metals melting. The dilution level of 304 is positively correlated with energy melting efficiency and negatively correlated with the ratio of two base metals melting. Defocusing distance and pulse width can affect dilution level of 304 by changing energy melting efficiency. Welding speed and laser beam offset can affect dilution level of 304 by changing the ratio of two base metals melting. At the same time, the influencing mechanism of the dilution level of 304 on the precipitated phase is revealed. The precipitated phase is directly related to the dilution level of 304. With the increase of dilution level of 304, the volume fraction of precipitated phase increases first and then decreases. When the dilution level of 304 is 24.0% ~ 35.2%, the volume fraction of precipitated phase is the biggest. And when the dilution level of 304 arrives to about 73.0%, the precipitated phase approximately disappears. As the result, the dilution level of 304 can be adjusted to suppress the precipitated phase by the dilution model in the laser welding Hastelloy C-276/SUS 304 with filler wire.

Experimental investigation of Hastelloy C-276 using abrasive waterjet milling

Abrasive waterjet milling (AWJ Milling) is a machining method as it can be used to quickly process a wide range of industrial materials without adversely affecting their properties. The viability of using AWJ milling to machine Hastelloy C-276 Ni-Mo-Cr super alloy was investigated here in detail for the first time. Experiments were performed by varying AWJ milling process parameters, including the water jet pressure, standoff distance, traverse speed, and abrasive flow rate using the Taguchi orthogonal array. A desirability function analysis was applied to identify the optimum AWJ milling conditions for maximizing material removal rate and minimizing surface roughness. The surface morphology of the super alloy samples was studied to determine the material removal mechanism under the optimal milling conditions. In addition, a semi-empirical model was developed to predict the surface roughness of Hastelloy C-276 processed using AWJ milling. These findings are expected to promote the wider use of AWJ milling for machining of Hastelloy C-276 super alloy, which could improve the processing efficiency and quality of parts for chemical and nuclear industries, among others.

Electrochemical response of various metals to oxygen gas bubbling in molten LiCl–Li2O melt

The electrochemical response of several alloys (stainless steel 316, Hastelloy C276, Inconel 600, and tantalum) was investigated in molten LiCl–Li2O (1 wt%) at 923 K while bubbling oxygen gas into the molten salt. Tafel and zero resistance ammeter (ZRA) electrochemical methods were used to measure electrochemical effects of oxidation processes at the surface of each alloy. The Tafel method required approximately 15 min and was, thus, applied only in intervals between periods of oxygen bubbling in the salt. ZRA measurements were made in real time, while the O2 was actively being bubbled into the salt. This method recorded both open circuit potential of the alloy relative to a Ni/NiO reference electrode and current between the alloy and the galvanically coupled platinum plate that served as the counter electrode. Both open circuit potential and galvanic oxidation current started to increase at the initiation of oxygen flow. Based on the observed oxidation current trend, it was inferred that the metals in order of increasing resistance to oxidation in molten LiCl–Li2O are as follows: tantalum < SS-316 < Inconel 600 < Haynes C276. Scanning electron microscopy images indicated formation of an oxide layer of thickness 560–3370 nm that correlates with the galvanic oxidation current measurements.

Experimental and numerical investigations on machining of Hastelloy C276 under cryogenic condition

In this study, an attempt has been made to investigate the influences of cryogenic coolant on cutting temperature, cutting force, thrust force and feed force while turning the Hastelloy C276 – a nickel-based superalloy. Numerical simulation was carried out using Deform 3D analytical tool for the machining process performed at the optimal cutting conditions using Lagrangian formulation. CNC turning experiments were also performed with different cutting parameters. The results observed from the simulation were compared with the experimental investigations and were found to be in good agreement with experimental results. The results inferred that the cutting temperature was reduced up to 57% by involving machining in cryogenic condition. It was concluding from both the simulation and experiment studies that the machining under cryogenic condition effectively reduces the cutting temperature and machining forces when compared with that of dry condition.

Microstructure and Abrasive Wear Behaviour of Nickel Based Hardfacing Stainless Steel Deposited by Gas Metal Arc Welding

Wear is one of the foremost issues faced in manufacturing industries that reduces the lifestyles of machine elements and will increase the running costs. Therefore, hardfacing is extensively employed by industry professionals to minimise the wear of moving components. In this research work, a nickel based alloy recognized as Hastelloy C-276 was strengthened on stainless steel (316L) substrate via the usage of Gas Metal Arc Welding (GMAW) technique. The coating thickness used to be assorted was from 1 to 3 mm on the substrate. The optical microstructure of the interface revealed the defect-free fusion between hardface and substrate metals. Microhardness (Hv) and three-body abrasive put on test have proven that the hardfaced alloy metal posses higher hardness and effective wear resistance. The worn surface morphologies have been found using SEM in order to perceive the involved wear mechanisms.

Prediction of Material Removal in Extrusion Honing of Hastelloy C22 Using Artificial Neural Network

The traditional finishing processes are incapable of producing required surface finish and other characteristics in difficult-to machine materials like Nickel based superalloys and also complex geometrical shapes of engineering components. Hence to achieve these goals non-traditional micro-machining processes have been developed. Extrusion honing (EH) is one of the non-traditional micro-machining process to debur, radius, polish, and remove recast layer of components in a wide range of applications. In this process material is removed from the work-piece by flowing abrasive laden medium under pressure through or past the work surface to be finished. Components made up of complex passages having surface/areas inaccessible to traditional methods can be finished to high quality and precision by this process. Hastelloy C22 offers resistance to both aqueous corrosion and attack at elevated temperatures and it is a difficult metal to machine using traditional techniques. In this study, micro finishing of internal surface of Hastelloy C22 material having predrilled passage diameters 7, 8, 9 and 10 mm have been performed in an indigenously built hydraulic operated one way extrusion honing setup. For the present EH process, patented polymer mixed with SiC abrasive at 35% volume concentration was used as carrier medium. The study was performed for 46, 54, and 60 grit sizes of SiC abrasive. The material removal in EH process varies with passage diameter and grit size of abrasives at each trial. A feed forward back propagation neural network model has been developed for the prediction of material removal and it has successfully predicted material removed in each trial of EH process.

Hardness Along with Electrochemical Corrosion Performance Examination of Hastelloy C276

Hastelloy C276 a versatile corrosion resistant alloy, is investigated at 298 K. The tribological properties such as frictional force, In the micro-hardness test at 40 N load, the hardness is increased by 25 % as compared to 10, 20, 30 N loading conditions. The experimental results indicated reduction in coefficient of friction values and thus an increase in the frictional force with the increase in normal load. The images of worn out surfaces confirm that the delamination and adhesion causes the material removal from the surface in dry sliding. Further, the analysis of the hardness characteristics of worn out surfaces shows surface hardening during sliding wear process under 40 N loads. The study on the corrosion wear behavior in the sulphuric acid showed a significantly lower value of corrosion rate (0.0016579 mm/y in H2SO4 solution) in comparison to other alloys frequently used in industries.

Microstructural Characterization and Evaluation of Sliding Wear of Hastelloy C276 under Different Loading Conditions

Hastelloy C276 is investigated for dry sliding wear against an EN 31 stainless steel (hardness 60 HRC) at 298 K. The tribological properties such as frictional force, coefficient of friction and the wear rate on the material surface at different sliding distance are examined under different loading conditions. In the dry wear test at 40 N load, the wear rate increased by 300% as compared to 10, 20, 30 N loading conditions. The experimental results indicated reduction in coefficient of friction values and thus an increase in the frictional force with the increase in normal load. SEM images of worn out surfaces confirm that the delamination and adhesion causes the material removal from the surface in dry sliding. Further, the analysis of the hardness characteristics of worn out surfaces shows surface hardening during sliding wear process under 40 N loads.

Corrosion Properties of Thermally Sprayed Bond Coatings Under Plasma-Sprayed Chromia Coating in Sulfuric Acid Solutions

Plasma-sprayed chromia coatings are known to have excellent corrosion and wear properties in highly acidic conditions at ambient and elevated temperatures, but are not watertight due to their intrinsic porosity. Therefore, in applications involving aggressive environments, the whole component is usually made of a corrosion-resistant alloy, to which the Cr2O3 coating imparts the necessary wear resistance. However, in such aggressive environments, the survival of thermal spray metallic bond layers becomes an issue. The present study deals with the performance in sulfuric acid solutions of coated systems consisting of a Hastelloy C-276 substrate and a plasma-sprayed Cr2O3 top coating with four different intermediate bond coatings. The bond coatings were HVOF-sprayed Ni-20Cr, Hastelloy C-276 and Ultimet alloys and plasma-sprayed tantalum. Open-circuit measurement, electrochemical polarization and electrochemical impedance spectroscopy tests were carried out at room temperature (RT) in solutions with various concentrations. Also, static immersion tests were performed at RT and 60 °C. The results revealed that the HVOF-sprayed Ni-20Cr and Ultimet alloy coatings were significantly attacked by the sulfuric acid electrolyte, especially at 60 °C, whereas the HVOF-sprayed Hastelloy C-276 and plasma-sprayed Ta coatings performed significantly better.

Flow characteristics of the molten pool in pulsed laser welding of thin sheet with filler wire

A 3D transient model has been developed to analysis the molten pool flow characteristic in pulsed laser welding thin sheet with filler wire. The free surface is tracked by VOF method, and the filler metal is simplified as droplets. The flow characteristics in welding of Hastelloy C-276 sheets with 0.5 mm in thickness are analyzed with this model. The calculated weld appearance fits well with the experimental one. Before the droplet contacts with the molten pool, the liquid metal driven by surface tension flows towards the center and downward at the upper surface. The max velocity at the center is about 0.97 m/s. At the trailing portion of lower surface, two eddies with similar spin direction are generated due to the outward surface flow and the downward flow. The filler metal has significant influence on the convection pattern in the molten pool, and results in the disappearance of flow characteristics dominated by surface tension. The filler metal flows downward and outward rapidly after the droplet contact with molten pool. The maximum velocity is about 1.74 m/s and appears at the location where the droplet enters into the molten pool. The droplet has an impact effect on the molten pool and the convection pattern is changed. The molten pool shows oscillation characteristic due to the combined effect of droplet impact and surface tension. The volume of the molten pool dose not decrease right after the laser pulse ends, the lower part of the molten pool expands for about 3–4 milliseconds. And this phenomenon is related to the pulse effect of the laser beam, the flow pattern of the molten pool and the thermal properties of the material. Due to high pulse frequency of the laser beam and low thermal conductivity of the material, the molten pool always exists during welding process.

Corrosion of alloys in high temperature molten-salt heat transfer fluids with air as the cover gas

The state-of-the-art concentrated solar power tower technology requires novel heat transfer fluids which can operate at a temperature as high as 700 °C. Several molten eutectic salt mixtures are promising heat transfer fluid candidates because they are thermally stable at such high temperature and have good thermophysical properties. However, their corrosion properties to alloys are not investigated thoroughly in the literature. Molten salts usually have high corrosion to alloys, which is a critical issue since the piping and containing materials of the heat transfer fluid in a solar power plant are generally alloys. In this study, the corrosion of three eutectic mixtures including NaCl-KCl-ZnCl2, Li2CO3-Na2CO3-K2CO3 and LiF-Na2CO3-K2CO3 to different alloys were experimentally studied at isothermal condition of 700 °C in contact with air. Alloys tested were stainless steel 316 (SS316), Hastelloy C276 (C276), Inconel 625 (In625) and 718 (In718). Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were employed to characterize the coupon surfaces after corrosion tests. Results show that all the alloys have corrosion rates higher than 450 μm/year immersed in the NaKZn chloride-salt. Therefore, the NaKZn chloride-salt is not applicable as a heat transfer fluid if air cannot be evacuated. C276 immersed in the LiNaK carbonate-salt and In718 immersed in the LiF-NaK carbonate-salt may form protective compact layers on the alloy surfaces to resist corrosion. However, the high cost of lithium salts is another major obstacle to commercialize heat transfer fluids.

Evaluation of materials of construction for the sulfuric acid decomposition section in the sulfur–iodine (S–I) cycle for hydrogen production: Some preliminary studies on selected materials

Water splitting by Sulfur–Iodine (S–I) cycle is one of the promising thermochemical processes for hydrogen production due to its high efficiency. The decomposition of H2SO4 to produce SO2 is the reaction with the highest energy demand in the S–I cycle and it shows a large kinetic barrier. Sulfuric acid is highly corrosive and its endothermic decomposition needs elevated temperatures (>800 °C). Henceforth, before the scale-up of the process plant there is a need to explore various materials of construction under very harsh acidic environments and phase changing conditions. Corrosion studies on some of the possible materials of construction (SS-304, SS-310, SS-316, Inconel-800, Alloy-20, Inconel-600, Incoloy-800H, Hastelloy C-276) were performed in detail and the most corrosion resistant material is suggested for the construction of sulfuric acid decomposition unit. The studies were performed at low temperatures (60 °C and 120 °C) as well as at high temperatures (700 °C, 800 °C and 900 °C). The corrosion rates were determined using weight loss method at low as well as high temperature and by using electrochemical method at low temperature (80 °C). The phase changing condition was more severe and resulted in higher corrosion rate. Hastelloy C-276 showed the least corrosion rate. SYNOPSIS In order to identify the suitable materials of construction for sulfuric acid decomposition in the S–I cycle, corrosion rates of different materials were determined. Materials were exposed to the various phases of sulfuric acid. The phase changing conditions had the most adverse effect on the materials.

Parameter optimization in laser welding of Hastelloy C-276 using TOPSIS

Abstract In this work, an attempt was made to identify optimized parameter combination in the laser welding of Hastelloy C-276. Bead on plate welding was carried out on Hastelloy C-276 sheet of thickness 1.6 mm using CO2 laser welding process. Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) Optimization technique was used to identify the optimized parameters combination. In addition to that Analysis of Variance (ANOVA) was utilized to determine the most significant parameters on the overall Multiobjective function. From ANOVA results, it is understood that laser power had considerable control on the overall Multiobjective function.

Hot corrosion of different alloys in chloride and carbonate molten-salt mixtures under argon atmosphere

Molten eutectic salt mixtures can be used as thermal energy storage materials or heat transfer fluids at concentrated solar power plants. The targeted operating temperature for the next generation concentrated solar power plants is 700 °C. Although chloride and carbonate eutectic salt mixtures with high thermally stable temperatures were reported to have great thermophysical properties, their corrosion to alloys at high temperature has not been thoroughly studied. Corrosion of the thermal energy storage materials and heat transfer fluids to alloys is critical, and oxygen in air is confirmed to accelerate the corrosion significantly. In the present study, three eutectic mixtures of NaCl-KCl-ZnCl2, Li2CO3-Na2CO3-K2CO3 and LiF-Na2CO3-K2CO3 were considered as high temperature thermal energy storage materials or heat transfer fluids. Corrosion of stainless steel 316, Hastelloy C276, Inconel 625 and 718 immersed in the three salt mixtures up to 21 days were experimentally investigated at 700 °C under argon atmosphere. The specimens after corrosion tests were characterized by scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. The results show that SS316 is only compatible with the LiNaK carbonate-salt and the corresponding corrosion rate is lower than 95 μm/year. Both C276 and In625 have relatively good corrosion resistance for the NaKZn chloride-salt and LiF-NaK carbonate-salt, and the corrosion rates are lower than 78 μm/year. The highest corrosion rate over 1700 μm/year is detected for In625 immersed in the LiNaK carbonate-salt. In addition, In718 shows excellent corrosion resistance less than 10 μm/year immersed in all the three salt mixtures.

Effect of low energy laser shock peening on the mechanical integrity of Hastelloy C-276 welds

The pulsating current approach in tungsten inert gas (TIG) welding is adapted for joining Hastelloy C-276. Microstructure examination revealed the absence of micro-segregation while employing UNS N06022 filler. Due to the prevalence of higher tensile stresses in the un-peened conditions, tensile failures were observed in the weld regions of both the joints irrespective of fillers. Low energy laser shock peening without coating (LSPwC) was carried out on the weld zones on both the sides of the joints with the pulse densities 2500 and 7500 pulses per cm2. This laser surface treatment had remarkably increased the tensile strength of the welded joints by shifting the location of tensile failures well away from the fusion zones for all the cases. Similarly, a considerable increase is observed in the notch toughness of both the joints in the LSPwC condition. The enhancement in tensile strength and notch impact toughness of the welds could be ascribed to the residual compressive stresses induced which were then confirmed by Sin2ψ method in X-ray diffraction (XRD) technique.

Study of melting efficiency, micro-segregation, and corrosion resistance of Ytterbium fiber laser welded Hastelloy C-276 sheet in pulsed wave mode

ABSTRACTWelding of Hastelloys using higher value of ‘linear heat input' decreases corrosion resistance due to the increase in micro-segregation of elements in the weld zone. 'Melting efficiency' of heat source could be an important parameter to control the heat input and micro-segregation of elements in the weld zone. In the present study, bead-on-plate welding was carried out on 3-mm-thick Hastelloy C-276 sheet at constant laser power and varying scan speed in pulsed mode, and the melting efficiency was found to be 30%. A study of ‘segregation ratio’ of elements in the weld zone showed that the amount of micro-segregation of molybdenum was found to increase with the increase in linear heat input. Increase in the segregation of molybdenum could cause a decrease in corrosion resistance of the welded specimen. Hence, a confirmation test (i.e., corrosion test) was performed to study the effect of linear heat input on the corrosion resistance of the welded sample due to micro-segregation. It was observed that the increase in linear heat input causes an increase in micro-segregation as well as an increase in corrosion rate. X-ray diffraction analysis showed that the concentration of passivating phases was found to increase with the increase in scan speed.

Study of intergranular corrosion mechanism of fiber laser welded 3-mm-thick Hastelloy C-276 sheet

Specimens of laser welded Hastelloy C-276 were immersed in the ASTM G-28 test solution to study the intergranular corrosion mechanism of BM, HAZ and WZ. The variation in concentration of molybdenum at different sub-zones within the respective BM, HAZ and WZ was found to be responsible for the formation of a galvanic couple consisting of cathode and anode. The rate of corrosion was found to increase with the rise in concentration gradient of molybdenum between cathode and anode. Compositional analysis showed that (concentration gradient)WZ > (concentration gradient)BM > (concentration gradient)HAZ, hence, the (corrosion rate)WZ > (corrosion rate)BM > (corrosion rate)HAZ.

Stainless Steel as Substrate Material for High-Temperature Superconducting Tapes Processed Via the ISD MgO Route

Second-generation high-temperature superconducting (HTS) tapes strongly rely on the substrate material, in many cases Hastelloy C276 (“H-C276”). In order to ameliorate performance (and reduce the price) of superconducting tapes, replacement of H-C276 has been investigated. In this paper, the potential of the readily available austenitic stainless steels X2CrNiMo17-12-2 (“CrNiMo”) and X11CrNiMnN19-8-6 (“CrNiMnN”) as substrates is assessed. It was found that CrNiMnN is not suitable as a replacement for H-C276. Tensile stresses occurring at elevated temperatures during the HTS tape production result in plastic deformation of the CrNiMnN substrate. In the case of CrNiMo, however, plastic deformation was not observed after processing of the HTS tape. Electrical losses as a result of alternating currents beyond those of H-C276 did not occur due to the paramagnetic nature of CrNiMo. It is demonstrated that, for the very same processing parameters, HTS films deposited on electrochemically polished and buffered CrNiMo substrates exhibit similarly high critical current densities as on polished and buffered H-C276 substrates. The application of CrNiMo stainless steel reduces substrate costs considerably. More importantly, tapes processed on CrNiMo substrates withstand higher tension strains with respect to the reduction of the critical current compared to H-C276 substrates. This effect is interpreted to be a result of the matching coefficients of thermal expansion of the HTS layer and CrNiMo, resulting in lower residual tensile stress in the HTS layer after processing.

Investigation into the intergranular corrosion behaviour of electron beam welded Hastelloy C-276 sheet using laser displacement sensor

The laser displacement sensor scan technique proposed in the present study helps to calculate the corrosion rate (CR), and subsequently, determine the susceptibility to intergranular corrosion, without preparing separate samples for the weld zone (WZ), adjacent heat affected zone (HAZ) and unaffected base metal (BM). Processing of the displacement data collected during laser displacement sensor scan of the electron beam welded Hastelloy C-276 sample before and after the corrosion test shows that the (CR)WZ > (CR)BM > (CR)HAZ. The (CR)WZ was found to higher due to the (a) lower concentration of Mo and Cr in the dendrite body (of WZ) and (b) higher non-uniformity in Mo concentration per unit length within the WZ. The weld thermal cycle did not cause sensitization of HAZ (i.e., the formation of Mo depleted regions), and hence, the intergranular attack was not evident along the grain boundaries of the HAZ and the (CR)HAZ was lower.