UNS N06600 Research Articles

Corrosion mechanisms of plasma sprayed porous coatings of Ni80Cr20 and alloy C-276 investigated by numerical and experimental method

Abstract: In this study, the corrosion performance of Ni80Cr20 and alloy C-276 (UNS N10276) coatings on 7075 aluminum alloy substrates was evaluated using a variety of performance characterization tests. Significant amounts of nickel oxide were found in the corrosion products of the two coatings that were stripped, with molybdenum in the two coatings that were not stripped effectively slowing down the corrosion rate. Both coatings selectively corrode Cr, where it is worth noting that the preferential corrosion of W elements in alloy C-276 has a positive effect on its surface protection. It is not only the amount of molybdenum content, but also the influence of the W element that leads to better corrosion resistance of alloy C-276 coating than Ni80Cr20 alloy coating. The coating spraying process due to process parameters and its own nature, etc. has caused different sizes of pores, while these pores in the corrosion process will have a certain degree of influence on the corrosion process. The size of the pore defects for the coating transverse corrosion effect was more significant, and small pore defects accelerated the corrosion process. The number of pore defects had a more significant effect on the longitudinal corrosion of the coating, and multiple pore defects slowed the corrosion process.

Nitriding Treatments in Nickel–Chromium-Based Superalloy INCONEL 718: A Review

This literature review focuses on the nitriding treatments of nickel-based superalloy UNS N07718, also called INCONEL 718. This alloy was selected due to the relevance of this alloy in the aerospace and oil and gas industries. The referenced studies reflect a clear trend towards improving superalloys through advanced nitriding processes, highlighting plasma nitriding as one of the most promising techniques to enhance alloy 718 against corrosion and wear. The importance of optimizing nitriding parameters, such as temperature and time, is emphasized to increase wear and corrosion resistance while minimizing adverse effects like delamination or the formation of undesirable phases. Finally, the most appropriate alternatives for future research are recommended.

Sensitivity of mechanical properties to processing defects: Is tensile testing an appropriate metric for laser beam metal powder bed fusion machine qualification?

The Laser-based Powder Bed Fusion of Metals (PBF-LB/M) process has shown potential in the manufacturing of critical flight components, yet also has faced difficulties in achieving reproducibility. One potential reason for this is that tensile testing, which is one of the methods traditionally used to ascertain quality in the additive manufacturing (AM) industry, is insufficient for capturing underlying flaws in an additively manufactured component. To quantify the ability of tensile testing to detect underlying flaws in a component, a generalized full factorial experiment was performed where the tensile properties of UNS N07718 were measured across several types of build conditions. Combinations of differently sized bars and surface conditions were investigated. Defects were induced by amplifying the polygon delay parameter, hence prolonging the dwell time of the laser in the contours. The authors found that those tensile bars that experienced increased polygon delay had ∼10x more pores than those built with nominal parameter values while still maintaining an average porosity of <0.25 % (i.e., a total part porosity that is acceptable by NASA-STD-6030). Regardless of the specimen geometry and surface condition, differences between parts which had undergone polygon delay and those that had not were either statistically insignificant or were too small to be relevant, indicating that tensile testing may not be an effective metric for identifying the quality of a PBF-LB/M process.

Enhancing ASTM B424 UNS N08825 Long Seam Weld Liner Material with Annealing Quenching Techniques in the Cladding Process on the Surface of Steel Pipes

The use of cladding methods in manufacturing corrosion-resistant pipes is crucial for industries such as oil and gas, chemical plants, and pressure vessel manufacturing. This study focuses on ASTM B424 UNS N08825, a corrosion-resistant alloy (CRA) to be used as the surface layer for steel pipes. The cladding method involves forming CRA sheets into longitudinal pipes, followed by welding the joints, annealing, and rapid cooling before high process expansion to surface layer the steel pipes. At a temperature of 930-990°C, the annealing process aims to reduce stress and improve material properties, followed by rapid cooling to stabilize the microstructure. Various tests were conducted on the CRA liner pipes with or without annealing and quenching, including tensile testing, hardness testing, chemical composition analysis, and microstructure examination. The results showed that the material's ultimate tensile strength and hardness significantly increased after the treatment, with better uniformity in the microstructure. This study concludes that annealing and rapid cooling enhance the mechanical properties and stability of ASTM B424 UNS N08825, allowing the cladding process on steel pipe surfaces to be performed flawlessly and making it suitable for high-performance applications in corrosive environments.

Modeling hydrogen diffusion in precipitation hardened nickel-based alloy 718 by microstructural modeling

Abstract Environmentally assisted cracking can significantly affect the performance of high strength alloys and limit material selection to minimize the risk of subcritical crack growth in service. UNS N07718 is widely used in marine service applications and under a variety of conditions, such as: alternate immersion, different levels of cathodic protection, and freely corroding galvanic couples, because of its demonstrated corrosion and fracture resistance in these environments. In this work we developed a representative model of the material microstructure including the metal grains, the material texture, and the precipitates along the grain boundaries and within the grains. The microstructural model was subjected to the boundary conditions identified at the notch root of a fracture mechanics sample and the results are used as input for a simulation of hydrogen diffusion from the surface of the notch, assuming the material has been introduced to a hydrogen producing environment. The diffusion of hydrogen was modeled by Fick’s law and included both hydrostatic stress and mobile dislocation velocity as driving forces. The influence of immobile dislocations was also modeled to account for the irreversible trapping. The results show that hydrostatic stress and immobile dislocation trapping can significantly alter the highest concentration of hydrogen and its location within the microstructure towards the fracture process zone. Mobile dislocation velocity has a small influence in determining the hydrogen distribution near the fracture process zone.

Electrochemical characteristics and damage mechanism in scrubber washing water of UNS N08367 with plasma ion nitriding and electropolishing

In this investigation, electropolishing and plasma ion nitriding are applied to super austenitic stainless steel for the purpose of improving its corrosion and pitting resistance. Electrochemical experiments are conducted with washing water collected directly from the ship’s scrubber. After electropolishing, the surface roughness is improved by about 73.6% compared to mechanical polishing. After plasma ion nitriding, CrN (precipitate), Fe4N (compound), and γN (solid solution) are observed on the surface. The thickness of the layer formed on the surface is measured to be about 10 μm. A hysteresis loop is observed in the cyclic potentiodynamic polarization curves of mechanical polishing and electropolishing, and the areas are calculated as 23.33 mW cm−2 and 0.17 mW cm−2, respectively. The polarization curve of plasma ion nitriding presents perfect passivation characteristics. Accordingly, mechanical polishing and electropolishing reveal local corrosion, whereas plasma ion nitriding presents a tendency towards general corrosion. In the mechanical polishing, electropolishing, and plasma ion nitriding, the corrosion current densities are 0.665 μA cm−2, 0.093 μA cm−2, and 16.47 μA cm−2, respectively, and the maximum damage depth is observed to grow progressively smaller from plasma ion nitriding to electropolishing and then mechanical polishing.

Hydrogen embrittlement of the nickel alloy UNS N07718 for two different heat-treating schedules

The role of the nickel alloy 718 microstructure has been widely discussed and it is well established the δ phase detrimental effect on the material’s ductility and toughness when exposed to hydrogen. However, other microstructural features that might influence the embrittlement process are more elusive, which requires more in-depth studies. Having selected heat-treating schedules to mitigate δ phase precipitation, this work aims to assess the hydrogen embrittlement of two alloy 718 variants with nominal yield strengths of 120 and 150 ksi. Fundamentally, the idea is to understand the extent of the hydrogen damage caused by an increase in mechanical strength beyond the limit of 140 ksi specified in the API 6ACRA. Slow strain rate (SSR) and fracture toughness (FT) testing were applied to evaluate the mechanical behavior under cathodic polarization. The microstructure of both variants is comprised of recrystallized austenite grains and a very low content of grain boundary δ phase. Nanosized disk-shaped γ″ particles are also present for both variants, although the 150 ksi material shows a higher volume fraction and a finer distribution of this phase. Despite having the same overall fracture features, nanostructure differences between the variants and the consequent impact on hydrogen apparent solubility and slip planarity produced lower values of plastic elongation and initiation fracture toughness for the stronger material.

The Effects of Cl− and Selected Deoxidizers on the High-Temperature Corrosion Electrochemistry of Alloy 690 in Nuclear Steam Generator Water

The heat transfer tube in a steam generator serves as a critical heat exchange component in the primary and secondary loops of pressurized water reactor (PWR) nuclear power plants. The corrosion resistance of the heat transfer tube material directly influences the longevity of PWR nuclear power plants. This study investigated the electrochemical corrosion properties of 690 alloy (UNS N06690) in a simulated secondary water environment of PWR, focusing on different chloride ion concentrations and combinations of deoxidizers. The findings reveal a gradual decrease in the corrosion potential of 690 alloy, accompanied by an increase in self-corrosion current and a progressive reduction in the passivation range, ultimately leading to its disappearance as chloride ion concentration rises from 0 µg/L to 500 µg/L. Moreover, the impedance value of the inner film exhibits a declining trend with an increase in chloride ion concentration. Conversely, the resistance value of the outer film remains relatively stable while the size and spacing of oxide particles on the surface of the 690 alloy continuously increase. This observation suggests that chloride ions primarily influence the formation of the inner passivation film, which in turn determines the corrosion resistance of the 690 alloy. Notably, the performance of the 690 alloy is similar when the deoxidizer combination is ammonia (NH3) + erythorbic acid (ERA) or NH3 + hydrazine (N2H4), demonstrating the ability to form a relatively complete passivation film and exhibit improved corrosion resistance compared to NH3+N-isopropyl hydroxylamine, additionally, when the deoxidizer combination is NH3+N2H4, the 690 alloy exhibits lower self-corrosion current density across different chloride ion concentrations, indicating enhanced corrosion resistance.

Hardening behavior of nickel-base alloy irradiated by multi-energy Fe ions

The multi-energy Fe ions irradiation was performed to avoid the effect of non-uniformity of the ion irradiation damage on the mechanical test of nickel-base alloy (UNS N10003). In this study, the hardening behavior of GH3533 alloy (nickel-base alloy) under the multi-energy Fe ions irradiation at RT and 700 °C was investigated by using nanoindentation, micro-pillar compression techniques, SEM and TEM. The hardness value saturated at 0.5 dpa at RT, according to the nanoindentation results, however the hardness curve sharply rose at the dose of 8 dpa at 700 °C. The plastic deformation curves of the samples at 700 °C had fewer jagged amplitude behaviors and no slip band on the surface, according to the stress-strain curves and in-situ SEM images obtained following the micro-pillar compression test. TEM characterization showed only the dislocation loops and lines were observed at the dose of 8 dpa at RT. However, at 700 °C, precipitates deprived of Fe and Ni and enriched in Mo and Cr were seen close to the dislocation lines at 700 °C. The smooth curves during micro-pillar compression at 700 °C and the abrupt increase in hardness were caused by the high density and uniform dispersion of these precipitates. Additionally, a technique for assessing the hardening behavior under multi-energy ion irradiation was devised, which combines nanoindentation with micro-pillar compression testing.

Room Temperature Corrosion Behavior of Selective Laser Melting (SLM)-Processed Ni-Fe Superalloy (Inconel 718) in 3.5% NaCl Solution at Different pH Conditions: Role of Microstructures

Inconel 718 (UNS N07718) is a nickel-base superalloy containing iron that is used at cryogenic temperatures (arctic pipe components) and at high temperatures (gas turbines). This alloy is also used in off-shore oil drilling due to its high overall strength and resistance to corrosion. Inconel 718 components are created by a selective laser melting (SLM) additive manufacturing route and result in isotropic fine-grained microstructures with metastable phases (such as Laves phases) that are not usually present in conventional manufacturing processes. In this work, SLM Inconel 718 alloy specimens were investigated in four different conditions: (1) As-manufactured (AS-AM), (2) Additively manufactured and hot isostatically pressed (AM-HIP), (3) As-manufactured and heat-treated (solution annealing followed by two-step aging), and 4) AM-HIP and heat-treated. Localized corrosion behavior was evaluated at room temperature in a 3.5% NaCl solution at three different pH conditions (pH 1.25, 6.25, and 12.25). Electrochemical tests, including linear polarization, cyclic polarization, potentiostatic conditioning, electrochemical impedance spectroscopy, and Mott–Schottky analyses, were used to compare the corrosion behaviors of the SLM specimens with that of the conventionally wrought IN718 samples. The results showed that the additively manufactured specimens showed better corrosion resistance than the wrought material in the acidic chloride solution, and the AM-HIP specimens exhibited superior corrosion resistance to the as-manufactured ones. Hot isostatic pressing resulted in the visible elimination of the dendritic structure, indicating compositional homogeneity as well as a significant decrease in porosity. In addition, the deleterious secondary phases, such as Laves and δ phases, were not observed in the microstructure of the HIPed samples. The AM-HIP material showed the highest corrosion resistance in all the pH conditions. The two-step aging treatment, in general, resulted in the deterioration of corrosion resistance, which could be attributed to the formation of γ′ and γ″ precipitates that increased the cathodic reaction catalytic activities. In the additively manufactured samples, the presence of the Laves phase was more detrimental to corrosion resistance than any other phases and MC carbide and grain boundary δ phase increased the susceptibility to corrosion in wrought materials.

Corrosion behavior of UNS N10003 alloy in molten LiF-BeF2-ZrF4 with phosphide impurity

The corrosion behavior of UNS N10003 alloy in molten LiF-BeF2-ZrF4 salt with phosphide impurity was investigated by static immersion test at 700 °C. Results show that an outer layer of Ni3P and an inner layer of mixed Ni3P and Mo3Ni2P1.18 formed on the alloy surface after corrosion. The depth of both corrosion layers increased linearly with the increasing immersion time and suffered severe spallation after 400 h. Cr and Fe were depleted in the inner corrosion layer indicating the phosphide corrosion layers did not prevent the selective dissolution of active alloying elements.

Nd: YAG laser beam welding of UNS N07718 superalloy and UNS S32304 duplex stainless steel: Phase transformations and mechanical properties of dissimilar joints

This article implies the phase transformations and mechanical behavior of dissimilar laser welded UNS N07718 superalloy/UNS S32304 duplex stainless steel. Laser power, welding speed, and focal point were the variables of the laser beam welding (LBW) approach. Optical microscopy and electron backscattered diffraction (EBSD) analysis were utilized. They demonstrated that the weld metal (WM) mainly had an austenitic microstructure with a face-centered cubic structure in the form of columnar and equiaxed dendrites. Also, the occurrence of directional solidification in WM was verified by EBSD. The heat-affected zone (HAZ) microstructure of Inconel 718 superalloy included austenite grains with normal grain growth, annealing twins, and precipitates. There was a ferritic-austenitic microstructure in the HAZ of 2304 duplex stainless. In this area, the volume fraction of the ferrite phase was excessively higher than that of the austenite phase and the austenite was characterized as Widmanstätten plates and grain boundary austenite. Furthermore, abnormal ferrite grain growth was identified in this. Welding defects e.g., molten spatter, solidification crack, and lack of penetration were observed, as well. Based on the uniaxial tensile test, it was realized that the highest failure load (9.7 ± 0.4 kN) was achieved in the laser power of 1900 W, welding speed of 3 mm/s, and focal point of 0 mm. Therefore, these variables were known as the optimum variables of the LBW process. All laser weldments failed from the WM and fractography via scanning electron microscopy (SEM) showed a mixture of dimple and cleavage features in the fracture surfaces of the laser welds.

Optimization of machining parameters & studies on characteristics of Monel k400 alloy using abrasive water jet Machining using ANFIS

The Monel k400 alloy is a nickel-copper based alloy with an excellent corrosion resistance that exhibits better weldability and high strength. Also, it exhibits excellent resistance to either rapid flowing brackish water or seawater. Monel k400 alloy (UNS N04400) is widely used in oil, chemical and marine industries. Therefore, machinability of material plays a vital role in adopting material. As a result, in the current work, Monel k400 is used and manufactured utilizing an advanced machining method called an AWJM to examine the impact of process parameters on the machinability of alloy. The purpose of this study was to investigate the effects of abrasive mass flow rate, nozzle traverse speed, and stand-off distance on surface roughness. Adaptive Neuro-Fuzzy Inference System (ANFIS) model is used in order to predict surface roughness upon varying Abrasive Water Jet Machining process parameters for a lesser prediction error. In AWJM process Mean Absolute Percentage Error (MAPE) in between experimental, predicted surface roughness is found to be 3.46% which reflects efficacy of ANFIS model in predicting of surface roughness was evaluated to an extent of credibility. Also, the coefficient of determination R2 is evaluated and found to be 0.943, which indicates a good fit for prediction using the model against measured surface roughness values.

Localized Corrosion Behavior of UNS N07718 in a Solution Simulating a Diluted-sour Environment

The localized corrosion behavior of precipitation-hardened UNS N07718 was investigated by immersion tests in 6 wt% FeCl3 + 1.0 wt% HCl and the use of electrochemical techniques in a simulating solution of a diluted-sour environment of 25 wt% NaCl + 0.5 wt% CH3COOH. The Ti carbides and Nb-Mo carbides with 1-10 µm size were distributed in the alloy. After immersion at a solution temperature higher than 45oC, localized corrosion with a depth of over 25 µm was identified, and the critical pitting temperature was determined to be 45oC. Potentiodynamic polarization showed that the surface of the UNS N07718 was immediately passivated in the experimental solution. The passivity-maintaining current density was gradually increased with increasing solution temperature, and finally, localized corrosion was initiated or propagated at 0.5 VSSE in 80oC. The localized corrosion was initiated or propagated at the interface between the Ti and Nb-Mo carbides and the alloy substrate. Scanning Kelvin probe microscopic images revealed that the contact-potential difference values were in the order of Ti carbide &gt; Nb-Mo carbide &gt; alloy substrate, indicating that the carbides and alloy substrate act as a cathode and an anode, respectively, forming a micro-galvanic couple. Therefore, it is concluded that localized corrosion is initiated at the interface between the carbides and substrates in UNS N07718.

Low-Potential Zone at the Interface of Precipitate and Austenite Affecting Intergranular Corrosion Sensitivity in UNS N08028 Nickel–Iron–Chromium Alloy

The precipitates and the intergranular corrosion behavior of a UNS N08028 nickel–iron–chromium alloy sensitized at different temperatures were studied by employing transmission electron microscopy, Kelvin probe force microscopy and other methods. It was found that sigma precipitates appeared at the grain boundaries of the alloy being sensitized. There was a Cr-depleted zone and a low-potential zone around these precipitates. The potential difference between the sigma precipitates and the low-potential zone was 102 mV, and this increased with the growth of the sigma precipitates. At this potential difference, the migration of the vacancies in the passive film accelerated significantly, and then the protectiveness of the passive film decreased. The intergranular corrosion mechanism of the steel has also be discussed.

Mechanical Properties Of Welding API 5l X-65 Cladded UNS N08825 Material Due To The Effect of Welding Repair

Abstract This study evaluate the mechanical characteristics and microstructure of API 5L X-65-clad UNS N08825 during repair welding. Gas tungsten arc welding (GTAW) and shielded metal arc welding were used in combination to carry out the welding and the repair welding (SMAW). Filler metals ER NiCrMo3 and E NiCrMo3 were used throughout the GTAW and SMAW welding processes. The first specimen served as the primary focus, after which the weld areas of the remaining four specimens were ground, re-beveled, and then re-welded using the same parameters. It performed tensile testing, bending tests, Impact Charpy tests, macro photography tests, and Vickers hardness tests. Repairs weld carried out, the heat-affected zone's hardness in the capping region increased. The findings of the tensile test demonstrate that the tensile strength is not considerably impacted by the welding repair at any particular welding repair location. The biggest decline in the number is caused by the welding repair at PTR 2, which is 0.83 percent. The heat affected area (FL) value decreased by 10.44 percent according to the charpy impact test results. The PTR 1 and PTR 2 areas in the weld metal area had the lowest charpy impact test results, respectively, of 88 J and 258 J.

TUBING HANGER INVESTIGATION OF LOADING

In this article, the failures of tube hangers made from UNS N07718 are discussed. An arrangement known as a tubing hanger may be found in wells that produce either oil or gas. It is positioned in the upper tubing head’s bowl after it has been installed. The tubing is held in place by this, and a main annulus seal is created between tubing also the production casing. This holds the tubing in place, and at the same time, it creates a primary annulus seal between tubing also production casing. When compared to odd component in wellhead system, tubing hangers are available in a broader range of styles and sizes than any other option. Tubing hangers made of UNS N07718 are often used in the installation process of sour service oil and gas wells that operate under high pressure and also high temperatures. Afterwards more than 10 years of service, it was only recently found that the tubing hanger made of UNS N07718 had failed in sour wells. Failures of the tubing hanger will inference in substantial production delays as well as high workover expenses. The purpose of this research is to demonstrate the failure mechanism of tubing hanger furthermore its ramifications on existing wells that were erected with material that is comparable to what was used here. In order to establish what caused the failure, each and every exposure that was brought on by well intervention efforts was evaluated. The manner of failure of stringer head suspension was researched, as was its influence on already existing wells that had been erected with materials that were comparable. Keywords: tubing head, tubing hanger, tubing thread, back pressure valve profile, landing shoulder, snap ring, running thread,

Investigation on the effective factor calculation of electropolishing using full factorial design and mechanism model by microscopic analysis for super austenitic stainless steel

This investigation is to calculate the effective factors of the electropolishing by using the full factorial design for UNS N08367. In addition, based on the calculated effective factors, the electropolishing mechanism model was researched on 3D microscopy and scanning electron microscopy analysis. The parameters were selected as electrolyte composition ratio, electropolishing process time and applied current density. Calculation of effective factors was performed through analysis of variance (ANOVA). As a result of ANOVA, it was observed that the electrolyte composition ratio had the greatest effect on surface planarization. As a result of surface analysis after electropolishing, the maximum height difference is about 54 times. Also, the minimum value of surface roughness after electropolishing was 0.129 μm, which was improved by more than 70% compared to mechanical polishing. As a result of all analysis, it was most flat to perform electropolishing with a sulfuric acid and phosphoric acid ratio of 3:7, 300 mA/cm2 and 5 min.

Optimization of Electropolishing Process Using Taguchi Robust Design for UNS N08367 in a Mixed Solution of Sulfuric Acid and Phosphoric Acid

The purpose of this investigation was to determine the optimal conditions for UNS N08367 electropolishing using the Taguchi method. The investigated factors were the electrolyte composition ratio, applied current density, and electrolyte temperature. Each factor was tested at three levels. Electropolishing was optimized using analysis of variance (ANOVA), signal-to-noise ratio (the smaller the better the characteristics), and surface analysis. The ANOVA results showed that among the three factors, only the electrolyte composition ratio was effective in surface planarization. The optimal conditions for electropolishing determined according to the signal-to-noise ratio were a sulfuric acid-to-phosphoric acid ratio of 2:8, a current density of 400 mA/cm2, and an electrolyte temperature of 75 °C.

Electrochemical Properties of Super Austenite Stainless Steel with Temperature in a Green Death Solution

In this investigation, potentiodynamic polarization experiments were conducted on UNS S31603 and UNS N08367 in a modified green death solution, which simulates the environment of a desulfurization device (scrubber), using temperature as a variable. A Tafel analysis showed that the corrosion current density of UNS S31603 at the highest temperature (90 °C) was approximately 4.5 times higher than that of UNS N83067. A surface analysis using a scanning electron microscope revealed that pitting and intergranular corrosion occurred simultaneously in UNS S31603, whereas UNS N83067 exhibited a stronger tendency toward intergranular corrosion. After electrochemical experiments, the corrosion rates according to maximum damage depth were compared with the corrosion rates according to corrosion current density; the relationships between the two values were expressed as α values. The α values of UNS N08367 were higher than those of UNS S31603, indicating that the local damage rate of UNS N08367 was higher.