Showing papers on "Inconel 625 published in 2013"

Corrosion Behavior of Ni-Based Alloys in Supercritical Water Containing High Concentrations of Salt and Oxygen

Abstract: The Ni-based alloys Incoloy 800, Incoloy 825, Inconel 625, and Hastelloy C-276 exposed to subcritical water (350 °C, 25 MPa) and supercritical water (450 °C, 25 MPa) with high concentrations of chloride and oxygen were analyzed by using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. There is a strong synergistic effect between salt and oxygen, leading to severe corrosion. The selective dissolution of nickel is the severest of all alloying elements, and a stable oxide in oxidizing condition is formed by chromium. Molybdenum improves the resistance to pitting corrosion when chromium is present. Without molybdenum, Incoloy 800 exhibits the severest pitting corrosion of the test alloys under subcritical condition. Inconel 625 and Hastelloy C-276 exhibit good corrosion resistance under the condition of oxygen and salt existing. NiO, NiCr2O4, and Cr2O3 are the three main components of oxide films on Ni-based alloys. The possible corrosion mechanisms of Ni-based alloys are...

Comparative study of mechanical properties using standard and micro-specimens of base materials Inconel 625, Inconel 718 and Ti-6Al-4V

Abstract: To improve innovative joining and deposition technologies for the construction of dissimilar joints, precise knowledge of the local mechanical properties of materials must be obtained. In the present article a comparative study of the tensile properties and fatigue behaviour in case of flat standard and micro-specimens of base materials Inconel 625, Inconel 718 and Ti-6Al-4 V was accomplished. The aim of the study was to develop an efficient method for the investigation of the local mechanical properties by the use of micro-specimens subjected to electro discharge machining treatment and to obtain reliable tensile and fatigue test results. By the miniaturization of specimens a significant effect of roughness on mechanical properties was obtained. By considering a correction for the effective load-bearing cross-section the data obtained from micro-specimens are within 3% error with respect to standard specimen results. The results showed that the proposed technique can be successfully used to determine the tensile and fatigue properties of a small material volume.

Concurrent Inconel 625 wire and WC powder laser cladding: process stability and microstructural characterisation

Abstract: The microstructure and hardness property of WC powder–Inconel 625 wire single tracks deposited by laser cladding at varying processing parameters were investigated using a combination of scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, image processing software and hardness testing. The results include the generation of process maps that predict the cladding process characteristics at varying processing conditions. High dissolution of WC particles at high energy input resulted in a decrease in retained WC volume fraction with increasing laser power. The negative dependence of the retained WC volume fraction on the transverse speed and wire feedrate showed that the decreasing powder catchment efficiency with increasing the two parameters is primarily significant to the amount of WC contained in a track. The dissolution of WC in the matrix resulted in the formation of W2C and Fe3W3C hard phases, which mainly contributed to high hardness (540–690 HV0·3) of the composite matrix.

Fiber laser welding of nickel based superalloy Inconel 625

Abstract: The paper describes the application of single mode high power fiber laser (HPFL) for the welding of nickel based superalloy Inconel 625. Butt joints of Inconel 625 sheets 0,8 mm thick were laser welded without an additional material. The influence of laser welding parameters on weld quality and mechanical properties of test joints was studied. The quality and mechanical properties of the joints were determined by means of tensile and bending tests, and micro hardness tests, and also metallographic examinations. The results showed that a proper selection of laser welding parameters provides non-porous, fully-penetrated welds with the aspect ratio up to 2.0. The minimum heat input required to achieve full penetration butt welded joints with no defect was found to be 6 J/mm. The yield strength and ultimate tensile strength of the joints are essentially equivalent to that for the base material.

Hot Corrosion of Inconel 625 Overlay Weld Cladding in Smelting Off-Gas Environment

Abstract: Degradation mechanisms and hot corrosion behavior of weld overlay alloy 625 were studied. Phase structure, morphology, thermal behavior, and chemical composition of deposited salt mixture on the weld overlay were characterized utilizing XRD, SEM/EDX, DTA, and ICP/OES, respectively. Dilution level of Fe in the weldment, dendritic structure, and degradation mechanisms of the weld were investigated. A molten phase formed on the weld layer at the operating temperature range of the boiler, which led to the hot corrosion attack in the water wall and the ultimate failure. Open circuit potential and weight-loss measurements and potentiodynamic polarization were carried out to study the hot corrosion behavior of the weld in the simulated molten salt medium at 873 K, 973 K, and 1073 K (600 °C, 700 °C, and 800 °C). Internal oxidation and sulfidation plus pitting corrosion were identified as the main hot corrosion mechanisms in the weld and boiler tubes. The presence of a significant amount of Fe made the dendritic structure of the weld susceptible to preferential corrosion. Preferentially corroded (Mo, Nb)-depleted dendrite cores acted as potential sites for crack initiation from the surface layer. The penetration of the molten phase into the cracks accelerated the cracks’ propagation mainly through the dendrite cores and further crack branching/widening.

In situ corrosion testing of various nickel alloys at Måbjerg waste incineration plant

Abstract: The majority of waste in Denmark is disposed via waste to energy (WTE) incineration plants which are fabricated from carbon steel. However, due to the increasing corrosiveness of waste over the years, more corrosion resistant alloys are required. In Denmark, Inconel 625 (UNSN06625) is the weld overlay material currently being used to give improved corrosion resistance. In order to assess the use of alternative nickel alloys, test panels have been manufactured and inserted into Mabjerg waste incineration plant. Inconel 625 as a 50% weld overlay, two layered weld overlay and as a spiral weld overlay was exposed. Other nickel materials exposed were weld overlay Alloy 686, Alloy 50 and Sumitomo Super 625 coextruded tube. Exposure has been undertaken from 2003 to 2009 in the first pass and 2005–2009 in the second pass, and sections have been removed and investigated during this period. The composition of the deposits from the exposed waterwall panels was also analysed each time sections were removed. This paper will compare the various nickel alloys in the two areas and assess the results of the long-term testing project.

Brazing Inconel 625 Using the Copper Foil

Abstract: Brazing Inconel 625 (IN-625) using the copper foil has been investigated in this research. The brazed joint is composed of nanosized CrNi3 precipitates and Cr/Mo/Nb/Ni quaternary compound in the Cu/Ni-rich matrix. The copper filler 50 μm in thickness is enough for the joint filling. However, the application of Cu foil 100 μm in thickness has little effect on the shear strength of the brazed joint. The specimen brazed at 1433 K (1160 °C) for 1800 seconds demonstrates the best shear strength of 470 MPa, and its fractograph is dominated by ductile dimple fracture with sliding marks. Decreasing the brazing temperature slightly decreases the shear strength of the brazed joint due to the presence of a few isolated solidification shrinkage voids smaller than 15 μm. Increasing the brazing temperature, especially for the specimen brazed at 1473 K (1200 °C), significantly deteriorates the shear strength of the joint below 260 MPa because of coalescence of isothermal solidification shrinkage voids in the joint. The Cu foil demonstrates potential in brazing IN-625 for industrial application.

Effects of Laser Re-melting on the Corrosion Properties of HVOF Coatings

Abstract: HVOF coating of Inconel 625 powder on carbon steel is carried out. Laser melting of the resulting coating is realized to improve coating structural integrity. Morphological and microstructural changes are examined in the coating prior and after laser treatment process using scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction (XRD). The residual stress developed is measured on the surface vicinity of the laser-treated coating using the XRD technique. The corrosion resistance of the laser-treated and untreated coating surfaces is measured, incorporating the potentiodynamic tests in 0.5 M NaCl aqueous solution. It is found that laser treatment reduces the pores and produces cellular structures with different sizes and orientations in the coating. Laser-controlled melting improves the corrosion resistance of the coating surface.

Evaluation of ice adhesion strength on erosion resistant materials

Abstract: Ice-adhesion properties were evaluated for coating systems based on titanium nitride applied via cathodic-arc physical vapor deposition developed for rotorcraft erosion caps. The ice-adhesion strength of titanium nitride and titanium aluminum nitride was determined experimentally and compared to the ice-adhesion strength of uncoated metallic materials currently used on rotor-blade leading-edge caps: stainless steel 430, Inconel 625, and titanium grade 2. Environmental and material parameters were investigated to identify which were most influential on impact ice-adhesion strength. The effects of median volumetric diameter of the cloud droplets, liquid water content of the cloud, ambient temperature, surface roughness, and material grain direction were tested on stainless steel 430. Tests revealed that surface roughness and temperature have the greatest effect on ice-adhesion strength. There was an increase in adhesion strength of 670% from −8 to −16 °C and 250% increase from 0.61 to 2.67Ra μm. An increas...

Effect of anions in seawater to corrosion attack on passive alloys

Abstract: Some metals and alloys have special characteristics that enable them to provide superior corrosion-res istant metal surfaces. These protective passive films are responsible for the phenomenon of passivity. Metals with this chara cteristic can be categorized as passive materials such as stainless steel 316L a nd nickel alloy Inconel 625. However, in corrosive environment this protective passive film may breach and exposed bare metal for further corrosion attack. Corrosive environment can be refer as metal is susceptible to corrosion attack such as seawater wh ich contain aggressive ions (salt) with negative ch arge (anion). An electrochemical test has been carried out to determ ine the effect of anion on corrosion attack of 316L and Inconel 625. The objective is to identify the breakdown potential (E b) in different anion ratio (chloride (Cl - ) : sulphate(SO 4 2- ). The anions concentration was decided as Cl - : SO 4 2- ; 35:0, 25:10, 10:25, 0:35 and was compared to art ificial seawater, 3.5% NaCl. The pH values were set in neutral in static condition. The materials were run for cyclic polarization with a scan rate of 2mV/sec. The E b value for 316L decreased in every solution as the tincreased from 30°C to 80°C. The results explain that SO 4 2- has inhibiting effect to passive alloy showing that the highest E b value detect at 30°C and highest concentration of SO 4 2- . Optical observations elucidate that, the number of pits inc reased in high concentration of Cl - than SO 4 2- . Both materials presents pits reducing as the temperature and concentration of SO 4 2- ions increased. Nevertheless, the E b value for 316L is likely to has a competition effect between Cl - and SO 4 2- anion as the graph shows no significant effect at Cl - : SO 4 2- ,25:10, 10:25. The same scenario is not shown by Inconel 625 because this m etal is highly corrosion resistance compared to 316 L.

Research on Mechanical Properties of Thin Sheets Blanks Made of Creep-Resisting Nickel Superalloys

Abstract: Mechanical working manufacturing methods of nickel alloys used conventionally strips and blanks need to solve many problems concerning high strength material forming which is characteristic limited plasticity. The production pressed elements of vehicle constructions and aircraft engine elements requires the high quality drawpieces since these are essential for safety. They are also the main structural components. Conventional methods of mechanical working such as pressing can be used in quantity production of the above mentioned elements and their production can also be cost-effective. Forming nickel alloys generates a lot of technological wastes resulting from back-springing effects determining the most appropriate pressure in the process of pressing. Failure holes in the process of bulging as well as cracking of drawpieces in the process of deep drawing. The heterogeneous mechanical properties distribution on thin sheet blanks made of Inconel alloy, which is different than material quality certificate shows, produces also a lot of manufacturing problems. These problems are usually solved by production engineers in the following way: dividing the production of ready drawpieces into a bigger number of simple blank profiling operations, shallow pressing, using a rubber punch for pressing or hydroforming. Complex drawpieces shapes are quite often made of several parts which are next welded. In the case of presented tube a tubular diffuser made of Inconel 718 alloy blank and cone made of Inconel 625. However the process of forming high strength materials like nickel alloys requires the application bigger forming forces than in the same kind of conventional formable steel processes. Tools get jammed quite often in the process and high force presses of 10 MN or more need to be used so is very expensive. The aspect of cold mechanical forming discussed materials has been a particular interest. The researches based on precise evaluation mechanical properties and technological plasticity of the selected materials in basic mechanical and technological tests as well as in FEM numerical simulation (finite elements method). The material models applied to simulation contain the pointed out experimentally the mechanical characteristics of Inconel alloys. The thin sheets blanks made of 0,9 mm thick Inconel 718 alloy and 0,45 mm thick Inconel 625 alloy blanks have been examined. The possibilities of using numerical simulations for solving the problems of selecting or modifying the pressing technology and hydroforming that type materials as well as forecasting the results of forming processes have been also presented. The evaluation of drawability of thin sheets blanks made of Inconel 718 and 625 alloys has also been discussed in the paper.

In-Situ Study on Coaxing During Vibration-Based Bending Fatigue of Inconel 625 and 718

Abstract: This study observes coaxing effects on aerospace nickel alloys during vibration-based bending fatigue loading. The purpose of this analysis is to determine if Goodman diagrams can be constructed using bending fatigue life data at experimentally defined cycles to failure. The methodology for controlling the number of cycles to failure requires a series of understressing steps, where stress amplitude is incrementally increased at each step. This method, known as the step-test procedure, states that, for some materials, the stress amplitude corresponding to the controlled cycles-to-failure can be determined through linear interpolation between the failure step and the previous non-failure step. Using the step-test procedure, experimental bending fatigue life results were gathered from cold-rolled Inconel 625 and 718 plate specimens. These bending loads are applied with a vibration-based experimental method, known as the George fatigue method, which utilizes modal vibration for fatigue loading. The fatigue life results from the George fatigue method are compared to life data from previously published constant stress amplitude experiments to determine if coaxing affects the fatigue performance of the Inconel materials. Results show that Inconel 625 has an improved fatigue performance that could be attributed to several possible factors, including coaxing, while the Inconel 718 data is shown to be within a 50% confidence band of constant stress amplitude data from the same material stock. The findings in this study increases the knowledge necessary to attain more relevant and less conservative empirical data for designing against high cycle fatigue (HCF) failure of complex gas turbine engine components.Copyright © 2013 by ASME

Effect of electromagnetic field on micro-structure and mechanical property for inconel 625 superalloy

Abstract: Inconel 625 is a Ni-Cr-Mo-Nb alloy which was developed primarily for high turbine applications. The elemental addition of Nb increases the solidification temperature range, which ex- hibits a strong propensity to form interdendritic segregation. The enrichment of elements Nb and Mo at the terminal stage of solidification leads to the formation of brittle eutectic structure, i.e., +Laves phases, which becomes potential crack origin during the subsequent hot processing and application. The present work has demonstrated that, the introduction of electromagnetic field (EMF) to the so- lidification process of Inconel 625 alloy has the obvious effect on grain refinement. The EMF can also effectively influence the segregation ratio of Nb and Mo. However, the inappropriate application of electric current intensity and frequency will lead to more severe segregation of elements Nb and Mo, which causes the increment of eutectic structure volume fraction. Further analysis illustrates that both of the grain refinement and eutectic volume fraction control the tensile property at room tem- perature, increasing the yield strength and decreasing the tensile plasticity for Inconel 625 alloy. It has been proven that a proper selection of input current intensity (100 A) and frequency (8 Hz) can effectively dominate the segregation behavior during solidification process under EMF with more than 30% increase of yield strength and a minute loss of plasticity.

On critical criteria for shifting towards plastic strain localization during explosive cladding of Inconel 625 on low-carbon steel

Abstract: The present study aims at detecting the critical criteria and corresponding critical impact energy for initiation of strain localization during explosive cladding of the Inconel 625 superalloy as a cladding material and low-carbon steel as a substrate. The results do not reveal adiabatic shear bands, which are the main signs of strain localization, within the superalloy in all studied impact energies up to 205 kJ. At impact energies greater than 78–114 kJ, strain localization is observed in low-carbon steel, and microcracks develop within the adiabatic shear bands. The Johnson-Cook model is used to explains the results obtained and to study the thermomechanical behavior of materials.

Future HFO/GI exhaust valve spindle

Abstract: State of the art for exhaust valve spin- dles for large two stroke heavy fuel diesel engines is currently either a fully forged Nimonic 80A version or a cost effective version based on an austenitic valve steel weld coated by a specially hardened Inconel 718 seat hardfacing and Inconel 625 disc coating. These three alloys, originally developed more than 50 years ago for the gas turbine and process industry, show comparable corrosion resistance at usual heat load. The general trend in engine design is steadily pushing combustion chamber component tempera- tures towards higher levels and the hot corrosion re- sistance of these alloys is currently being tested to the limit. Furthermore operation on LNG will introduce new challenges. Indeed, it would appear that there is much room for improvement as no focused alloy development has been performed aimed at the spe- cial conditions found on the thermally and mechani- cally stressed parts of the exhaust valve spindle. In the present work new coating alloys, meeting the re- quirements for the future valve spindle, have been developed by combining litterature study, service ex- perience, experimental data and numerical thermody- namic calculations. This paper describes the consid- erations and results of this alloy development as well as the details of a required new production technique for manufacturing a compound product by the Hot Isostatic Pressing (HIP) technology which has been developed applying advanced Finite Element Method (FEM) modelling.

Modeling of Inconel 625 TIG welding process

Abstract: Inconel 625 alloy is widely used in the aerospace industry because of its high strength, especially at high temperatures, corrosion resistance and excellent weldability. The study presents modeling of the TIG welding process using a Gaussian heat source. The calculations were performed using our in-house software Mod_FEM_met, designed for modeling, among others, welding processes using finite element method and employed as a service of PL-Grid+ infrastructure. The program has a modular structure, with the modules for solving the Navier-Stokes and heat transport equations together with a coupling super-module used in welding simulations. To increase computing speed and accuracy in areas with large error of approximation, adaptive meshes were used. Calculations were performed for plate made of Inconel 625. In the calculations the temperature dependent properties of Inconel 625 alloy, as well as thermal phenomena at the edges and inside the weld pool were taken into consideration. The results of the calculations include the dimensions and shape of the weld pool, as well the velocity and temperature fields. The results indicate how the efficiency of heat source can be used as a parameter to optimize the fitting of calculations to the experimental data.

Material compatibility study for thermal energy storage containment structure with phase change material

Abstract: A desirable feature of concentrated solar power system is to provide electricity in a dispatchable manner during cloud transients and non-daylight hours. A DishStirling concentrating solar power prototype demonstration system was built to incorporate a thermal energy storage (TES) module containing a phase-change material between the solar thermal receiver and the Stirling engine. This paper presents the results of a material compatibility study conducted to determine the suitability of two different metal alloys for use in the construction of the TES module. Key requirements of the materials include strength and corrosion resistance at elevated temperatures, commercial availability, and manufacturability using common fabrication methods. The TES module contains a NaCl/NaF eutectic salt, at temperatures ranging from local ambient to 700°C, where the salt is slightly superheated above its melt temperature. Sample containers made from SS316L and Inconel 625 were fabricated and thoroughly cleaned for compatibility studies based on an extensive literature review. Both the containers and the salt constituents were subjected to a bake-out cycle to drive off moisture, and permit out-gassing of contaminants. The containers were filled with salt in a controlled-atmosphere glove box. Filled containers were crimped and sealed by electron-beam welding. The finished samples were placed in a furnace, heated, and held at 750°C. One of each sample container material was removed from the furnace at both 100 and 2500 hours. The containers were cut open to analyze and evaluate the material surface and cross-section. After 100 hours, both SS316L and Inconel 625 exhibited a very small amount of corrosion. The stainless steel suffered a shallow inter-granular grain boundary attack, on the order of 1-2 mm in depth. The Inconel 625 surface formed an oxide complex, which is resistant to dissolution into the molten salt. After 2500 hours, the surface morphology for both materials was largely unchanged, with the corrosion process having switched from an initial localized pattern, to a more uniform pattern. The corrosion depth measured at 2500 hours remained near 1-2 mm, suggesting that the corrosion rate decelerated. Both materials showed promise for compatibility with the chosen salt.

Complementary use of electrochemical testing techniques to study corrosion processes of HVOF Inconel 625, CoNiCrAIY and WCCoCr coatings

Abstract: The purpose of coating is to get a blend of unique properties at low cost which is not possible from other manufacturing processes. High velocity oxygen fuel (HVOF) is one of the most commonly used thermal spraying processes to produce wear and corrosion resistant coatings. Alongside wear and corrosion resistant properties the HVOF thermally sprayed coating process also induces microstructural heterogeneities which decreased the corrosion resistant properties. Considerable research has been reported on corrosion testing of the HVOF sprayed coatings by using electrochemical techniques. Some electrochemical techniques give area average results whilst other allows the effect of different features to be determined. The complementary use of basic electrochemical techniques with more advance techniques is missing in most of the previous research. In this research work potentiodynamic polarization testing, electrochemical impedance spectroscopy and scanning electrochemical microscopy were used to see if the combined results could provide a broader picture of corrosion processes taking place at HVOF coatings. Three HVOF coatings of different microstructural complexity i.e. γ-phase Inconel 625, γ + β-phase CoNiCrAlY and WC-CoCr cermet coating were tested. Potentiodynamic polarization results gave overall current response of the applied potential which included the current responsible for chemical reaction and current for charging and discharging of the double layer. The general corrosion ranking of different materials was established by measuring corrosion potential, corrosion current density and passive current density from polarization curves. The analysis of the polarization curves revealed that without careful consideration of experimental details significant errors can be introduced. Improved procedures for potentiodynamic polarization testing were demonstrated by deliberately altering experimental parameters. The localized corrosion due to chloride ions and Cr-depleted regions was also studied by potentiodynamic polarization testing. The correlation between individual microstructural features and their electrochemical response was established by EIS including equivalent circuit modelling. The impedance spectroscopy results also revealed the electrochemical changes due to immersion time and polarization. The electrochemical activity at high resolution was studied by more sophisticated spatially resolved SECM. The SECM imaging and heterogeneous electron transfer rate constant studies in feedback mode pin point the regions of different electrochemical activity. The SECM imaging and SECM feedback approach curves at stainless steel and bulk Inconel showed negative feedback all over the surface. The Inconel 625 coating showed both positive and negative feedback from the surface. The positive feedback regions correspond to less electrochemically active and negative feedback regions correspond to electrochemically active regions. The comparison between SECM images and microscopy images confirmed that the splat boundaries were the most active regions in the HVOF Inconel 625 coating. The heterogeneous ET kinetic study determined higher rate constant values at positive feedback regions and lower rate constant values at negative feedback regions.

The Effect of Process Parameters on Pulsed Nd:YAG Laser Welding of Inconel 625

Abstract: The bead on plate welding specimens with the 1mm thickness was fabricated by Nd:YAG pulsed laser SW-1 . The effects of laser process parameters on the weld dimensions, metallurgical and mechanical properties of weld metal were investigated. The results showed that both weld depth and weld width increase with voltage. Unlike base metal that has coaxial grain structure, weld metal is composed of a dendritic structure. Grain growth in the heat affected zone did not occur. However, ultrafine precipitations were deposited at the HAZ which their size was approximately between 500 nm to microns. All tensile specimens failed in the fusion zone.