Search Results for nickel-iron base superalloys

The aim of this work was to reveal the effects of trace elements on the creep properties of nickel-iron base superalloys, which are the candidate material for the large components of the advanced-ultrasupercritical (A-USC) power generation plants. High temperature tensile and creep properties of forged samples with seven different compositions were examined. No significant differences were observed in the creep rate versus time curves of the samples, of which contents of magnesium, zirconium, manganese and sulfur were varied. In contrast, the curves of phosphorus-added samples showed very small minimum creep rates compared to the other samples. The creep rupture lives of phosphorus-added samples were obviously longer than those of the other samples. Microstructure observation in the vicinity of grain boundaries of phosphorus-added samples after aging heat treatment revealed that there were fine precipitates consisting of phosphorus and niobium at the grain boundaries. The significant suppression of the creep deformation of phosphorus-added sample may be attributed to the grain boundary strengthening caused by the fine grain boundary precipitates.

To improve microstructure stability at temperature up to 700°C and avoid segregation of Nb during melting processes, we modified the chemical composition of conventional Ni-Fe base super alloy(Ni-36Fe-16Cr-3Nb-1.7Ti-0.3Al:Alloy706). It is known that Alloy706 is strengthened by γ'(Ni 3 Al) phase and γ”(Ni 3 Nb) phase. But these phases are unstable at high temperature and transform into Nb rich δ or η) phase after long-term exposure to elevated temperature. Therefore modified alloy contains lower Nb and higher Al than those of Alloy706, and it is mainly strengthened by γ’(Ni 3 Al) phase. In fact we could not find δ or η phase in the modified alloy after creep and aging at 700 °C. Tensile strengths of the modified alloy at temperature from room temperature to 700 °C were almost same as those of Alloy706. Yield strength of modified alloy at room temperature was slightly lower than that of Alloy706, but equivalent to that of Alloy706 at higher temperatures. Tensile and yield strengths of the modified alloy at temperature from room temperature to 700 °C were higher than those of Alloy706 after aging at 700 °C. In this paper, we discuss effects of Nb and Al on mechanical properties and microstructure at elevated temperature up to 700 °C, using mechanical testing, TEM observations and thermodynamics calculation results. And we show advantages of the microstructure stabilized Ni-Fe base superalloy(FENIX-700), which is a candidate material for 700 °C class USC steam turbine rotor.

The trial production of FENIX-700 turbine rotors for advanced-ultra super critical (A-USC) power generation was conducted, and their microstructure, tensile, impact, and creep properties were evaluated. Two 10-ton class trial forgings were successfully produced through double melting of VIM and ESR and free forging with a 14,000 ton hydraulic press. For examining the effect of the forging condition on the microstructure of the rotors, we adopted lower finish temperatures and an increased forging ratio on the last forging for the second trial. The grains of the second trial forging were refined by changing the forging condition. In particular, the grain size of the center of the rotor was remarkably decreased from the grain size number 0.5 to 2.8. Grain refinement improved the permeability of the ultrasonic wave in the ultrasonic inspection test, resulting in decreasing the minimum detectable flaw size (MDFS). The ductility and toughness were also improved by grain refinement. Although the grain size was decreased, the time to rupture in the creep test at 700 °C was comparable to the previous results of FENIX-700, and the estimated 105 h rupture stress at 700 °C was sufficiently higher than 100 MPa. However, it was clarified that the particles of gamma-prime in the center of the rotor had been coarsened due to the mass effect. The slight decrease of 0.2% proof stress and shortening of creep rupture time at 700 °C were attributed to the coarse gamma-prime particles. The results of the present trial expressly demonstrated that it is possible to manufacture 10-ton class A-USC turbine rotors of FENIX-700 with excellent mechanical properties and good permeability of the ultrasonic wave.

In this work, the effects of phosphorus addition on the creep properties and microstructural changes of wrought γ’-strengthened Ni-based superalloys (Haynes 282) were investigated, focusing on the effects of carbides precipitation. In an alloy with a phosphorus content of 8 ppm, precipitation of M 23 C 6 carbides was observed in both grain boundaries and the grain interior prior to the creep tests. Grain boundary coverage by carbide increased with phosphorus content up to approximately 30 ppm. On the other hand, the amount of M 23 C 6 in the grain interior decreased with phosphorus content. The results of the creep tests revealed the relationship between the time to rupture and the grain boundary coverage by carbides. The microstructure of the crept specimens showed the existence of misorientation at the vicinity of grain boundaries without carbides, as demonstrated via electron backscattered diffraction (EBSD) analysis. These results suggest that the observed improvement in the time to rupture is due to a grain-boundary precipitation strengthening mechanism caused by grain boundary carbides and that phosphorus content affects the precipitation behavior of M 23 C 6 carbides in the grain interior and grain boundaries. These behaviors were different between alloys with the single addition of phosphorus and alloys with the multiple addition of phosphorus and niobium.

This overview paper summarizes part of structure stability study results in China on advanced heat-resistant steels, nickel-iron and nickel base superalloys such as 12Cr2MoWVTiB(GY102) ferritic steel, Super 304H austenitic steel, GH2984, Nimonic 80A and INCONEL 740 superalloys for fossil power plant application. China had established first USC power plant with steam parameters of 650°C and 25 MPa in the year of 2006. Austenitic heat-resistant steel Super 304H is mainly used as boiler superheater and reheater material. Ni-Cr-Fe base superalloy GH2984 was used as tube material for marine power application. Ni-Cr-Co type INCONEL 740 has been studied in a joint project with Special Metals Corp., USA for European USC model power plant with the steam temperature of 700°C. Nimonic 80A has been used as several stage USC steam turbine bucket material at 600°C in China. Structure stability study of Nimonic 80A shows its possibility of 700°C application for USC steam turbine buckets.

Materials are developed and improved by adjusting both the alloy chemistry and the processing conditions to achieve desired microstructures and properties. Traditionally, these improvements have been made by a slow and labor-intensive series of experiments. But it is now possible to replace this expensive trial and error process by carrying out only a few ‘key’ experiments in conjunction with thermodynamic calculations. These calculations are powerful tools for alloy design, enabling improvement in the selection of alloy chemistry and the parameters used for fabrication steps such as heat treatments. In order to have the utmost confidence in the results obtained from the calculations, it is essential to have high quality thermodynamic databases. Such databases can be used not only in phase equilibrium calculations but also as the critical input for further kinetic simulations. In the present paper, we present our work on the development of reliable thermodynamic databases for nickel-based superalloys and iron alloys. We first briefly describe the methodology of developing these databases and then discuss some specific examples using the databases. With the aid of these examples, the usefulness of thermodynamic databases in aiding the development of advanced materials is discussed.

Coal burning power companies are currently considering FeAlCr weld overlay claddings for corrosion protection of waterwall boiler tubes located in their furnaces. Previous studies have shown that these FeAlCr coatings exhibit excellent high-temperature corrosion resistance in several types of low NOx environments. In the present study, the susceptibility of FeAlCr weld overlay claddings to hydrogen cracking was evaluated using a gas-tungsten arc welding (GTAW) process. Microsegregation of alloying elements was determined for the FeAlCr welds and compared to a currently used Ni-based superalloy. Long-term gaseous corrosion testing of select weld overlays was conducted along with the Ni-based superalloy in a gaseous oxidizing/sulfidizing corrosion environment at 500°C. The sample weight gains were used along with analysis of the corrosion scale morphologies to determine the corrosion resistance of the coatings. It was found that although there were slight differences in the corrosion behavior of the selected FeAlCr weld coatings, all FeAlCr based alloys exhibited superior corrosion resistance to the Ni-based superalloy during exposures up to 2000 hours.

To develop 10-ton class forgings with adequate long-term strength and without segregation defects for A-USC steam turbine rotors, researchers modified the chemical composition of Alloy 706 to improve its microstructure stability and segregation properties. The modified Alloy, named FENIX-700, is a γ' phase strengthened alloy without a γ" phase, and its microstructure stability is superior to Alloy 706 at 700°C, as demonstrated by short-term aging tests and phase stability calculations using the CALPHAD method. A trial disk 1-ton class forging of FENIX-700 was manufactured from a double-melted ingot, with tensile and creep strength of the forging equivalent to that of 10-kg class forgings, indicating a successful trial. Long-duration creep tests were performed using 10-kg class forgings, revealing an approximate 105-hour creep strength at 700°C higher than 100 MPa. Manufacturability tests showed that FENIX-700 performs better than Alloy 706, as evidenced by segregation tests using a horizontal directional solidification furnace and hot workability tests. Microstructure observation and tensile tests on 10,000-hour aged specimens (at temperatures of 650, 700, and 750°C) revealed degradation of tensile strength and yield stress due to coarsening of the γ' phase, but also showed enhanced ductility through aging. The microstructure stability of FENIX-700 at 700°C was confirmed as excellent through microstructure observation of the 10,000-hour aged sample and supporting thermodynamic considerations.

Gas turbine blades made from nickel-based superalloys, valued for their high temperature stability and creep resistance, undergo various forms of microstructural degradation during extended service at elevated temperatures that can ultimately lead to blade failure. To extend blade and turbine rotor life, Sulzer has developed evaluation and rejuvenation processes that include microstructural assessment and stress rupture testing of specimens from service-exposed blades. While stress rupture testing presents certain limitations and challenges in evaluating material condition, Sulzer has successfully rejuvenated hundreds of gas turbine blade sets across multiple superalloy types, including GTD 111, IN 738 LC, and U 500, demonstrating the effectiveness of heat treatment rejuvenation in improving microstructure and mechanical properties of service-degraded components.

Additive manufacturing (AM) is a process where, as the name suggests, material is added during production, in contrast to techniques such as machining, where material is removed. With metals, AM processes involve localised melting of a powder or wire in specific locations to produce a part, layer by layer. AM techniques have recently been applied to the repair of gas turbine blades. These components are often produced from nickel-based superalloys, a group of materials which possess excellent mechanical properties at high temperatures. However, although the microstructural and mechanical property evolution during the high temperature exposure of conventionally produced superalloy materials is reasonably well understood, the effects of prolonged high temperature exposure on AM material are less well known. This research is concerned with the microstructures of components produced using AM techniques and an examination of the effect of subsequent high temperature exposures. In particular, the paper will focus on the differences between cast and SLM IN939 as a function of heat treatment and subsequent ageing, including differences in grain structure and precipitate size, distribution and morphology, quantified using advanced electron microscopy techniques.

The rapid development of Chinese economy (recently in the order of 10%/year) is requiring sustainable growth of power generation to meet its demand. In more than half century after the foundation of People's Republic of China, the Chinese power industry has reached a high level. Up to now, the total installed capacity of electricity and annual overall electricity generation have both jumped to the 2 nd position in the world, just next to United States. A historical review and forecast of China electricity demand to the year of 2010 and 2020 will be introduced. Chinese power plants as well as those worldwide are facing to increase thermal efficiency and to decrease the emission of CO 2 , SO X and NO X . According to the national resources of coal and electricity market requirements in the future 15 years power generation especially the ultra-super-critical (USC) power plants with the steam temperature up to 600°C or higher will get a rapid development. The first two series of 2×1000MW USC power units with the steam parameters 600°C, 26.25MPa have been put into service in November and December 2006 respectively. In recent years more than 30 USC power units will be installed in China. USC power plant development will adopt a variety of qualified high temperature materials for boiler and turbine manufacturing. Among those materials the modified 9- 12%Cr ferritic steels, Ni-Cr austenitic steels and a part of nickel-base superalloys have been paid special attention in Chinese materials market.

The effect of grain size after solution treatment on the mechanical properties of FENIX-700, including its cooling rate, was investigated. In addition, the dependance of precipitation observed at grain boundaries on the heat treatment conditions was also discussed on the basis of the results of microstructure observations. It was confirmed that the tensile ductility, the creep rupture ductility, and the absorbed energy decreased as the grain size increased. The creep rupture strength, in contrast, increased remarkably as the grain size increased. The tensile strength increased as the cooling rate increased. Experimental results showed that satisfactory mechanical properties would be obtained for a grain size of ASTM G.S.No. 1.0-3.0.

To save fossil fuel resources and to reduce CO 2 emissions, considerable effort has been directed toward researching and developing heat-resistant materials that can help in improving the energy efficiency of thermal power plants by increasing their operational temperature and pressure conditions. Instead of conventional 9-12Cr ferritic heat-resistant steels with a tempered martensitic microstructure, we developed “Precipitation Strengthened 15Cr Ferritic Steel” based on a new material design concept: a solid-solution treated ferrite matrix strengthened by precipitates. Creep tests for 15Cr-1Mo-6W-3Co-V-Nb steels with ferrite matrix strengthened by a mainly Laves phase (Fe 2 W) showed that the creep strengths of 15Cr ferritic steel at temperatures ranging from 923 K to 1023 K were twice as high as those of conventional 9Cr ferric heat-resistant steel. 15Cr steels have higher steam oxidation resistance than that of conventional steel in the same temperature range as the creep tests. Thus, the new material design concept of heat-resistant steel pro- vides improved creep strength and steam oxidation resistance. We are attempting to determine the optimum compositions, especially that of carbon, in order to improve the high-temperature creep strength.

This study explores the expanded applications of Alloy J513, a high-performance material traditionally used in cast engine valvetrain components, for powder metallurgy and surface cladding applications. While already recognized for its superior heat and wear resistance at a lower cost compared to cobalt-based hardfacing materials, J513 demonstrates additional advantages in powder metallurgy applications due to its ability to achieve desired powder characteristics through atomization without requiring post-atomization annealing. Through experimental investigation based on fundamental metallurgical principles and cladding engineering processes, the presented research demonstrates J513’s exceptional weldability and favorable weldment structure compared to conventional cobalt-based alloys. The study establishes crucial relationships between weldment behavior and unit energy input, providing valuable insights for advanced cladding techniques while highlighting J513’s potential as a sustainable alternative to traditional nickel- and cobalt-based alloys in various manufacturing processes, including surface overlay and additive manufacturing.

An approach to phase analysis called multiphase separation technology (MPST) has been developed to determine phase chemistries of precipitated particles with sizes visible under SEM/EPMA observations based on the data from the conventional EDS measurements on bulk steel/alloy material samples. Quite accurate results from its applications have successfully been demonstrated by comparisons of SEM/EPMA - EDS + MPST with some other currently available means, for instance, chemical extractions (CA), TEM-EDS, AP-FIM and Thermo-Calc. etc. Applied examples regarding the relations of change in phase parameters including type, composition, volume fraction, size and distribution of the precipitated particles with material qualities, creep rupture lives, property stabilities, property recovery and boiler tube failures for some advanced heat resistant steels (P92, Super304H, HR3C, TP347HFG (H)) are given through the use of the SEM/EPMA - EDS + MPST in this contribution. Examples on phase quantifications of some nickel base superalloys (Nimonic263, Inconel 740 and Rhenium-containing alloys) are also shown to reveal the feasibility of its use in determining phase chemistries of precipitated particles under different measurement conditions. Practical applications of this combined technology to the material quality control and assessments, processing parameter improvements, as well as fracture/failure analyses of high temperature components have shown that this technology is quite convenient and effective when used for microstructural analysis purposes during R&D, manufacturing and operating processes.

The Advanced Materials and Manufacturing Technologies (AMMT) program is aiming at the accelerated incorporation of new materials and manufacturing technologies into nuclear-related systems. Complex Ni-based components fabricated by laser powder bed fusion (LPBF) could enable operating temperatures at T > 700°C in aggressive environments such as molten salts or liquid metals. However, available mechanical properties data relevant to material qualification remains limited, in particular for Ni-based alloys routinely fabricated by LPBF such as IN718 (Ni- 19Cr-18Fe-5Nb-3Mo) and Haynes 282 (Ni-20Cr-10Co-8.5Mo-2.1Ti-1.5Al). Creep testing was conducted on LPBF 718 at 600°C and 650°C and on LPBF 282 at 750°C. finding that the creep strength of the two alloys was close to that of wrought counterparts. with lower ductility at rupture. Heat treatments were tailored to the LPBF-specific microstructure to achieve grain recrystallization and form strengthening γ' precipitates for LPBF 282 and γ' and γ" precipitates for LPBF 718. In-situ data generated during printing and ex-situ X-ray computed tomography (XCT) scans were used to correlate the creep properties of LPBF 282 to the material flaw distribution. In- situ data revealed that spatter particles are the potential causes for flaws formation in LPBF 282. with significant variation between rods based on their location on the build plate. XCT scans revealed the formation of a larger number of creep flaws after testing in the specimens with a higher initial flaw density. which led to a lower ductility for the specimen.

The U.S. Department of Energy (DOE) and the Ohio Coal Development Office (OCDO) are sponsoring the “Boiler Materials for Ultrasupercritical Coal Power Plants” program. This program is aimed at identifying, evaluating, and qualifying the materials needed for the construction of critical components for coal-fired boilers capable of operating at much higher efficiencies than the current generation of supercritical plants. Operation at ultrasupercritical (USC) conditions (steam temperatures up to 760°C (1400°F)) will necessitate the use of new advanced ferritic materials, austenitic stainless steels and nickel-based alloys. As well as possessing the required mechanical properties and fireside corrosion resistance, these materials must also exhibit acceptable steamside oxidation resistance. As part of the DOE/OCDO program, steamside oxidation testing is being performed at the Babcock & Wilcox Research Center. More than thirty ferritic, austenitic and nickel-based materials have been exposed for up to 4,000 hours in flowing steam at temperatures between 650°C (1202°F) and 800°C (1472°F). In addition to wrought materials, steamside oxidation tests have been conducted on weld metals, coated materials and materials given special surface treatments. Exposed specimens were evaluated to determine oxidation kinetics and oxide morphology. High chromium ferritic, austenitic and nickel-based alloys displayed very good oxidation behavior over the entire temperature range due to the formation of a dense chromium oxide. With increasing steam temperature, low chromium ferritic materials experienced breakaway oxidation, and low chromium austenitic materials experienced significant oxide exfoliation. Special surface treatments that were applied to these materials appeared to have a beneficial effect on their oxidation behavior.

Inconel alloy 740 is a precipitation-hardenable nickel-chromium-cobalt alloy with niobium, derived from Nimonic 263, and is considered a prime candidate for the demanding conditions of advanced ultrasupercritical boilers. It offers an exceptional combination of stress rupture strength and corrosion resistance under steam conditions of 760°C (1400°F) and 34.5 MPa (5000 psi), surpassing other candidate alloys. Initially, Inconel alloy 740 was prone to liquation cracking in sections thicker than 12.7 mm (0.50 in), but this issue has been resolved through modifications in the chemical composition of both the base and weld metals. Current concerns focus on the weld strength reduction factor for direct-age weldments. This has led to further development in welding Inconel alloy 740 using Haynes 282, which has higher creep strength and may mitigate the weld strength reduction factor. This study details successful efforts to eliminate liquation cracking and compares the properties of Inconel alloy 740 and Haynes 282 filler materials using the gas tungsten arc welding process.

Nitridation is a high-temperature material degradation issue that can occur in air and in environments containing nitrogen, ammonia, etc., and in a variety of industrial processes. The nitridation behavior of several commercial nickel- and cobalt-based alloys is reviewed in this paper. The alloys include Haynes 230, Haynes 188, Haynes 625, Haynes 617, Haynes 214, Hastelloy X, and Haynes 233. The environments discussed are high-purity nitrogen gas between 871°C and 1250°C, 100% ammonia gas at 982°C and 1092°C, and a simulated combustion atmosphere at 982°C. The results showed that nitridation occurred in all the environments containing nitrogen. The nitridation attack was strongly influenced by the alloy compositions and the type of oxide formed (i.e., chromia or alumina), as some degree of oxidation was expected in the environments in which residual oxygen was present. Thermal cycling is briefly discussed because the integrity of protective oxides is also an important factor in resisting high-temperature oxidation and nitridation attack.

This overview paper contains a part of structure stability study on advanced austenitic heat-resisting steels (TP347H, Super304H and HR3C) and Ni-base superalloys (Nimonic80A, Waspaloy and Inconel740/740H) for 600-700°C A-USC fossil power plant application from a long-term joint project among companies, research institutes and university in China. The long time structure stability of these advanced austenitic steel TP347H, Super304H, HR3C in the temperature range of 650-700 °C and Ni-base superalloys Nimonic80A, Waspaloy and Inconel740/740H in the temperature range of 600-800°C till 10,000h have been detailed studied in this paper.