Superalloys 2020

Inhaltsverzeichnis

1. Frontmatter

2. Keynote

   1. Frontmatter

   2. Advanced Modeling Tools for Processing and Lifing of Aeroengine Components

      Arnaud Longuet, Christian Dumont, Eric Georges

      Abstract

      Lifing is one of the main challenges for aeroengine manufacturers. For fatigue prediction, attention has been focused on the crack initiation mode depending on stress level and initial microstructure. Microstructure prediction during the component manufacturing, especially for final heat treatments and final forging operations, is required if it is to be included in fatigue analysis. Reliable tools are now available for basic nickel-based alloys such as Inconel 718. For other alloys, notably γ/γ′ alloys, research is still being performed in close partnership with academia. Globally, two main trends are emerging; first, one of our main interests is to develop the modeling capability for the entire manufacturing process, including ingot conversion and billet forging. Second, new approaches are still under development by introducing more physical considerations through full-field models, which are very useful for a better understanding of specific issues such as heterogeneous grain growth. From a component lifing point of view, the initial state of stress is also a key parameter to be considered. One method for the control of residual stresses is application of a pre-spinning process. Finally, a standard lifing methodology is explained and improvements are proposed; in particular, size effect is used to model notch specimen life considering surface or internal initiation.

3. Alloy Development

   1. Frontmatter

   2. Developing Alloy Compositions for Future High Temperature Disk Rotors

      M. C. Hardy, C. Argyrakis, H. S. Kitaguchi, A. S. Wilson, R. C. Buckingham, K. Severs, S. Yu, C. Jackson, E. J. Pickering, S. C. H. Llewelyn, C. Papadaki, K. A. Christofidou, P. M. Mignanelli, A. Evans, D. J. Child, H. Y. Li, N. G. Jones, C. M. F. Rae, P. Bowen, H. J. Stone

      Abstract

      Two new alloy compositions for possible disk rotor applications have been examined. Both were intended to have higher \( \gamma ^{{\prime }} \) content than the existing alloy, RR1000, and be produced using powder metallurgy and isothermal forging to enable forgings to show a consistent coarse grain microstructure. Small pancake forgings of the new alloys and RR1000 were made and from these, blanks were cut, solution heat treated, cooled at measured rates and aged. Results of screening tests to understand the tensile, creep and dwell crack growth behavior, oxidation resistance and phase stability of these new alloys and coarse grain RR1000 are reported. The development alloys were similar in composition but exhibited different tensile and creep properties, phase stability and resistance to oxidation damage. Despite attempts to minimize variation in microstructure from heat treatment, differences in \( \gamma ^{{\prime }} \) size distribution were found to influence tensile and creep behavior. One of the new alloys (Alloy 2) showed improved yield and tensile strength compared to RR1000. Alloy 2 displayed similar initial creep strain behavior to RR1000 but superior resistance to subsequent creep damage, producing longer creep rupture lives. All of the alloys showed crack retardation at low stress intensity factor ranges (ΔK) from 3600 s dwell cycles at 700 °C in air. This occurred whilst crack growth was intergranular. Alloy 1 was found to precipitate C14 Laves phase from long term exposure at 800 °C. Like RR1000, σ phase was not detected in the new alloys after 750 h at 800 °C.

   3. Development of AGAT, a Third-Generation Nickel-Based Superalloy for Single Crystal Turbine Blade Applications

      J. Rame, P. Caron, D. Locq, O. Lavigne, L. Mataveli Suave, V. Jaquet, M. Perrut, J. Delautre, A. Saboundji, J.-Y. Guedou

      Abstract

      The new third-generation single crystal superalloy AGAT has been developed for aircraft engine turbine blade applications. Alloy design procedure is described and AGAT alloy properties are presented and compared with those of, respectively, first-, second-, and third-generation AM1, CMSX-4 and CMSX-10 alloys. AGAT alloy exhibits high creep resistance at very high temperature (1200 °C) compared with first- and second-generation superalloys while maintaining moderate density (8870 kg m⁻³) and stable microstructure unlike the third-generation superalloy. High cycle fatigue (HCF) and low cycle fatigue (LCF) properties of AGAT alloy are similar to second-generation CMSX-4 alloy. AGAT solution heat treatment allows suppressing the γ/γ′ interdendritic eutectic pools at a temperature 30 °C lower than for CMSX-10 with a shorter duration. Oxidation resistance of AGAT alloy at 1150 °C is lower than that of second but higher than that of third-generation reference superalloys. AGAT shows low sensitivity to secondary reaction zone (SRZ) formation under β-NiPtAl bond coat (BC) and great spallation resistance of YPSZ EB-PVD thermal barrier coating (TBC) compared with reference alloys. Finally, single crystal turbine blades were successfully manufactured through industrial processes to be tested in engine conditions.

   4. Segregation of Solutes at Dislocations: A New Alloy Design Parameter for Advanced Superalloys

      Lola Lilensten, Philipp Kürnsteiner, Jaber Rezaei Mianroodi, Alice Cervellon, Johan Moverare, Mikael Segersäll, Stoichko Antonov, Paraskevas Kontis

      Abstract

      The interactions of solutes with crystal defects at near-atomic-level were investigated in five single-crystal nickel-based superalloys deformed at temperatures between 850 and 1160 °C and various deformation conditions. These interactions, and consequently the composition of a particular solute that segregates at a crystal defect, are controlled by the type of the crystal defect, the deformation conditions, i.e., temperature and stress, and the overall alloy composition. Atomistic phase-field simulations also reveal the effect of dislocation velocity on the amount of solutes that can segregate on dislocations. The observed plasticity-assisted redistribution of interacting solutes phenomena results in microstructural and chemical alterations, which are associated with recrystallization, rafting, and the formation of topologically close-packed phases. Deciphering these interactions by enabling quantitative three-dimensional imaging of solutes at crystal defects with high sensitivity and spatial resolution will allow to develop a solute–defect database that can be used as a key-design parameter for advanced superalloys.

   5. Ni–Co-Based Wrought Superalloys Containing High W—Microstructure Design for a Balance of Properties

      Akane Suzuki, Steve J. Buresh, Richard DiDomizio, Scott M. Oppenheimer, Soumya Nag, Ian M. Spinelli, P. R. Subramanian, Stephen G. Pope, Jon C. Schaeffer

      Abstract

      Ni–Co-based γ + γ′ superalloys were explored in a wide range of Co/Ni ratios for designing a wrought superalloy with a combination of superior high temperature strength and environmental resistance at temperatures above 927 °C (1700 °F). While alloys with high Co/Ni ratios possess superior creep resistance, reductions of the Co/Ni ratio and additions of Fe and B are effective in improving ductility in the intermediate temperature range and hold-time low cycle fatigue resistance. A formation of fine, discrete Co₂W Laves precipitates covering a large fraction of grain boundaries is responsible for the improvements. The experimental alloys exhibited excellent oxidation resistance at 982 °C (1800 °F) by forming a protective alumina scale during cyclic exposure.

   6. On the Influence of Alloy Composition on Creep Behavior of Ni-Based Single-Crystal Superalloys (SXs)

      O. M. Horst, S. Ibrahimkhel, J. Streitberger, N. Wochmjakow, P. Git, F. Scholz, P. Thome, R. F. Singer, C. Körner, J. Frenzel, G.  Eggeler

      Abstract

      In the present work, three Ni-based single-crystal superalloys (SXs) were investigated, a Re-containing alloy ERBO/1 (CMSX-4 type) and two Re-free SXs referred to as ERBO/15 and ERBO/15-W, which differ in W content. The microstructural evolution of the three alloys during heat treatment and their creep behavior is investigated. When one applies one heat treatment to all three alloys, one obtains different γ/γ′-microstructures. Subjecting these three alloys to creep in the high-temperature low-stress creep regime, ERBO/15 outperforms ERBO/1. In order to separate the effects of alloy chemistry and microstructure, the kinetics of the microstructural evolution of the three alloys was measured. The results were used to establish similar microstructures in all three alloys. Comparing ERBO/15 with ERBO/15-W, it was found that in ERBO/15-W particles grow faster during the first precipitation heat treatment and that ERBO/15-W creeps significantly faster. At constant microstructures, ERBO/15 and ERBO/1 show similar creep behavior. In the high-temperature and low-stress creep regime, ERBO/15 shows lower minimum creep rates but ERBO/1 features a slower increase of creep rate in the tertiary creep regime. It was also found that in the high-temperature low-stress creep regime, ERBO/1 shows a double minimum creep behavior when particles are small.

   7. Platinum-Containing New Generation Nickel-Based Superalloy for Single Crystalline Applications

      Jérémy Rame, Satoshi Utada, Luciana Maria Bortoluci Ormastroni, Lorena Mataveli-Suave, Edern Menou, Lucille Després, Paraskevas Kontis, Jonathan Cormier

      Abstract

      TROPEA, a new platinum-containing single crystal (SX) superalloy, has been developed for high-temperature components of aircraft engines. Criteria used for the alloy design procedure to target specifications are presented. TROPEA properties have been characterized and compared to reference alloys. First casting showed good castability of the alloy with no tendency to freckles formation. TROPEA exhibits excellent yield stress up to 800 °C compared to second- or third-generation SX superalloys and resistance above 800 °C similar to second-generation superalloys. This new alloy shows high low cycle and very high-cycle fatigue properties, particularly at low temperature. TROPEA exhibits high creep resistance at temperatures above 1200 °C, stable microstructure (no TCP phases) with a density (8.83 g.cm⁻³) intermediate to that of second- and third-generation SX superalloys. Atome probe tomography measurements show that platinum preferentially partitions to γ′ precipitates. Platinum additions significantly stabilize γ′ phase near solvus temperature and consequently increase alloys properties at (very) high temperature despite a low rhenium content. Thus, platinum emerges as a promising element to enhance high-temperature properties of SX superalloys in addition to or as an alternative to rhenium. The high creep properties at very high temperature combined with excellent fatigue properties at low temperature make TROPEA a promising SX superalloy for highly cooled turbine components.

   8. Development and Application of New Cast and Wrought Ni-Base Superalloy M647 for Turbine Disk

      Naoya Kanno, Masaya Higashi, Ryosuke Takai, Shigehiro Ishikawa, Kota Sasaki, Kenji Sugiyama, Yoshinori Sumi

      Abstract

      The cast and wrought nickel base superalloy M647 has been developed with high mechanical performance and deformability. This study describes an overview of the microstructure and the properties of M647. A full scale forging process has been developed with uniform fine grain distribution. The detrimental effect of thermal exposure at 700 °C ~ 800 °C on mechanical properties was evaluated. M647 showed good mechanical properties and equivalent thermal stability to conventional turbine disk alloys. M647 offers good balance of deformability and mechanical properties with lower cost than powder metallurgy alloys.

   9. Alloy Design and Microstructural Evolution During Heat Treatment of Newly Developed Cast and Wrought Ni-Base Superalloy M647 for Turbine Disk Application

      Kenji Sugiyama, Yoshinori Sumi, Naoya Kanno, Masaya Higashi, Ryosuke Takai, Shigehiro Ishikawa, Kota Sasaki

      Abstract

      A new cast and wrought Ni-base superalloy, M647, has been developed for turbine disk application with high mechanical properties at elevated temperatures and reasonable hot deformability. Conventional Ni-base superalloys are known to be strengthened by primary, secondary, and tertiary γ′, but optimal heat treatment is dependent upon specific chemical composition. For optimal mechanical properties, microstructural evolutions including austenitic γ grain size and γ′ morphology were identified for M647. To evaluate these properties, a full-scale low-pressure turbine disk was manufactured. This was subjected to a sub-solvus solution heat treatment, such that primary γ′ remained to prevent grain growth, enabling required mechanical properties, especially proof stress and low-cycle fatigue, to be achieved. As for secondary γ′, precipitation behavior was controlled intentionally by changing cooling rate after solution treatment, and this also resulted in modifying the precipitation behavior of tertiary γ′ during aging. In this study, microstructural evolution and tensile properties at 650 °C were investigated to clarify the relationship between them and to identify the strengthening mechanisms. From the result of SEM observation, size distributions of secondary γ′ had a clear relationship with cooling rate. Moreover, the mean diameter of secondary γ′ was unchanged during aging and this suggested that only tertiary γ′ was precipitated during aging. Finally, critical resolved shear stress was calculated using both weakly and strongly coupled dislocation models, and it was clear that M647 was strengthened by a high volume fraction of secondary γ′ and a small volume fraction of fine tertiary γ′ precipitates.

   10. γ′ Thermodynamic Simulation and Experimental Validation of Phase Stability in Ni-Based Superalloys

       Kyle Ventura, David Beaudry, Alex Aviles, Anna Kapustina, Phillip Draa, Kirtan Patel, Raymond Snider, Gerhard Fuchs

       Abstract

       There is a constant push for higher efficiencies, lower cost, and increased power in power-generating and propulsion gas turbines. In order to meet these requirements, hot section materials with higher temperature capabilities are needed. Ni-base superalloys are selected for these applications. In this study, commercially available and model Ni-based superalloy compositions were simulated with thermodynamic calculations using Thermo-Calc software, which were then experimentally evaluated. Previously, alloy development campaigns have relied heavily on preparing many heats of alloys to examine the effect of various alloying additions and various levels to down-select a single alloy. Methods like PHACOMP have used understanding of partitioning behavior for alloy design. More recent studies have utilized regression analysis of empirical data to inform new alloy design. Physical models can be used to improve upon these methods. The ability to use computational materials science approaches to reduce the number of heats processed in an alloy development program was explored. By validating database sensitivity to compositional changes, future alloy development work can be performed precisely, leading to faster alloy development, validation, and implementation. Model alloys were optimized for phase stability, cost, and density. Continued experimental validation of thermodynamic prediction databases will create a more robust system for alloy property prediction and development.

   11. Composition and Temperature Stability of η and δ Phases for Future Nickel-Base Superalloys for Turbine Disks Application

       Laurane Finet, Vladimir A. Esin, Vincent Maurel, Loïc Nazé

       Abstract

       To provide precipitation hardening of nickel-base superalloys, γ′ and γ″ phases can be partially replaced by phases like eta (η) and delta (δ), which may be stable up to temperatures higher than 800 °C. Nevertheless, there is still a lack of information about these phases in terms of crystal structure, composition, thermodynamic stability, and precipitate morphology. Therefore, the present study focuses on the composition and temperature stability of η and δ phases in alloys with high Nb and Ta contents. Various experimental nickel-base alloys were designed using literature and thermodynamic calculations. After solution and aging treatments, they were characterized using SEM to determine precipitate morphology and distribution, and TEM-EDS to determine crystal structure and composition of precipitated phases. Combined in situ HE-XRD experiments followed by metallographic analysis were performed to determine the solvus temperature of η phase in several alloys. Results on the nature of the precipitated phases show that thermodynamic calculations (TCNI7 database) and composition criteria are not always consistent with experimental data. The investigation also reveals that Ta is more favorable to form η phase than Nb and that other elements than Nb, Ta, Al, and Ti have an effect on η and δ phases, such as Cr, Co, and Fe. Hence, the composition criteria for the formation of η and δ phases in alloys with high Ta content are discussed.

   12. Advanced Alloy Design Program and Improvement of Sixth-Generation Ni-Base Single Crystal Superalloy TMS-238

       Tadaharu Yokokawa, Hiroshi Harada, Kyoko Kawagishi, Toshiharu Kobayashi, Michinari Yuyama, Yuji Takata

       Abstract

       This paper describes the advanced alloy design program (AADP) and improvement of a sixth-generation single crystal superalloy, TMS-238, using this AADP. Creep rupture life prediction equations for five different creep conditions, 800 °C/735 MPa, 900 °C/392 MPa, 1000 °C/245 MPa, 1100 °C/137 MPa, and 1150 °C/137 MPa, were obtained with excellent determination coefficients from 0.95 to 0.98. Using the AADP, we successfully developed three alloys, TMS-238mod-A, TMS-238mod-B, and TMS-23mod-C, which have 10–22 °C higher-temperature capabilities than those of the TMS-238 alloy. The AADP successfully predicted that the creep life was maximized when the volume fraction of γ′ phase was approximately 65% at low-temperature and high-stress conditions, such as 900 °C/392 MPa, compared to that of approximately 60% under high-temperature and low-stress conditions, such as 1100 °C/137 MPa. This prediction enables us to precisely optimize the creep property. Moreover, the prediction equation of the weight change after 1100 °C/1 h oxidation was also updated. The determination coefficient of this equation was R² = 0.90.

   13. Phase Equilibria Among A1/TCP/GCP Phases and Microstructure Formation in Ni–Cr–Mo System at Elevated Temperatures

       Ryota Nagashima, Ryosuke Yamagata, Hirotoyo Nakashima, Masao Takeyama

       Abstract

       Phase equilibria among the A1 (γ-fcc), Ni₂Cr (oP6) and TCP phases in Ni–Cr–Mo system at temperatures above 973 K have been investigated, in order to evaluate the possibility for utilizing a novel microstructure design principle for Ni-based alloys having TCP phase at grain boundaries and GCP phase other than γ′ phase within grain interiors. Unlike the phase diagram calculated based on commercially available thermodynamic databases, the Ni₂Cr phase in the binary system becomes stabilized by the presence of Mo solute atoms in solution at temperatures greater than 200 K, and the Ni₂(Cr, Mo)-oP6 single-phase region exists as an island at around the composition of Ni–20Cr–15Mo (at.%) at temperatures above 973 K. The oP6 phase decomposes to γ and P (oP56) phase at temperatures above 1073 K. Two distinct three-phase regions of γ + oP6 + P and γ + oP6 + NiMo (oP56) were found to exist around the oP6 single-phase region. In case of the decomposition of high-temperature γ phase to the three-phase mixture comprised of γ + oP6 + P, very fine coherent particles of oP6 phase that are only a few hundred nanometers in size form in the γ matrix with a tweed-like morphology. These precipitates possess an orientation relationship of \(\left\{ {1\bar 10} \right\}\)_γ//(100)_oP6, <001>_γ//[010]_oP6, just like precipitation behavior of γ′ particles in Ni-base superalloys. In contrast, the TCP phase preferentially precipitates at the γ grain boundaries. The novel phase transformations and microstructures occurring in this class of alloys may potentially lead to advances in the design of novel Ni-based alloys.

   14. A New Co-free Ni-Based Alloy for Gas Turbine and Exhaust Valve Applications

       Karl A. Heck, Ning Zhou, Samuel J. Kernion, Danielle Rickert, Filip Van Weereld

       Abstract

       A new Ni-based cast-and-wrought alloy designed for high temperature strength, stability, notch ductility, and minimal elevated temperature dwell fatigue crack growth rate has been laboratory developed and scaled up in the mill. Based on studies of a relatively wide compositional space, a Co-free composition was selected. Other properties, including tensile strength, stress rupture, creep, low cycle fatigue, oxidation, and sulfidation resistance, as well as hot workability were also studied. Several heat treatments were developed to achieve property balances as appropriate for various end-user applications such as those limited by damage tolerance, creep, fatigue, or tensile strength. Microstructural stability after extended exposure at temperatures ranging from 704 to 871 °C was studied. Multiple 12-ton heats have been successfully processed as VIM/VAR and VIM/ESR ingots converted into forged billets, rolled bar, and strip products. Potential applications for this alloy include turbine disks, gas turbine engine casings, high temperature fasteners, heavy duty diesel engine exhaust valves, and high temperature gaskets. This paper discusses alloy and process development as well as microstructure--property relationships of the alloy.

   15. On the Influence of Alloy Chemistry and Processing Conditions on Additive Manufacturability of Ni-Based Superalloys

       Joseph N. Ghoussoub, Yuanbo T. Tang, Chinnapat Panwisawas, André Németh, Roger C. Reed

       Abstract

       Additive manufacturing trials are carried out on two new nickel-based superalloys designed specifically for this processing method. Their performance—with emphasis on their capability to resist cracking—is assessed by comparing with the two legacy alloys IN939 and CM247LC. The two new alloys are found to have demonstrably superior printability. Thermophysical testing and quantitative characterization, particularly via stereology, are used to help rationalize the physical basis of the improved manufacturability displayed.

   16. Alloying Effects on the Competition Between Discontinuous Precipitation Versus Continuous Precipitation of δ/η Phases in Model Ni-Based Superalloys

       Satoru Kobayashi, Tomoki Otsuka, Rikuryo Watanabe, Kyosuke Sagitani, Masaki Okamoto, Kako Tokutomi

       Abstract

       Alloying effects on the competition between discontinuous and continuous precipitation of δ-Ni₃Nb (D0_a) phase and η-Ni₃Ti (D0₂₄) phase were investigated in model Ni-Cr-Fe-Nb and Ni-Ti-based alloys, respectively, to aim at designing polycrystalline Ni based superalloys with better temperature capability. Discontinuous precipitation tends to occur at lower temperatures, while continuous precipitation dominates at higher temperatures in the two alloy systems. The addition of Mo promotes continuous precipitation with respect to discontinuous precipitation while that of Ti promotes discontinuous precipitation rather than continuous precipitation in δ phase precipitation alloys. A replacement of Ti with Mo promotes continuous precipitation with respect to discontinuous precipitation in η phase precipitation alloys at 800 °C. The observed alloying effects are discussed in terms of chemical driving force, interfacial energy between the matrix phase and the δ(η) phases, and coherency strain caused by the formation of the metastable phases prior to the formation of δ/η phases.

   17. Precipitate Phase Stability and Mechanical Properties of Alloy 263 and Variants in Wrought or Cast Form

       Martin Detrois, Paul D. Jablonski, Jeffrey A. Hawk

       Abstract

       Alloy 263 is a candidate Ni-based superalloy for use in advanced ultra-supercritical (AUSC) power plants that are targeted to operate above 700 °C. Exposure times in this type of environment are considerable with target creep properties specified at 100,000 h making phase stability an important parameter in the alloy selection process. In this investigation, the microstructure of alloy 263 and two modified compositions in both cast and cast/wrought forms were investigated after exposure at 800 °C for various times ranging from 1000 to 10,000 h. Tension and creep properties were assessed for all alloys in both forms. Modification to the Ti and Al concentrations successfully slowed down the γ′ to η transformation while doubling the γ′ fraction. Thin elongated η needles or platelets formed in the wrought products, while thicker, plate-like, η precipitates were found in the castings. The effect of the various microstructures on the creep properties was determined using isothermally aged specimens aged at 800 °C for 3000 and 10,000 h prior to creep screening. Strong precipitation of the η phase was found to considerably decrease creep life and increase minimum creep rate. By modifying the Ti and Al content, the creep life and ductility of the new formulation tested on specimens isothermally aged for 3000 and 10,000 h were near that of the nominal alloy in its standard aged condition.