Superalloys 2021: Monday Interactive Session on Alloy Design
Program Organizers: Sammy Tin, University of Arizona; Christopher O'Brien, ATI Specialty Materials; Justin Clews, Pratt & Whitney; Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346; Qiang Feng, University of Science and Technology Beijing; Mark Hardy, Rolls-Royce Plc; John Marcin, Collins Aerospace; Akane Suzuki, GE Aerospace Research
Monday 3:10 PM
September 13, 2021
Room: Poster Area
Location: Virtual Event
On the Influence of Alloy Composition on Creep Behavior of Ni-based Single Crystal (SX) Superalloys: Oliver Horst1; Sadaf Ibrahimkhel1; Jonathan Streitberger1; Nick Wochmjakow1; Paul Git2; Felicitas Scholz1; Pascal Thome1; Robert Singer3; Jan Frenzel1; Carolin Körner3; Gunther Eggeler1; Marc Sirrenberg4; 1Ruhr-Universitaet Bochum; 2Friedrich-Alexander-Universitaet ; 3Friedrich-Alexander-Universitaet; 4Ruhr-University Bochum
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 microstructure, 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.
Development and Application of New Cast & Wrought Ni-base Superalloy M647 for Turbine Disk: Naoya Kanno1; Masaya Higashi1; Ryosuke Takai1; Shigehiro Ishikawa1; Kota Sasaki1; Kenji Sugiyama2; Yoshinori Sumi2; 1IHI Corptation; 2Daido steel Co.
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.
Alloy Design and Microstructural Evolution during Heat Treatment of Newly Developed Cast & Wrought Ni-base Superalloy M647 for Turbine Disk Application: Kenji Sugiyama; Yoshinori Sumi1; Naoya Kanno1; Masaya Higashi1; Ryosuke Takai1; Shigehiro Ishikawa1; Kota Sasaki1; 1IHI
A new Cast & 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 ã′, but optimal heat treatment is dependent upon specific chemical composition. For optimal mechanical properties, microstructural evolutions including austenitic grain size and ã′ 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 ã′ remained to prevent grain growth, enabling required mechanical properties, especially proof stress and low-cycle fatigue, to be achieved. As for secondary ã′, precipitation behavior was controlled intentionally by changing cooling rate after solution treatment, and this also resulted in modifying the precipitation behavior of tertiary ã′ 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 ã′ had a clear relationship with cooling rate. Moreover, the mean diameter of secondary ã′ was unchanged during aging and this suggested that only tertiary ã′ 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 ã′ and a small volume fraction of fine tertiary ã′ precipitates.
Thermodynamic Simulation and Experimental Validation of Phase Stability in Ni-based Superalloys: Kyle Ventura1; David Beaudry1; Alex Aviles1; Anna Kapustina2; Phillip Draa2; Kirtan Patel2; Raymond Snider2; Gerhard Fuchs1; 1University of Florida; 2Siemens Energy, Inc.
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.
Suppression of Sulfur Segregation at Scale/Substrate Interface for 6th Generation Single Crystal Ni-base Superalloy: Kyoko Kawagishi1; Chihiro Tabata2; Takuya Sugiyama2; Tadaharu Yokokawa1; Jun Uzuhashi1; Tadakatsu Ohkubo1; Yuji Takata1; Michinari Yuyama1; Shinsuke Suzuki2; Hiroshi Harada1; 1National Institute for Materials Science; 2Waseda Unversity
It is known that a single-crystal Ni-base superalloy containing a trace amount of sulfur has reduced high-temperature oxidation resistance. Our previous study has shown that melting of Ni-base superalloys in a CaO crucible can eliminate the effect of sulfur on oxidation resistance, but the mechanism was not completely clear. In this study, we finally succeeded in detecting the segregation of sulfur at the oxide / substrate interface of 6th generation single-crystal superalloys using STEM-EDS analysis, and confirmed that segregation could be suppressed by melting in the CaO crucible. As a result, it was found that melting in the CaO crucible can improve the oxidation resistance while maintaining the creep characteristics of 6th generation single-crystal Ni-base superalloy.
Composition and Temperature Stability of η and δ Phases for Future Nickel-base Superalloys for Turbine Discs Application: Laurane Finet1; Vladimir Esin2; Vincent Maurel2; Loïc Nazé2; 1R&D Department, Aubert & Duval, BP1, 63770 Les Ancizes, France; 2Centre des Matériaux, MINES ParisTech
To provide precipitation hardening of nickel-base superalloys, ã' and ã'' phases can be partially replaced by phases like eta (ç) and delta (ä), 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 ç and ä 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 ç 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 ç phase than Nb and that other elements than Nb, Ta, Al and Ti have an effect on ç and ä phases, such as Cr, Co and Fe. Hence the composition criteria for the formation of ç and ä phases in alloys with high Ta content are discussed.
Advanced Alloy Design Program and Improvement of 6th Generation Ni-base Single Crystal Superalloy TMS-238: Tadaharu Yokokawa1; HIroshi Harada1; Kyoko Kawagishi1; Toshiharu Kobayashi1; Michinari Yumaya2; Yuji Takata1; 1National Institute for Materials Science; 2National Institute for Materials Sci
This paper describes the advanced alloy design program (AADP) and improvement of a 6th 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 °C to 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 g' 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/1h oxidation was also updated. The determination coefficient of this equation was R2=0.90.
Computational Methods to Accelerate Development of Corrosion Resistant Coatings for Industrial Gas Turbines: Rishi Pillai1; Kenneth Kane1; Michael Lance1; Bruce Pint1; 1Oak Ridge National Laboratory
Oxidation resistant overlay coatings protect the underlying superalloy component in industrial gas turbines from oxidation attack. Rate of depletion of the Al-rich b-phase in the bond coat governs the lifetime of these coatings. The applicability of a computational method in accelerating the development of corrosion resistant coatings and significantly reducing the extensive experimental effort to predict coating lifetimes and microstructural changes in three coated Ni-base superalloys for real operational durations (20-40 kh) was undertaken in the present study. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and electron microprobe analysis (EPMA) were employed to characterize MCrAlY coated superalloy substrates (1483, 247 and X4) after exposure at 900 °C in air + 10% H2O for up to 20,000 h. The model predicted the longest coating lifetime for the coating on X4 substrate. Precipitation of g in the coatings was correctly predicted for all three coating systems. Additionally, the model was able to predict the formation of topologically close packed (TCP)-phases in the investigated coating systems.
The Yield Strength Anomaly in Co-Ni Design Space: K V Vamsi1; Sean Murray1; Tresa Pollock1; 1University of California Santa Barbara
A new computational approach to model precipitate compositions and properties in the CoNi-design space for yield strength anomaly prediction is presented. The antiphase boundary (APB) energies on {111} and {010} and the degree of elastic anisotropy are known to influence the yield strength anomaly. APB energies were estimated by a diffuse multi-layer fault (DMLF) model using the structural energies of proximate structures: L12, and D023. The elastic moduli were calculated via the energy-strain approach using density functional theory calculations. (Ni1-xCox)3(Al1-yWy) was chosen as the model system and Yoo’s criterion is evaluated over the entire range of compositions to identify regions that exhibit the yield strength anomaly. (Ni0.65Co0.35)3(Al0.5W0.5) has the maximum APB(111) and any two-phase alloy (ã+ãʹ) in Ni-Co-Al-W system with this precipitate composition might exhibit higher strength upon shearing by a matrix dislocation. ThermoCalc was employed to identify stable L12 regions in (Ni1-xCox)3(Al1-yWy). The effect of Co on the yield strength anomaly was investigated experimentally in three (Ni1-xCox)3Al alloys with L12 structure. All three alloys exhibited the yield strength anomaly, validating the computational approach. The addition of Co provides solid solution strengthening to Ni3Al at room temperature, however this contribution to the overall strength diminished as a function of temperature. CoNi-alloys displayed strengths similar to Ni3Al at elevated temperatures with Co addition resulting in a marginal increase in strength at the peak temperature. The present study elucidates that APB energies from a DMLF model combined with elastic moduli can be employed to predict yield strength anomaly using Yoo’s criteria.
Phase Equilibria Among A1/TCP/GCP Phases and Microstructure Formation in Ni-Cr-Mo System at Elevated Temperatures: Ryota Nagashima1; Ryosuke Yamagata1; Hirotoyo Nakashima1; Masao Takeyama1; 1Tokyo Institute of Technology
Phase equilibria among the A1 (g-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 g' 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 g and P (oP56) phase at temperatures above 1073 K. Two distinct three-phase regions of g+oP6+P and g+oP6+NiMo (oP56) were found to exist around the oP6 single-phase region. In case of the decomposition of high temperature g phase to the three-phase mixture comprised of g+oP6+P, very fine coherent particles of oP6 phase that are only a few hundred nanometers in size form in the g matrix with a tweed-like morphology. These precipitates possess an orientation relationship of {10}g//(100)oP6, <001>g//[010]oP6, just like precipitation behavior of g' particles in Ni-base superalloys. In contrast, the TCP phase preferentially precipitates at the g 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.