Superalloys 2024: Interactive Session C: Blade Alloy Processing & Mechanical Behavior
Program Organizers: Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346
Tuesday 10:10 AM
September 10, 2024
Room: Winterberry
Location: Seven Springs Mountain Resort
C-1: Effect of Re Addition on the Sensitivity to Recrystallization in As-cast Ni-based SX Superalloys: Yihang Li1; Zhipeng Jiang1; Longfei Li1; Guang Xie2; Jian Zhang2; Qiang Feng1; 1University of Science and Technology Beijing; 2Institute of Metal Research, Chinese Academy of Sciences
The recrystallization of nickel-based single-crystal superalloys during solution treatment may be promoted by local deformation induced during the cooling stage of directional solidification and is related to alloy chemistry. In this study, the effect of Re addition on the sensitivity to recrystallization of nickel-based single-crystal superalloys and the ways in which Re affects nucleation and growth of recrystallized grains are investigated using the as-cast alloy without Re addition and those with Re addition of 2 and 4 wt.%. It is suggested that 4 wt.% Re addition can significantly increase the propensity to nucleate recrystallized grains but significantly inhibit grain growth of the as-cast SX superalloy. The former is attributed to the increase of Re segregation at the dendrite scale, which leads to the increase of strength difference in ă matrix of the dendrite core and interdendritic region, as well as the increase in eutectics and casting pores, thus providing higher stored energy and more nucleation sites for recrystallization nucleation. Meanwhile, the severe Re segregation in ă matrix of high-Re alloys increases the ă′ solvus temperature and reduces the precipitate-free zone, thus inhibits growth of recrystallized grains. These insights will be beneficial to alloy design and process optimization and allow further improvement of the casting costs.
C-2: Effects of Trace Impurities in Ni-base Single Crystal Superalloys on High-temperature Properties and Disablement of Impurities by CaO for Recycle of Superalloys: Kyoko Kawagishi1; Chihiro Tabata2; Tadaharu Yokokawa1; Yuji Takata1; Michinari Yuyama1; Takahide Horie2; Hirotoshi Maezawa2; Shinsuke Suzuki2; Hiroshi Harada1; 1National Institute for Materials Science; 2Waseda University
In determining the specifications for the production or recycling process of Ni-base single crystal superalloys, it is important to clarify the allowable trace impurity concentration. In this study, the effects of Pb and Sb on high-temperature strength and oxidation resistance of 6th generation superalloy TMS-238 were summarized. It was found that both Sb and Pb do not have a large effect on creep rupture life, but they degrade oxidation resistance. The removal of impurities by melting in a CaO crucible was tested and its mechanism was examined. It was found that Ca forms a compound with impurities within the alloy and prevents the segregation of impurities at the oxide film/substrate interface. The effect of CaO was also confirmed in an experiment in which impurity S was removed from 1st generation Ni-base superalloy TMS-1700 by adding CaO particles in a 3-ton commercial melting furnace. Similar results were obtained for this alloy, where it was also found that CaS had formed inside the alloy, thus improving the oxidation resistance of TMS-1700.
C-3: On the Effect of Super-solidus Heat Treatments on the Microstructure and Creep Properties of a Third-generation Single Crystal Ni-based Superalloy: Inmaculada Lopez Galilea1; Lisa Hecker1; Marc Sirrenberg1; Sebastian Weber1; 1Ruhr University Bochum
A Super-Solidus Hot Isostatic Pressing, SSHIP, heat treatment has been developed and applied to the third-generation Ni-based single crystal superalloy CMSX-4 Plus. The aim of this new type of heat treatment is to significantly reduce the solution heat treatment time and improve the mechanical properties compared to those resulting from subjecting the single crystal to conventional heat treatment routes. The partial melting of the regions with the lowest solidus temperatures during SSHIP results in the acceleration of the diffusional processes, while the control of the cooling rate after SSHIP results in the optimum precipitation of the fine γ/γ' microstructure. This innovative type of heat treatment, which can significantly reduce the economic penalties associated with lengthy high-temperature solution treatments while having a positive effect on the final mechanical properties, could be applied to other complex single crystal Ni-based superalloys containing large amounts of refractory elements (like rhenium, tungsten, and tantalum), showing strong dendritic segregation and / or a large volume fraction of eutectics in the as-cast state.
C-4: Exploring Microstructural Characteristics, Mechanical Behavior, Hydrogen Embrittlement and Long-term Stability of Polycrystalline CoNiCr-based Superalloys: Svetoslava Tsankova1; Oliver Nagel1; Andreas Bezold1; Bianca Grandjean1; Andreas Kirchmayer1; Mathias Göken1; Steffen Neumeier1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg
Polycrystalline γ/γ' CoNiCr-based superalloys have a promising combination of properties for aerospace and stationary gas turbine applications. In this study, four alloys, CoWAlloy1, 2, 3 and 6, were selected for further investigation. Microstructures of fully heat-treated materials were characterized by scanning and transmission electron microscopy and long-term stability at 750 °C was examined for various durations up to 1000 h. Tensile tests were performed between 25 °C and 700 °C, revealing dynamic strain aging in CoWAlloy2, 3 and 6 at intermediate temperatures of 400-650 °C. Hydrogen charging induced a decrease in tensile ductility at 25°C in the µ phase containing CoWAlloy3. Creep experiments were performed on CoWAlloy1, an alloy with increased Ti and Ta content, at 750 °C and 800 MPa, with variations of the secondary γ' precipitate size and grain size to identify optimal microstructural parameters. It was found that smaller grain sizes lead to a significantly higher creep resistance at these testing conditions.
C-5: Revisiting Nanoscale Microstructural Features of Alloy 680 to Understand its Remarkable Mechanical Strength in the As-welded Condition: Cleiton Silva1; Rafaella Silva1; Émerson Miná1; Ricardo Reppold2; Marcelo Paes2; Giovani Dalpiaz2; Marcelo Motta1; Hélio de Miranda1; Irina Wossack3; Alisson Kwiatkowski da Silva3; Christian Liebscher3; 1Universidade Federal do Ceará; 2Petróleo Brasileiro S/A; 3Max-Planck-Institut für Eisenforschung GmbH
The present study assesses the microstructure of a new Ni-based alloy filler metal, Inconel® 680, at high resolution to understand the underlying mechanisms behind its remarkable mechanical properties. Investigations using aberration-corrected (scanning) transmission electron microscopy (TEM/STEM) were performed to complement the previous microstructural analysis. The results from TEM analysis confirmed Nb-rich C14-type Laves phase precipitation, besides different types of carbides in the interdendritic spacings. However, the advanced microstructural characterisation has also shown a heterogeneous pattern in terms of microstructure between the cellular-dendrite core and interdendritic region. A higher dislocation density was noticed in the interdendritic spacings accompanied by nanometric precipitation. These nanoprecipitates were identified as being tined globular-shape -Ni3Nb phase. The -Ni3Nb phase precipitation resulted from an intense microsegregation of Nb during the solidification. This precipitation of the -Ni3Nb phase plays an essential role in the enhanced yield strength of alloy 680.
C-6: Creep Properties Dependence to Solution Heat Treatment of Second and Third Generation Ni-based Single Crystal Superalloys: Luciana Maria Bortoluci Ormastroni1; Jeremy Rame2; Jonathan Cormier3; 1Safran Aircraft Engines; 2NAAREA; 3Institut Pprime/ENSMA
Computational design is increasingly being used by industry and research institutes for the development of new compositions of Ni-based single crystal (SX) superalloys. Alloy selection is often based on the mechanical properties of the fully heat-treated Ni-based SX superalloys. However, a more complex chemical composition leads to a more complex solution heat treatment (ST). The development of a ST to reach optimum homogenization, requires time and resources, overall penalizing the time/cost savings provided by computational design approaches. Thus, the present study investigates several superalloys “as cast” mechanical properties to predict the creep life of the solution heat treated alloy. Four commercial superalloys with distinct chemical composition were chosen. Each alloy was investigated in (i) the as cast (AC) and (ii) solution treated and aged (ST) states. The superalloys were creep tested at 950 °C/390 MPa and 1050 °C/190 MPa. A creep life improvement by a factor of 1.5 to 3 times has been observed after the ST, irrespective of the alloy chemical composition or creep test conditions. Down-selecting alloys’ composition from the as-cast creep properties can be a viable approach to speed-up alloy design.
C-7: Option of HIP Implementation Scheme and its Effects on the Mechanical Properties of a Nickel-based Single-crystal Superalloy: Siliang He1; Longfei Li1; Song Lu1; Yunsong Zhao2; Jian Zhang2; Qiang Feng1; 1University of Science and Technology Beijing; 2Science and Technology on Advanced High Temperature Structural Materials Laboratory Beijing Institute of Aeronautical Materials
The micropores and residual eutectic in nickel-based single crystal (SX) superalloys can promote crack initiation in the SX turbine blades during service, threating the components safety. Hot isostatic pressing (HIP) treatment is an effective technique to reduce micropores and enhance the mechanical properties of the alloys. This work investigated the effect of two typical HIP implementation schemes on a nickel-based SX superalloy compared with a conventional heat treatment scheme (without HIP). The results show that the HIP-treated samples had fewer micropores, residual eutectic and better mechanical properties than that of the non-HIP sample. The HIP treatment can increase the yield strength, elongation and reduction in area of tensile properties at 760 °C compared with the non-HIP sample, but had no noticeable effect on that at 980 °C. The HIP treatment on the solution-treated sample enhanced the creep rupture life more than that of the as-cast sample at 980 °C/ 250 MPa, but had no influence on it at 1100 °C/ 130 MPa. The HIP effect on the fatigue rupture cycles was closely related to the type of crack initiation site. The HIP treatment significantly prolonged the rupture cycles of low-cycle fatigue (LCF) at 760 °C and high-cycle fatigue (HCF) at 850 °C of HIP-treated samples by changing the crack initiation sites, but had no impact on that at 980 °C. Comparing different HIP implementation schemes on microstructures and comprehensive mechanical properties, the HIP treatment on the solution-treated sample was better than that on the as-cast sample. This work can improve the mechanical properties and provide guidance for HIP implementation scheme of nickel-based SX superalloys.
C-8: Tensile Behavior of TMS-238 Ni-based Single-crystal Superalloy at 650°C: Benoît Mansoz1; Pierre Caron2; Kyoko Kawagishi3; Luciana Maria Bortoluci Ormastroni4; Patrick Villechaise5; Jonathan Cormier5; Florence Pettinari-Sturmel1; 1CEMES - CNRS, University of Toulouse; 2Scientific Consultant; 3National Institute for Materials Science (NIMS); 4Safran Aircraft Engines; 5Institut PPrime, ISAE-ENSMA
TMS-238 is a promising 6th generation superalloy with impressive high temperature creep performance but it exhibits a particular tensile behavior at 650 °C with low yield strength, limited ductility and a non-classical hardening behavior. To study this behavior, TMS-238 specimens with different misorientations away from the perfect [001] crystallographic orientation were tensile tested at 650 °C. Mechanical tests revealed that highly misoriented specimens do not exhibit this atypical hardening behavior but a classical “plateau” behavior and keep a similar low yield strength. TEM investigations were conducted with post mortem observations in order to interpret these macroscopic tensile characteristics. Similar TEM experiments were also performed using other more classical alloys for reference. TEM investigations in TMS-238 revealed a high density of dislocations and stacking faults in the γ phase and a homogeneous deformation in the perfect [001] oriented samples, contrarily to the heterogeneous deformation observed in the misoriented specimen. TEM energy disperse X-ray spectroscopy analysis confirmed significant amounts of Re and Ru in γ, two elements known to increase the γ/γ' misfit and decrease fault energy, resulting in a lower mobility of dislocations in the matrix, the presence of extended stacking faults in the vertical γ - channels and a strong hardening.
C-9: In Situ Imaging of Misorientation Changes During Tensile Loading in Single Crystal Nickel-base Superalloys by High-resolution X-ray Diffraction Mapping: Robert Albrecht1; 1University of Silesia
Recently, the method called high-resolution imaging of misorientations in single crystals has demonstrated its usefulness in accurately determining the single crystal quality in superalloys. This was made possible by obtaining high-resolution angular measurements of misorientation (arc-sec) and high-resolution imaging (µm) combined with a relatively large measurement area. The technique combines traditional X-ray diffraction topography with high-resolution diffraction and advanced data post-processing, including color coding and 3D projections of diffraction images. It was demonstrated that the mosaic structure of superalloys is highly complex and varies at both the micro and macro levels. In the present work, the advanced high-resolution X-ray diffraction method for imaging misorientation and mosaicity in single crystal superalloys was used to observe structural changes during uniaxial tensile loading. This research utilized single crystal flat tension samples from CMSX-4 superalloy prepared from the casting produced at a 3 mm/min withdrawal rate. The results indicate that the crystallographic orientation changes are within a few degrees up to the rupture. The evolution of the plastic deformation region was directly observed on the samples by contrast blurring.
C-10: A Prediction Method for Local Creep Strain of Directionally Solidified Superalloys and Turbine Blades: Song Lu1; Yikai Shao1; Weiwei Zheng1; Longfei Li1; Qiang Feng1; 1University of Science and Technology Beijing
Evaluating the service conditions and the corresponding strain at high-pressure turbine blades is crucial for the safe service and maintenance of aircraft engines. However, due to the harsh environment in turbines and the complex geometry of blades, it is difficult to directly monitor the variation of their service temperatures, stresses and strains. In this work, an approach to predicting the equivalent service conditions and the local strain of directionally solidified superalloys and turbine blades was developed by integrating high-throughput creep tests and machine-learning tools. A large amount of experimental data was obtained using the flat specimens with the continuously variable cross-section and digital image correlation technique. Then, the quantitative relationship between temperature, stress, strain, time and the essential microstructure parameters was established under the help of machine learning models. The established machine learning models were then employed to predict the service conditions and the corresponding strain of a directionally solidified superalloy and a turbine blade. Finally, the applicability and limitations of this method were discussed. The development of this method provides guidance for the service evaluation of turbine blades.
C-11: Prediction of the Creep Strength of Single Crystalline Superalloys via a Microstructure-informed Deep Neural Network: Andreas Bezold1; Toni Albert1; Mathias Göken1; Steffen Neumeier1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg
The design of superalloys is traditionally based on numerous experimental iterations guided by expert insights. The advent of computational tools that can calculate and predict thermophysical and mechanical properties has transformed this process. These tools have facilitated the discovery and evaluation of new alloys, leading to advancements in high-temperature capabilities and other design objectives, such as reducing the content of Re.
C-12: Temperature and Time Dependence of Elemental Segregation at Stacking Faults in Ni- and Co-base Superalloys: Nicolas Karpstein1; Mingjian Wu1; Andreas Bezold1; Steffen Neumeier1; Jonathan Cormier2; Erdmann Spiecker1; 1FAU Erlangen-Nürnberg; 2Institut Pprime, ISAE-ENSMA
Elemental segregation at stacking faults in the γ' phase is a crucial part of the stacking-fault based deformation of superalloys, and the local composition of a stacking fault critically affects the resistance of γ' to further shearing. Here, the process of elemental segregation at extrinsic stacking faults in γ' is examined in Ni-base superalloy CMSX-4 and Co-base superalloy ERBOCo-4. By measuring fault compositions not only after deformation, but also after additional load-free annealing steps of different durations and temperatures between 700 °C and 900 °C, time- and temperature-dependent aspects of the segregation process are revealed. It is shown that elemental segregation continues to evolve toward an equilibrium composition after a fault has formed, indicating that fully formed stacking faults still provide a driving force for segregation processes and that their equilibrium composition can differ from that which they obtain during their formation. As the elemental segregation process is diffusion-based, it is observed to be considerably slower at a lower temperature. In both alloys, the segregation trends observed after annealing depend on the annealing temperature: A lower temperature promotes a more γ-like fault composition associated with γ' softening; conversely, at higher temperatures, the fault composition tends toward that of the η phase, which is considered beneficial in the context of local phase transformation strengthening. As η-like segregation also involves the enrichment of slowly diffusing tungsten, kinetics likely play a role in the observed temperature dependence.
C-13: A Coupled Numerical Scheme for Simulating Liquid Metal Cooling Process and its Validation: Shengxu Xia1; Zhaofeng Liu2; Jianzheng Guo2; Yuzhang Lu3; Jian Zhang3; 1Shenzhen Wedge Central South Research Institute Co., Ltd.; 2State Key Laboratory of Powder Metallurgy, Central South University; 3Institute of Metal Research, Chinese Academy of Sciences
The heat transfer dynamics in the Liquid Metal Cooling (LMC) process, aimed at the production of directionally solidified single crystal, is intricate due to the involvement of two primary heat exchange pairs: the interaction between the mold and the casting metal, and the interaction between the mold and its environment including liquid metal coolant and the furnace. Present numerical simulations face challenges especially in accurately capturing the temperature and flow field evolution within the coolant, resulting in potential inaccuracies in calculating the solidification process. In response to this, the current study proposes a coupled model designed to concurrently calculate the solidification process in a single crystal casting and simulate the temperature and flow fields within the coolant. This coupling is achieved through a mutual exchange of results, where the outcomes of each process serve as boundary conditions for the other. The computational results obtained from the coupled model are compared with experimental measurements taken within the casting and coolant (Sn), revealing a commendable level of agreement. Subsequently, the coupled model is applied to explore the influence of casting sizes and arrangements on temperature and flow of coolant. The simulations yield preliminary yet insightful findings, offering valuable information that may contribute to the optimization of the LMC process.