Advanced Characterization of High-temperature Alloys: Phase Evolution during Manufacturing and Service-induced Deformation: Deformation Determined In-service Performance
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee
Program Organizers: Katerina Christofidou, University of Sheffield; Benjamin Adam, Oregon State University; Stoichko Antonov, Max-Planck Institut für Eisenforschung GmbH; James Coakley, Chromalloy; Martin Detrois, National Energy Technology Laboratory; Paraskevas Kontis, Norwegian University of Science and Technology; Stella Pedrazzini, Imperial College London; Sophie Primig, University of New South Wales
Tuesday 8:00 AM
March 21, 2023
Room: 29D
Location: SDCC
Session Chair: Martin Detrois, National Energy Technology Laboratory; Katerina Christofidou, The University of Sheffield
8:00 AM Invited
Monotonic Mechanical Behavior of a Nickel-based Single Crystal Superalloy with a Bimodal Precipitation: Jérémy Rame1; Dominique Eyidi2; Anne Joulain2; Jonathan Cormier3; 1Safran Aircraft Engines; 2Institut Pprime - University of Poitiers; 3ENSMA - Institut Pprime - UPR CNRS 3346
Nickel-based single crystal superalloys are key materials for the manufacturing of airfoils in aircraft engines. These materials are commonly casted using directional solidification Bridgman method. Then, solution heat treatment and agings are usually applied to (i) homogenize the chemistry across the dendritic structure; (ii) suppress the γ/γ’ interdendritic eutectic pools ; (iii) achieve a regular unimodal distribution of cuboidal γ′ precipitates (400 – 500 nm). Such microstructure is known to be optimal for creep strength. However, part’s microstructure can evolve during service operations. In particular, when exposed at a close-to-solvus temperature, γ′ precipitates dissolve which can lead to a bimodal microstructure with usual regular primary precipitates and smaller ~ 50 nm tertiary precipitates. In this presentation, a special focus will be paid to the impact of such a bimodal precipitate distribution on the tensile and creep behavior, analysed in the light of various SEM and TEM observations.
8:30 AM Invited
A Microscopy Investigation on the Nucleation and Propagation of Superlattice Stacking Faults in Nickel-based Superalloys: Fernando Leon-Cazares1; Regina Schluetter2; Francesco Monni2; Mark Hardy3; Catherine Rae2; 1University of Cambridge and Sandia National Laboratories; 2University of Cambridge; 3Rolls-Royce Plc
Superlattice intrinsic stacking faults (SISF) are the main culprit for the low temperature creep deformation of modern nickel-based superalloys used in jet engines. These defects were identified over five decades ago, but their nucleation mechanism remains unclear. This work provides the first ever experimental evidence, via transmission electron microscopy, of a SISF nucleating from a cross-slip event in a polycrystalline alloy. This allows the two dissimilar dislocations required to form a SISF to meet on adjacent planes at a precipitate interface. The concept of a nascent fault is introduced: the initial stacking fault that forms on a crystallographic plane and the dislocations of which continue to form coplanar faults as they glide away. Cross-slip and the subsequent fault propagation are detailed considering the resolved shear stresses on the dislocations involved. These findings will guide future characterisation efforts in the field and inform more realistic predictive models of creep behaviour.
9:00 AM
The Role of Ru on the Deformation Mechanism of a Single Crystal Superalloy during Thermomechanical Fatigue: Paraskevas Kontis1; Zhicheng Ge2; Guang Xie2; Di Wan1; Jinghao Xu3; Mikael Segersäll3; Viktor Norman3; Johan Moverare3; Jian Zhang2; 1Norwegian University of Science and Technology; 2Institute of Metal Research; 3Linköping University
The deformation mechanisms during out-of-phase thermomechanical fatigue of a Ru-doped and Ru-free single crystal nickel-based superalloy were studied and compared. The addition of Ru was found to enhance the thermomechanical fatigue performance of the single crystal superalloy at the temperature cycle of 400-900 °C. Scanning and transmission electron microscopy revealed a change on the deformation mechanism between the two alloy variants, which will be presented. In addition, atom probe tomography provided new insights on the partitioning of Ru, among other solutes, at dislocations and stacking faults after thermomechanical fatigue. These atomic scale insights combined with microstructural observations will be presented, aiming to provide us with a fundamental understanding on the role of Ru on high temperature thermomechanical fatigue behaviour of single crystal nickel-based superalloys.
9:20 AM
Variations in γ′ Formers and Refractory Elements for Enhanced Creep Resistance and Phase Stability of Alloy 282: Martin Detrois1; Stoichko Antonov1; Chantal Sudbrack1; Jonathan Poplawsky2; Paul Jablonski1; 1National Energy Technology Laboratory; 2Oak Ridge National Laboratory
Modifications to the chemistry of alloy 282 were performed to improve the alloy’s resistance to long term creep deformation as well as phase stability. Alloys were prepared using vacuum induction melting, computationally optimized homogenization heat treatment and hot working. Phase stability studies were carried out for up to 5,000 hours at 800°C and 900°C while creep testing was performed at conditions leading to lives past 7,000 hours for temperatures ranging from 740°C to 900°C. The formation of σ and μ phases were reduced in the modified alloy. Atom probe tomography (APT) was performed on the specimens from the phase stability study to investigate changes in the elemental partitioning to the γ and γ′ phases. Post deformation microstructures were analyzed using EBSD and TEM to study the influence of the detrimental phases on damage accumulation during creep.
9:40 AM Break
10:00 AM Invited
Comparison of Laboratory-generated and Ex-service Fractography for a 4th Generation Single Crystal Ni-based Superalloy: Jane Woolrich1; Simon Gray2; Ian Edmonds1; Edward Saunders1; Catherine Rae3; 1Rolls-Royce; 2Cranfield University; 3University of Cambridge
The aerospace approach to fracture analysis is fundamentally ‘understand and fix’ before escalation to ‘break and replace’. As such, a detailed understanding of fractography is key to underpinning aerospace safety. Introduction of new alloys into a gas turbine engine does, occasionally, result in the exhibition of novel fractography, which must be understood to implement fleet mitigations and demonstrate continued safety and airworthiness. The original ex-service fractography from a 4th generation SX alloy component is compared with that generated under various laboratory conditions, and is presented with a detailed analysis of the crack propagation data from dwell fatigue testing. These results suggest an important element of mechanical control of fatigue crack growth following surface-initiating crack formation.
10:30 AM
Creep Assisted Phase Transformation Deformation Mechanisms in Polycrystalline Ni-based Superalloys and Their Impact on the Creep Performance: Daniel Barba Cancho1; Ashton Egan2; Satoshi Utada1; Yilun Gong3; Yuanbo Tang1; Veronika Mazanova2; Michael Mills2; Roger Reed1; 1University of Oxford; 2The Ohio State University; 3Max-Planck-Institut für Eisenforschung GmbH
In-service creep deformation in polycrystalline Ni-based superalloys is controlled by the formation of a rich variety of complex shearing faults forming at the core of the γ' phase. The lengthening and thickening rate of these faults depends on an intriguing combination of dislocation interactions and diffusional processes of the alloy elements at the core of the fault. The effect of alloy composition on this process is still not fully understood. In this work, cutting edge correlative HR-TEM and EDX spectroscopy is used to study the deformation mechanisms of three different Ni-based superalloys with carefully designed ratios of disordering-to-ordering promoting elements (Co-Cr against Nb-Ta-Ti). The results shows that additions of ordering promoting elements reduce the diffusional processes required for the faults to lengthen thus reducing the creep rates for higher Nb-Ta-Ti alloys. These insights provide a path to follow in the design of improved grades of creep-resistant polycrystalline alloys beyond 700°C.
10:50 AM
Superalloys by Computational Optimization: Phase Evolution and Creep Properties: Tobias Gaag1; Julius Weidinger1; Jakob Bandorf1; Christopher Zenk1; Carolin Körner1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg
The multi-criteria optimization algorithm MultOpt is a powerful tool for computational alloy design based on CALPHAD calculations and models to describe properties such as the γ/γ′ lattice misfit of Ni-based superalloys. A series of four Ni-based superalloys was designed with MultOpt using a variation of the databases TCNI10 and TTNI8 and the property models for the γ/γ′ lattice misfit and the mass density as input. Experimental results of various thermophysical and mechanical properties, the accuracy of database and property model predictions and the alloys’ competitiveness will be presented. The new mass density model uses the molar mass of the alloying elements as input and predicts the mass density of low-density alloys more accurately, whereas both databases describe certain properties quite precisely while failing for others. The TCNI10-based alloys show more desirable physical properties such as a slower γ′-coarsening rate and less TCP phase formation but are inferior concerning high-temperature-low-stress creep.
11:10 AM
High Temperature Creep Properties along Concentration Gradients in Superalloys: Lukas Haussmann1; Steffen Neumeier1; Mathias Göken1; 1FAU Erlangen
A high temperature indentation creep approach with a 20 µm cylindrical flat punch has been developed to allow creep measurements on the micrometer scale. We have used this technique combined with a newly developed 1D positioning system, to investigate the concentration gradients of a Co-Ni diffusion couple and a multinary CoNi-base superalloy diffusion couple with increasing Cr content. This approach allows the microstructural and mechanical characterization of many alloy compositions in only one sample. For the Co-Ni diffusion couple it could be shown, that the creep strength at 550°C and the hardness increase up to 50Ni-50Co due to an increasing solid solution hardening. In the Co-base superalloy diffusion couple, a significantly increased content of Cr leads to additional tertiary phases and a decrease of γ′ volume fraction. However, hardness measurements and indentation creep experiments reveal an optimal Cr content for the best hardness, creep and oxidation properties.