Advancing Current and State-of-the-Art Application of Ni- and Co-based Superalloys: Ni-based Superalloys – Modeling Structure & Properties
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Chantal Sudbrack, National Energy Technology Laboratory; Mario Bochiechio, Pratt & Whitney; Kevin Bockenstedt, ATI Specialty Materials; Katerina Christofidou, University of Sheffield; James Coakley, Chromalloy; Martin Detrois, National Energy Technology Laboratory; Laura Dial, Ge Research; Bij-Na Kim; Victoria Miller, University of Florida; Kinga Unocic, Oak Ridge National Laboratory
Wednesday 2:00 PM
February 26, 2020
Room: 11B
Location: San Diego Convention Ctr
Session Chair: James Coakley, University of Miami; Victoria Miller, University of Florida
2:00 PM
Is the Carbon Content Really an Issue for the LCF Durability of Forged γ/γ′ Ni-based Disk Alloys?: Adele Govaere1; Anne-Laure Rouffié2; Florence Hamon3; Patrick Villechaise3; Jean-Michel Franchet2; Alexandre Devaux4; Coraline Crozet4; Paraskevas Kontis5; Jonathan Cormier3; 1Ensma / Pprime Institute - Safran Tech; 2Safran Tech; 3Pprime Institute; 4Aubert & Duval; 5Max Planck Institute
The nickel-based superalloy AD730TM is considered for turbine disks application. To understand the role of non-metallic inclusions, a carbon-doped version of the material was studied. Thus, the impact of the inclusions chemical compositions, density and size distribution on the low cycle fatigue and tensile properties was investigated. The nature of the particles was obtained by EDS and APT analysis. Their sensitivity to oxidation was examined. Strain-controlled LCF tests were carried out in air at intermediate and high temperature to characterize the cyclic behavior and identify the crack initiation sites for both materials. In order to investigate the influence of the environment, tests were performed on pre-oxidized specimens in vacuum. The results showed that the size of the inclusions appears to be an important parameter in terms of LCF durability, rather than their density. And the cracking due to oxidation of the particles is strongly influenced by their chemical composition.
2:20 PM
Phase-field-informed Modeling of γ’ Rafting in 3D during High-temperature Creep in Ni-based Single Crystal Superalloys: Jean-Briac le Graverend1; Rajendran Harikrishnan1; 1Texas A&M University
Rafting during high-temperature/low stress creep is an important microstructural evolution in Ni-based single crystal superalloys. In fact, the evolution of the γ channel widths directly affects the mechanical behavior and damage. Even if many constitutive models considered the effect of rafting on the mechanical behavior through the use of a scalar, a few have been done to predict rafting in 3D. It is, however, a requirement for multiaxial loading and not-<001>-oriented specimens. It is why a vectorial formulation is proposed and implemented in a crystal plasticity framework. Since continuous 3D characterizations of rafting are not yet available, the model is validated with 3D phase field simulations on different crystallographic orientations and temperature/stress conditions.
2:40 PM
Modeling the Dependence of Microstructural Evolution on the Crystallographic Orientation in Ni-based Single Crystal Superalloys: Harikrishnan Rajendran1; Jean- Briac le Graverend1; 1Texas A&M University
The structural components made of Ni-based single crystal superalloys, mostly turbine blades with complex geometries, has its exceptional properties significantly dependent on the microstructural integrity within the 5-degree tolerance for crystallographic misorientation. The blades are usually cast <001> crystallographic direction upwards. The present study, using realistic phase-field simulations, will demonstrate the dependence of perfect <001>, <011>, <111> crystallographic orientations and deviations from perfect orientations on the directional coarsening (rafting) of γ’ precipitates during high-temperature/low-stress creep conditions. The insights from this study will help investigate and compare the stability of various crystal orientations. We will also present the phenomenological formulations in our phase-field model such as the constrained lattice misfit, viz. the γ/γ’ lattice misfit during deformation, needed for such realistic predictions during creep.
3:00 PM
Competitive Mechanisms of Fatigue Crack Initiation Around Non-metallic Inclusions of a Polycrystalline Ni-base Superalloy: Alexander Bergsmo1; Fionn Dunne1; 1Imperial College London
Non-metallic inclusions in polycrystalline Ni-base superalloys can develop accumulated damage that results in fatigue crack initiation during fatigue loading by either particle fracture, interfacial decohesion or slip-driven initiations in the metal matrix. In this work, we investigate the micromechanical drivers of cracking and decohesion in a Ni-base superalloy, RR1000. A representative crystal plasticity finite element model, which incorporates traction-separation behaviours of interfaces has been developed in conjunction with an experiment. The development of stress within the model suggest that cracking and decohesion are stress driven and thus are dependent on the degree of strain hardening behaviour in the matrix. Predictions are made for nucleation of slip-driven cracks within the matrix using a stored energy criterion. The cycles to nucleation are then mapped on a maximum applied remote stress for the various modes of initiation and show particle fracture and decohesion occur at elevated stresses within the very first few cycles.
3:20 PM
Competing Mode of Failure Predictions in a Ni-based Superalloy using Crystal Plasticity Finite Element Simulations: Ritwik Bandyopadhyay1; Michael Sangid1; 1Purdue University
Two competing failure modes, namely inclusion- and matrix-driven failures, are observed in Ni-based superalloys which are subjected to fatigue loading. In the present work, the emergence of the failure mode is predicted in a powder metallurgy produced Ni-based superalloy using the plastic strain energy density stored within the material and accounting for multiple factors influencing the two failure modes. In particular, crystal plasticity finite element simulations and a Bayesian inference framework are used to compute the microstructure-sensitive critical plastic strain energy density, associated with fatigue failure, for the material, as a function of loading conditions including multiple strain amplitudes and temperatures.
3:40 PM Break
4:00 PM
On the Temperature Limits of Ni-based Superalloys: Daniel Barba Cancho1; Ashton Egan2; Michael Mills2; Roger Reed1; 1University of Oxford; 2Ohio State University
The peculiar atomic structure of γ’ precipitates [Ni3(Al/Ti)-L12] in Ni-based superalloys produces high-energy faults when dislocations glide them, giving their significant strength at high temperatures. The mechanisms behind the strength failure of these alloys above 800°C are still controversial. Recent advances in atomic resolution microscopy have allowed to study these mechanisms with unprecedented detail. In our study, we have characterised a SX superalloy from RT to 1000°C. Multiscale microscopy (TEM and SEM) is combined with physical modelling to fully understand the correlation between the strength drop and the changes in the γ’ shearing mechanism. Our results show that, far from previous beliefs, the initial failing of alloy strength is not a consequence of dislocation climbing. Instead, local chemical changes around the γ’ shearing dislocations boost their gliding, thus producing the sudden drop of strength. This new understanding can be used to beat the current temperature limits of these alloys.
4:20 PM
Probing Effects of Alloying Additions and Local Phase Transformation Strengthening on Creep Deformation in Nickel Based Superalloys: Ashton Egan1; Lola Lilensten2; Paraskevas Kontis2; Sammy Tin3; Michael Mills1; 1Ohio State University; 2Max-Planck-Institut für Eisenforschung GmbH; 3Illinois Institute of Technology
Historically, nickel based superalloys have been designed using classical, empirically-based metallurgy principals, but this is no longer sufficient. Physics based models connecting composition, microstructure and properties are needed to enable rapid and cost-effective alloy development. Our work supports this by probing effects of critical alloying additions found to promote Local Phase Transformation (LPT) strengthening, which occurs along planar defects and benefits creep resistance. The effects of LPT promoters on creep properties were elucidated by performing compression creep tests on compositionally simplified alloys, as well as studying several commercial alloys, thereby exploring desired composition regimes. Scanning Transmission Electron Microscopy and Atom Probe Tomography were coupled to analyze both local atomic structure and associated segregation events of the deformation processes occurring. This work will serve to inform future studies involving modeling and simulation, as well as materials data analytics, to enable rapid alloy design with predicted mechanical response.
4:40 PM
Applying APT and LKMC Simulations to a Model Ni-based Superalloy: Chantal Sudbrack1; Zugang Mao2; David Seidman3; 1Northwestern University Center of Atom-Probe Tomography; 2Northwestern University, Department of Materials Science & Engineering; 3Northwestern University Center of Atom-Probe Tomography; Northwestern University, Department of Materials Science & Engineering,
Precipitation strengthened nickel-based superalloys are used in a variety of demanding, structural applications due to their excellent mechanical properties at elevated temperatures. The ability to control microstructure stability of these complex alloys requires an understanding of the fundamental aspects of the gamma-prime precipitate evolution. In this talk, atom-probe tomography (APT) measurements and lattice kinetic Monte Carlo (LKMC) simulations are combined to reveal aspects of the nucleation, growth, and coarsening sequence in a model Ni-Al-Cr superalloy that is isothermally aged at 600°C. This combined approach allows precise compositional measurement on a nanometer scale, and gives insight into the short-range ordering present prior to precipitation, 3D morphological development, and diffusional processes that drive the solid-state transformation. Early-stage coagulation and coalescence of neighboring precipitates is established and is uniquely shown by LKMC simulations to result from correlated cluster diffusion, primarily along the <110>-directions, where the experimentaland simulated compositional profiles show good agreement.
5:00 PM
Numerical Calculation of Antiphase Boundary Energy of Ni-superalloys: Mohammad Dodaran1; Ali Hemmasian Ettefagh1; Shengmin Guo1; Shuai Shao1; 1Louisiana State University
Energetics of planar defects, such as antiphase boundary (APB), in the γ’ precipitates strongly affects tensile and fatigue properties in γ-γ’Ni-superalloys. For monotonic strength, APB energy represents the resistance of precipitates to slip. For fatigue, APB energy is closely related to the cross-slip tendency of superscrew dislocations. Cross-slip induces irreversible cyclic plastic deformation and, therefore, accumulation of fatigue damage. In this study, the effect of composition on APB energy is explored using cluster expansion (CE) method combining density function theory (DFT) calculations and Monte Carlo (MC) sampling. DFT calculations were performed by Quantum Espresso package to obtain energies of symmetrically inequivalent family of clusters providing input for CE. CE extracts the interaction among different alloying elements and calculates energy of atomistic structures with chemical disordering introduced by MC technique. APB energy, as a function of composition, is finally calculated by comparing the energies of structures with and without APBs.
5:20 PM Cancelled
Nano-twinning in a γ Precipitate Strengthened Ni-based Superalloy: Yong Zhang1; Shengyun Yuan1; Zhihao Jiang1; Jizi Liu1; Yizhe Tang2; 1Nanjing University of Science and Technology; 2Shanghai University
Twinning has been found to be a dominate mechanism in the γ' precipitate strengthened Ni-based superalloys during creep and tension with low strain rates at high temperatures. Here, high-resolution transmission electron microscopy and atomistic simulations based on embedded atom method potentials have been combined to show that the twin nucleation process is facilitated by the high content of Co replacing Al in the Ni3Al-type γ' precipitates. Contrast to the positive binding energy of Al-Al atoms, the negative binding energy of Co-Co atoms significantly lowers the energy barrier for twinning in the γ' phase. The study further reveals that the presence of Co in the γ' precipitates promotes a new twinning pathway featured with one stacking fault nucleated on the middle plane in between two separated stacking faults, which has a much lower energy barrier as compared to the classical model of successive twinning partials gliding on the consecutive {111} planes.