Deformation and Damage Mechanisms of High Temperature Alloys: On-Demand Oral Presentations
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee
Program Organizers: Mark Hardy, Rolls-Royce Plc; Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346; Jeremy Rame, Naarea; Akane Suzuki, GE Aerospace Research; Jean-Charles Stinville, University of California, Santa Barbara; Paraskevas Kontis, Norwegian University of Science and Technology; Andrew Wessman, University of Arizona
Monday 8:00 AM
March 14, 2022
Room: Mechanics & Structural Reliability
Location: On-Demand Room
Microstructurally-sensitive Fatigue Crack Nucleation and Growth in Nickel Single Crystals: Vassilios Karamitros1; Duncan Maclachlan1; Fionn Dunne1; 1Imperial College
This paper explores the mechanistic basis of crack nucleation and growth in single crystal nickel alloy under fatigue loading. Crack paths are hypothesised to be crystallographic and controlled by maximum crystal planar slip, with rate of growth determined by local crack tip stored energy density [1]. Crystal plasticity modelling is developed to replicate experimental single-crystal edge-cracked samples with multiple crystal orientations and to test the mechanistic basis of tortuous crack paths and growth rates obtained from experiment. The characteristics of the independent experiments are captured by the mechanistic model, including path tortuosity, with unique critical stored energy density of 385 Jm-2. Critical appraisal of the model results in the context of other experimental observations will also be presented. [1] Wilson, D., et al. J. Mech. Phys. Solids https://doi.org/10.1016/j.jmps.2019.02.012[2] Sakaguchi, M., et al. Int. J. Fatigue https://doi.org/10.1016/j.ijfatigue.2019.02.003
Microstructural Evolution of Borides at 850°C in a Polycrystalline Superalloy and Implications on Creep Performance: Lola Lilensten1; Aleksander Kostka2; Sylvie Lartigue-Korinek3; Baptiste Gault4; Sammy Tin5; Stoichko Antonov4; Paraskevas Kontis4; 1Chimie ParisTech; 2Ruhr-Universität Bochum; 3Institut de Chimie et des Matériaux Paris Est; 4Max-Planck-Institut für Eisenforschung GmbH; 5University of Arizona
The microstructural evolution of Cr-rich intergranular borides after creep at 850°C/185MPa and annealing at 850°C for approximately 3000h in a polycrystalline nickel-based superalloy has been studied. Scanning electron microscopy revealed the coarsening of borides, with the borides after creep exhibiting the largest thickness (800–1100 nm), compared to those annealed without an external applied load (400–600 nm). The coarsened borides were systematically found to contain a very high density of planar faults, as observed by transmission electron microscopy. Borides were found to have either a tetragonal I4/mcm, or an orthorhombic Fddd structure, with those two structures coexisting in a single particle. Finally, atom probe tomography has shown a correlation of chemical fluctuations of B and Cr with the planar faults, while partitioning of Ni and Co at dislocations within the borides after creep was also found. Ramifications of coarsened borides on the creep performance of polycrystalline superalloys will be presented.
Design of Cast Alumina-forming Austenitic Alloys for Extreme Environments: Yukinori Yamamoto1; Michael Brady1; Govindarajan Muralidharan1; James Haynes1; Arun Devaraj2; Bharat Gwalani2; Libor Kovarik2; 1MSTD, Oak Ridge National Laboratory; 2Pacific Northwest National Laboratory
A new alloy design approach for cast, creep-resistant alumina-forming austenitic alloys is proposed, targeting the use in combustion exhaust gas environments at ≥900-950°C. Computational thermodynamics guided the alloy design to maximize the strengthening second-phase formation and promote a protective, external alumina-scale formation, which minimized the experimental iteration and accelerated the alloy design validation. An alloy based on Fe-17Cr-4Al-22Ni-Nb-C, wt.%, successfully achieved ~20 times longer creep-rupture life than chromia-forming cast austenitic steel HK30Nb (Fe-25Cr-20Ni-Nb-C base) at 900°C and 50MPa, and significantly improved oxidation resistance which maintained the surface protectiveness for more than 1,000h of cyclic exposure at 950°C in 10% water vapor containing environment. This paper will report on the results from detailed microstructure characterization correlating the creep deformation behavior with the controlled second phase precipitation within the matrix. Research sponsored by U.S. DOE, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office (VTO), Powertrain Materials Core Program.
Cancelled
Quantification of the Temperature and Strain Rate Dependent Evolution of Defect Structures in a CoNi-base Superalloy: Andreas Bezold1; Nicklas Volz1; Jan Vollhüter1; Malte Lenz1; Nicolas Karpstein1; Christopher Zenk1; Erdmann Spiecker1; Mathias Göken1; Steffen Neumeier1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg
The present work investigates the evolution of the defect structures of a single crystalline multi-component CoNi-base superalloy during compressive yielding as a function of plastic strain, strain rate and temperature. Shearing under stacking fault formation is favored compared to shearing by APB-coupled dislocation pairs with increasing plastic strain, at lower strain rates and at higher temperatures. The change of the deformation mechanism to shearing under stacking fault formation leads to pronounced work-hardening anomalies, i.e. the initial work hardening magnitude increases with decreasing strain rate or increasing temperature. By using a novel approach to quantify the defect structures in combination with atomic-scale structural and chemical characterization, the share of each deformation mechanism and the propagation velocity of the leading dislocations are calculated and thus the anomalous behaviors are rationalized. Finally, the role of segregation on the occurring deformation mechanisms and the strengthening effect of stacking faults are discussed.
Enhanced 900 °C-yield Strength in Inconel 738 Superalloys While Reducing Expensive Co Compositions: Hyo Ju Bae1; Kwang Kyu Ko1; Joong Eun Jung2; Jung Gi Kim1; Hyokyung Sung1; Jae-Bok Seol1; 1Gyeongsang National University; 2Korea Institute of Materials Science
Inconel 738 series are suitable for aircraft engines and gas-turbine plants for power generation because of their high-temperature capability > 940 °C. However, the high cost of the alloy remains one of the most challenging topics due to high amounts of expensive Co (8.00-9.00 wt%). Herein, with the aim of reducing the Co contents in bulk, the chemical composition and heat treatment routes of typical Inconel 738LC are modified while increasing the yield stress by 8.5%. Their mechanical properties significantly depended on the morphology and composition of constituent phases formed: Ni3(Al, Ti, Nb)-type precipitation(γ′) and MC-type carbides. Therefore, the microstructure of the modified Inconel 738LC was investigated with comparing that of typical Inconel 738LC. We discovered that, despite reducing Co contents 50 wt%, high-temperature compressive strength at 900 °C is improved with the increased fraction of γ′. Details of the property-microstructure relations will be explained.
Ferritic Bcc-Superalloys – Slip System Control Through Alloying: Johan Pauli Magnussen1; David Collins1; Alexander Knowles1; 1University of Birmingham
Iron-based ferritic superalloys with an A2-Fe matrix reinforced by B2-NiAl precipitates are candidate materials for low cost, high strength, creep resistant, and oxidation resistant materials for applications reaching 500°C–800°C. However, attaining good room temperature ductility is difficult due to slip incompatibility between A2 Fe ½<111> and B2 NiAl <100>. By adding ternary additions or utilising off-stoichiometric compositions, as demonstrated in monolithic NiAl intermetallics, the primary slip system can be altered; this strategy is extended here onto dual-phase A2-B2 ferritic superalloys. This study investigated two Fe-NiAl alloys with controlled Al:Ni ratios ~1:1 and ~2:1, where each alloy exhibited similar NiAl precipitate morphologies. A combination of Vickers indentation and EBSD was used to analyse the macroscopic slip traces and associated slip planes, with the 2:1 alloy exhibiting A2-like macroscopic slip, and 1:1 alloying B2-like macroscopic slip. This is a promising result, offering new design and testing approaches for ductilising ferritic superalloys.
The Effect of Carbon on the Fabricability and Mechanical Performance of Nimonic 105: Martin Detrois1; Kyle Rozman1; Paul Jablonski1; Jeffrey Hawk1; 1National Energy Technology Laboratory
Commercially available Ni-based superalloys, originally designed for aerospace applications, have been considered for use in next generation power plants. Nimonic 105 is a candidate for use as bolts and blades, and the alloy could potentially be used for other components. The specified carbon concentration calls for a maximum of 0.17 wt.% with nominal values on the higher end. In this work, the effect of carbon was investigated using two formulations with 0.15 and 0.03 wt.% carbon manufactured using a conventional cast/wrought processing route. The high carbon version revealed 400% increase in MC carbides density with the particles being 55% larger than in the low carbon version. The carbides were responsible for facilitating breaking the cast structure during the early steps of forging. The low carbon alloy showed significant surface cracking. The mechanical performance of the two alloys will be presented and discussed with regards to tensile and creep behavior.
Investigating the Role of Dynamic Strain Aging in 347H Steel Using Crystal Plasticity: Veerappan Prithivirajan1; M Arul Kumar1; Bjorn Clausen1; Ricardo Lebensohn1; Laurent Capolungo1; 1Los Alamos National Lab
Dynamic strain aging (DSA) is a process in which solute atoms diffuse towards the mobile dislocations, temporarily pinned at the obstacles. Under certain conditions of strain rate and temperature, DSA causes jerky motion on the dislocations, which can manifest into unusual macroscopic responses like the anomalous yield strength dependence with temperature, negative strain rate sensitivity, serrated yielding, etc. In this work, we develop a physics-based constitutive model for DSA within the crystal plasticity modeling framework to capture its effect on mechanical behavior. We performed in-situ neutron diffraction experiments on 347H steel under uniaxial tension with stress hold to validate our DSA model.
Machining-induced Microstructural Deformation and Grain Refinement of Ni-base Superalloys under Controlled Thermal Conditions: Andrea la Monaca1; Dragos Axinte1; Zhirong Liao1; Rachid M'Saoubi2; Mark Hardy3; 1Rolls-Royce UTC in Manufacturing and On-Wing Technology, University of Nottingham, Nottingham, NG8 1BB, United Kingdom; 2 R&D Material and Technology Development, Seco Tools AB, 737 82, Fagersta, Sweden; 3Rolls-Royce plc, PO Box 31, Derby, DE24 8BJ, United Kingdom
When machining Ni-base superalloys for safety-critical applications, excellent levels of microstructural surface integrity are to be achieved to ensure in-service part performance. In fact, machining processes can locally generate severe thermo-mechanical conditions, which may induce microstructural distortion in the near-surface region and submicron grain refinement in the most severe cases. Thus, significant research effort is focused on understanding the mechanisms of machining-induced microstructural deformation in these materials. In this context, a new method has been developed to investigate the machining-induced surface deformation of heat-resistant superalloys under controlled thermal conditions. In synergy with in-situ process monitoring, this approach has been employed to understand the role of thermal effects on the machinability and surface integrity of Ni-base superalloys. Thus, this discloses the interplay between the temperature-dependent behaviour of Ni-base superalloys and their microstructural surface deformation mechanisms in mechanical machining, effectively supporting the development of next-generation Ni-base superalloys.
Strengthening via Chemical Segregation to Deformation Twin Boundaries in Co-Ni-Cr-Mo Superalloy: Stoichko Antonov1; Qing Tan1; Baptiste Gault1; 1Max-Planck-Institut für Eisenforschung GmbH
The processing and deformation of low stacking fault energy superalloys leads to a characteristically high amount of micro and nano-twins. As these faults effectively obstruct the dislocation motion, the yield strength and ultimate tensile strength are significantly increased when compared to a twin-free microstructure. In this study, we show that a critically high density of twins can lead to a transformation of high angle grain boundaries to a Σ3n network structure. Interestingly, secondary hardening is observed during thermal exposure and the strengthening increment is increased by increasing Mo content. We use transmission electron microscopy and atom probe tomography to reveal Cr segregation to the deformation twin boundaries, which effectively further hinders dislocation motion and increases the strength at the expense of the ductility. Computational modeling was used to show that the Cr segregation reduces the twin boundary energy, however, Mo increases the propensity for Cr segregation.
Coupled Diffusional-mechanical Modeling of Hydrogen Embrittlement in Polycrystalline Materials: Sofia Yassir1; 1Mississippi State University
This study will carry a numerical approach of a coupled temperature-displacement procedure in ABAQUS to model the coupling of the Hydrogen-Enhanced-Localized-Plasticity mechanism (HELP) with hydrogen transport in polycrystalline materials. Hydrogen embrittlement (HE) is a complex scientific topic that has been subjected to different studies due to diverse hypotheses behind the strength degradation in metals due to hydrogen. The role of plasticity in hydrogen embrittlement has been one of the primary debates between camps since the late 1980s. Unlike other mechanisms that suggest or study the hydrogen adsorbed at the crack tip, this mechanism studies the hydrogen ahead of the crack tip which has been shown to be responsible for the highly localized plasticity. Hydrogen accumulation in the vicinity of the crack tip leads to a brittle fracture due to dislocation motion increase in that region.
Ultra-high Temperature Deformation in a Single Crystal Superalloy: Mesoscale Process Simulation and Micro-mechanisms: Yuanbo Tang1; Neil D'Souza2; Bryan Roebuck3; Phani Karamched1; Chinnapat Panwisawas4; David Collins5; 1University of Oxford; 2Rolls-Royce plc; 3National Physical Laboratory; 4University of Leicester; 5University of Birmingham
A mesoscale study of a single crystal nickel-base superalloy subjected to an industrially relevant process simulation, relevant to casting, investigates the interplay between microstructural development and micromechanics. Test samples were smaller than the periodicity of the cored solidification structure, permitting the study of subtle composition variations. Foremost, hardening rates, influenced by differing γ’ precipitate solvus temperatures, were heavily influenced. Observed post-mortem, γ’ precipitates possessed a butterfly morphology, resulting from concurrent octodendritic growth and N-type rafting. High resolution-electron backscatter diffraction revealed deformation patterning follows the γ/γ’ microstructure, with high dislocation densities at γ/γ’ interfaces. Examination of residual elastic stresses indicated the butterfly γ’ precipitate morphology had enhanced deformation heterogeneity, resulting in stress states within the γ channels that favour slip, and encourages further growth of γ’ protrusions. The combination of localised plasticity and residual stresses are considered critical in the formation of the recrystallisation defect in subsequent post-casting homogenisation heat treatments.
Microstructure and Mechanical Properties of Rotary Friction Welded IN-600 and SS316L with Copper Interlayer: Neeraj Mishra1; Amber Shrivastava1; 1Indian Institute of Technology Bombay
Ability to weld Inconel with stainless steel would enable design simplification for various high temperature applications. Fusion welding and plastic deformation based solid-state joining techniques lead to intermetallics and significant deformation zone, respectively, which lead to inferior joint performance. In this work, rotary friction welds of In-600 and SS316L are performed with and without Cu interlayer, at 2000 rpm, 5 mm/min friction feed rate and 25 mm/min plunge feed rate. Mechanical interlocking and 300 to 400 microns thick deformation zone is observed in the joints made without interlayer. No grain refinement is noticed in joints with Cu interlayer. Further, intermetallics are not observed at Cu and In-600 interface, as Ni and Cu form an isomorphous system. Tensile testing results show that a Cu interlayer leads to improved joint performance. Fractured surfaces from tension tests are characterized and damage is discussed.