Microstructural Template Consisting of a Face-Centered Cubic Matrix with Ordered Precipitates: Microstructural Evolution and Properties: Ni Base Superalloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Rajarshi Banerjee, University of North Texas; Eric Lass, University of Tennessee-Knoxville; Ashley Paz Y Puente, University of Cincinnati; Tushar Borkar, Cleveland State University; Keith Knipling, Naval Research Laboratory; Sophie Primig, University of New South Wales
Monday 2:30 PM
February 24, 2020
Room: 30D
Location: San Diego Convention Ctr
Session Chair: Sophie Primig, University of New South Wales
2:30 PM Keynote
Precipitation and Deformation Mechanisms of γ’/γ” Co-precipitates in Alloy 718: Hariharan Sriram1; Kamal Kadirvel1; Rongpei Shi1; Longsheng Feng1; Michael Mills1; Yunzhi Wang1; 1The Ohio State University
Alloy 718, widely used in aerospace and power industries, is strengthened by both γ’ (L12) and γ” (D022) intermetallic phases that are coherently embedded in a γ (FCC) phase matrix. Experimental characterizations have revealed a rich variety of γ’/γ” co-precipitate microstructures and puzzling deformation microstructures. We present a simulation study of the nucleation, growth and coarsening mechanisms associated with the formation and stability of such γ’/γ” co-precipitates, as well as their deformation mechanisms, in contrast to those of individual precipitates, using a combination of CALPHAD, ab initio, and phase-field approaches. Co-precipitation is found energetically favorable during nucleation because of the synergistic effect in reducing the coherency elastic strain. Co-precipitates have significantly different growth and coarsening behaviors, and their deformation mechanisms are extremely complicated. This work is supported by DOE/NETL.
3:10 PM Invited
Correlative High-resolution Characterization of the Early Stages of Precipitation During Direct Aging of Alloy 718: Felix Theska1; Vitor Rielli1; Keita Nomoto2; Flora Godor3; Bernd Oberwinkler3; Aleksandar Stanojevic3; Simon Ringer2; Sophie Primig1; 1University of New South Wales Sydney; 2The University of Sydney; 3voestalpine BÖHLER Aerospace GmbH & Co KG
Alloy 718 is a polycrystalline, precipitation strengthened Ni-based superalloy used for aircraft engine turbine discs. High-temperature yield strength and creep resistance are achieved by precipitation of nanoscale γ'- (L12 Ni3(Al,Ti)) and γ"- (D022 Ni3(Nb)) particles via coherency and anti-phase boundary strengthening. Compared to conventional ageing, yield strength increments of +10% are achieved via direct ageing by changes in the δ-phase volume fraction, dislocation density, and γ'- and γ"-precipitate duplet and triplet morphology. However, the detailed γ'- and γ"-precipitate nucleation and growth mechanisms during direct ageing of Alloy 718 remain unknown. Therefore, various high-resolution transmission electron microscopy (HR-TEM) and atom probe microscopy (APM) techniques were used to study the early stages of precipitation for γ'- and γ"-particle volume fraction, radii, density, and morphology. A qualitative microstructural model is introduced to discuss heterogeneous versus homogeneous precipitate nucleation and growth, based on dislocation-precipitate interaction and γ'- and γ"-precipitate morphology evolution.
3:40 PM
In-situ Transmission Electron Microscopy Investigation of Continuous Precipitation of Ni3Mo in a Ni-25Mo-8Cr Alloy Formed by Direct Current Magnetron Sputtering: Megan Emigh1; Jessica Krogstad2; 1University of California, Santa Barbara; 2University of Illinois at Urbana-Champaign
The microstructure of Ni-25Mo-8Cr superalloy thin films prepared via direct current magnetron sputtering (DCMS) is shown to be key to manipulating and understanding phase transformations. Specifically, the columnar, highly textured, and nanotwinned grains are shown to facilitate precipitation of the equilibrium DOa (Ni3Mo) phase during a mild heat treatment. In situ observation in diffraction mode confirms that precipitation behavior in these defect-dense thin films is not merely kinetically accelerated; instead, the pathway is fundamentally altered. Short-range ordering (SRO) behavior was observed upon reaching 650ºC. SRO has been documented as part of the FCC-precipitation pathway, but has not previously been reported for HCP-based precipitates. Conversely, elimination of the nanotwins leads to precipitation of metastable Ni2(Mo,Cr) precipitates. The straightforward capacity to select one of several possible phase transformation pathways presents an opportunity to create precisely tuned microstructures, while simultaneously providing unprecedented insight on these complex phase transformations.
4:00 PM Break
4:30 PM Invited
Ordered Precipitates and Mechanical Properties of Nickel-base Superalloys Studied by Analytical Scanning and Transmission Electron Microscopy: Micheal Kattoura1; Jie Song2; Anurag Sharma2; Seetha Mannava2; Vijay Vasudevan2; 1LSP Technologies; 2University of Cincinnati
In the first part of this talk, we will report on the evolution, kinetics and mechanisms of γ', γ'', Ni2(Mo,W,Cr),η-Ni3Ti and δ precipitation and solute partitioning utilizing a combination of conventional TEM, HRTEM, STEM-HAADF, STEM-EDS and counterpart APT measurements and related analyses in Ni-Al-Cr-Nb (ATI 718 Plus, IN625) and Ni-Mo-W-Cr (Haynes 242, 244) alloys. In the second part of the talk, the temperature and strain rate dependence of strength, ductility and fracture behavior of the alloys, followed by results of the impact of advanced mechanical surface treatments like LSP and UNSM on near-surface microstructure, stress states, strengthening, fatigue and failure mechanisms at room and elevated temperatures, will be presented and discussed.
5:00 PM Invited
The Quantitative Model for Heat Treatment Parameters and Gamma Prime Variations on Nickel-base Superalloys: Nishan Senanayake1; Jennifer Carter1; 1Case Western Reserve University
Accurate measurements of the microstructure produced from different processing paths are foundational to understanding processing|structure|performance (P|S|P) of Ni-base superalloys systems.Time-dependent process models must be calibrated from statistically significant experimental measures of microstructure and performance from specific alloys; requiring high-throughput methods of analysis.In this work, we will demonstrate a predictive P|S|P model to design processing paths for desired microstructure and performance of nickel-based alloy ME3.This physics-based statistical model enables both predictive capabilities (i.e., performance from processing) but also the design of a microstructure from the measured performanceThis data-driven approach relies on training data from high-throughput measurements of γ′ distributions and indentation strength ME3 samples that underwent various heat treatment parameters.A k-fold cross-validation approach, coupled with R-squared statistics was used to validate the P|S|P model.
5:30 PM Invited
Alloying for Corrosion Resistance: the Effect of Manganese and Silicon on a Polycrystalline Nickel-based Superalloy: Stella Pedrazzini1; Noel Glaenzer2; Mark Hardy3; Paul Mignanelli3; T. William Clyne2; Howard Stone2; 1Imperial College London; 2University of Cambridge; 3Rolls-Royce plc
Nickel superalloys are employed in the hottest part of jet engines and industrial gas turbines for power generation. In these harsh environments, sulphur contamination can occur in-service, causing reductions in the predicted component lifetime. Our work uses environmental exposures and state of the art characterisation to explore the effect of low-level silicon (0.5 wt%) and manganese (1 wt%) additions on the sulphidation and type-2 hot corrosion response of a polycrystalline nickel superalloy. Silicon was added promote formation of a compact dual-layer chromia-alumina scale that reduced oxidation rate in long-term experimentsand improved resistance to hot corrosion from coupled NaCl + SOx exposure.Manganese improved oxidation resistance by creating MnCr2O4, which reduced the oxidation rate but did not change the oxide scale morphology. The presence of Mn (a known sulphur scavenger) proved less effective than silicon, reducing the sulphidation and corrosion damage extent but not the overall depth.