Advancing Current and State-of-the-Art Application of Ni- and Co-based Superalloys: Environmental Damage and Protection
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
Monday 2:30 PM
February 24, 2020
Room: 11B
Location: San Diego Convention Ctr
Session Chair: Mario Bochiechio, Pratt & Whitney; Kinga Unocic, Oak Ridge National Laboratory
2:30 PM Invited
Environmental Effect Solutions for Superalloys Today and Tomorrow: Bruce Pint1; 1Oak Ridge National Laboratory
Most power generation technologies create extreme environments and superalloys in turbines are no exception. Coatings are commonly used, both for the highest temperatures and for lower temperatures where hot corrosion may be a concern. For new superalloys, the challenge is to demonstrate acceptable uncoated oxidation resistance in case the coating fails. Coatings can fail due to the service conditions or manufacturing issues and needing the coating to be prime reliant is a concern. For current coated superalloys, the lifetime limitation in power generation is often interdiffusion rather than oxidation and/or thermal barrier coating spallation. As temperatures increase in the turbine, new issues have arisen such as under platform corrosion and superalloy cracking. As these failures are better understood, there may be opportunities to develop new alloys for these conditions. Research was sponsored by the U. S. Department of Energy, Office of Fossil Energy, Advanced Turbine Program.
3:00 PM
Enhancement of EB-PVD Thermal Barrier Coating Adhesion Strength by Laser Surface Texturing: Lucille Despres1; Jonathan Cormier1; Sophie Costil2; Romain Cariou3; Aurélien Joulia3; Amar Saboundji3; 1Institut Pprime; 2ICB-LERMPS; 3SAFRAN TECH
The development of internal cooling network in HP blades coupled with the use of thermal barrier coating allows to increase the turbine entry temperature in order to improve the efficiency of aero-engines. The thermal barrier system which is composed of three different layers deposited on a nickel-based superalloy substrate, is submitted during service to complex thermo-mechanical paths. The resulting damage mechanisms may lead to a premature spallation of the coating and a substantial deterioration of the substrate. To ensure a mechanical anchoring between layers leading to the slowdown of the coating spallation, different patterns have been developed on the bond coat by laser texturing. Damage mechanisms of the textured thermal barrier coating systems after thermal cycling tests at 1150°C will be presented during this presentation.
3:20 PM
Formation and Composition of Hot Corrosion Deposits on Model Ni-Cr-Al Alloys: Kevin Meisner1; Elizabeth Opila1; 1University of Virginia
Hot corrosion of superalloys in gas turbines is caused by salt deposits, but the deposit compositions, structure, and mechanisms of formation are poorly understood. Salt deposits were collected on model Ni-Cr-Al, Al2O3, and Pt substrates at 700 °C in a Low Velocity Burner Rig (LVBR). The LVBR combusted marine diesel (0.5 wt% S) and 10 ppmw sea salt was injected into the combustion gases. Deposition kinetics were measured for 14-day exposures by mass changes and Inductively-Coupled Plasma Optical Emission Spectroscopy (ICP-OES) of deposit species. The phases in the deposit mixture were determined by hot stage X-ray Diffraction (XRD). These results were compared to FactSage thermochemical equilibrium predictions. A Chemically Frozen Boundary Layer (CFBL) theory was used to model deposition kinetics and the results were compared to the burner rig data. Implications of the composition, structure, and kinetics of deposit formation on hot corrosion mechanisms are discussed.
3:40 PM
High-temperature Corrosion of Ni-based Superalloys in Impure CO2 Power Cycle Environments: Richard Oleksak1; Joseph Tylczak1; Gordon Holcomb1; Omer Dogan1; 1National Energy Technology Laboratory
Emerging fossil fuel power systems require structural alloys resistant to oxidation/corrosion in CO2-rich gases/fluids containing combustion impurities. The high-temperature portions of heat exchangers in these systems require strength beyond that of steels. Therefore, Ni-based superalloys are candidate materials. However, their oxidation behavior in impure CO2 environments is largely unknown and potentially life-limiting. In this study, we evaluated several Ni-based superalloys at conditions expected in a direct-fired supercritical CO2-based power cycle. Some or all of alloys 617, 230, 625, 263, 740H, and 282 were exposed to 95%CO2-4%H2O-1%O2, with and without 0.1% SO2 at 1 bar and temperatures ranging from 600-800 °C. Gravimetric, SEM, and XRD analyses are presented for exposures to 2500 h. Thin Cr-rich oxide layers formed on all alloys at 700-800 °C, while temperatures ≤650 °C resulted in S-rich compounds and higher corrosion rates. The results are rationalized by considering the thermodynamic and kinetic driving forces during the reaction.
4:00 PM Break
4:20 PM Invited
New Insights on Al2O3-Scale Growth on Ni-Based Alloys and the Influence of Reactive Elements: Arthur Heuer1; Brian Gleeson2; 1Case Western Reserve University; 2University of Pittsburgh
Oxygen and Al grain boundary diffusivities have been determined by the 16O/18O double oxidation technique on a suite of γ/γ’ Ni-20Al-5Cr alloys, undoped or doped with 0.05 at% Y, 0.05 at% Zr, or 0.05 at% Hf. The 18O distribution in the Al2O3 scales following high temperature oxidation was determined by high resolution TOF-SIMS imaging, and allowed determination of oxygen and aluminum grain boundary diffusivities. Improved oxidation resistance of the “reactive element” (RE) Y-, Zr-, and Hf-doped samples was clearly manifested in reduced values of the diffusivities. We conclude that the RE effect is due to a reduction in the electrical conductivities of the scales, rather than a “steric hindrance” or other similar mechanisms reducing grain boundary diffusivities, as has previously been postulated. The conventional view that grain-boundary diffusivities determined from tracer experiments can be used, ipso facto, to rationalize the scaling kinetics of RE-doped alloys is not viable.
4:50 PM
A Damage Model with Oxidation Effects: Jean-Briac le Graverend1; Seungjun Lee1; 1Texas A&M University
When superalloys are exposed to oxidizing environments, the growth of the oxide scale can affect the microstructural stability and, therefore, their mechanical behavior and lifetime. The fundamental reason of this phenomenon is the depletion process of the γ’ precipitates during the formation of the oxide scale. γ’ depletion is equivalent to have a decrease in the load carrying capacity, as pores in a continuum damage mechanics approach. The oxidation kinetics is not only affected by temperature, but also by surface roughness and plastic strain. A surface-rougheness and accumulated-plastic-strain dependent model is developed for the oxide thickness and is employed in a hardening-based damage model. The new damage model is validated with 3D finite-element simulations.
5:10 PM
A Comparative Study of the Effects of Surface Treatments and Finishes on the High Temperature Oxidation Behavior of Alloy 800 in a 400 °C Steam Environment: Richard Chiang1; Sebastien Teysseyre2; Jeffery Aguiar3; Geogy Abraham4; Vivekanand Kain4; Vijay Vasudevan1; 1University of Cincinnati; 2Canadian Nuclear Laboratories; 3Idaho National Laboratory; 4Bhabha Atomic Research Centre
This study investigates the effect of various surface finishes/treatments (as-received, machined, ground, buffed, electropolished, pickled and passivated, and shot peened) on the oxidation behavior of Alloy800 exposed to 400°C high temperature steam for 336hrs. Characterization of the resulting film layer were conducted using SEM, S/TEM, and Raman spectroscopy. The results indicated that the more deformation-inducing processes (shot peened and machined) produced a more protective film layer while the baseline as-received and processes like electropolishing were observed to have signs of degradation. The specifics of each processes’ effect on the oxidation as a result of alterations to relevant parameters were discussed.