High Temperature Corrosion and Degradation of Structural Materials: Effects of Water Vapor/Ni-based Alloys and High Temperature Effects
Sponsored by: TMS Corrosion and Environmental Effects Committee
Program Organizers: Kinga Unocic, Oak Ridge National Laboratory; Raul Rebak, GE Global Research; David Shifler, Office of Naval Research; Richard Oleksak, National Energy Technology Laboratory
Monday 2:00 PM
November 2, 2020
Room: Virtual Meeting Room 31
Location: MS&T Virtual
Session Chair: David Shifler, Office of Naval Research
2:00 PM
Influence of the Water Vapor on Oxide Scale and Alpha Case Layer in Ti6Al4V: Beyza Öztürk1; Lukas Mengis1; Mathias Galetz1; 1DECHEMA-Forschungsinstitut
The Ti6Al4V alloy is extensively used in aerospace, automotive or biomaterial applications. In the aerospace industry, the service temperature of Ti6Al4V is currently limited to 350 °C due to its insufficient oxidation resistance. Oxidation causes the formation of an unprotective oxide scale and an oxygen enriched subsurface layer, which is known as “alpha-case”. Additionally, the effect of water vapor on oxidation resistance is critical. In the present study, the oxidation behavior of Ti6Al4V in dry air and air containing 10 vol. % H2O at 500, 600 and 700 °C for up to 500 hours has been investigated. The main focus of this study is the examination of oxide scale morphologies and oxygen enrichment in the subsurface zone. From the oxygen concentration profiles the alpha-case thickness as a function of temperature and time is determined. In addition, the influence of nitration and the beta-stabilizing element vanadium is discussed.
2:30 PM Invited
Thermochemical Stability of EBC Silicates in High-temperature High-velocity Water Vapor: Mackenzie Ridley1; Elizabeth Opila1; 1University of Virginia
Complex silicates such as hafnium silicates, barium strontium alumino silicates, and rare earth-monosilicates and -disilicates are candidates for environmental barrier coating systems. One key property requirement of these materials is their thermochemical stability in water vapor-containing combustion environments. All these complex silicates react with high temperature water vapor to form Si(OH)4(g) and solid silica-depleted product phases. The rate of this reaction depends on the temperature, water vapor partial pressure, gas velocity and the silica activity in the silicate. However, other factors such as the stability of the other oxide components and the resulting product microstructure also play a role in determining the material degradation rate. Results from “steam-jet” furnace exposures of complex silicates in high-temperature (1200 to 1400C) high-velocity (up to 200 m/s) water vapor will be presented, exploring the rate limiting mechanisms for thermochemical degradation of these EBC candidate materials.
3:00 PM
Metal Dusting of Ni-based Alloys at Elevated Pressure in Different Gas Compositions: Clara Schlereth1; Mathias Galetz1; 1DECHEMA-Forschungsinstitut
Metal dusting is a high temperature corrosion mechanism characterized by carbon deposition and disruptive graphite formation. It is observed in gas mixtures of CO, CO2, CH4, H2 and H2O with carbon activities ≥ 1 and low oxygen partial pressures. In this study, different gas mixtures with the same carbon activity, but varying H2/H2O and H2/CO ratios were tested in order to evaluate the influence of each gas component on the mechanism. Exposures were performed at an elevated pressure of 18 bar to simulate industrial applications and shorten the time until pit initiation. Several commercial Ni-based alloys were exposed and characterized with SEM, EPMA and Raman spectroscopy. Formation of different oxide scales and carbon ingress into the material were studied.
3:20 PM
The Effect of Surface Treatment on the Formation, Structure, and Chemistry of Protective Oxide Scale on High-temperature Oxidation-resistant Nickel Alloys: Stephen House1; Henry Ayoola1; John Lyons1; Meng Li1; Bingtao Li1; Judith Yang1; Wissam Saidi1; Brian Gleeson1; 1University of Pittsburgh
High-temperature oxidation-resistant alloys often have finishes – such as polishing or vapor-blasting – applied to their exposed surfaces for aesthetic or practical reasons, which introduce deformation into the surface grain structure. Upon heating, a region of recrystallized grain structure can form at the surface. The degree and depth of the recrystallized zone depends on the type of surface finishing treatment, which in turn affects the extent of imposed surface deformation. Haynes 214® is a high-temperature oxidation-resistant nickel-aluminum-chromium-iron alloy that is known to form adherent alumina scales above 955 °C. Below this temperature, however, it can form either an alumina, chromia, or a combined oxide scale. In this work we employed surface (SEM, AFM) and subsurface (S/TEM, FIB) imaging and spectroscopic techniques to investigate the effect of various surface finishes on oxide scale formation and the surface and subsurface structure of the alloy resulting from the deformation and high-temperature oxidation processes.