Materials Week '97: Thursday AM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Thursday morning, September 18.

RELIABLE OXIDE SCALES AND COATINGS FOR HIGH-TEMPERATURE INDUSTRIAL ENVIRONMENTS

Session Chairs: K. Natesan, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439; R.J. Gottschall, U.S. Dept. of Energy, Division of Materials Sciences, 19901 Germantown Road, Germantown, MD 20874-1290

OPENING REMARKS: Organizers and Session Chairs

8:45 am KEYNOTE

NECESSARY PROPERTIES/PERFORMANCE CHARACTERISTICS OF PROTECTIVE SURFACE OXIDES FOR USE IN ENERGY AND UTILITY APPLICATIONS: J. Stringer, Electric Power Research Institute, P.O. Box 10412, Palo Alto, CA 94303

In utility systems, alloys for use in components exposed to high temperatures in use ultimately depend generally rely on adherent, slowly-growing, protective scales formed by the oxidation of one of the alloy constituents. The properties required of this protective oxide will be determined by what is frequently a very complex service environment. Other processes taking place during periods when the equipment is not operating may also produce effects which may affect the protectiveness of the oxide when the surface is again heated to operating temperature. These effects have to be considered in the context of how long the component is required to remain operational, what the most probable mode of failure is, and with what degree of confidence the lifetime may be predicted.

9:30 am

MICROSTRUCTURAL BASIS FOR OXIDE SCALE AND COATING FAILURES: K.B. Alexander, K. Prüßner, B.A. Pint, P.F. Tortorelli, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6156; K. Natesan, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439

Electron microscopy techniques are applied to the microstructural and chemical characterization of the alumina scale/coating, oxide-metal interface, and substrate for Fe-Al, FeCrAl(Y), and NiCrAlY alloys. These observations are used to establish links between oxidation performance and microstructural factors. Differences between alumina scales and coatings after high-temperature exposure help identify factors related to the dynamics of the oxide growth process as they affect surface oxide reliability and failure.

10:00 am

ANALYSIS OF STRESSES IN OXIDE LAYERS: J.K. Wright, R.L. Williamson, Idaho National Engineering and Environmental Laboratory, 2151 N. Boulevard St., Idaho Falls, ID 83415-2218; R.M. Cannon, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Mail Stop 8-200, Berkeley, CA 94720; M. Grimsditch, B.W. Veal, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439

Analysis of residual stresses is important to understanding the driving forces for crack propagation and spallation of protective oxides. Finite elemental analysis is used to calculate thermally-induced stresses when alumina layers on alloys are cooled from high temperatures. The effects of specimen geometry, surface roughness, and substrate properties on the magnitude and distribution of stresses in the oxide and alloy are modeled and the stresses are compared with photostimulated luminescence measurements.

10:30 am

RELATING RELIABILITY OF SURFACE OXIDES TO INTERFACIAL PROCESSES: P.Y. Hou, R.M. Cannon, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Mail Stop 62-203, Berkeley, CA 94720

The adherence of oxide scale on alumina-forming alloys is examined in terms of segregation of sulfur, interface roughness, and substrate composition. These factors are related to observed failure modes in the context of energy considerations for crack propagation at and near oxide-metal interfaces. Correlations between materials parameters and spallation resistance are being used to develop preliminary capabilities for predicting appropriate conditions for scale adherence.

11:00 am

MAINTAINING SCALE/COATING INTEGRITY IN THE PRESENCE OF SALT DEPOSITS AND OTHER ENVIRONMENTAL IMPURITIES: N.S. Bornstein, United Technologies Research Center, East Hartford, CT 06108

The use of alumina-forming alloys in high-temperature industrial environments present the additional complications of the effects of alkali metal and other contaminants on the integrity of the oxide scales that proffer oxidation protection and coating durability. This work examines the critical factors associated with maintaining oxide scale integrity in complex, application-relevant environments.