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Oxidation Resistant High Temperature Materials – The Remarkable Performance of α-Al2O3 Scales

  • April 23, 2018
  • NASA Glenn Research Center
  • Cleveland , OH , United States

Description

For more than 75 years, high temperature materials have been and continue to be developed for improved oxidative performance.  They are needed to increase durability and temperature capability in aggressive environments, such as those in the gas turbine engine.  Great success has been realized for Ni-base superalloys and coatings, both enabled by the formation of protective α-Al2O3 scales.   The superior performance of these scales derives from the thermodynamic stability and low defect chemistry of the stoichiometric compound.  Slow growth and diffusivity are interrelated by a modified Wagner relation for grain boundary short circuit paths dominated by oxygen vacancy transport.  Excellent adhesion of the scale to the substrate is obtained via interfacial chemistry, i.e., reactive element doping and control of sulfur impurities.  This presentation highlights some of the underlying concepts that describe these attributes.  Superior performance has been demonstrated by FeCrAlY heater alloys, NiAl(Zr) intermetallics, Ni(Pt)Al aluminized coatings, single crystal superalloys (+Y), and Ti2AlC MAX phase compounds.  Attention is given to key, phenomenological results, unconventional creative thinking - (from interfacial bonding to DFT conduction bands), - and special analytical techniques – (from SEM to SAM) - that sparked progress in development and understanding.

 

James. L. Smialek
1968 B.S., 1972 M.S., 1981 PhD., Metallurgy, Materials Science
Case Tech, Case Western Reserve University
 
Dr. Smialek is a senior technologist at NASA Glenn (Lewis) where he has worked for 49 years in high temperature oxidation and corrosion of aerospace engine materials.  These high temperature materials include coatings, superalloys, intermetallics, and ceramics.  His primary research addressed the microstructure, growth, and adhesion of protective alumina scales, desulfurization of superalloys, and thermal barrier coating (TBC) durability.  Other pioneering areas included the hot corrosion and recession of SiC-based ceramics in molten salts or water vapor.  These activities were enabled by close collaborations with CWRU, U. Pittsburgh, Ohio State, NASA Ames, Oak Ridge National Laboratory, General Electric, and UTRC/Pratt and Whitney,  
 
Jim has authored 160 research papers, 9 book chapters, 14 patents, and 60 invited talks.  He was awarded the NASA Medal for Exceptional Scientific Achievement, twice, and the Abe Silverstein Medal for engineering.  He is a Fellow of ASM, TMS, and the American Ceramic Society and received the ASM Cleveland Chapter Award of Distinction.   He was chairman of the Gordon Conference on High Temperature Corrosion (1993) and serves as contributing editor for Oxidation of Metals and the Journal of the American Ceramic Society (since 1988).

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