Simultaneous aluminizing and chromizing of steels to form (Fe,Cr){sub 3}Al coatings and Ge-doped silicide coatings of Cr-Zr base alloys [electronic resource].

Published:: Washington, D.C. : United States. Dept. of Energy, 1997.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description:: pages 331-340 : digital, PDF file
Additional Creators:: Oak Ridge National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information

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Summary:

A halide-activated cementation pack involving elemental Al and Cr powders has been used to achieve surface compositions of approximately Fe₃Al plus several percent Cr for low alloy steels (T11, T2 and T22) and medium carbon steel (1045 steel). A two-step treatment at 925 C and 1150 C yields the codeposition and diffusion of aluminum and chromium to form dense and uniform ferrite coatings of about 400 {micro}m thickness, while preventing the formation of a blocking chromium carbide at the substrate surfaces. Upon cyclic oxidation in air at 700 C, the coated steel exhibits a negligible 0.085 mg/cm² weight gain for 1900 one-hour cycles. Virtually no attack was observed on coated steels tested at ABB in simulated boiler atmospheres at 500 C for 500 hours. But coatings with a surface composition of only 8 wt% Al and 6 wt% Cr suffered some sulfidation attack in simulated boiler atmospheres at temperatures higher than 500 C for 1000 hours. Two developmental Cr-Zr based Laves phase alloys (CN129-2 and CN117(Z)) were silicide/germanide coated. The cross-sections of the Ge-doped silicide coatings closely mimicked the microstructure of the substrate alloys. Cyclic oxidation in air at 1100 C showed that the Ge-doped silicide coating greatly improved the oxidation resistance of the Cr-Zr based alloys.

Report Numbers:

E 1.99:conf-9705115--proc.
E 1.99: ornl/fmp--97/1
ornl/fmp--97/1
conf-9705115--proc.

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Published through SciTech Connect.
12/01/1997.
"conf-9705115--proc."
" ornl/fmp--97/1"
"DE98007329"
11. annual conference on fossil energy materials, Knoxville, TN (United States), 20-22 May 1997.
Rapp, R.A.; He, Y.R.; Zheng, M.

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