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Simultaneous Aluminizing and Chromizing of Steels to Form (Fe, Cr)3Al Coatings

Authors
  • Zheng, Minhui
  • Rapp, Robert A.
Type
Published Article
Journal
Oxidation of Metals
Publisher
Kluwer Academic Publishers-Plenum Publishers
Publication Date
Feb 01, 1998
Volume
49
Issue
1-2
Pages
19–31
Identifiers
DOI: 10.1023/A:1018870105824
Source
Springer Nature
Keywords
License
Yellow

Abstract

A cementation pack involving halide activatorsand elemental Al and Cr powders has been used to achievethe codeposition and diffusion of aluminum and chromiuminto low-alloy steels. A two-step treatment at 925°C and 1150°C yields dense anduniform ferrite coatings of about 400-μm thickness,with surface compositions of approximatelyFe3Al plus several percent Cr. The two stepheating schedule prevents the formation of a blocking chromium carbide atthe substrate surface. An attempt was made to add atrace of Ce to the Al + Cr content of the coating byintroducing Ce oxide into the pack, but there is no evidence that this doping was achieved. Uponcyclic oxidation in air at 700°C, the coated steelexhibits a negligible 0.085 mg/cm2 weightgain for 1900 one-hour cycles. Virtually no attack wasobserved on coated steels tested in a simulated boileratmosphere at 500°C for 500 hr. But coatings with asurface composition of only 8 wt.% Al and 6 wt.% Crsuffered limited sulfidation attack in the simulated boiler atmosphere at temperatures higher than500°C for 1000 hr.

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