Codeposited chromium and silicon diffusion coatings for Fe-base alloys via pack cementation

Journal Article · Sat Oct 01 04:00:00 EDT 1994 · Oxidation of Metals; (United States)

DOI:https://doi.org/10.1007/BF01052029· OSTI ID:6740271

Harper, M A; Rapp, R A ^[1]

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1. Ohio State Univ., Columbus, OH (United States)

The simultaneous deposition of Cr and Si into plain carbon, low-alloy, and austenitic steels using a halide-activated pack-cementation process is described. Equilibrium partial pressures of gaseous species have been calculated using the STEPSOL computer program to aid in designing specific processes for codepositing the desired ratios of Cr and Si into a given alloy. The calculations indicate that NaCl-activated packs are chromizing, while NaF-activated packs deposit more Si with less Cr. THe use of a [open quotes]dual activator[close quotes] (e.g., NaF+NaCl) allows for the deposition of both Cr and Si in the desired amounts. Single-phase ferritic coatings (150-250 microns thick) with a surface concentration of 20-35 wt.% Cr and 2-4% Si have been grown on AISI 1018, Fe-2.25Cr-1.0Mo-0.15C, and Fe-0.5Cr-0.5Mo-0.2C steels using packs containing a 90 wt.% Cr-10Si binary source alloy, a NaF+NaCl activator, and a silica filler. Two-phase coatings (approximately 75 microns thick) containing 20-25 wt.% Cr and 2.0-2.4% Si have been obtained on 304 stainless steel using packs containing a 90 wt.% Cr-10Si binary source alloy, a NaF activator, and an alumina filler. The same pack chemistry allowed the diffusion of Cr and Si into the austenitic Incoloy 800 alloy without a phase change. A coated Fe-2.25Cr-1.0Mo-0.15C coupon with a surface concentration of Fe-34 wt.% Cr-3Si was cyclically oxidized in air at 700[degrees]C for over four months and 47 cycles. The weight gain was very low (<0.2 mg/cm[sup 2]) with no scale spalling detected. Coated coupons of AISI 1018 steel, and Fe-0.5Cr-0.5Mo-0.2C steel have shown excellent oxidation-sulfidation resistance in reducing, sulfur-containing atmospheres at temperatures from 400 to 700[degrees]C and in erosion and erosion-oxidation testing in air at 650 and 850[degrees]C.

• OSTI ID: 6740271
• Journal Information: Oxidation of Metals; (United States), Journal Name: Oxidation of Metals; (United States) Vol. 42:3-4; ISSN OXMEAF; ISSN 0030-770X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals &amp; Alloys-- Corrosion &amp; Erosion
ALLOYS
AUSTENITIC STEELS
CARBON STEELS
CHEMICAL COATING
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMICAL VAPOR DEPOSITION
CHROMIUM ALLOYS
COATINGS
CORROSION PROTECTION
DEPOSITION
DIFFUSION COATINGS
FLUE GAS
GASEOUS WASTES
IRON ALLOYS
IRON BASE ALLOYS
KINETICS
LOW ALLOY STEELS
OXIDATION
REACTION KINETICS
SILICON ALLOYS
STEELS
SURFACE COATING
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
WASTES