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Title: Interdiffusion Behavior of Aluminide Coatings on Fe-Base Alloys

Abstract

One of the potential degradation modes of oxidation-resistant iron aluminide coatings is the loss of Al from the coatings into Fe-base substrate alloys that typically contain no Al. To address this issue, interdiffusion between aluminide coatings and steel substrates was studied for times up to 10,000 h in the temperature range of 500-800 C. Coatings were synthesized in a laboratory chemical vapor deposition (CVD) reactor on representative commercial ferritic alloy Fe-9Cr-1Mo and type 304L austenitic stainless steel. The microstructural and compositional changes after diffusion anneals were examined in detail. An initial attempt to model the interdiffusion behavior was carried out by applying an existing software program COSIM (coating oxidation and substrate interdiffusion model). Complementary work was conducted using a simple mathematic model developed by Heckel et al. Reasonable agreement was observed between the simulated and experimental composition profiles for the aluminide coatings on ferritic alloys. Model results were then applied to predict coating lifetime.

Authors:
 [1];  [1];  [2]
  1. Tennessee Technological University
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); High Temperature Materials Laboratory; Shared Research Equipment Collaborative Research Center
Sponsoring Org.:
FE USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
931922
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials and Corrosion; Journal Volume: 58; Journal Issue: 10
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; IRON BASE ALLOYS; CHEMICAL VAPOR DEPOSITION; COATINGS; DIFFUSION; IRON; LIFETIME; OXIDATION; STAINLESS STEELS; STEELS; SUBSTRATES; ALUMINIUM; Coatings; Aluminide; Oxidation; Interdiffusion; Model

Citation Formats

Zhang, Ying, Liu, A. P., and Pint, Bruce A. Interdiffusion Behavior of Aluminide Coatings on Fe-Base Alloys. United States: N. p., 2007. Web. doi:10.1002/maco.200704057.
Zhang, Ying, Liu, A. P., & Pint, Bruce A. Interdiffusion Behavior of Aluminide Coatings on Fe-Base Alloys. United States. doi:10.1002/maco.200704057.
Zhang, Ying, Liu, A. P., and Pint, Bruce A. Mon . "Interdiffusion Behavior of Aluminide Coatings on Fe-Base Alloys". United States. doi:10.1002/maco.200704057.
@article{osti_931922,
title = {Interdiffusion Behavior of Aluminide Coatings on Fe-Base Alloys},
author = {Zhang, Ying and Liu, A. P. and Pint, Bruce A},
abstractNote = {One of the potential degradation modes of oxidation-resistant iron aluminide coatings is the loss of Al from the coatings into Fe-base substrate alloys that typically contain no Al. To address this issue, interdiffusion between aluminide coatings and steel substrates was studied for times up to 10,000 h in the temperature range of 500-800 C. Coatings were synthesized in a laboratory chemical vapor deposition (CVD) reactor on representative commercial ferritic alloy Fe-9Cr-1Mo and type 304L austenitic stainless steel. The microstructural and compositional changes after diffusion anneals were examined in detail. An initial attempt to model the interdiffusion behavior was carried out by applying an existing software program COSIM (coating oxidation and substrate interdiffusion model). Complementary work was conducted using a simple mathematic model developed by Heckel et al. Reasonable agreement was observed between the simulated and experimental composition profiles for the aluminide coatings on ferritic alloys. Model results were then applied to predict coating lifetime.},
doi = {10.1002/maco.200704057},
journal = {Materials and Corrosion},
number = 10,
volume = 58,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • We investigated interdiffusion of thin Al-rich coatings synthesized by chemical vapor deposition (CVD) and pack cementation on 9Cr ferritic–martensitic alloys in the temperature range of 650–700°C. The compositional changes after long-term exposures in laboratory air and air + 10 vol% H 2O were examined experimentally. Interdiffusion was modeled by a modified coating oxidation and substrate interdiffusion model (COSIM) program. The modification enabled the program to directly input the concentration profiles of the as-deposited coating determined by electron probe microanalysis (EPMA). Reasonable agreement was achieved between the simulated and experimental Al profiles after exposures. Moreover, the model was also applied tomore » predict coating lifetime at 650–700°C based on a minimum Al content (Cb) required at the coating surface to re-form protective oxide scale. In addition to a C b value established from the failure of a thin CVD coating at 700°C, values reported for slurry aluminide coatings were also included in lifetime predictions.« less
  • Aluminide and Al-containing coatings were synthesized on commercial ferritic (P91) and austenitic (304L) alloys via a laboratory chemical vapor deposition (CVD) procedure for rigorous control over coating composition, purity and microstructure. The effect of the CVD aluminizing parameters such as temperature, Al activity, and post-aluminizing anneal on coating growth was investigated. Two procedures involving different Al activities were employed with and without including Cr-Al pellets in the CVD reactor to produce coatings with suitable thickness and composition for coating performance evaluation. The phase constitution of the as-synthesized coatings was assessed with the aid of a combination of X-ray diffraction, electronmore » probe microanalysis, and existing phase diagrams. The mechanisms of formation of these CVD coatings on the Fe-based alloys are discussed, and compared with nickel aluminide coatings on Ni-base superalloys. In addition, Cr-Al pellets were replaced with Fe-Al metals in some aluminizing process runs and similar coatings were achieved.« less
  • The nonisothermal oxidation behavior of pure iron and a few iron-chromium alloys in dry air has been studied. The effects of a superficial coating of a reactive oxide, CeO{sub 2}, on the oxidation behavior were studied. Linear heating rates of 3 K/min and 6 K/min were maintained up to a final temperature ranging from 1,273-1,473 K. Coatings were applied either from a slurry or an aqueous bath. The CeO{sub 2} coating has been found to be effective not only in decreasing the nonisothermal oxidation rate but also in improving the scale adherence. Moreover, the coated samples withstood a number ofmore » heating cycles without scale rupture. The mass gain of the samples as a function of temperature was recorded by means of a sensitive balance, and the scales have been characterized by SEM, EPMA, and x-ray diffraction analysis.« less