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Title: Evaluation of Iron Aluminide Coatings for Oxidation Protection in Water Vapor Environment

Abstract

Long-term (> 10,000h) oxidation behavior of aluminide coatings made by chemical vapor deposition (CVD) or pack cementation on representative ferritic (Fe-9Cr-1Mo) and austenitic (type 304L stainless steel) are being studied in air + 10% water vapor in the temperature range of 650-800 C. Unlike the uncoated alloys, which are severely attacked in this environment, the CVD aluminide coatings have not failed after 16,000h at 700 C or 10,000h at 800 C. The pack aluminide coatings also show good oxidation protection after testing for {approx}5,000h at 700 C. In addition, initial efforts have been made to fabricate coatings at lower aluminizing temperatures and the current results suggest that FeAl coatings can be synthesized at temperatures as low as 700 C.

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
Sponsoring Org.:
FE USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
931306
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: NACE Corrosion 2007, Nashville, TN, USA, 20070313, 20070317
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AIR; ALLOYS; CHEMICAL VAPOR DEPOSITION; COATINGS; CORROSION; EVALUATION; IRON; OXIDATION; STAINLESS STEELS; TESTING; WATER VAPOR; Aluminide coatings; oxidation; water vapor; ferritic martensitic steel

Citation Formats

Zhang, Ying, Wang, Y. Q., and Pint, Bruce A. Evaluation of Iron Aluminide Coatings for Oxidation Protection in Water Vapor Environment. United States: N. p., 2007. Web.
Zhang, Ying, Wang, Y. Q., & Pint, Bruce A. Evaluation of Iron Aluminide Coatings for Oxidation Protection in Water Vapor Environment. United States.
Zhang, Ying, Wang, Y. Q., and Pint, Bruce A. Mon . "Evaluation of Iron Aluminide Coatings for Oxidation Protection in Water Vapor Environment". United States. doi:.
@article{osti_931306,
title = {Evaluation of Iron Aluminide Coatings for Oxidation Protection in Water Vapor Environment},
author = {Zhang, Ying and Wang, Y. Q. and Pint, Bruce A},
abstractNote = {Long-term (> 10,000h) oxidation behavior of aluminide coatings made by chemical vapor deposition (CVD) or pack cementation on representative ferritic (Fe-9Cr-1Mo) and austenitic (type 304L stainless steel) are being studied in air + 10% water vapor in the temperature range of 650-800 C. Unlike the uncoated alloys, which are severely attacked in this environment, the CVD aluminide coatings have not failed after 16,000h at 700 C or 10,000h at 800 C. The pack aluminide coatings also show good oxidation protection after testing for {approx}5,000h at 700 C. In addition, initial efforts have been made to fabricate coatings at lower aluminizing temperatures and the current results suggest that FeAl coatings can be synthesized at temperatures as low as 700 C.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • Iron aluminide weld overlay coatings are currently being considered for enhanced sulfidation resistance in coal-fired low NO{sub x} boilers. The use of these materials is currently limited due to hydrogen cracking susceptibility, which generally increases with an increase in aluminum concentration of the deposit. The overall objective of this program is to attain an optimum aluminum content with good weldability and improved sulfidation resistance with respect to conventional materials presently in use. Research has been initiated using Gas Tungsten Arc Welding (GTAW) in order to achieve this end. Under different sets of GTAW parameters (wire feed speed, current), both singlemore » and multiple pass overlays were produced. Characterization of all weldments was conducted using light optical microscopy, scanning electron microscopy, and electron probe microanalysis. Resultant deposits exhibited a wide range of aluminum contents (5--43 wt%). It was found that the GTAW overlays with aluminum contents above {approximately}10 wt% resulted in cracked coatings. Preliminary corrosion experiments of 5 to 10 wt% Al cast alloys in relatively simple H{sub 2}/H{sub 2}S gas mixtures exhibited corrosion rates lower than 304 stainless steel.« less
  • The present study focused on the effect of N in ferritic Fe-9Cr-1Mo and austenitic 304 L alloy substrates on the formation and cyclic oxidation behavior of aluminide coatings fabricated by chemical vapor deposition (CVD). Relatively high N contents in the commercial alloys caused the formation of AlN precipitates in the CVD aluminide coating, which adversely affected the adhesion of the as-deposited coatings, particularly on 304 L. The reduction of N content in the substrate alloys resulted in a cleaner coating layer with fewer precipitates and Kirkendall voids. However, the cyclic oxidation behavior of the aluminide coatings in air + 10more » vol.% H{sub 2}O at 700 C was not noticeably changed by the N reduction« less
  • Iron aluminides containing > 20-25 at. % Al have oxidation and sulfidation resistance at temperatures well above those at which these alloys have adequate mechanical strength. Accordingly, these alloys may find application as coatings or claddings on more conventional higher-strength materials which are generally less corrosion-resistant at high temperatures. To this end, iron-aluminide coatings were prepared by gas tungsten arc and gas metal arc weld-overlay techniques. Specimens were cut from weld deposits and exposed to a highly aggressive oxidizing-sulfidizing (H2S-H2-H2O-Ar) environment at 800 C. All the weld overlayers showed good corrosion behavior under isothermal conditions, including a gas metal arc-producedmore » deposit with only 21 at. % Al. Rapid degradation in corrosion resistance was observed under thermal cycling conditions when the initally grown scales spalled and the rate of reaction was then not controlled by formation of slowly growing Al oxide. Higher starting Al concentrations (> {approximately} 25 at. %) are needed to assure overall oxidation-sulfidation resistance of the weld overlays, but hydrogen cracking susceptibility must be minimized in order to physically separate the corrosive species from the reactive substrate material.« less
  • Low NOx burners are being installed in many fossil fired power plants in order to comply with new Clean Air Regulations. Due to the operating characteristics of these burners, boiler tube sulfidation corrosion is often enhanced and premature tube failures can occur. Failures due to oxidation and solid particle erosion are also a concern. A program was initiated in early 1996 to evaluate the use of iron aluminide weld overlays for erosion/corrosion protection of boiler tubes in Low NOx boilers. Composite iron/aluminum wires will be used with the Gas Metal Arc Welding (GMAW) process to prepare overlays on boiler tubesmore » steels with aluminum contents from 8 to 16wt%. The weldability of the composite wires will be evaluated as a function of chemical composition and welding parameters. The effect of overlay composition on corrosion (oxidation and sulfidation) and solid particle erosion will also be evaluated. The laboratory studies will be complemented by field exposures of both iron aluminide weld overlays and co-extruded tubing under actual boiler conditions.« less