Performance of Al-rich Oxidation Resistant Coatings for Fe-Base Alloys
- ORNL
- Tennessee Technological University
Aluminum-rich coatings made by chemical vapor deposition and pack cementation on ferritic (e.g. Fe-9Cr-1Mo) and austenitic (Type 304L) substrates are being evaluated at 650-800 C. For oxidation testing, a humid air environment was used to quantify coating performance, as uncoated substrates experience rapid oxidation at these temperatures. A main goal of this work is to demonstrate the potential benefits and problems with alumina-forming coatings. The higher exposure temperatures were selected to accelerate the degradation of the coating by interdiffusion with the substrate. A general conclusion of this testing was that coatings with less Al and a ferritic Fe(Al) structure could be more durable than higher Al content aluminide coatings which have a large thermal expansion mismatch with these substrates. A lifetime model has been developed using diffusion and oxidation observations to predict coating performance as a function of temperature and initial coating composition. To test and improve the model, additional experiments are now being conducted to determine the effect of substrate composition (e.g. Cr content using Fe-12Cr and Fe-9Cr-2W substrates) and exposure temperature on the critical Al content for coating failure. Because of the unexpectedly low level of Al measured at coating failure ({approx}3.5 at.% at 700 C), exposures of specimens with thick ({approx}200 {micro}m) high Al content coatings were stopped after 10kh at 800 C and 20kh at 700 C because extremely long times to failure were predicted. Post-exposure Al concentration profiles for these specimens were measured using electron microprobe.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- FE USDOE - Office of Fossil Energy (FE)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1017299
- Resource Relation:
- Conference: EFC Workshop, Frankfurt, Germany, 20090930, 20090930
- Country of Publication:
- United States
- Language:
- English
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