An Aluminide Surface Layer Containing Lower-Al on Ferritic-Martensitic Steel Formed by Lower-Temperature Aluminization

An aluminide (AlFe and alpha-(FeAl)) surface layer containing lower-Al was formed on ferritic-martensitic steel P92 by means of surface mechanical attrition treatment (SMAT) combined with a duplex aluminization process at lower temperatures, i.e. a packed aluminization followed by a diffusion annealing treatment below its tempering temperature. Indentation tests indicated that the lower-Al surface layer formed on the SMAT sample is more resistant to cracking and has better adhesion to the substrate in comparison with the Al5Fe2 layer formed on the as-received sample after the duplex aluminization process. Isothermal steam oxidation measurements showed that the oxidation resistance is increased significantly by the lower-Al surface layer due to the formation of a protective (Fe,Cr)A(2)O(4) layer. The rate constant of oxidation was estimated to decrease from similar to 0.849 mg(2)cm(-4)h(-1) of the as-received material to similar to 0.011 mg(2)cm(-4)h(-1) of the AlFe layer at 700 degrees C. Copyright (C) 2015, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited. All rights reserved.