Laser-Assisted Surface Modification of 4340 Steel with Iron-Aluminum Alloys
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Laser-Assisted Surface Modification of 4340 Steel with Iron-Aluminum Alloys G. Muralidharan1, P. G. Engleman1,2, C. A. Blue1, V. K. Sikka1, A. K. Singh2, A. Khangar2, and N. B. Dahotre2 1 Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN-37831-6083. 2 Department of Materials Science and Engineering, Center for Laser Applications, University of Tennessee, Knoxville, TN 37932. ABSTRACT High power Nd-YAG laser was used to fuse coatings containing a mixture of FeAl and Al, with 4340 steel. It was observed that good quality coatings could be obtained using this process. Detailed microstructural studies show that Fe aluminides and/or a solid solution of Al in Fe can form within the coating, depending on the processing conditions. Wear measurements show that the best wear properties are obtained in the presence of an aluminide in the coating and that the wear properties significantly degrade when the coating consists primarily of a solid solution of Al in Fe. INTRODUCTION Iron aluminides possess several attractive properties motivating significant research and development efforts over the past years [1]. Fe3Al and FeAl show excellent resistance to oxidation and sulfidation in aggressive environments[1-5]. Due to their excellent properties and cost considerations, appropriate compositions of iron aluminides could find applications as coatings on more traditional higher-strength materials with inferior corrosion resistant properties at higher temperatures. Previous studies on the corrosion resistance of weld overlays of iron aluminides on stainless steels have shown that weld overlays with atleast 30 at. % Al provided adequate corrosion resistance in oxidizing/sulfidizing atmospheres [4]. Other experiments with bulk iron aluminides have shown that these aluminides have superior wetting characteristics with hard particles such as TiB2 [6]. Thus, iron aluminide coatings reinforced with hard, wearresistant TiB2 particles could potentially possess a combination of superior oxidation/sulfidation properties along with excellent wear-resistance. The purpose of this study was to explore the use of high-powered Nd-YAG lasers to synthesize iron aluminide coatings on 4340 steel. The approach used in this study was to coat substrates made of 4340 steel with iron aluminide-based precursor coatings and subsequently fuse this coating with the substrate using lasers. Based on preliminary work and earlier work on weld overlays [2-5], it was expected that the aluminum content in the final coatings would be less than that in the precursor iron aluminide coatings due to loss of aluminum through evaporation, and dilution that occurred during processing. Hence excess aluminum was added to the precursor coatings. The effects of the composition of the precursor coatings and the laser power used to fuse the coatings to the substrate, on the microstructure and properties of the final coating will be outlined in this paper.
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EXPERIMENTAL METHOD Argon gas-atomized FeAl alloy powder (Fe-41.7Al-0.18Mo-0.04Zr-1.
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