Microstructure and Properties of Fe 3 Al-Fe 3 AlC x Composite Prepared by Reactive Liquid Processing
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INTRODUCTION
IRON aluminides based on Fe3Al and FeAl have received special attention because of their beneficial properties at high temperatures, such as their oxidation resistance,[1–4] carburization resistance,[5,6] and sulfidation resistance,[7–9] and have thus been used in the manufacture of structural components for application at high temperatures and in aggressive media.[2,10,11] Nevertheless, these intermetallics exhibit poor room-temperature ductility and toughness as well as low mechanical strength at temperatures below 873 K (600 C).[12] This poor room-temperature ductility is attributed to hydrogen embrittlement due to the presence of atmospheric moisture.[13,14] The addition of carbon to Fe3Al contributes to increased mechanical strength at high temperatures[15,16] and reduced hydrogen brittleness.[17] The carbon addition also improves the wear resistance.[18–20] The benefits provided by the introduction of carbon result from the formation of Fe4yAlyCx carbide, where 0.8 < y < 1.2 and 0 < x < 1. This carbide is known as the j phase[21,22] and exhibits a crystalline structure similar
MARIA NALU VERONA and DALMARINO SETTI are with the Department of Mechanical Engineering, Federal Technological University of Parana´, Pato Branco, 85503-390, Brazil. Contact e-mail: [email protected] RAMO´N SIGIFREDO CORTE´S PAREDES is with the Department of Mechanical Engineering, Federal University of Parana´, Curitiba, 81531-980, Brazil. Manuscript submitted March 9, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
to that of cubic perovskite.[23,24] In this study, the j phase is represented by the stoichiometry Fe3AlCx. Fe3Al-Fe3AlCx composites exhibit processing advantages, including low raw material costs[25] and the capability of being processed by induction air melting with slag cover.[26] In addition, their room-temperature ductility,[27] creep resistance,[28] wear resistance,[18,19] and hardness and mechanical strength[29] are improved compared with those of Fe3Al. The oxidation and sulfidation properties of Fe3Al-Fe3AlCx composites are also similar to those of Fe3Al,[30] and their use results in a significant improvement in the resulting machinability.[31] Fe3Al-Fe3AlCx composites have been prepared using different processing methods, including self-propagating high-temperature synthesis,[32] powder processing,[33] mechanical alloying,[34] and additive manufacturing by welding.[35] However, liquid-state processing techniques have been the most widely used. The methods of melting and casting[5,26,36,37] are well developed, and the use of carbon contents greater than 0.22 wt. pct favors the application of processing methods using melting.[38] Reactive liquid processing (RLP) is a processing technique used to prepare composites from the liquid state. The fundamental factor in this processing route is the reactivity of the liquid with the other component in the system, usually a solid. The best-known RLP route involves the infiltration of metal into a ceramic pre-form.[39] This route has been used in the production of i
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