Hot deformation behavior of a spark plasma sintered Fe-25Al-1.5Ta alloy with strengthening Laves phase

Abstract

Intermetallic iron aluminide alloys show various advantages such as low material cost and a good creep resistance that is superior to the P92 martensitic-ferritic steel at 650 °C, nominating them as potential candidates for steam turbine applications. However, cast preforms for hot forging show a rather coarse microstructure and limited workability. Recent research thus introduced Fe-25Al-Ta alloys, where tantalum prevents excessive grain growth during solidification. This paper, for the first time, investigates the possibility of producing the Fe-25Al-1.5Ta (at.%) alloy by spark plasma sintering (SPS) from pre-alloyed powder particles and investigates its deformation behavior under compression in the temperature range of 900–1100 °C using the concept of processing maps. SPS is mainly used to analyze the possibility of inheriting the size of the initial powder particles into the sintered material.The SPSed specimen at room temperature reveals a homogeneous equiaxed microstructure consisting of fine A2-phase grains with an average size of 7 μm surrounded by the ternary (Fe, Al)2Ta, C14, Laves phase particles. Laves phase particles are precipitated predominantly on grain boundaries of the Fe-Al matrix grains. Several particles are also dispersed inside the grains.The presence of a fine-grained equiaxed microstructure at hot working temperature seems to improve workability and leads to a wide processing window. The optimum processing domain for the studied Fe-25Al-1.5Ta alloy locates at 1050–1100 °C/0.0013–0.01 s−1 with a power efficiency of 40–50%, where the material undergoes dynamic recrystallization. At low temperature and high strain rates, dynamic recovery is the major softening mechanism observed for the samples, where the efficiency of power dissipation reaches around 40%.The current study offers a possibility to produce a homogeneous fine-grained Fe-25Al-1.5Ta alloy strengthened by dispersed Laves phase particles using SPS compared to the coarse and columnar microstructure commonly obtained by casting. Such a refined microstructure leads to a good hot forgeability.