Abstract
Precipitation and growth behavior of Fe2Nb-type Laves precipitates are crucial for the mechanical behavior of FeCrAl-based cladding alloys containing Mo and Nb. In this study, the age hardening response of a Fe-13Cr-4Al-2Mo-1.2Nb alloy at 600–800 °C and the corresponding precipitation behavior were systematically investigated. The alloy exhibited a typical two-stage hardening behavior separated by a plateau during aging at all the temperatures. For the alloy aged at 700 °C, the total hardness increment by aging reached ~102.7 HV (40%), with an aging time of 60 min to reach the peak-aged state. Based on detailed transmission electron microscopy (TEM) investigations, the precipitation sequence of the alloy was elucidated as: Supersaturated solid solution → γ″ → γ' → C14-Fe2(Nb,Mo) Laves phase. As the aging proceeded, the Fe2(Nb,Mo) precipitates also evolved from a needle-like morphology with a semi-coherent interfacial structure into a short-rod-like and finally a blocky morphology with a non-coherent interfacial structure. The JMA equation describing the aging kinetics of the alloy was established. The apparent activation energy for the precipitation of the Fe2(Nb,Mo) phase was calculated as 141.5 KJ/mol.
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