ABSTRACT
Fe-Al based alloys have a remarkable potential for high temperature structural applications, provided that the limitation of their low creep resistance is solved. Third element addition (Nb, Ti, Zr or Ta) has proven to per-form the task, at the expense of a low ductility. In previous works we have investigated ferritic alloys in the Fe-Al-V system with coherent precipitation of the L21 phase (Fe2AlV) in the A2 matrix. Among possible alloys, we chose the 76Fe-12Al-12V superalloy for filing a L21 precipitation with spherical morphology and void coalescence at high temperature. The new task is to find a fourth alloy element in order to increase the temperature equilibrium of the two phases A2+L21 field and consequently the maximum application tem-perature. Isothermal sections of the Fe rich corner on ternary Fe-Al-V and Fe-Al-Ti phase diagrams have similar phase fields. Besides, by comparing the formation energies between L21 intermetallics of Ti and V, it is expected a higher equilibrium temperature for the Fe2TiAl than for Fe2VAl. Therefore we select titanium as a possible 4th alloy element in the 76Fe-12Al-12V superalloy We show in this work that vanadium substi-tution by titanium slightly increases the temperature limit for the A2 + L21 phase field while cancelling the lattice misfit between matrix and precipitates for Ti content between 0.5 and 1 at. % and positively increasing it for Ti contents greater than 1 at. %. Besides, we demonstrate that coarsening rate is increased with Ti addi-tion and morphology is modified from spherical to cubic.
Keywords
Ferritic superalloy; Phase transformation; Lattice misfit
