Effects of Iron Addition on the Microstructures and Mechanical Properties of Two-Phase Ni₃Al-Ni₃V Intermetallic Alloys

Microstructures and mechanical properties of dual two-phase Ni₃Al (L1₂)-Ni₃V (D0₂₂) intermetallic alloys to which iron (Fe) was added in different substitution manners were investigated by scanning electron microscopy, transmission microscopy, Vickers hardness, and tensile tests. Primary Ni₃Al precipitates were extremely fine in the alloys in which Fe was substituted for Al. The changes of the volume fraction in the Ni₃Al precipitates by the addition of Fe were explained in association with the partition behavior of Fe into the constituent phases and the relative content of Al to V which was affected by the substitution manner of Fe. The microstructures in the channel region of the alloys in which Fe was substituted for Ni, Al, and V were suggested to be comprised of L1₂ and D0₂₂ phases, L1₂, D0₂₂ , and Ni slid solution (A1) phases, and A1 phase, respectively. From the partition coefficients of Fe estimated using the alloys constituted by L1₂, D0₂₂ , and A1 phases, it was shown that Fe evenly destabilizes the two intermetallic phases. For the alloys in which Fe was substituted for Al and V, the yield strength (or hardness) decreased and the tensile elongation conversely increased with increasing Fe content. For the alloys in which Fe was substituted for Ni, the tensile elongation as well as strength remained unchanged. The changes of the strength (hardness) as well as tensile elongation in the alloys in which Fe was substituted for Al and V were attributed to the imperfect ordering in the two intermetallic phases and/or the presence of the Ni solid solution (A1) phase.