Effect of Ti/Nb/Ta addition on high-temperature microstructural stability of coherent γ/γ′ in Ni–Al–(Cr,Mo,W) superalloys

The present work studied the effect of Ti, Nb, or Ta addition on the microstructural stability of coherent γ/γ′ phases in the designed [Al-Ni12](Al1(Al/Ti/Nb/Ta)0.5(Cr0.5Mo0.5W0.5)) superalloys. The coherent microstructure with cuboidal γ′ nanoparticles could be formed during aging at 1173 K in these designed superalloys due to the moderate lattice misfit. The addition of Ti, Nb, or Ta element can not only reduce the size of γ′ nanoparticles, but also improve the microstructural stability during aging, as evidenced by smaller coarsening rate constant in Ti/Nb/Ta-added alloys than that in Al-added alloy. Moreover, Ti/Nb/Ta-added alloys exhibit prominent mechanical properties, which are ascribed to the γ′ particle size since the volume fraction values of γ′ in designed alloys are comparable and it keeps nearly constant during aging. Besides, the addition of Ti, Nb, or Ta could also enhance the precipitation of W/Mo-enriched μ phase on grain boundaries.