An important disadvantage of polycrystalline NiAl-based alloys are their room-temperature and high-temperature brittleness, which interferes with potential structural applications. This brittleness is generally attributed to the inability of dislocations to move in the highly ordered lattices. The introduction of small amount of boron can drastically increase the ductility by suppressing intergranular fracture.
Ni-based superalloys derive their strength from the formation of γ precipitates (NiAl) in the γ phase (Ni) which strengthen the alloys through precipitation hardening. In these alloys the volume fraction of the γ precipitates is as high as 80%. Because of this high volume fraction, the evolution of these γ precipitates during the alloys life cycles is important: a major concern is the coarsening of these γ precipitates at high temperature (800 to 1000 °C), which greatly reduces the alloys strength. This coarsening is due to the balance between interfacial and elastic energy in the γ + γ phase and is generally inevitable over long durations of time. This coarsening problem is addressed by introducing other elements such as Fe, Cr and Mo, which generate multiphase configurations that can significantly increase the creep resistance. This creep resistance is attributed to the formation of inhomogeneous precipitate CrMoNi, which pins dislocations and prevents further coarsening of the γ phase. The addition of Fe and Cr also drastically increases the weldability of the alloy.