Grain boundary precipitation of γ in γ′ Ni3(Al,Ti)

The mechanical properties of polycrystalline nickel aluminides are controlled by the structure of grain boundaries and by the presence of precipitates. No systematic study of precipitation of Ni-rich γ at grain boundaries in Ni3(Al,Ti) has been undertaken prior to this work. Precipitation of γ in recrystallized cold-rolled single crystals of composition Ni78Al18Ti4 was studied by TEM. itation of γ was found at Σ3(111) coherent twin boundaries and is expected to reduce total energy by relieving the energy due to the ordering at the boundary. The observation of precipitation at coherent twin boundaries suggests that the reported value of symmetrical coherent twin energy of 6 mJ m−2 may be underestimated. bservations suggest that precipitation may also occur at low-angle and special boundaries. No precipitation was observed at high-angle boundaries.