Precipitation of the γ phase in recrystallized cold-rolled single crystals of Ni78Al18Ti4 was studied using transmission electron microscopy. Precipitation of γ was found at Σ3(111) coherent twin boundaries and was expected to reduce the total energy by relieving the energy due to ordering at the boundary. The observation of precipitation at coherent twin boundaries suggested that the reported value of the symmetrical coherent twin energy, 6mJ/m2, might be an underestimate. Some observations suggested that precipitation could also occur at low-angle and special boundaries. No precipitation was observed at high-angle boundaries.

Grain Boundary Precipitation of γ in γ′ Ni3(Al,Ti). M.L.Turi, G.Weatherly, G.Purdy: Materials Science and Engineering A, 1995, 192-193[2], 945-9