Retarded coarsening phenomenon of γ′ particles in Ni-based alloy

An anomalous coarsening behavior has been observed after aging an alloy Ni-14.5 at .%Al-5.9 at. % Mo at 1453 K. It was found that the initial cubic γ′ (ordered Ll 2 Ni 3Al phase) particles began to split into smaller ones after short aging ( t < 3 min). After continued aging, the particles agglomerated into large groups of many particles, and the distribution of the particles became non-uniform. The kinetics of coarsening did not obey the typical linear dependence between the cube of the particle size and aging time. Instead, a retardation of the coarsening process was found. Convergent beam electron diffraction (CBED) was applied to measure the distribution of the lattice strains around particles. The result indicated that there was an inhomogeneous distribution of lattice strain in the matrix around the coherent particles.