HREM analysis of γ′ particles in late stages of coarsening in Ni alloys

The mechanism of coarsening of coherent particles in solids is investigated via HREM. Ni based alloys are used for experiments. HREM observations are used to determine translation order domains in neighboring particles. The investigated materials include model Ni-Al alloys and Ni-based alloys of technological application (MC2 and MCNG). The determination of translation order domain in particle arrays allows discussion of the coarsening mechanism with special attention to the mechanism of particle splitting against an alternative mechanism of migration and coalescence of particles. Various techniques of image processing have been employed to analyze the HREM images of γ-γ′ interfaces. Digital Moire patterns, geometric phase image and phase profiles from HREM images have been obtained. The present results show that most particles (around 79 %) in a variety of arrangements and sizes, have different order domains. This suggests that splitting has not taken place since otherwise particles in a given group would have an identical order domain. This leads to discussion of the coarsening mechanism in the late stages of a first order phase transformation in solids.