Dispersoid growth in Ni-2ThO2 due to self-diffusion sintering of particle clusters

The growth rates and activation energy for growth of thoria particles in thoria dispersion-strengthened nickel were measured after elevated temperature exposure. Growth was determined by direct measurement of thoria particle size on transmission electron micrographs. The thoria particles were distributed spatially in clusters in the hot consolitated alloy. Presence of particle clusters was found to provide the proper environment for a self-diffusion sintering-type particle coarsening. The rapid particle growth observed in this alloy form had too high a rate constant and too low an activation energy to constitute an Ostwald ripening mechanism, and was considered to reflect the grain growth stage of sintering. Further studies showed that thermomechanical treatments of hot consolidated material retarded this type of particle growth, by mechanically dispersing the ThO₂ particle clusters. W. SCHEITHAUER, JR. is currently on leave of absence at Lehigh University, Department of Industrial Engineering.