THEORETICAL AND EXPERIMENTAL DETERMINATIONS OF THE THERMAL-STABILITY OF RARE-EARTH OXIDE PARTICLES IN RAPIDLY SOLIDIFIED TITANIUM-ALLOYS

The general stability of a dispersion of rare earth oxide particles in Ti has been considered analytically and determined experimentaly. Regarding the analytical approach, the solubility product for the formation of erbia from its constituents in a Ti matrix has been calculated using thermodynamic data. This allows the concentration term in the equation for Ostwald ripening to be calculated. This calculation predicts different stabilities for a dispersion of erbia particles depending on whether the alloy contains an excess of Er or oxygen with respect to the formation of the rare earth oxide Er//2O//3. The rate of coarsening is more rapid in samples with an excess of Er compared to those with an excess of oxygen. Both predictions have been verified experimentally by forming the dispersion through heat treatment at 700 degree C and performing isochronal anneals at higher temperatures to determine the resistance to particle coarsening. Isothermal annealing has been employed to demonstrate that the coarsening involves bulk diffusion, i. e. t**1**/**3 kinetics.