Possibility of Spinodal Decomposition in ZrO₂‐Y₂O₃ Alloys: A Theoretical Investigation

The thermodynamics and kinetics of cubic → tetragonal phase transformations in ZrO₂‐Y₂O₃ alloys were investigated by using thermodynamic stability analysis and kinetic computer simulations to explore the possibility of a spinodal mechanism during decomposition. Based on a simple free energy model, it is shown that, depending on the alloy composition, a cubic phase aged within the t + c two‐phase field may result in three different sequences of phase transformations: (1) direct nucleation and growth of the equilibrium t‐phase from the c‐phase matrix; (2) formation of a metastable t′‐phase followed by nucleation and growth of the equilibrium c‐ and t‐phases; and (3) formation of a transient t′‐phase followed by its spinodal decomposition into two tetragonal phases with one of the tetragonal phases eventually transforming to the equilibrium c‐phase. The temporal microstructure evolutions for different compositions were studied by using computer simulations based on the time‐dependent Ginzburg‐Landau (TDGL) model which incorporates the long‐range elastic interactions.