Phase-field method simulation of the effect of elastic strain energy on coarsening dynamics during the α ₂→O phase transformation in Ti-Al-Nb alloys

The Ti-Al-Nb alloys have received significant attention due to its excellent properties for high-temperature applications. The α ₂→O phase transformation taking place in these alloys leads to complex multi-variant and multi-domain microstructure, which has been extensive researched by experimental studies. The morphology, size, spatial arrangement of multi-variant and the volume fraction of precipitated phase, which are determined by the elastic strain energy, affect the important physical and mechanical properties of these alloys. So it is important to examine the effect of elastic strain energy on coarsening dynamics during the α ₂→O phase transformation. In this study, phase- field method has been used to simulate the α ₂→O phase transformation, and the effect of elastic strain energy on coarsening dynamics especially the morphology, orientation, number and the volume fraction of precipitated phase particles have been discussed. The results show that elastic strain energy has great impact on the morphology and orientation of precipitated phase particles. As the result of elastic strain energy, particles transformed into block and aligned along the elastic soft directions. The greater elastic strain energy in system without applying any external stress, the easier nucleation and the smaller volume fraction and mean size of particles when system was steady. An applied stress can result in the selective growth of precipitated phase variants, which promotes the precipitation of favored variants and retards the precipitation of other variants, finally changes the morphology. When system applied small pressure stress, the number of particles increased which eventually led to the reduction of mean size. Volume fraction of precipitated phase increased with increasing external stress when it is over a certain extent.