EFFECT OF THE PRECIPITATE MORPHOLOGY ON THE PHASE SEPARATION BEHAVIOUR OF γ' PRECIPITATE IN A Ni-Al-Ti ALLOY

摘要

When the γ+γ' two-phase microstructure of an elastically constrained Ni-Al-Ti alloy is aged, γ' precipitates sometimes exhibit a phase separation and y particles newly appear in the γ' precipitates under the influence of chemical free energy. The morphological changes of γ particles are influenced by the γ' precipitate morphology. In coherent γ' particles or those surrounded by misfit dislocations, γ particles grow to the plates each of which is parallel to any of the three equivalent {001} planes. When γ' precipitates are in a queue along [010], all the surfaces of γ' precipitates except for (010) are accompanied by misfit dislocations, and γ particles become flat plates parallel to (010). Microstructure changes observed are governed by not only the elastic energies but also the chemical free energy.