Abstract:In order to obtain the essence of the nucleation phase and its variants selected of secondary α. Electronic backscatter diffraction (EBSD) has been employed to study the relationship between the crystal orientation, geometric growth direction, quantity, distribution of secondary α-phase and β-phase grain boundaries properties on nearly β-type Ti-1300 alloy. The alloy was equilibrated for 2 h at 910℃ and handled by water quenching. The alloy occurs a certain percentage of <110> 70.5° special boundaries. The alloy was slowly cooled in the furnace since 910℃, it has a significant relationship between the secondary α phase which from β→α phase transformation and β-phase grain boundaries properties. Common β/β grain boundary generated orientation is not unique, which has little effect on the nuclear of the Self -α phase grain boundary α phase variations, its relatively small number of both sides of since grain boundary α phase. The α phase grain boundary was generated by the common β/β grain boundary, its orientation was not unique. The common β/β grain boundary has little effect on the nuclear of the Self-α phase grain boundary α phase variations, and there are small number Self-α phase grain boundary both sides the α phase grain boundary. Both sides of the β grain which boundary is special high angle grain boundaries (<110>70.5°) have the same (110) plane. The orientation of the α phase grain boundary is favor for the formation of the heterogeneous nucleation of the Self-α phase grain boundary, which causes selective growth of the α variant on both sides in grain boundary; Special small-angle grain boundaries (<110>10.5°) also can cause α variant’s selective growth, but it is different from high-angle grain boundaries, the selective growth may only occur on one side of the grain boundary.