Microstructure evolution and mechanical properties of directionally solidified large size Ti-47Al-5Nb-0.18C-0.3Si alloy by electromagnetic confinement

Abstract

Newly designed Ti-47Al-5Nb-0.18C-0.3Si alloys were directionally solidified by electromagnetic confinement with seed method at the pulling rate of 5–20 µm/s. The macro/microstructure evolution, fracture toughness and high temperature tensile property of the alloy were investigated in detail. The results indicate that the large size single crystals with aligned lamellar microstructure are obtained at the pulling rate of 10 µm/s and 15 µm/s, however, when the pulling rate is lower than 10 µm/s or higher than 15 µm/s, the equiaxed crystals and the divergent columnar crystals are presented instead of the single crystals. Solidification process and macro/microstructure evolution are expressed by schematic, and they display the primary α phase solidification characteristic at the pulling rate of 10–20 µm/s. It is found that the interlamellar spacing gradually decreases with the increase of pulling rate, and the relationship between them can be described as d=14174V−0.83. The single crystal with aligned lamellar microstructure at 10 µm/s possesses the better fracture toughness and high temperature tensile properties. Finally, toughening mechanism and strengthening mechanism are analyzed and discussed.