Growth directions of primary phases in directionally solidified Ti-45Al-7Nb alloys

Ti-45Al-7Nb alloys are produced by liquid-metalcooling (LMC) directional solidification (DS) furnace with different temperature gradients (G) at a range of 40-80 K/cm. The growth directions of primary β phases and the deflection angles relative to the «100»_β direction were investigated. The solidification pathway of alloy is: Liq. → Liq. + β → β → β + α → α + γ → lamella (α₂ + γ) + B2. Primary dendrite arm spacing δ reduced from 611.4 μm to 508.7 μm when G increased from 40 K cm ^-1 to 80 K cm^-1. Grains with lamellar orientation aligned at the angles of 12-15° and 55° to growth direction were favored for various G. The orientations of the γ lamellas in steady-state regions were identified by the electron backscattered diffraction analysis (EBSD). The results indicated that the growth directions of primary bcc-β dendrites were «211»_β and «110»_β at 40 K/cm, «210»_β and «211» _β at 50 K/cm and «211»_β at 80 K/cm, the deflection angle of «211»_β relative to «100»_β direction is 35.3°.