Lamellar orientations and growth directions of β dendrites in directionally solidified Ti–47Al–2Cr–2Nb alloy

Abstract

Lamellar orientations and growth directions of β dendrites are investigated in Ti–47Al–2Cr–2Nb alloy with different temperature gradients ( G) and growth rates ( v) by directional solidification technique. It shows that β phase is the primary solidification phase when G/v ratio is equal to or less than 4.8×10 8 K s m −2, while the lamellar orientations vary with G and v. At G of 40 K/cm and v of 1 mm/min, lamellar orientation inclined at the angle of 74° to growth direction is preferred. As G is increased to 125 K/cm, or v is increased to 10 mm/min, lamellar orientation aligned at about 45° to growth direction is favored. At intermediate G and v, the orientations are aligned in the range of 45–78° to growth direction. Calculation of β-dendrite growth direction shows that growth direction is 〈2 2 1〉 β at low G or v, while the direction tends to be 〈1 0 0〉 β at high G or v.