Continued growth controlling of the non-preferred primary phase for the parallel lamellar structure in directionally solidified Ti-50Al-4Nb alloy

Bridgman-type directional solidification experiments were conducted for Ti-50Al-4Nb alloy. The continued growth of the non-preferred primary phase with the effect of the growth rate was investigated for the parallel lamellar structure. The planar-cellular-dendritic growth of primary α phase is observed with increasing growth rate and α2/γ lamellar structure is obtained finally. The growth of the non-preferred crystals is blocked by the nucleated preferred crystals at low growth rates (<3 μm/s) due to the external particles, as well as that at high growth rates (⩾15 μm/s) due to the tilting crystals and the high undercooling. While the continued growth of the non-preferred crystals is achieved at proper middle growth rates, which always takes on a slope form owning the developed lateral dendrites. Finally the parallel columnar crystals with the parallel lamellar structure are obtained at selected growth rates (5-7 μm/s) by controlling the continued growth of the preliminary non-preferred crystals at the initial interface.