Study of twinned dendrite growth stability

Under certain thermal conditions (G ≈ 1 × 104 K m−1, νs ≈ 1 × 10−3 m s−1), 〈1 1 0〉 twinned dendrites appear in aluminum alloys and can overgrow regular columnar dendrites, provided that some convection is also present in the melt. In order to check the stability of such morphologies, directionally solidified twinned samples of Al–Zn were partially remelted in a Bridgman furnace and then resolidified under controlled conditions, with minimal convection. It was found that, although twin planes remain stable during partial remelting, non-twinned dendrites regrow during solidification. They have a crystallographic orientation given by those of the twinned and untwinned “seed” regions, and grow along preferred directions that tend to be those of normal specimens.