Study of growth advantage of twinned dendrites in aluminum alloys during Bridgman solidification

摘要

The growth advantage of twinned dendrites over regular columnar ones was systematically investigated during Bridgman solidification. An experimental approach was designed and the results indicated that the strong twin growth advantage lost its efficiency in the coexisting microstructure containing both twinned and regular dendrites at a low growth rate of 10 mu m/s. The twin growth advantage derives from three essential components: the lateral twin propagation perpendicular to twin plane (R-x), the propagation parallel to twin plane (R-y), and the dendrite tip growth (R-z). The lateral extension component R-x played a vital role and would be limited at a low rate. Meanwhile, the tip undercooling of the twinned dendrite was estimated based on its plate-like growth morphology. Furthermore, the competitive growth between twinned dendrites was investigated in different feathery grains. When the included angle between twin planes was relatively large, the lateral twin propagation would keep down the in-plane twin propagation.