Impurity distribution In commercial Al-Ti and Al-Ti-B hardeners

AbstractThe concept of nucleation entropy has been developed in previous papers and applied to interpret the markedly enhanced grain refinement of Al by Ti when small amounts of Si (Refs. 2 and 3) and Be (Ref. 4) are added. In the theory, the nucleation entropy and the corresponding rate of nucleation of the peritectic compound increase if the third element concentrates in the peritectic compound. In the case of Si additions, incorporation of Si into the binary TiAl3 phase is required at a level which exceeds the concentration in the liquid alloy. The presence in an annealed and equilibrated Al-Ti-Si alloy of the compound TiAl2.4Si0.6, which has the body centred tetragonal (bct) structure of TiAl3, has been reported by Ramon and Schubert. In a more recent communication, Youdelis and Yang have shown that the bct Ti(Al, Si)3 compound (ranging in composition from TiAl1.83Si0.04 to TiAl2.38Si0.19)forms in a solidified non-equilibrated Al-Ti-Si alloy. The above conclusion that Si is incorporated into the TiAl3...