Direct nucleation and growth of peritectic phase induced by substantial undercooling condition

Peritectic phase forms through peritectic transformation in most cases. Here we predicted theoretically a growth mechanism transition from peritectic transformation to the direct nucleation and growth of peritectic phase during rapid solidification. To demonstrate this experimentally, liquid Cu-Sn alloy was undercooled by up to 268 K (0.31T_L). Once the undercooling exceeds a critical value of about 220 K, peritectic η phase forms directly from the metastable liquid phase by suppressing the nucleation of primary ε phase and peritectic transformation. As undercooling increases in the range below 201 K, the primary ε phase is refined and peritectic transformation is promoted.