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

• Rapid solidification of Cu–70%Sn peritectic alloy is realized by two methods.
• We report peritectic growth mechanism transition induced by sufficient undercooling.
• Direct nucleation and growth of peritectic phase occurs if undercooling exceeds 220 K.
• Increasing undercooling induces nucleation competition between ε and η phases.

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 (0.31TL). 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.