Peritectic solidification mechanism of substantially undercooled liquid Fe-Y-B ternary alloys

Liquid Fe₈₄Y₁₀B₆ and Fe₇₄Y₁₆B₁₀ peritectic type alloys were substantially undercooled up to 382 (0.25 T_L) and 400 K (0.26 T_L) with drop tube technique. The molecular dynamics simulation results revealed that the former alloy was characterized by larger Fe, Y and B self-diffusion coefficients and activation energies. In low undercooling regime, γFe phase in Fe₈₄Y₁₀B₆ alloy and Y₂Fe₁₇B_x phase in Fe₇₄Y₁₆B₁₀ alloy formed preferentially, faceted τ₁(Y₂Fe₁₄B) phase subsequently developed through peritectic transitions. With the increase in undercooling, peritectic transitions were promoted by the refined primary phases. Once liquid undercoolings reached certain critical values, a stronger nucleation driving force is provided for τ₁ phase, resulting in its direct nucleation and growth by suppressing the formation of primary phases and the following peritectic transformations. If liquid undercooling rose further, there occurred the faceted to non-faceted growth mode transition of the main peritectic τ₁ phase. This indicates that high undercooling and rapid solidification is an effective approach to modulate phase transition pathway and microstructural evolution of rare earth alloys.