Fig. 9: Illustration of proposed grain refinement mechanism.

a Intermetallic phase solidifies prior to matrix material nucleation, b Heterogeneous nucleation sites on the intermetallic phase, c Refined grains in matrix material, d Impurities and grains from the prior layer in unreinforced matrix material, e Nucleation from impurities and directional grain growth, f Large directional grains with potential solidification cracks.