Effect of solute content on grain refinement microstructure of rapid solidified Co-Cu immiscible alloy

Adopting molten glass purification combined with cycle superheating method, the effect of solute content on grain refinement regularity of Co₇₀Cu₃₀ and Co₅₀Cu₅₀ immiscible alloys was investigated under non-equilibrium condition. With the increase of initial undercooling, the trunk of primary dendrite decreases, which generates serious dendrite fragmentation. For samples without liquid separation, the solute undercooling of Co₅₀Cu₅₀ alloy increases because of its higher solute content. Consequently, the kinetics undercooling for growth is suppressed, which leads to refined and broken-up dendrite. With the further increase of undercooling, the immiscible effect is strengthened and liquid separation occurs, which forms Co-rich and Cu-rich regions. As for Co₇₀Cu₃₀ alloy undercooled by 237 K and Co₅₀Cu₅₀ alloy undercooled by 188 K, the influence of solute content on rapid solidified microstructure is weakened, which can be inferred from the almost same of the grain size and solute concentration. Moreover, liquid separation proceeds more completely for Co₅₀Cu₅₀ alloy due to the sufficient duration time for immiscible stage arising from the lower critical immiscible undercooling.