溶质含量对快速凝固 Co­Cu 不混溶合金晶粒细化组织的影响

摘要

采用熔融玻璃净化与循环过热相结合手段，研究 Co70Cu30和 Co50Cu50亚稳不混溶合金的非平衡凝固组织细化规律。结果表明：随着过冷度的增加，不混溶合金的初生枝晶主干不断细化，枝晶碎断现象更加明显。在未发生液相分离条件下，Co50Cu50合金由于具有更高的溶质含量，溶质过冷度增加，动力学过冷度降低，枝晶细化更加明显而易发生碎断。在大过冷度条件下，合金不混溶效应不断增强，液相分离现象发生，凝固组织中分别出现富 Co 和富 Cu 区。对于 Co70Cu30(ΔT=237 K)和 Co50Cu50(ΔT=188 K)合金，溶质含量对快速凝固过程中初生枝晶的影响程度减弱，非平衡凝固组织的晶粒尺寸及成分未发生明显变化。Co50Cu50合金由于具有更低的临界分离过冷度，不混溶阶段经历的时间更长，液相分离进行得更彻底。%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 non­equilibrium 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 broken­up dendrite. With the further increase of undercooling, the immiscible effect is strengthened and liquid separation occurs, which forms Co­rich and Cu­rich 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.