Ag-Cu/Co-Sn共晶合金深过冷快速凝固反常共晶的形成研究

利用熔融玻璃净化循环过热的方法进行了Ag-Cu/Co-Sn共晶合金的深过冷快速凝固实验，并系统研究了熔体过冷度和微量Nb添加对反常共晶形成的影响。结果表明，快速凝固过程中共晶枝晶内部首先重熔形成反常共晶，随着过冷度的增大，共晶相的形貌从蠕虫状转变为球形颗粒，被重熔形成的固相颗粒将作为剩余液相形核生长的基底，Ag-Cu共晶中共晶两相形核具有非互惠性。Co-Sn共晶合金中添加Nb元素后样品内部反常共晶形成的临界过冷度由23 K降低至15 K，而表面组织中过冷度从45 K降低至30 K。由于样品表面与坩埚壁接触有利于结晶潜热消散，反常共晶形成的临界过冷度较高。Ag-Cu共晶合金温度再辉曲线上慢速凝固阶段持续的时间较Co-Sn共晶合金要长。

Study on the formation of anomalous eutectic during undercooled rapidly solidification of Ag-Cu/Co-Sn eutectic alloys

The undercooled solidification experiment of Ag-Cu/Co-Sn eutectic alloy was performed by means of molten glass purification and cyclic overheating, and the effects of undercooling and minor Nb addition on the formation of anomalous eutectic were systematically studied. The results show that anomalous eutectic is formed by remelting in the eutectic dendrite during rapid solidification. With the increase of undercooling, the morphology of eutectic phase changes from vermicular to spherical particles. The solid particles formed by remelting will be used as the substrate for the nucleation of residual liquid phase. The nucleation of two-phase in Ag-Cu eutectic is non reciprocal. With the addition of Nb to Co-Sn eutectic alloy, the critical undercooling of anomalous eutectic formation inside the sample decreases from 23 K to 15 K, and from 45 K to 30 K in the surface microstructure. Because the sample surface contact with the crucible wall which is conducive to the dissipation of latent heat of solidification, the critical undercooling of anomalous eutectic formation is higher. The duration of slow solidification stage on the temperature recalescence curve of Ag-Cu eutectic alloy is longer than that of Co-Sn eutectic alloy.