题目: The formation of anomalous eutectics and recalescence characteristic of eutectic alloys

报告人: 康纪龙

时间:  2013年4月13日09:00 开始

地点：B314

摘要:

Many research have shown that exists a critical undercoolingduring the process of microstructure evolution of undercooled eutectic alloy , When the undercooling greater than the critical undercooling ，the anomalous eutectic is produced. For the forming mechanism of anomalous eutectics, at present there are still great controversies.Several theories have been advanced to explain the formation of anomalous eutectic.

Figure1 is the typical cooling curves of Ni-Si eutectic alloy. Its show that at low undercooling, there are only one recalescence while two nucleation points and two recalescence runs on the cooling curves at large undercooling.

Fig.1The typical cooling curves of Ni-Si eutectic alloy at different undercooling

Theprimaryphasenucleatesattemperature T_N1, thefirstrecalescencetakes place because ofreleasedlatentheat.Theundercooling is expressed as ΔT₁=T_E-T_N1.The secondaryphaseand/oreutectics nucleate at temperature T_N2 causes the second recalescence. Theundercooling isΔT2=T_E-T_N2. These two recalescence phenomenon be ascribed to the non-reciprocal nucleation of the two competing phases. Anumberofexperimentalresultsindicatethatfig.1(b) correspondstothecasewhereNi₃Si is theprimaryphaseandfig.1(c)tothecasewherea-Ni is theprimaryphase.