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对空间环境条件下偏晶凝固过程中壳核组织的形成机制进行了数值模拟研究.在总自由能中引入表面自由能项对H模型进行了修正,使之能够描述表面偏析作用下的相分离.选取Fe-Cu合金作为模型体系,系统模拟了微重力状态下深过冷合金液滴的亚稳相分离过程,揭示了表面偏析效应和温度梯度引起的Marangoni对流对微观组织演化的影响.模拟结果表明,Fe65Cu35合金的相分离组织从弥散结构演化为3层壳核组织;Fe50Cu50合金经历了“双连续相→4层壳核→3层壳核”的组织演化;Fe35Cu65合金的组织由弥散结构向两层壳核组织演化.偏析作用使得最外层总是富Cu相,温度梯度引起的Marangoni对流决定了内部体相的组织演化过程.
The formation mechanism of putamen in the process of crystallite deformation under space environment was numerically simulated. The surface free energy was introduced into the total free energy to modify the H model so that it could describe the phase separation under surface segregation The Fe-Cu alloy was chosen as the model system to systematically simulate the metastable phase separation process of the microgravity supercooled alloy droplets, and the effect of the surface segregation and the temperature gradient on the microstructure evolution of the Marangoni convection was simulated. The results show that the phase-separated microstructure of Fe65Cu35 alloy evolves from diffuse structure to three-layer shell nucleus. Fe50Cu50 alloy undergoes the microstructure evolution of “bicontinuous phase → four-layer shell core → three-layer shell core.” The microstructure of Fe35Cu65 alloy consists of dispersed structure Which evolves into two layers of putamen.The segregation makes the outermost Cu-rich phase always.The convection of Marangoni caused by the temperature gradient determines the microstructure evolution of the inner bulk.