Solidification from highly undercooled iron base alloys and formation of metastable phases

通过快速凝固工艺生产的非平衡晶体和非晶态材料得到了发展，并正在成长为新的先进材料。它们的特性在很大程度上取决于快速凝固变量，因此了解组织和性能的加工与控制之间的关系是非常重要的。液态金属在结晶前的快速冷却中高度过冷。为了模拟快速凝固过程，知道在多大程度上达到最大过冷和形成什么相是一个基本问题。本文研究了含半金属铁基合金的成分、过冷度与相形成的关系。在Fe- b合金中，首先观察到亚稳共晶（Fe+FeB）。Fe-P合金中也存在亚稳共晶。在Fe-C合金中，亚稳的< δ >相在超晶组成的1.2%范围内形成。这些亚稳相可以用过冷的热力学考虑来解释。在Fe-Si-B合金中，初生FeB的过冷范围大，与非晶的形成范围一致。

Non-equilibrium crystals and amorphous materials produced by rapid solidification processings have developed and are growing to new advanced materials. Their characteristics largely depend on the rapid solidification variables and therefore it is very important to understand the correlation between processing and controlling of structures and properties. Liquid metals are highly undercooled in rapid cooling prior to crystallization. To simulate the rapid solidification, it is a basic problem to know to what extent the maximum undercooling is achieved and what phase is formed. In this research, relationship between composition,undercooling and phase formed is considered for iron base alloys containing semi-metals. In Fe-B alloys, metastable eutectic ( Fe+FeB ) is first observed. In Fe-P alloys, metastable eutectic are also confirmed. In Fe-C alloys, metastable <delta> phase is formed in the range of the hyperperitectic composition of 1.2%. These metastable phases can be explained by the thermodynamic consideration for undercooling. In Fe-Si-B alloys, large undercooling range for primary FeB is consistent with the formation range of amorphous.