Catalytic nucleation of a meta-stable δ phase in phase-seeded undercooled Fe_(75)Ni_(25) melts  

作　　者：Y.Z. Chen, X.H. Shi, F. Liu, G.C. Yang, Y.H. Zhou State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an, Shaanxi 710072, China 

出　　处：《Progress in Natural Science:Materials International》2012年第3期258-262,共5页自然科学进展·国际材料（英文版）

基　　金：National Nature Science Foundation of China (Nos. 50395103, 50501020, and 51101121);the Research Fund of the State Key Lab. of Solidification Processing (NWPU), China (No. 79-TP-2011);the Fundamental Research Fund of NWPU (No. JC201134)

摘　　要：Undercooled Fe75Ni25 melts were phase-seeded by a high purity iron. It was found that above a critical undercooling, △Tc 135 K, a metastable δ phase (b.c.c) solidifies from the iron-seeded melts instead of a thermodynamically stable γ phase (f.c.c). While undercooling of the melt (△T) is below △Tc, solidification of the γ phase prevails in the iron-seeded melts. For the undercooled melts subjected to spontaneous nucleation, the γ phase always solidifies. After solidification, the as-solidified γ phase transforms completely to martensite; whereas the as-solidified metastable δ phase partially transforms to the γ phase, and then to martensite. The untransformed δ phase retains as a-ferrite particles in the microstructures. Based on the classical nucleation theory, catalytic nucleation of the metastable δ phase in the phase-seeded undercooled Fe75Ni25 melts was analyzed. It was quantitatively demonstrated that when △T>△Tc, the formation of the δ phase can be ascribed to a better catalytic effect of the iron on its nucleation than that on the nucleation of the γ phase.Undercooled Fe75Ni25 melts were phase-seeded by a high purity iron. It was found that above a critical undercooling, △Tc 135 K, a metastable δ phase (b.c.c) solidifies from the iron-seeded melts instead of a thermodynamically stable γ phase (f.c.c). While undercooling of the melt (△T) is below △Tc, solidification of the γ phase prevails in the iron-seeded melts. For the undercooled melts subjected to spontaneous nucleation, the γ phase always solidifies. After solidification, the as-solidified γ phase transforms completely to martensite; whereas the as-solidified metastable δ phase partially transforms to the γ phase, and then to martensite. The untransformed δ phase retains as a-ferrite particles in the microstructures. Based on the classical nucleation theory, catalytic nucleation of the metastable δ phase in the phase-seeded undercooled Fe75Ni25 melts was analyzed. It was quantitatively demonstrated that when △T>△Tc, the formation of the δ phase can be ascribed to a better catalytic effect of the iron on its nucleation than that on the nucleation of the γ phase.

关 键 词：Iron-nickel alloy Rapid SOLIDIFICATION Microstructure NUCLEATION UNDERCOOLING 

分 类 号：O643.3[理学—物理化学]