Microstructure evolution and non-equilibrium solidification of undercooled Ni-29.8at% Si eutectic alloy melts  

作　　者：LU YiPing1,LI TingJu1,TENG HaiTao1,FU YaBo1,LUO DaWei1 &YANG GenCang2 1 School of Materials Science and Engineering,Dalian University of Technology,Dalian 116024,China 2 State Key Laboratory of Solidification Processing,Northwestern Polytechnical University,Xi’an710072,China 

出　　处：《Science China(Technological Sciences)》2010年第4期1043-1048,共6页中国科学（技术科学英文版）

基　　金：supported by the China Postdoctoral Science Foundation (Grant No 20090450102)

摘　　要：Microstructure formation and transition of undercooled bulk Ni70.2Si29.8 eutectic alloy melt were investigated by melt fluxing,cyclical overheating and cooling under high-frequency vacuum melting.The maximum undercooling of the alloy melt amounted to 428 K.Scanning electron microscope(SEM),energy-dispersive X-ray spectroscopy(EDS) and optical microscopy techniques(OM) were adopted to investigate the microstructure and identify the phase composition.The cooling curves of eutectic alloys upon solidification which were subjected to different undercoolings were described and compared.The complex microstructure evolution was observed in the as-solidified samples with the increase of undercooling.Surprisingly,an extremely fine microstructure was achieved at the max undercooling of 428 K,and the lamellar distance of about 50-100 nm was observed.Based on the solution entropy of eutectic phases,the microstructure transition with the undercooling was analyzed.Calculated results showed that the microstructure transition process was ascribed to solution entropy of transition,i.e.,the complex microstructure evolution was attributed to a transition from faceted-faceted(FF)→faceted-nonfaceted(FN)→nonfaceted-nonfaceted(NN) eutectic systems concurring with increased undercooling.Microstructure formation and transition of undercooled bulk Ni70.2Si29.8 eutectic alloy melt were investigated by melt fluxing,cyclical overheating and cooling under high-frequency vacuum melting.The maximum undercooling of the alloy melt amounted to 428 K.Scanning electron microscope(SEM),energy-dispersive X-ray spectroscopy(EDS) and optical microscopy techniques(OM) were adopted to investigate the microstructure and identify the phase composition.The cooling curves of eutectic alloys upon solidification which were subjected to different undercoolings were described and compared.The complex microstructure evolution was observed in the as-solidified samples with the increase of undercooling.Surprisingly,an extremely fine microstructure was achieved at the max undercooling of 428 K,and the lamellar distance of about 50-100 nm was observed.Based on the solution entropy of eutectic phases,the microstructure transition with the undercooling was analyzed.Calculated results showed that the microstructure transition process was ascribed to solution entropy of transition,i.e.,the complex microstructure evolution was attributed to a transition from faceted-faceted(FF)→faceted-nonfaceted(FN)→nonfaceted-nonfaceted(NN) eutectic systems concurring with increased undercooling.

关 键 词：interface structure SOLIDIFICATION ENTROPY METALS and ALLOYS 

分 类 号：TG146.15[一般工业技术—材料科学与工程]