1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2 School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China
Cite this article:
Zhongyuan WANG,Jie HE,Baijun YANG,Hongxiang JIANG,Jiuzhou ZHAO,Tongmin WANG,Hongri HAO. LIQUID-LIQUID PHASE SEPARATION AND FORMA-TION OF TWO GLASSY PHASES IN Zr-Ce-Co-CuIMMISCIBLE ALLOYS. Acta Metall Sin, 2016, 52(11): 1379-1387.
The liquid-liquid phase separation has been used recently to design two-glassy-phase alloys with desirable mechanical, magnetic and thermal properties. The occurrence of the liquid-liquid phase separation in the Zr-Ce binary immiscible alloys can lead to the formation of two coexistent crystalline Zr-rich and Ce-rich phases after complete solidification. In this work, a new quaternary complex alloy system (ZraCeb)(1-x)(CocCud)x was designed on the basis of the addition of metastable Co-Cu immiscible alloys in the stable Zr-Ce immiscible alloys. Distribution ratio of Co and Cu in two coexistent liquids was calculated. The mechanisms of phase formation and microstructure evolution were investigated using OM, SEM, EDS, XRD and DTA. The results show that a single-phase homogeneous melt of (ZraCeb)(1-x)(CocCud)x alloys takes place the liquid-liquid phase separation during cooling through the miscibility gap. The metal elements Co and Cu are mainly concentrated in the Zr-rich and Ce-rich liquids, respectively, which results in the formation of the two coexistent Zr-Co-rich and Ce-Cu-rich liquids. It was found that the coexistent Zr-Co-rich and Ce-Cu-rich liquids undergo liquid-to-glass transition and thus form dual glassy phases under the rapid quenching, respectively. The effects of the atomic ratio of Co and Cu, the addition amount and the cooling rate on the formation of the glassy phases have been discussed in detail by combining the experimental investigation with the thermodynamic analysis. A strategy for synthesizing liquid-phase-separated metallic glasses on the basis of suitably designed immiscible alloys has been proposed. Two-glassy-phase alloys can be obtained by rapidly quenching alloy melt in which the atomic ratio of Co and Cu and the addition amount are 4∶1 and 38.5%, respectively.
Fund: Supported by National Natural Science Foundation of China (Nos.51374194, 51574216 and 51271185) and Natural Science Foundation of Liaoning Province (No.2015020172)
Table 1 Nominal compositions of (ZraCeb)(1-x)(CocCud)x alloys
Fig.1 Microstructure in the vicinity of the liquid-liquid phase separation boundary of No.1 alloy (a) and the locally magnified image of Zr-rich region in Fig.1a (b)
Fig.2 SEM image of the as-cast alloy No.8 (a), elements Zr (b), Co (c), Ce (d) and Cu (e) distributions along the line AB in Fig.2a, distribution ratio of elements Co (KCo) and Cu (KCu) in the two coexistent immiscible Zr and Ce liquids (f)
Fig.3 Microstructures, Ce-Cu-rich phase distribution and phase composition of No.8 alloy solidified under different cooling conditions(a) OM image of the transverse section of the suction-cast rod with 2 mm in diameter (d)(b) SEM image of core microstructure for suction-cast rod in 2 mm diameter (c) SEM image of the cross section of melt-spun alloy ribbon (d) SEM image of core microstructure of melt-spun alloy ribbon(e) average diameter and the volume fraction of the Ce-Cu-rich particles vs radial position of the rod (r) in Fig.3a(f) XRD spectra of the suction-cast rod and ribbon
Fig.4 XRD spectra of melt-spun ribbons of No.2~No.8 alloys
Fig.5 DTA heating traces for No.3, No.5 and No.8 alloys at rate of 10 K/min
Fig.6 Microstructures of Zr-Co-rich region (a) and Ce-Cu-rich region (b) originated from the liquid-liquid phase separation of No.8 alloy under the normal solidification
Fig.7 Microstructures of Zr-Co-rich region produced from the liquid-liquid phase separation of No.3 (a) and No.5 (b) alloys
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