The spheroidization behavior of the dendritic b.c.c. phase dispersed in a bulk metallic glass (BMG) matrix was investigated through applying semi-solid isothermal processing and a subsequent rapid quenching procedure ...The spheroidization behavior of the dendritic b.c.c. phase dispersed in a bulk metallic glass (BMG) matrix was investigated through applying semi-solid isothermal processing and a subsequent rapid quenching procedure to a Zr-based β-phase composite. The Zr-based composite with the composition of Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 was prefabricated by a water-cooled copper mold-casting method and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the composite consists of a glassy matrix and uniformly distributed fine dendrites of the β-Zr solid solution with the body-centered-cubic (b.c.c.) structure. Based on the differential scanning calorimeter (DSC) examination results, and in view of the b.c.c. β-Zr to h.c.p. α-Zr phase transition temperature, a semi-solid holding temperature of 900℃ was determined. After reheating the prefabricated composite to the semi-solid temperature, followed by an isothermal holding process at this temperature for 5 min, and then quenching the semi-solid mixture into iced-water; the two-phase microstructure composed of a BMG matrix and uniformly dispersed spherical b.c.c. β-Zr particles with a high degree of sphericity was achieved. The present spheroidization transition is a thermodynamically autonomic behavior, and essentially a diffusion process controlled by kinetic factors; and the formation of the BMG matrix should be attributed to the rapid quenching of the semi-solid mixture as well as the large glass-forming ability of the remaining melt in the semi-solid mixture.展开更多
基金supported by the Natural Science Research Projects of The Education Department of Henan Province,China(Grant No.2008A430010)the R&D start-up projects of high-level talents of North China University of Water Resources and Electric Power(Grant No.200709)
文摘The spheroidization behavior of the dendritic b.c.c. phase dispersed in a bulk metallic glass (BMG) matrix was investigated through applying semi-solid isothermal processing and a subsequent rapid quenching procedure to a Zr-based β-phase composite. The Zr-based composite with the composition of Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 was prefabricated by a water-cooled copper mold-casting method and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the composite consists of a glassy matrix and uniformly distributed fine dendrites of the β-Zr solid solution with the body-centered-cubic (b.c.c.) structure. Based on the differential scanning calorimeter (DSC) examination results, and in view of the b.c.c. β-Zr to h.c.p. α-Zr phase transition temperature, a semi-solid holding temperature of 900℃ was determined. After reheating the prefabricated composite to the semi-solid temperature, followed by an isothermal holding process at this temperature for 5 min, and then quenching the semi-solid mixture into iced-water; the two-phase microstructure composed of a BMG matrix and uniformly dispersed spherical b.c.c. β-Zr particles with a high degree of sphericity was achieved. The present spheroidization transition is a thermodynamically autonomic behavior, and essentially a diffusion process controlled by kinetic factors; and the formation of the BMG matrix should be attributed to the rapid quenching of the semi-solid mixture as well as the large glass-forming ability of the remaining melt in the semi-solid mixture.
