The Research On The Crystallization And Crystal Dynamics Of Zr₆₅Cu_27.5Al_7.5 Block Amorphous Alloy

Ternary Zr₆₅Cu_27.5Al_7.5 alloys were prepared with different raw materials, and the Zr-based amorphous ribbons with different oxygen concentration were prepared with the melt-spinning method. Based on the construction of time-temperature-transformation diagrams by isothermal DSC measurements, the isothermal stability of the Zr₆₅Cu_27.5Al_7.5 glassy alloy with oxygen-induced I-phase precipitation was compared with that of the same base alloy without I-phase precipitation. The changing tendencies of the thermal stability were validated by XRD analyses and TEM observations. It was found that although oxygen promotes the precipitation of I-phase, retards the formation of stable b.c.t.-Zr2Cu phase in the glassy alloy. If the main-crystallization event for b.c.t.-Zr₂Cu is taken as thermal stability criterion, it was revealed that the higher oxygen-containing alloy with oxygen-induced I-phase precipitation has longer onset time for crystallization within a rather large supercooled temperature range. The crystallization kinetic characteristics of oxygen-induced I-phase and b.c.t.-Zr2Cu phase in the glassy alloy are discussed. The possibility for the preparation of Zr₆₅Cu_27.5Al_7.5 glassy alloy-based composite containing oxygen-induced I-phase is also forecasted.To study the casting atmosphere pressure to form ability and the mechanical properties influence to these two kind of Zr₆₅Cu_27.5Al_7.5 alloy glass , a series of cylindrical rod samples for the Zr₆₅Cu_27.5Al_7.5 alloy containing 0.68 at % oxygen and containing 0.06 at % oxygen was prepared by arc-remelting and Cu-mold casting under different atmosphere pressures. The results show that: increased atmosphere pressure can significantly improve the alloy glass-forming ability and improve the mechanical properties of alloys,to To oxygen-induced I-phase precipitation as a first phase in Zr₆₅Cu_27.5Al_7.5 alloy.The sensitive'pressure-retarding effect'during casting on oxygen-induced icosahedral phase precipitation provides a new method to improve the GFA of the Zr-based alloy with high oxygen impurity content. Contrariwise when casting atmosphere pressure change on the KPa pressure,the alloy melting glass-forming ability will perform of a sensitive response to the pressure of lower or higher and will have glass-forming ability decreased.with micro- mechanism of casting atmosphere pressure changing and the structure of oxygen-induced I-phase precipitation, the alloy melting glass-forming ability will change .Under low smelting atmosphere pressure, superfine nanometer size f.c.c. - The Zr₂Cu separation may enable the alloy to have the good plastic deformation ability.