| Summary: | 碩士 === 義守大學 === 材料科學與工程學系碩士班 === 95 === Since rare earth metal such as Y and Gd needs amount of oxygen in melting process, it consumes a lot of oxygen in the chamber to produce rare earth oxide. Amorphous alloy would be formed easily due to the reduction of oxygen quantity. The effect of Gd substitution for Y on glass forming ability, thermal property and mechanical property is studied by adding Gd in ternary amorphous alloy, Mg-Cu-Y, to form quaternary Mg58Cu31Y11-XGdX (X=0、6、8、11).
Bulk metallic glass rods with varying diameters from 3mm to 6mm were successfully produced by injection casting. Structural analysis was performed by X-ray diffraction (XRD) experiment and the patterns of Mg58Cu31Y11-xGdx (X=0、11) show both shrap diffraction peak reflecting the presence of some crystalline phases and broad diffraction peak which is a characteristic of amorphous structure. JCPDS card comparison indicates that it is Mg2Cu crystal. The patterns of Mg58Cu31Y11-xGdx (X=6、8) show broad diffraction peak.
Among Mg58Cu31Y11-xGdx (X=0、6、8、11) amorphous alloy series, the Mg58Cu31Y5Gd6 and Mg58Cu31Y3Gd8 has the best glass forming ability. It shows that adding Gd can improve glass forming ability. Moreover, adding Gd appropriately can increase the nucleation point up to 19% and nucleation point of Mg58Cu31Y5Gd6 amorphous alloy can achieve 68. Incubation time of Mg58Cu31Y5Gd6 amorphous alloy would be 234s longer than Mg58Cu31Y11 at 451K,. Since nucleation point and incubation time can be increased by increasing Gd content appropriately, thermal stability of amorphous alloy can be raised with partial substitution of Y by Gd.
In mechanical property, Mg58Cu31Y3Gd8 amorphous alloy has the best fracture toughness and it is about double of the traditional Mg alloy AZ91 with strength147 MPa．cm3/g. The elastic limit of Mg58Cu31Y3Gd8 is also the best. Having pop-in in nanoidenation experiment and observing many nano-scale striation pattern and vein pattern by SEM show that Mg58Cu31Y３Gd８ amorphous alloy has the property of plastic deformation.
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