| Summary: | 碩士 === 國立中正大學 === 物理學系暨研究所 === 102 === The effect of the composition on the glass forming ability (GFA) and magnetic properties of the Fe76-xP8.7C7.0B5Si3.3Mx (M = B, C and Si; x = 0-5) bulk metallic glass has been studied. By adding 1% Si to the alloy, the GFA was increased. On the other hand, the GFA and magnetic properties were not enhanced with the addition of the B and C elements. Among the studied alloys, Fe75P8.7C7.0B5Si3.3Si4.3 sample shows the best GFA due to its widely supercooled liquid region ΔTx = 24 K and relatively high reduced glass transition temperature Trg = 0.62. In addition, bulk metallic glass (BMG) with cylindrical shape as large as 3 mm in diameter can be obtained in Fe75P8.7C7.0B5Si4.3 alloy. Furthermore, the effect of external magnetic field on the microstructure and magnetic properties of directly cast FePCBSi alloys were also studied. For bulk sample with 2 mm in thickness, the grain size was refined from 10-20 nm to 2-4 nm with increasing the applied magnetic field from 0 kOe to 3 kOe. It implied that the effect of external magnetic field could change the free energy of the critical nucleus size, leading to the improved GFA. On the other hand, the Hc of the samples without and with 2 kOe applied magnetic field is 682 A/m and 159 A/m, respectively. The enhancement of Hc also verifies the grain size refinement by an additional magnetic field. However, when the external magnetic field increased up to 3 kOe, the enhancemant of Hc is almost identical to that with 2 kOe. It shows that the effect of magnetic field on grain refinement size has a limit at 2 kOe. Meanwhile, the resistivity increased from 175 to 350 Ω-cm as the external magnetic field increasing from 0 to 2 kOe. This phenomenon is also arisen from the field-induced grain refinement.
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