- 學位論文
鐵基塊狀非晶及塊狀奈米晶軟磁合金
Fe-Based Bulk Amorphous and Bulk Nanocrystalline Soft Magnetic Alloys
並列摘要
This work focused on the development and study of Fe-based soft magnetic bulk metallic glasses (BMGs) and a strategy to produce bulk nanocrystalline alloys (BNCAs). Ternary Fe-based bulk metallic glasses were for the first time in the world developed. The BMG research contains two parts: (1) Ternary Fe-R-B (R= Sc, Y, Dy, Ho and Er). (2) Quaternary, Fe-(Co or Ni)-Y-B and Fe-Y-(Nb or Ta)-B BMG systems. Thermal properties, glass forming ability and magnetic properties were investigated. Ternary Fe-based BMGs represented by the formulae FeaMbBc are based on two simple selection rules: (1) M is an element with atomic radius at least 130% that of Fe; (2) M possesses an eutectic point with Fe and the M-Fe eutectic is at the Fe-rich end. The M elements, Sc, Y, Dy, Ho and Er fulfill the two rules exhibit BMG capability at the wide composition range, in atomic %, 3 < b < 10, 18< c < 27, whereas a+b+c = 100. It is much remarkable that bulk amorphous state is achievable with only 3 elements (conventional ones 4 to 7 elements). The ternary BMGs thus developed are characteristic of high saturation magnetization 1.2 to 1.56 T, low coercivity less than 40 A/m, and high electrical resistivity, larger than 200 microphm-cm. Among the explored ternary BMGs, Fe-Y-B alloys show the highest saturation magnetization 1.56 T. The properties of subsequently modified Fe-Y-B by Co, Ni and other transition metal (Nb and Ta) were also investigated. It shows a wide composition range retaining the BMG capability while replacing Fe by Co or Ni revealing a great advantage in modifying the magnetic properties to suit various industrial applications. The partial replacement of Y by Nb or Ta greatly improves the GFA and also retains the soft magnetic properties. The reduction of Y content to decrease the high chemical reactivity to improve industrial production is achieved. The Fe-Y-Nb-B and Fe-Y-Ta-B BMG exhibits extreme high compressive strength above 4000 MPa. New bulk nanocrystalline alloys were successfully achieved in Fe-Y-Nb-Cu-B, Fe-Si-B-Nb and Cu-Zr-Al alloy systems according to proposed “crystallization-and stop” model including (1) there is at least one principal element (PE) that dominates the crystallization temperature (Tx) and the Tx increases steeply with PE concentration, (2) the PE is barely soluble in the primary crystallites so that they pile up around the crystallizing nano-grains hence the Tx is manifestly increased locally, (3) once the increased Tx is higher than the raised sample temperature (due to heat of crystallization), the crystallization will be stopped to maintain a nano-grain structure, and (4) a nucleation agent is much helpful to enhance nucleation frequency hence reduce the resultant nano-sizes. The development of this model unveils a simpler and more practical way to design an alloy which can achieve bulk nanocrystallization.