Research On The Preparation And Properties Of High Bs Fe-based Nanocrystalline Soft Material

Nanocrystalline Fe_82.65Cu_1.35Si₂B₁₄ alloy is one of high Bs soft magnetic materials which have great potential in future. However, compared with the traditional nanocrystalline soft materials, this alloy has some disadvantages including low temperature difference between the first and second crystallization temperature(ΔT_x), large grain size, low Curie temperature(Tc) of amorphous phase. Moreover, there are few reports on the processing parameters of this alloy. In this thesis, the efforts aimed to solve above problems are as follows:(1) The effect of the ejection temperature (1200, 1300, 1400℃) on the melt-spun structure and properties was investigated keeping roller speed at 50m/s. Moreover, the effect of roller speed (50, 40, 30, 25 m/s) on the structure and properties of melt-spun and annealed state was studied keeping ejection temperature at 1200℃. The results showed that melt-spun structure has little effects on the final magnetic properties.(2) The crystallization temperature (Tx) of Fe_82.65Cu_1.35Si₂B₁₄ alloy is lower than Fe₈₄Si₂B₁₄ alloy because the former one has lower crystallization activation energy which is calculated by Kissinger method. This result indicates that the element Cu promotes crystallization process and decreases coercive force (Hc). Besides, effect of 1at% substitution of Fe by refractory metals (Nb, Zr, Ta) on structure and properties was studied. It was shown that the addition of Zr has increased ? Tx from 90℃to 155.2℃. Additionally, these elements can also reduce grain size. The addition of Ta can keep the grain size below 30nm until 450℃.The alloy with Zr addition has the best thermal stability which has good soft magnetic properties even at 500℃.(3) The effects of partial replacement of Fe with Co in the (Fe_1-xCo_x)_82.65Cu_1.35Si₂B₁₄ alloys(x=0, 0.3, 0.5, 0.7) on the structure and magnetic properties have been investigaged.It was found that increasing Co content can reduce T_x1 and Ms but increase Hc and Tc of amorphous phase. The alloy for x=0.5 has the best thermal stability which has low Hc even at 550℃.