鐵矽合金一直以來都是廣為討論之鐵基合金，而矽鋼片則是鐵矽合金主要的應用，在不同之使用狀況會使用不同矽量，高矽量之鐵矽合金具有高電阻(80μΩ-cm)以及高相對導磁率(2.8*104)等優異之磁性質，但因為其較差之加工性，較難使用傳統滾軋加工成矽鋼片，商業化之高矽矽鋼片多使用純鐵片或是低矽矽鋼片再加上化學氣象沉積法將矽擴散至矽鋼片內，製成昂貴，且容易有成分均勻性之問題。本篇論文嘗試使用已經先預合金之Fe-6.5Si球型粉末加上有別一般傳統之雷射積層製程，製備出Fe-6.5Si合金塊材。本實驗先以thermo-calc計算合金融點作為熔煉參數的參考，透過雙氣體霧化製程製備高矽鐵合金之粉末，利用此製程能得到球型且成分均勻之合金粉末。在本實驗中，將在雷射積層製程的過程中調整氧含量，在材料表面創造出絕緣層結構。本實驗將討不同雷射參數、氧化時掃描次數對相比例、晶粒尺寸、孔隙率及殘留應力之影響，在針對這些結果探討其對磁性質之影響。

Study of Magnetic Properties of silicon steel Composite Synthesized by Dual-Jet Atomization and Additive Manufacturing
De-Hau Tseng
Chi-Yuan A. Tsao
Department of Material Science and Engineering, National Cheng Kung University, Tainan City 701, Taiwan(R.O.C)

SUMMARY
In this study, Fe-6.5wt.% Si prealloyed powders were prepared by Dual-jet atomization process to prepare fully alloyed iron-based metal spherical powders , The RSAed powder is pre-alloyed and thus has more uniform homogeneity. The effects of various laser power, scanning rate and segregation on the phase ratio, magnetic properties, microstructures, density, and mechanical property of SLM Fe-6.5wt. %Si bulks were investigated.

INTRODUCTION

Magnetic materials play an important role in our life, due to energy saving and environmental protection. Soft magnetic materials is often studied in the field, because the soft magnetic materials often used in the core material, and under the alternating current Such as transformers, generators, motors, etc., where often use of silicon steel material, mainly because the silicon can increase the resistance and reduce the coercive force to reduce energy loss.
Reducing the spacing of insulating layer which is to reduce the thickness of silicon steel sheet can mainly reduce the eddy current loss. The current commercial specifications of the largest silicon steel sheet thickness of 0.37mm, special specifications of the silicon steel sheet thickness of 0.1mm, while the increase in resistance is by The magnetization of Fe-6.5Si alloy has a relatively high relative permeability (2.8 * 104), and the magnetic properties of the Fe-6.5Si alloy have a relatively high relative magnetic permeability (2.8 * 104) High resistance (80μΩ-cm), high saturation magnetic flux density (1.8T), relatively low iron loss (> 0.77W / kg, 0.35mm, 1T, 60Hz)[1] , But because of its poor workability, the application is limited

MATERIALS AND METHODS
Material
Fe-6.5wt. %Si pre-alloyed powders was synthesized by rapid-solidifying atomization
Selective laser melting process
These two powders were than consolidated into bulks of 7 mm Cylindrical and 4 mm height by selective laser melting (SLM) with different laser powers(150 to 180W) and scanning rates(650, 750, 850, 950 mm/s).

RESULTS AND DISCUSSION

Microstructure analysis
Fig.1 Fe-6.5 Si Fe - 6.5 Si laser fusion. Can be observed inside the main two main defects, the first is a circular hole. The second is a crack, It can be observed the more to the border, The number of gradually increased, because the cooling rate is faster, stir into the gas too late to escape the material inside. In the laser input energy, the pool of agitation is more intense, more gas will be inserted into the material to form pores, resulting in a significant increase in porosity. The other can be observed 180W, 750mm / s and 170W, 850mm / s these two parameters of the cracks caused by the sudden increase in the porosity of the substrate surface with varying degrees of oxidation, it can result of different heating conditions, and these two parameters just in the low heating area, so there may be a large-scale cracks.

It can be found that the internal grain of the material is the type of casting crystal, the direction is towards the BD (build direction), this phenomenon can be seen as Epitaxy (Epitaxy), the direction of the material according to the substrate grain Direction of growth, casting materials to form columnar crystal elements, SLM process also meet the necessary conditions, the necessary conditions are as follows
1. The direction of the single heat flow, the main heat flow direction for the BD direction (guide plot board), SD direction of the heat flow is very small, because the thermal diffusion coefficient between each powder than the bulk of the thermal diffusion coefficient to small, so the column The growth direction of the crystal is BD direction.
2. Each layer of the process of metal melting soup has a high overheating temperature, inhibit the equiaxed zone (Equiaxed zone) formation.
3. The experimental results show that the agitation inside the pool is not enough to interrupt the columnar crystals, providing heterogeneous nucleation sites to form equiaxed crystal regions.

Phase analysis
Figure 2 Fe-Si ingot block and pre-alloy powder XRD pattern, in the part of the ingot block, because the cooling rate is slow, so there is the DO3 order phase generation, as shown in Table 6, about 11.7 wt% While the pre-alloy powder is due to the faster cooling rate, only the presence of Alpha-Fe.

CONCULUSION

With the higher the laser power, the higher the scanning rate, the higher the amount of silicon.phase analysis, Order phase DO3 mostly in the laser scanning rate 650mm / s and 750mm / s found, because the order phase requires a slower cooling rate to form
coercivity, DO3 phase, grain size and porosity are positively correlated with negative stress. Saturation magnetization of the part, did not find the saturation magnetic quantization with the laser parameters have a relationship

1. Stoimenov, S., NEW MAGNETIC MATERIALS, in Geomagnetics for Aeronautical Safety: A Case Study in and around the Balkans, J.L. Rasson and T. Delipetrov, Editors. 2006, Springer Netherlands: Dordrecht. p. 187-199.
2. Haiji, H., et al., Magnetic properties and workability of 6.5% Si steel sheet. Journal of Magnetism and Magnetic Materials, 1996. 160: p. 109-114.
3. Tian, G. and X. Bi, Fabrication and magnetic properties of Fe–6.5% Si alloys by magnetron sputtering method. Journal of Alloys and Compounds, 2010. 502(1): p. 1-4.
4. Yang, S.C.a.C., Rapidly Solidified Fe-6.5Siwt% Si Alloy Powders for High Frequency Use. Journal of Magnetics 1997: p. 12~15.
5. Kenji Narita, M.K., Effect of Ordering on Magnetic Properties of 6.5 percent silicon-iron alloy. IEE Proceedings A (Physical Science, Measurement and Instrumentation, Management and Education), 1979: p. 911-915.
6. Shokrollahi, H. and K. Janghorban, Soft magnetic composite materials (SMCs). Journal of Materials Processing Technology, 2007. 189(1–3): p. 1-12.
7. He, B., et al., Effect of Oxidation Temperature on the Oxidation Process of Silicon-Containing Steel. Metals, 2016. 6(6): p. 137.
8. Adachi, T. and G.H. Meier, Oxidation of iron-silicon alloys. Oxidation of Metals, 1987. 27(5): p. 347-366.
9. Takeda, M., et al., Physical Properties of Iron-Oxide Scales on Si-Containing Steels at High Temperature. MATERIALS TRANSACTIONS, 2009. 50(9): p. 2242-2246.
10. Lee, Y., A.J. Bevolo, and D.W. Lynch, Studies of the initial oxidation of Fe-Si alloys by AES, XPS and EELS. Surface Science, 1987. 188(1): p. 267-286.
11. Yamanaka, T., H. Shimazu, and K. Ota, Electric conductivity of Fe2SiO4–Fe3O4 spinel solid solutions. Physics and Chemistry of Minerals, 2001. 28(2): p. 110-118.
12. Bowen, H.K., D. Adler, and B.H. Auker, Electrical and optical properties of FeO. Journal of Solid State Chemistry, 1975. 12(3): p. 355-359.
13. Tadić, M., et al., Synthesis, morphology, microstructure and magnetic properties of hematite submicron particles. Journal of Alloys and Compounds, 2011. 509(28): p. 7639-7644.
14. Song, E.-J., High Temperature Oxidation of Si-Containing Steel. 2011.
15. Christodoulides, J.A., et al., Effect of Preparation Conditions on the Structural and Magnetic Properties of Granular Fe-SiO2, in Magnetic Hysteresis in Novel Magnetic Materials, G.C. Hadjipanayis, Editor. 1997, Springer Netherlands: Dordrecht. p. 321-325.
16. Lima, M.S.F.d., et al., Mechanical and Corrosion Properties of a Duplex Steel Welded using Micro-Arc or Laser. Materials Research, 2015. 18: p. 723-731.
17. R.K. Roy, M.G., A.K. Panda, R.N. Ghosh and A.Mitra, Development of rapidly solidfied 6.5 wt% silicon steel for magnetic applications. Transactions of The Indian Institute of Metals, 2010. 63(4): p. 745~750.
18. BOZORTH, R.M., Ferromagnetism. IEEE Transactions on Magnetics, 1993.
19. BUSCHOW, K.H.J., Handbook of Magnetic Materials. 1997. 10.
20. Gu, D., Laser Additive Manufacturing of High-Performance Materials. 2015.
21. Foroozmehr, A., et al., Finite Element Simulation of Selective Laser Melting process considering Optical Penetration Depth of laser in powder bed. Materials & Design, 2016. 89: p. 255-263.
22. Roberts, I.A., INVESTIGATION OF RESIDUAL STRESSES IN THE LASER MELTING OF METAL POWDERS IN ADDITIVE LAYER MANUFACTURING. 2012.
23. Yadroitsev, I., P. Bertrand, and I. Smurov, Parametric analysis of the selective laser melting process. Applied Surface Science, 2007. 253(19): p. 8064-8069.
24. N. Baba, I.W., Penetration Depth into Dental Casting Alloys by Nd:YAG Laser. 2004.