本研究利用快速凝固霧化製程製備Fe–30wt.%Ni預合金粉末，製備出完全合金化之鐵鎳基金屬圓球形粉末，以及純鐵粉末與純鎳粉末混合之不規則形狀元素混合粉末，將此兩種粉末搭配雷射積層製程製備融結體塊材，並探討兩者之相互關係。
本研究探討鐵鎳混合粉末及鐵鎳預合金粉末搭配雷射積層製程中，改變雷射掃描速率及雷射功率與相比例、晶粒尺寸、孔隙率及殘留應變之間的關係；並依照相比例、晶粒尺寸、孔隙率及殘留應變探討其與飽和磁化量及矯頑力之間的關係。

Study of magnetic properties of magnetic components produced by 3D laser Additive Manufacturing with Dual-Jet atomized Fe-Ni powder
Li-Kun Ho
Chi-Yuan A. Tsao
Department of Material Science and Engineering, National Cheng Kung University, Tainan City 701, Taiwan(R.O.C)

SUMMARY
Fe-30wt. %Ni pre-alloyed powders was synthesized by rapid-solidifying atomization(RSA) and Fe-30wt.%Ni mixed element powders was prepared by pure iron powders and pure nickel powders by v-blender. These two powders were than consolidated into bulks of 7 mm square and 4 mm height by selective laser melting (SLM) with different laser powers and scanning rates. The RSAed powder is pre-alloyed and thus has more uniform homogeneity on consolidated bulks compare to mixed powder. The effects of various laser power, scanning rate and segregation on the phase ratio, magnetic properties, microstructures, density, and mechanical property of SLM Fe-30wt. %Ni bulks were investigated.
Keywords：Fe-30wt.%Ni, Rapid-Solidifying Atomization, Selective Laser Melting(SLM), Soft Magnet

INTRODUCTION
Fe-Ni alloys have been widely used in the engineering application, because of their high saturation magnetization, low coercivity, corrosion resistance and good process ability. However, the traditional production of Fe-Ni alloy by casting will cause collision with the mold thus produce additional dislocation and stress field. It will increase the hysteresis loss and coercivity and need to be further heat treatment to eliminate the internal stress and dislocation in order to improve its magnetic properties, but it will increase the cost.
In recent years, the selective laser melting process has been used to prepare a variety of alloys, the laser lumping process for a rapid manufacture of complex shapes and maintain the mechanical properties of the process. It can be used by the 3D-CAD volume model to create a complex shape of the product directly, no need for special parts for post-processing. During the process, the material will not collision with the mold and thus produce additional stress and dislocation. Resulting in a decrease in magnetic properties. The above characteristics can effectively solve the problems encountered in the preparation of complex Fe-Ni alloy, with adjustable laser power and scanning rate, in order to control its macrostructure and microstructure and further control its magnetic properties.

MATERIALS AND METHODS
Material
Fe-30wt. %Ni pre-alloyed powders was synthesized by rapid-solidifying atomization(RSA) and Fe-30wt.%Ni mixed element powders was prepared by pure iron powders and pure nickel powders by v-blender.
Selective laser melting process
These two powders were than consolidated into bulks of 7 mm square and 4 mm height by selective laser melting (SLM) with different laser powers and scanning rates.

RESULTS AND DISCUSSION
The SLMed bulk with Fe-30wt.% Ni prealloyed powder
In the microstructure, there are many shrinkage holes in 850 mm / s, but when the scanning rate is increased to 950 mm / s, the shrinkage holes is reduced. 180 W compared to 150 W, because the scanning rate is the same but the effective energy is relatively high, so the cooling rate is relatively slow, no shrinkage formation. Above 850 mm / s, the cooling rate is too fast, resulting in the formation of shrinkage, but the size and number of shrinkage and scanning rate is not directly related. SEM images show that the crystal grains exhibit equiaxed crystal morphology and the grain size is about 0.7 ~ 1μm.
In the phase analysis, the ratio of Fe3Ni2 phase and FeNi phase increases with the increase of scanning rate. The ratio of FeNi3 phase decreases with the increase of scanning rate and maintain at 750 mm / s. At 150 W, the ratio of Fe7Ni3 phase decreases slightly with the increase of the scanning rate and is not generated at 850 mm / s, and no Fe7Ni3 phase is generated at the laser power of 180 W.
In the magnetic property, the higher the ratio of Fe3Ni2 phase and FeNi phase, the higher the saturation magnetization is. The ratio of Fe7Ni3 phase can’t determine the relationship with the saturation magnetization.
The SLMed bulk with Fe/30Ni mixed powder
In the component analysis, it is observed that the composition ratio is mixed by ratio Fe-30wt.% Ni, but two kinds of powder is relatively moved due to the addition into the powder supply tank and the scraper, thereby causing different components.
In the microstructure, it is observed that there is a shrinkage in the interior, and the higher the scanning rate is, the more the shrinkage number is. In the shrinkage size, 180 W is smaller than 150 W because the scanning rate is the same but the effective energy is high, the cooling rate is slower. SEM images show that the crystal grains exhibit equiaxed crystal morphology and the grain size is about 0.5 ~ 1.2μm.
In the phase analysis, the metastable phase, the Fe0.916Ni0.084 phase, Fe0.64Ni0.36 phase and γ-Fe phase are found. Also, the phase of the original powder, the α-Fe phase and Ni phase are found. The observed ratio of Fe3Ni2 phase and α-Fe phase increases with increasing scanning rate. The ratio of FeNi phase, Ni phase and Fe0.64Ni0.36 phase decreases with the increase of scanning rate, and the Ni phase and Fe0.64Ni0.36 are not generated at 850 mm / s. The ratio of Fe7Ni3 phase, Fe0.916Ni0.084 phase and γ-Fe phase are lack of data, so the relative relationship with the scanning rate can’t be determined.
In the magnetic property, the more the FeNi phase and the α-Fe phase, the higher the saturation magnetization is. The Fe0.64Ni0.36 phase, the non-magnetic γ-Fe phase and the low saturation magnetization Ni phase, the lower the saturation magnetization is. The Fe7Ni3 phase and the Fe0 .916Ni0.084 phase due to lack of data can’t determine the relationship between saturation magnetization. And because the α-Fe phase with a high saturation magnetization phase exists, the saturation magnetization of the Fe/30Ni SLMed bulk are all greater than Fe-30wt.% Ni SLMed bulk.

CONCULUSION
In the Fe/30Ni SLMed bulk, although the composition because two kinds of powder is relatively moved thereby causing different components, but there are have α-Fe phase with a high saturation magnetization phase exist, the saturation magnetization of the Fe/30Ni SLMed bulk are all greater than Fe-30wt.% Ni SLMed bulk.

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