Structure, Microstructure, Hyperfine, Mechanical and Magnetic Behavior of Selective Laser Melted Fe92.4Si3.1B4.5 Alloy
and Jean-Marc Greneche 5
Round 1
Reviewer 1 Report
This article presents the structure, mechanical and magnetic properties of SLM’d alloy.
Abstract: The authors need to state what is new in this work. The novelty or the new item reported in this work is unclear.
Introduction: The authors need to state how all the properties investigated in this paper affect alloy printing etc. For, eg, how does roughness affect the magnetic properties etc?
Section 3.5: The authors measure roughness using AFM profilometer. Both profile and AFM roughness should be reported. There are several challenges to measuring roughness using a profilometer and AFM. The authors should state this in the introduction by referring to articles recently published on this topic. For eg, https://doi.org/10.3390/app11115089
The authors should state what ASTM/ISO/BSI standards they followed for the characterization of each property.
Conclusion: Needs to be rewritten with how this SLM technique and printing parameters can help in actual application after this characterization.
Author Response
This article presents the structure, mechanical and magnetic properties of SLM’d alloy.
Abstract: The authors need to state what is new in this work. The novelty or the new item reported in this work is unclear.
Answer: We modify the abstract. The novelty is linked to the study of the effect of laser power on the phase formation, microstructure, morphology, mechanical, hyperfine and magnetic properties. Besides, the SLM process induces the formation of a disordered ε-FeSi type structure.
“Disordered ε-FeSi type structure was induced by selective laser melting in Fe92.4Si3.1B4.5 powder alloys fabricated with different laser powers at a laser scanning speed of 0.4 m/s. The phase formation, microstructure, roughness, microhardness, hyperfine and magnetic properties were studied using X-ray diffraction, scanning electron microscopy, atomic force microscopy, profilometer, microdurometer, transmission 57Fe Mössbauer spectrometry and vibrating sample magnetometry. The aim of this work is therefore to study the effect of laser power on the phase formation, microstructure, morphology, mechanical, hyperfine and magnetic properties. XRD patterns reveal the coexistence of a bcc α-Fe0.95Si0.05, a tetragonal Fe2B boride phase and a disordered ε-FeSi type structure. The existence of the disorder is confirmed by the presence of different FeSi environments observed in the Mössbauer spectra. The Fe2B boride contains about 51-54% of Fe atoms. The porosity and roughness decrease with increasing laser power. The sample produced with a laser power of 90 W has a smooth and dense surface, high microhardness (~1843 Hv) and soft magnetic properties (saturation magnetization Ms=200 emu/g and coercivity Hc=79 Oe).”
Introduction: The authors need to state how all the properties investigated in this paper affect alloy printing etc. For, eg, how does roughness affect the magnetic properties etc?
Answer: We modify the Introduction section. The magnetic behaviour is influenced by the phase formation and the density of the samples. Thus, all properties are related.
“SLM, as one of the layer additive manufacturing (AM) processes and rising 3D technologies, has received much attention due to its ability to build full density high precision and high performance metal parts, and fabricate various components of materials from powdered alloys and build parts with complex lattice structures particularly suitable for magnetic losses in electrical engineering [19, 20]. However, one of the challenges in SLM is the manufacturing of overhanging surfaces, defined as the bottom or downward facing surfaces of an object built on top of an underlying free powder material rather than a solidified material [21]. Many parameters such as powder surface quality, evaporation of elements, trapped gases, reduced solubility of dissolved elements in the melt pool during cooling and solidification can lead to the fabrication of almost full dense (98–99%) 3D objects [22] in order to improve magnetic response of bulk specimens.”
Section 3.5: The authors measure roughness using AFM profilometer. Both profile and AFM roughness should be reported. There are several challenges to measuring roughness using a profilometer and AFM. The authors should state this in the introduction by referring to articles recently published on this topic. For eg, https://doi.org/10.3390/app11115089
Answer: The data are reported I the manuscript and also in figures 9 and 10. Experiments are not performed in our labs, but standard procedures were followed. Regarding additional reference, we add the reference you suggest us as reference 21.
The authors should state what ASTM/ISO/BSI standards they followed for the characterization of each property.
Answer: We add additional information about standards in the manuscript.
(ISO 4288-section 7 for profile and ISO-25178-2 for areal surface texture)
Additional information about printing parameters is also given in the Materials and Methods section.
“An Ytterbium fiber laser source with a maximum theoretical power output of 120 W and a wavelength of 1064 μm was used. The laser focus beam has a diameter of 34 μm. The building chamber dimension is 25 × 25 × 25 cm. The vacuum atmosphere is controlled by a combination of a primary pump and a Roots system, providing an even and accurate vacuum level, reaching a minimum pressure of 10? 3 mbar. The machine was filled with a shielding gas during all experiments to remove smoke and maintain a stable pressure. The chamber was purged of residual oxygen below 0.1% to avoid oxidation. The obtained samples were sliced horizontally into several thin layers of two-dimensional images using a YLR-100-SM single mode CW Ytterbium fiber laser beam (1064-1100 nm). A set of 3D 5x5x5 mm cubic parts was prepared under argon atmosphere using different laser powers (50, 70, 90 and 110 W), laser scanning speed of 0.4 m/s, laser beam diameter of 34 mm, scan line spacing of 40 mm and powder layer thickness of 50 mm. The samples produced at 50, 70, 90 and 110 W are named hereafter P50, P70, P90 and P110, respectively.”
Conclusion: Needs to be rewritten with how this SLM technique and printing parameters can help in actual application after this characterization.
Answer: We modify the Conclusions section.
Fe92.4Si3.1B4.5 samples were prepared by the SLM method using different laser powers at a constant laser scanning speed of 0.4 m/s. The obtained results are summarized as follows:
- A disordered a-FeSi type structure is induced by SLM technology.
- The α-Fe95Si0.05 and Fe2B boride phases are retained from the feedstock powder with small variations in the lattice parameters.
- The crystallite size of both α-Fe95Si0.05 and Fe2B boride decreases with increasing the laser power.
- Mössbauer spectrometry results confirm the presence of Fe2B and a disordered FeSi-type structure.
- Almost completely dense samples could be obtained and their roughness and porosity decrease with increasing laser power.
- The selectively laser melted samples exhibit high microhardness values in the range of 1364-1843 Hv, and soft magnetic properties with Ms=188-201 emu/g and Hc= 70-83 Oe. Higher Ms and microhardness values are obtained for the P90
Furthermore, we modify several sentences taking into account the editor comments.
Reviewer 2 Report
In this paper, Fe92.4Si3.1B4.5 alloys was produced with different laser powers. Furthermore, the effect of the laser power on the phase formation, microstructure, and so on were investigated using several characterization techniques. The above results had important value for the study of partially or fully amorphous FeSiB alloys. It is recommended to accept after minor revision. The suggestions are as follows.
1、 It is recommended to add subtitles to the two figures in Figure 1.
2、 The X-axis of Figure 3(a) has no title.
3、 Please check the formatting of the tables in the text carefully, such as Table 3, Table 4.
4、 Please improve the picture quality, such as Figure 9.
Author Response
Reviewer 2:
In this paper, Fe92.4Si3.1B4.5 alloys was produced with different laser powers. Furthermore, the effect of the laser power on the phase formation, microstructure, and so on were investigated using several characterization techniques. The above results had important value for the study of partially or fully amorphous FeSiB alloys. It is recommended to accept after minor revision. The suggestions are as follows.
1、 It is recommended to add subtitles to the two figures in Figure 1.
Answer: We remark both figures in the figure 1 caption.
Figure 1. SEM micrograph (left) and particle size distribution (right) of the feedstock powders.
2、 The X-axis of Figure 3(a) has no title.
Answer: We agree this comment. We modify figure 3. The title of the X-axis is : 2 Theta [degrees]
3、 Please check the formatting of the tables in the text carefully, such as Table 3, Table 4.
Answer: The format of tables 3 and 4 has been modified.
4、 Please improve the picture quality, such as Figure 9.
Answer: It was difficult to improve figures quality, because sometimes we have only the images. In the case of figure 9 we increase the size to be more easy to see the details.
Furthermore, we modify several sentences taking into account the editor comments.
Reviewer 3 Report
This work is concern with the manufacturing of the Fe92.4Si3.1B4.5 alloy samples with laser 3D printer. This work is interesting and has high scientific merit. The study is in the scope of Metals MDPI.
However, there are some serious mistakes in obtained results, which should be checked and corrected.
Comments for author File: 
Comments.pdf
Author Response
Reviewer 3:
This work is concern with the manufacturing of the Fe92.4Si3.1B4.5 alloy samples with laser 3D printer. This work is interesting and has high scientific merit. The study is in the scope of Metals MDPI. However, there are some obtained results, which should be checked and corrected.
Comments:
1) Please used ASTM additive manufacturing terminology ISO/ASTM 52900:2015.
Answer: We add this Some ISO terminology in the manuscript.
(ISO 4288-section 7 for profile and ISO-25178-2 for areal surface texture)
2) P.11. Fig.6-7. According to Fig.6, the coercivity force of samples decreased with the increasing of the laser power, but according to Fig.7, the coercive force of samples increased with the increasing of the laser power. Also check, please the text in page 11.
Answer: Thank you for your comment. The low magnetic field region of the magnetization curve main reveals that the M(H) curves of the samples P50 and P90 exhibit a positive vertical shift and a negative horizontal shift. The information given in the manuscript has been modified as: “The M(H) curves of the P50 and P90 samples display a positive vertical shift and a negative horizontal shift. The former might be ascribed to strong antiferromagnetic (AFM) interactions and/or to the short range AFM magnetic coupling in the Si-rich zones due to the fast solidification that leads to structural heterogeneities, and the later can be linked to an exchange bias (EB) like behavior at room temperature” (lines 290-294).
The horizontal shift of the M(H) curves can be related to the development of magnetically non-homogeneous antiferromagnetic (AFM)/ferromagnetic (FM) matrix resulting from the pinning effect at the interface between soft and hard magnetic substances. Therefore, the EB effect can be ascribed to a FM unidirectional anisotropy (texture) developed at the interface between different magnetic phases (intergranular coupling) upon the fast solidification process during the SLM process. The exchange bias (HE=(H1+H2)/2) is about 33.9 Oe, 94.4 Oe and 40.6 Oe for the P70, P110 and the raw powders, respectively. The coercive fields (Hc=(H1H2)/2) are of about 50.5 Oe and 70.3 Oe for the P70 and P110 samples, respectively. The coercivity of the P70 and P110 samples is about 50.5 Oe and 70.3 Oe, respectively. (Lines 311-321).
3) Fig.8. Microstructure of the sample P110 does not show the big technological pores in compare with other samples like P50, P70, and P90. It means that the sample P110 has better printing conditions.
Answer: We agree this comment. We modify part of the paragraph.
The smooth and dense surface of P110 sample (without high pores) can be ascribed to the complete melting of the initial powders. Thus, sample P110 has better printing conditions.
Furthermore, we modify several sentences taking into account the editor comments.
Round 2
Reviewer 1 Report
NA
Reviewer 3 Report
All comments are correctected. May be recommended to publish.
