Effects of Static Magnetic Field on the Microstructure of Selective Laser Melted Inconel 625 Superalloy: Numerical and Experiment Investigations

Round 1

Reviewer 1 Report

The manuscript presents some multi-scale numerical models in an attempt to support some experimental data, on the effect of SMF on SLM microstructures.

The experimental data (basically a few SEM images) are extremely scarce.

The links between the presented simulations and and the experimental data were hardly visible, and not presented in a comparable format.

The manuscript is not recommended for publication in the current form.

Author Response

Thank you very much for your careful review and constructive suggestions regarding our manuscript entitled "Effects of static magnetic field on the microstructure of selective laser melted Inconel 625 superalloy: numerical and experiment investigations" with reference No. metals-1430918. Those comments are all valuable and very helpful for revising and improving our manuscript and our future research works. We would like to express our great appreciation to you and reviewers for comments on our manuscript. We have checked these comments carefully and tried our best to revise and improve the manuscript.

Appended to this letter is our point-by-point response to the comments raised by the reviewers. The comments are reproduced, and our responses are given directly afterward in a different color (blue).

The manuscript presents some multi-scale numerical models in an attempt to support some experimental data, on the effect of SMF on SLM microstructures.

The experimental data (basically a few SEM images) are extremely scarce.

Since the influence of magnetic field on the selective laser melting process has been reported frequently, the underlying mechanism becomes a major topic for the researchers. Thus, this work mainly emphasizes on the multi-scale numerical simulation of SLM process under magnetic field. In order validate the numerical models, the SLM experiments are also conducted as a comparison. It can be found that the experimental results and simulation results establish a reasonable relationship.

The links between the presented simulations and the experimental data were hardly visible, and not presented in a comparable format.

The idea of this paper is that the experimental results are employed to verify the simulation results and the simulation results are used to explain the experimental phenomena. First the experimental results of molten pool size are compared with the simulated results to illustrate the rationality of the numerical simulation and investigate the effect of static magnetic field on the molten pool size. Then The dendrite size obtained from the experiment is used as the basis for the establishment of the dendrite-scale model. In the experimental results, it can be found that due to the thermoelectric magnetic force, the dendrite is transformed from columnar crystal to equiaxed crystal, and it is found that the distribution of Laves phase under magnetic field is more uniform. A significantly high TEMF of about 10⁷ ~ 10⁸ N/m³ is obtained under magnetic field around the dendrites, which is sufficient to break the dendrites and induce the columnar-to-equiaxed transition.

Reviewer 2 Report

The authors report on the effects of static magnetic field on the microstructure of selective laser melted Inconel 625. Comments are provided below:

Figure 1: harmonize magnetic units (Gauss or Tesla);
It is not clear that the dendrite in the molten pool can be divided into three different regions. Please add a sketch to better illustrate your explanation.
How (and why) maximum and minimum tetrahedral mesh sizes were selected 0.06 μm and 6.0×10-4 μm?
The equation T=Ts+d×G is not well explained in the text. Please elaborate.
Table 1: kg, not Kg.
Table 2: Given the comment of statistical analysis, I assume that the reported refer to an average. Please include standard deviation since it might also indicate a limited variation of the pool dimensions due to the magnetic field effect.
Figure 4 is confusing with the yellow squared. Please edit it.
In Figure 6 is really hard to distinct differences in phases. Please update the images (considering collecting them with BSE if not used).

Author Response

Thank you very much for your careful review and constructive suggestions regarding our manuscript entitled "Effects of static magnetic field on the microstructure of selective laser melted Inconel 625 superalloy: numerical and experiment investigations" with reference No. metals-1430918. Those comments are all valuable and very helpful for revising and improving our manuscript and our future research works. We would like to express our great appreciation to you and reviewers for comments on our manuscript. We have checked these comments carefully and tried our best to revise and improve the manuscript.

Appended to this letter is our point-by-point response to the comments raised by the reviewers. The comments are reproduced, and our responses are given directly afterward in a different color (blue).

The authors report on the effects of static magnetic field on the microstructure of selective laser melted Inconel 625. Comments are provided below:

Figure 1: harmonize magnetic units (Gauss or Tesla);

Thanks for the suggestions. In order to avoid the misunderstanding, the units of magnetic field intensity have been unified as Tesla.

It is not clear that the dendrite in the molten pool can be divided into three different regions. Please add a sketch to better illustrate your explanation.

As shown in Fig 2 in the revised manuscript, the three positions are indicated in the schematic diagram on the liquid-solid interface in the molten pool.

How (and why) maximum and minimum tetrahedral mesh sizes were selected 0.06 μm and 6.0×10^-4 μm?

Because the shape of dendrites is irregular, the uniformly distributed grids are difficult to be adopted. Thus, the mesh size is determined at different regions in the dendrite model to improve the calculation efficiency and accuracy. For example, the minimum tetrahedral mesh size of 10^-4 μm was selected at the dendrite bottom region with small inter-dendrite distance. Meanwhile, the lager mesh size is chosen at the region away from dendrite to reduce the computational resource.

The equation T=Ts+d×G is not well explained in the text. Please elaborate.

Thanks for the comments. The temperature distribution within the dendrite model is obtained through the boundary condition and the thermal gradient from the molten-pool model. In detail, the solidus temperature Ts is the temperature at the bottom of the dendrite. The temperature gradient G from the bottom of the dendrite to the top of the dendrite is regarded as constant. The temperature difference between the bottom and top of the dendrite can be calculated by multiplying the length of the dendrite d by the temperature gradient G. In addition, T is the temperature at the top of the dendrite. T and Ts are regarded as the temperature boundary condition at the top and bottom of the dendrite. The corresponding description have been added in the revised manuscript.

Table 1: kg, not Kg.

The unit has been corrected in the revised manuscript.

Table 2: Given the comment of statistical analysis, I assume that the reported refer to an average. Please include standard deviation since it might also indicate a limited variation of the pool dimensions due to the magnetic field effect.

According to the statistical size of molten pool, the standard deviation is calculated, which has been added in Table 2.

Figure 4 is confusing with the yellow squared. Please edit it.

The yellow squared in Fig. 4 (a) refer to the magnified views in Fig. 4 (b) (c) and (d). The explanation for the yellow area has been added in the Figure 4.

In Figure 6 is really hard to distinct differences in phases. Please update the images (considering collecting them with BSE if not used).

As shown in the revised manuscript, the indications are made in the Fig. 6 to show the differences. It can be found that the dendrite growth mode has changed. It is columnar crystal growth without magnetic field and equiaxed crystal growth under magnetic field. Due to the different growth states of dendrites, the distribution of Laves phase is also different.

Reviewer 3 Report

[1] It would be good if the abstract was modified.

In the abstract, the summary of the background, experimental methods and numerical modeling used by this study should be supplemented or added.

Also, it would be better to present the summary of the conclusion in more detail in the abstract.

The current abstract does not sufficiently convey the content of the conclusion.

[2] In this study, the heat and mass loss due to vaporization were not considered in modeling for the molten metal scale model.

By the way, if the heat loss due to vaporization is not taken into account, isn't the error range large?

In this regard, it would be nice if an explanation could be added to the text.

[3] Since this study is a comparison of experiments and numerical modeling, the conclusions needs to consist of the summary of these. Therefore I think it would be good to modify it in addition to the current conclusion.

[4] References

1. Yang, N.; Tian, Y. ~ → 2. Yang, N.; Tian, Y.

Author Response

Thank you very much for your careful review and constructive suggestions regarding our manuscript entitled "Effects of static magnetic field on the microstructure of selective laser melted Inconel 625 superalloy: numerical and experiment investigations" with reference No. metals-1430918. Those comments are all valuable and very helpful for revising and improving our manuscript and our future research works. We would like to express our great appreciation to you and reviewers for comments on our manuscript. We have checked these comments carefully and tried our best to revise and improve the manuscript.

Appended to this letter is our point-by-point response to the comments raised by the reviewers. The comments are reproduced, and our responses are given directly afterward in a different color (blue).

[1] It would be good if the abstract was modified.

In the abstract, the summary of the background, experimental methods and numerical modeling used by this study should be supplemented or added.

Also, it would be better to present the summary of the conclusion in more detail in the abstract.

The current abstract does not sufficiently convey the content of the conclusion.

The summary of the background, experimental methods, numerical modeling and conclusion in more detail have added in the revised manuscript.

[2] In this study, the heat and mass loss due to vaporization were not considered in modeling for the molten metal scale model.

By the way, if the heat loss due to vaporization is not taken into account, isn't the error range large?

In this regard, it would be nice if an explanation could be added to the text.

This simulation adopts a single-phase simplified plate model, which cannot consider the influence of evaporation on the free surface of molten pool. It is a common practice in the literature to ignore evaporation [1-3]. In addition, the temperature obtained from the simulation results is not very high, which further confirms that the evaporation can be ignored.

1 Mukherjee, T.; Wei, H. L.; De, A.;Debroy, T. Heat and fluid flow in additive manufacturing—Part I: Modeling of powder bed fusion. Comput. Mater. Sci., 2018, 150:304-313.

2 Zhang, D.; T, C.; Zhang, P.; Liu, Z.; Feng, Z.; Wang, C.;Guoa, Y. Thermofluid field of molten pool and its effects during selective laser melting (SLM) of Inconel 718 alloy. Addit. Manuf., 2018, 21:567–578.

3 Raghavan N , Dehoff R , Pannala S , et al. Numerical modeling of heat-transfer and the influence of process parameters on tailoring the grain morphology of IN718 in electron beam additive manufacturing. Acta Mater., 2016, 112:303-314.

[3] Since this study is a comparison of experiments and numerical modeling, the conclusions needs to consist of the summary of these. Therefore I think it would be good to modify it in addition to the current conclusion.

The comparison between experiment and simulation has been supplemented in conclusion, including the dimension verification of molten pool and the modeling basis of dendrite.

[4] References

1. Yang, N.; Tian, Y. ~ → 2. Yang, N.; Tian, Y.

The reference format has been checked and updated in the revised mnuascript.

Round 2

Reviewer 1 Report

The authors responded to the reviews and made some modifications to the manuscript. However, the baseline of my first review is unfortunately still valid. Just a few examples:

1. Figure 3 (wrongly labelled Figure 2 on page 4):

Captions read: 'Comparison of experimental and simulation results ...'

What kind of results is compared (size and shape of the molten pool)? What data is plotted (SEM image versus temperature distribution)? Which value is used as cut-off temperature? What is the unit and scale for the colorbar on the right side (b, d) (temperature in Kelvin)? 

2. Figure 4 (on page 8):

Captions read: 'Dendrite growth and Laves phase precipitation in the molten pool ...'

The SEM images (presumably by SE detection) barely show dendrites. They hardly prove the existence of Laves phases. The meaning of the 5-lambda scalebar is not explained.

3. Figure 6 (on page 10):

Captions read: 'EDS analysis results of the bottom of the molten pool ...'

This figure does not contain any EDS analysis. It only indicates locations where such analyses were performed. The meanings of the black overlay lines are not explained.

The SEM parameters are not provided. The usefulness of such point analysis at 2 times 2 spots per sample is (at least) questioned. The simulations do not result in any data which could be compared to the EDX data of table 3. The analyses are not significant to prove any change in Laves phase content (text lines 257-258).

4. Figures 7 to 11:

Missing are units, scales for XYZ-dimensions, temperature, velocity etc.

Which experimental data should these simulations be compared to?

5. Conclusions:

First sentence reads: ' 1. The simulation results are in good agreement with the experimental results. ...'

What kind of results were available to be truly compared (see comments to Figure 3 and 6 above). It is not clear, which of the conclusions 1-5 come from either experimental evidence, from simulations, or from comparison of both.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors addressed the comments.

Author Response

Thanks the reviewer to the comments.