Strip Casting of Sm₂TM₁₇-Type Alloys for Production of the Metastable SmTM₇ Phase

Round 1

Reviewer 1 Report

This work studies the peculiarities of the metastable SmTM7 phase formation during strip casting of Sm2TM17-type alloys. The research is well-designed and presented clearly. A comparative analysis of existing publications and the tasks set in the work is quite concise. The methodological section of the manuscript is presented in sufficient detail. The authors used modern equipment for the preparation and testing of samples. They also utilized the equipment for visualization and assistance in interpreting the results. According to the authors’ findings, the adhesion between the melt and the wheel was critical for nucleation of SmTM7 grains and the wheel speed controlled the thickness of the flake. It was determined that in order to achieve a homogenous columnar SmTM7 structure, the maximum flake thickness should be limited to 280 μm to avoid formation of equiaxed Sm2TM17 grains through insufficient cooling.

However, some shortcomings should be corrected to make the manuscript acceptable for publication in Metals.

(1) In Line 23, a typo (a measurement unit) should be fixed.

(2) In Line 33, the phrase “The name 2:17 refers to the ratio …” can be replaced with “The name 2:17 refers to the atomic ratio …”

(3) In Lines 37–39, more recent references should be added concerning other characteristics of magnets in relation to the material microstructure and phase balance, as well as prediction of the performance of these materials. The suggested references are: https://doi.org/10.36547/ams.27.4.1173 and https://doi.org/10.15407/fm28.03.497

(4) In the caption of Figure 7, it is not a good idea to mark corresponding XRD patterns by giving a pattern color in parentheses, i.e. dark blue, light blue, orange, and green. It is better to mark them as (a), (b), (c), and (d). The same concerns Figure 8.

(5) Is the maximum flake thickness limit of 280 μm specified in the main text, as it is presented in the abstract?

(6) The Conclusions section: In the sentence “Further optimisation of the process could lead to fully homogenous 1:7H structures, removing the need for the homogenisation and solutionising stages of magnet production”, it should be specified what the further optimisation means (i.e., further optimisation of the tundish design to better control alloy flow onto the wheel would likely result in the desired columnar microstructure and phase balance of 1:7H and 1:5H without non-directional growth or unwanted minority phases; see Lines 257–260).

(7) Typos throughout the text of the manuscript should be checked.

Author Response

Comments from Reviewer 1:

• This work studies the peculiarities of the metastable SmTM7 phase formation during strip casting of Sm2TM17-type alloys. The research is well-designed and presented clearly. A comparative analysis of existing publications and the tasks set in the work is quite concise. The methodological section of the manuscript is presented in sufficient detail. The authors used modern equipment for the preparation and testing of samples. They also utilized the equipment for visualization and assistance in interpreting the results. According to the authors’ findings, the adhesion between the melt and the wheel was critical for nucleation of SmTM7 grains and the wheel speed controlled the thickness of the flake. It was determined that in order to achieve a homogenous columnar SmTM7 structure, the maximum flake thickness should be limited to 280 μm to avoid formation of equiaxed Sm2TM17 grains through insufficient cooling.

However, some shortcomings should be corrected to make the manuscript acceptable for publication in Metals.

The authors would like to thank the reviewer for the nice comments provided, and the shortcomings mentioned are addressed below.

• (1) In Line 23, a typo (a measurement unit) should be fixed.

The unit has been changed from an error box to the micron symbol.

• (2) In Line 33, the phrase “The name 2:17 refers to the ratio …” can be replaced with “The name 2:17 refers to the atomic ratio …”

The wording has been changed accordingly to incorporate the word “atomic”

• (3) In Lines 37–39, more recent references should be added concerning other characteristics of magnets in relation to the material microstructure and phase balance, as well as prediction of the performance of these materials. The suggested references are: https://doi.org/10.36547/ams.27.4.1173 and https://doi.org/10.15407/fm28.03.497

More recent references have been added to this section of the introduction. However, the references suggested by the reviewer here are not relevant to the this paper and thus have not been included and more relevant literature has been cited as reference [2].

• (4) In the caption of Figure 7, it is not a good idea to mark corresponding XRD patterns by giving a pattern color in parentheses, i.e. dark blue, light blue, orange, and green. It is better to mark them as (a), (b), (c), and (d). The same concerns Figure 8.

The figure has been adapted to include the labels (a),(b),(c),(d).

• (5) Is the maximum flake thickness limit of 280 μm specified in the main text, as it is presented in the abstract?

This value has been updated to 270mm based on further analysis, a paragraph has been added to the discussion (L315-323) to justify this.

• (6) The Conclusions section: In the sentence “Further optimisation of the process could lead to fully homogenous 1:7H structures, removing the need for the homogenisation and solutionising stages of magnet production”, it should be specified what the further optimisation means (i.e., further optimisation of the tundish design to better control alloy flow onto the wheel would likely result in the desired columnar microstructure and phase balance of 1:7H and 1:5H without non-directional growth or unwanted minority phases; see Lines 257–260).

Further results (Figure 5) and discussion have been added to highlight the importance of controlling the flow of molten alloy onto the wheel by showing the microstructural anomalies that can occur from turbulent flow. This further justifies the conclusion. Examples of optimisation added to conclusion as requested.

• (7) Typos throughout the text of the manuscript should be checked.

The manuscript has been checked for grammatical errors and typos.

Reviewer 2 Report

After the analysis of the manuscript: Strip Casting of Sm2TM17-type Alloys for Production of the Metastable SmTM7 Phase by Sheridan et. all, I conclude that:

Title: can be more concise and check the word production if it’s used correctly in this context

Abstract section:

L11: Re-phrase: This SmTM7 phase is phase is a vital precursor phase for magnet production in order 11 to precipitate the Sm2TM17 rhombohedral and SmTM5 hexagonal phases required to develop the 12 cellular structure responsible for high magnetic properties.

L23: modify :  280 @m to avoid formation

Introduction section:

It is satisfactory from the point of view of the information brought in this field and could be completed with the existing information in the specialized literature regarding the mechanical properties of the obtained products.

2. Materials and Methods

an accelerating voltage of 15 kV. Why not use 30 kV ? – the SEM image quality is low at this electronic gun voltage mention the detector type used for experiments SE or BSE

Based on the complex chemical composition of the sample why are not given EDS or WDX results?

 3. Results:

 L 129: Run 1 , why this notation ?

EDS/WDX investigation can be helpful, why are not given results?

Transversal image of the strips can present the structure from the sample on the thickness

L211: EDX detector is mention please mention the equipment in Section 2 please

In Figure 8. XRD traces for the free side (light blue) and wheel side (black) of median flakes from Run 1 there is a legend but not applied on graphs

Chemical composition (EDS: Element List and Mapping mode) should be performed on the free side (light blue) and wheel side (black) of the samples

Insert few comments about the material mechanical properties/ integrity in comparation with the results from literature

Conclusions are pertinent

References: more references should be given by the authors in the Results section in order to defend their affirmations (for example at this statement: L153: This is nearly the ideal microstructure for the strip cast flakes, it would be assumed that thinner flakes, and hence a higher cooling rate would be able to remove the equiaxed grains from the free side of the flake.)

Author Response

After the analysis of the manuscript: Strip Casting of Sm2TM17-type Alloys for Production of the Metastable SmTM7 Phase by Sheridan et. all, I conclude that: 

• Title:can be more concise and check the word production if it’s used correctly in this context

The authors would prefer to keep the current title as it maintains the context of the current work and planned future work in this area.

Abstract section: 

• L11: Re-phrase: This SmTM7 phase is phase is a vitalprecursor phase for magnet production in order 11 to precipitate the Sm2TM17 rhombohedral and SmTM5 hexagonal phases required to develop the 12 cellular structure responsible for high magnetic properties.

The wording has been changed to “This SmTM7 phase is a vital precursor phase required during magnet production to develop the complex cellular structure responsible for high magnetic properties.” In order to be more concise and avoid any confusion.

• L23: modify :  280 @m to avoid formation

This was also noted by Reviewer 1 and has been changed to the micron symbol as requested.

Introduction section: 

• It is satisfactory from the point of view of the information brought in this field and could be completed with the existing information in the specialized literature regarding the mechanical properties of the obtained products.

The mechanical properties are not the subject of this study so a detailed discussion of them would not be relevant, therefore the authors have agreed that it is not necessary as we are not presenting any result on effect of casting on mechanical properties at this point. However, one statement has been added in lines 85-87 to state that there could be an advantage for further processing compared to cast ingots.

Materials and Methods

• an accelerating voltage of 15 kV. Why not use 30 kV ? – the SEM image quality is low at this electronic gun voltage mention the detector type used for experiments SE or BSE 

This is the accelerating voltage of the equipment available for this research, the authors have mentioned that a BSE detector in used in the Materials and Methods section.

• Based on the complex chemical composition of the sample why are not given EDS or WDX results?

As requested, EDX data has now been included and is presented in Figure 8 with a specific focus on the difference in composition and phase balance between the wheel side and free side of the flake. Discussion of the figure has been included in the text.

Results:

• L 129: Run 1 , why this notation ?

This notation was used as an easy reference instead of repeating the wheel speeds throughout the document which could lead to confusion when discussing other numerical and quantitative results within the text.

• EDS/WDX investigation can be helpful, why are not given results?

As requested, EDX data has now been included and is presented in Figure 8 with a specific focus on the difference in composition and phase balance between the wheel side and free side of the flake. Discussion of the figure has been included in the text.

• Transversal image of the strips can present the structure from the sample on the thickness

The presentation used in this work allows for easy and direct comparison of the strips from the wheel side to free side and to compare samples side-by-side. This orientation also allows for the maximum amount of the cross-section of the alloy to be viewed within a single image.

• L211: EDX detector is mention please mention the equipment in Section 2 please

The authors have included EDX in the Materials and Methods section.

• In Figure 8. XRD traces for the free side (light blue) and wheel side (black) of median flakes from Run 1 there is a legend but not applied on graphs 

(This is now Figure 7). This has been corrected by including a comparison to the as-received cast alloy ingot, with discussion in the text to describe why these phases have not been labelled on the free side and wheel side of the flake, predominantly down to the surface texture and curvature as well as the presence of blue/gold oxides on the surfaces, masking the typical phases that would be detected on a clean flat surface.

• Chemical composition (EDS: Element List and Mapping mode) should be performed on the free side (light blue) and wheel side (black) of the samples

As requested, EDX data has now been included and is presented in Figure 8 with a specific focus on the difference in composition and phase balance between the wheel side and free side of the flake. Discussion of the figure has been included in the text.

• Insert few comments about the material mechanical properties/ integrity in comparation with the results from literature

The mechanical properties are not the subject of this study so a detailed discussion of them would not be relevant, therefore the authors have agreed that this is not necessary.

Conclusions are pertinent 

• References: more references should be given by the authors in the Results section in order to defend their affirmations (for example at this statement: L153: This is nearly the ideal microstructure for the strip cast flakes, it would be assumed that thinner flakes, and hence a higher cooling rate would be able to remove the equiaxed grains from the free side of the flake.)

This statement has been removed as the results section is purely a description of results and should not contain any discussion. Appropriate referencing is included in the discussion section where comparisons are made between the presented work and the literature.

Reviewer 3 Report

Review:

Strip Casting of Sm2TM17-type Alloys for Production of the Metastable SmTM7 Phase

In Part 2: describe the preparation of samples for SEM microscopy more professionally and specify the technical parameters at which the samples were observed in SEM.

Figures 4, 5 and 6 to form a collage. The scale in yellow is not clearly visible enough - improve the display! Figures 4, 5 and 6 should be included in the text, so that they follow the text.

Figures 7 and 8 should be improved so that the XRD graphs are more clearly displayed, the existing ones do not allow good visibility.

Comments for author File: Comments.pdf

Author Response

• In Part 2: describe the preparation of samples for SEM microscopy more professionally and specify the technical parameters at which the samples were observed in SEM.

Details have been added on each stage of grinding and polishing as well as relevant SEM parameters such as working distance and magnification .

• Figures 4, 5 and 6 to form a collage. The scale in yellow is not clearly visible enough - improve the display! Figures 4, 5 and 6 should be included in the text, so that they follow the text.

Figures 4, 5 and 6 have now been combined into a collage as requested (now Figure 4), which has allowed the authors to restructure the presentation of this section and the Figure is now proceeded by the descriptive text.

• Figures 7 and 8 should be improved so that the XRD graphs are more clearly displayed, the existing ones do not allow good visibility.

The authors have updated the images, there was an issue where a screenshot had been submitted rather than the image itself.

Round 2

Reviewer 1 Report

All of the reviewer’s comments were taken into account by the authors. The manuscript can now be accepted for publication in Metals.