Effect of the Laser Processing Parameters on the Selective Laser Melting of TiC–Fe-Based Cermets

Round 1

Reviewer 1 Report

This article deals with the preparation of cermets by the SLM method, mainly due to the different laser powers and its effect on the microstructure and hardness. This is a current topic that has not yet been fully explored, and the article shows that the team can prepare crack-free cermets using this method. However, only the characterization of microstructure, hardness and toughness (by the method based on hardness measurement) seems to me to be insufficient in terms of properties and I would recommend supplementing the results with wear tests, which should determine whether the prepared material is suitable for the proposed uses or not. However, it is only a recommendation and it must be stated that even in its current form, the article is suitable for publication after several necessary modifications.

Comments for authors:

• The dimensions of the prepared samples are not given in the materials and methods section, the statement that these are cuboidal shape samples is insufficient.
• For equation (1) they do not state what the individual characters characterize, I would recommend to state the individual characters in the previous sentence.
• line 162, incorrect numbering of figures, Fig. 3, but it should be Fig. 4.
• Figure 5 - materials after SLM are often anisotropic, the image should indicate in which direction the metallographic cuts were prepared.
• Line 228 and 229 - microhardness values are given here and then hardness, it would be appropriate to use either one or the other not both in the whole article.
• There is a very similar article on the internet that deals with the same things and there are similar results and the team is almost the same. I do not have it completely available only abstract, but the authors should explain how it differs, otherwise it is a duplicate and does not present new results. Here is the link:

https://www.liebertpub.com/doi/pdf/10.1089/3dp.2021.0221?download=true

Mainly for this reason,  I propose a major revision (authors should explain what in the article is different)

Author Response

• The dimensions of the prepared samples are not given in the materials and methods section, the statement that these are cuboidal shape samples is insufficient.

As suggested by the reviewer the dimensions (5 mm ⅹ 5 mm ⅹ 3 mm) are included in the experimental section.

• For equation (1) they do not state what the individual characters characterize, I would recommend to state the individual characters in the previous sentence.

As suggested by the reviewer, the individual characters in equation 1 were introduced.

• line 162, incorrect numbering of figures, Fig. 3, but it should be Fig. 4.

Sorry for the error and it was corrected accordingly.

• Figure 5 - materials after SLM are often anisotropic, the image should indicate in which direction the metallographic cuts were prepared.

The directionality of the SLM samples is introduced as suggested.

• Line 228 and 229 - microhardness values are given here and then hardness, it would be appropriate to use either one or the other not both in the whole article.

We have modified the term to microhardness throughout the manuscript.

• There is a very similar article on the internet that deals with the same things and there are similar results and the team is almost the same. I do not have it completely available only abstract, but the authors should explain how it differs, otherwise it is a duplicate and does not present new results. Here is the link:

https://www.liebertpub.com/doi/pdf/10.1089/3dp.2021.0221?download=true

Mainly for this reason,  I propose a major revision (authors should explain what in the article is different)

Ahead of the Print article in the journal "3D Printing and Additive Manufacturing" and the present submitted manuscript to JMMP deals with the same materials and same process. However, the core of the paper is completely different. The published paper in 3D Printing and Additive Manufacturing journal compares the microstructure and properties of TiC-Fe cermets produced with laser pulse shaping and without laser pulse shaping. However, the manuscript submitted to JMMP tries to portray the difference in terms of the microstructure and cooling rate effects when the parameters of the laser pulsing are varied. Excepting the material used and the process, both the manuscripts have no similarities in terms of the scientific goals. The material and the process used were kept the same just for comparison purposes.

Reviewer 2 Report

The authors presented a parametric investigation on selective laser melting of TiC-Fe-based cermets. Please address the following questions before the publication of the manuscript:

 

1. Please add “TiC-Fe based cermet” in the title.
2. Line 58, for reference 18, please add brackets in the text.
3. Line 162, It seems to be Fig 4 rather than Fig 3.
4. Line 191, Fig 5, please give EDS data to support the labels in Fig 5 “melted TiC“ and “Fe growth”

What is Fe growth?

5. Line 223 Fig 6, please also give EDS data to support the labels in Fig 6 “Fe, TiC”
6. Line 237 to 238, “However, increasing LMP....makes the microstructure more homogeneous, which can lead to higher hardness values”. Why more uniform microstructure can lead to higher hardness?

Author Response

• Please add “TiC-Fe based cermet” in the title.

As recommended, TiC-Fe based cermet is included in the title.

• Line 58, for reference 18, please add brackets in the text.

Brackets are introduced as recommended.

• Line 162, It seems to be Fig 4 rather than Fig 3.

Sorry for the mistake and it is corrected as pointed out.

• Line 191, Fig 5, please give EDS data to support the labels in Fig 5 “melted TiC“ and “Fe growth”

As suggested, EDS data is introduced in Fig. 5.

• What is Fe growth?

Fe binder segregation occurs in the melt pool due to high laser energy density, forming a region called Fe rich zone, in which small TiC particles can be seen and the size of the Fe binder segregation varies which we have correlated to Fe growth (based on their size).

• Line 223 Fig 6, please also give EDS data to support the labels in Fig 6 “Fe, TiC”

As suggested, EDS data is introduced.

• Line 237 to 238, “However, increasing LMP....makes the microstructure more homogeneous, which can lead to higher hardness values”. Why more uniform microstructure can lead to higher hardness?

When the microstructure is not uniform there might be areas that are dominated by high strength TiC and some areas dominated by low strength Fe. The areas that are dominated by low strength Fe will reduce the strength of the materials (also the hardness) leading to areas of lower hardness. When the microstructure is uniformly distributed, both Fe and TiC will be uniformly distributed without Fe segregation. When there is no Fe segregation there will be no areas with lower/inferior strength/hardness. Hence, the overall hardness of the material increases with the uniform distribution of the microstructure and phases.

Reviewer 3 Report

The manuscript deals with the laser pulse shaping of TiC-Fe-based cermets and studies the effect of various laser process parameters on the phase, microstucture and mechanical properties. The manuscript is well written and some minor revisions are needed:

1. Line 58, the bracket is missing for reference 18.
2. In 3.1, it is found that no major peak shift can be found for the SLM processed samples using differernt laser powers. Can the authors explain more for this observation?
3. In 3.3.2, it is found that the fracture toughness increases with laser power and then decreases. Why does this happens?

Author Response

• Line 58, the bracket is missing for reference 18.

As suggested by the reviewer, brackets were introduced.

• In 3.1, it is found that no major peak shift can be found for the SLM processed samples using different laser powers. Can the authors explain more for this observation?

Since there are no major differences in the microstructure (in terms of phases and their supersaturation) irrespective of the changes in the laser power, a shift in the XRD peak is not observed. This is also due to no changes in the lattice constant (no diffusion between the elements considered).

• In 3.3.2, it is found that the fracture toughness increases with laser power and then decreases. Why does this happens?

As suggested, the following sentences has been included in the revised version:

The crack propagation mechanism could explain the variation in the fracture toughness value. The finer TiC particles lead to crack deviation more often, causing crack length to increase. As a result, the fracture toughness value for LMP50 and LMP60 is higher. The coarser microstructures will impede the crack path, resulting in lower fracture toughness values for LMP84.

Round 2

Reviewer 1 Report

The authors removed and amended all the requirements. After studying and comparing of the articles, I can agree with the authors' statement and the difference can be taken into account despite very similar results. 

Reviewer 2 Report

The authors have responded to my questions properly