Submit to this Journal Review for this Journal Propose a Special Issue

Article Menu

Open AccessArticle

Peer-Review Record

Damping Behavior of Layered Aluminium and Aluminide Coatings on AISI 316 Austenitic Steel

Coatings 2020, 10(9), 888; https://doi.org/10.3390/coatings10090888

by Ennio Bonetti¹, Enrico Gianfranco Campari^1,*, Angelo Casagrande², Giuseppe Catania² and Andrea Garzoni²

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Coatings 2020, 10(9), 888; https://doi.org/10.3390/coatings10090888

Submission received: 27 July 2020 / Revised: 8 September 2020 / Accepted: 14 September 2020 / Published: 17 September 2020

Round 1

Reviewer 1 Report

The manuscript presents preliminary results on the production and characterization of several coatings configurations. This work corresponds to the Journal's aims and scope and provides a useful path for the readers. However, there are several major issues that the authors need to address. Below are comments and suggestions.

1. To make it easier for readers to understand, renumber the list of coatings on page 3. E.g. line 137: Figure 1a and 1e are compared. It would be better to put them together and number 1a and 1b. And so on.

2. Please, explain briefly the choice of oxidation and annealing temperature and time. If they are based on literature data, please, provide relevant references.

3. Al-Si alloys presented in Fig 1a and 1e were obtained under similar conditions. However, their tongue-like structures seem to differ in size. Can you explain that?

4. Give extended comments on Figure 1b in the text.

5. Figure 2a: please, add phase designations: e.g. substrate, FeAl phase, α-alumina, and so on. As well as for Figure 6.

6. It would be better if you added in Figures 3, 4 and 5 captions the samples to which the spectra relate.

7. Table 2 shows the elemental analysis of coating layers of the samples shown in Figures 1c and 1d, isn't it?. It would be better to separate these data in the Table.

8. Figure 4 demonstrates XRD spectrum of sample 1c. Where is α-Al₂O₃ in Figure 1c?

9 Upon the whole, I strongly recommend reorganizing the subsection “3.1. Microstructural characterization and composition identification”. Please, systemize data obtained and describe step by step microstructural design and processing effects of the coatings. In addition, it may be useful to systemize the conditions of samples produced in the form of a table.

10. Line 245 “This coating configuration possesses a high dislocation density at the interfaces, produced during the cooling process”. How the density of dislocations was estimated?

Author Response

Dear referee,

We carefully read your comments and suggestions regarding our article and how to improve it. Text and figures were modified accordingly, as you will read in the attached file. For your convenience, in the following I report a brief point by point response to each comment. Please note that some comments/suggestions were shared with those of the other referees so that I tried to take care of them at once.

Finally, excuse me for the late response, due to access limitations to my University Department in August for the Covid epidemic.

Enrico G. Campari

REVIEWER 1

To make it easier for readers to understand, renumber the list of coatings on page 3. E.g. line 137: Figure 1a and 1e are compared. It would be better to put them together and number 1a and 1b. And so on.

Specimens in figure 1a to f and the following are now relabeled in order to ease the reader understanding. As suggested by another referee figure 6 has been deleted and merged with figure 1.

Please, explain briefly the choice of oxidation and annealing temperature and time. If they are based on literature data, please, provide relevant references.

The oxidation temperature choice is now better explained in the “Materials and Methods” section:

Time and temperature were chosen for all coatings in order to create a thin a-Al₂O₃ layer (at least 900 °C are required to this purpose) and to modulate the thickness of the brittle Fe₂Al₅layer…….

Al-Si alloys presented in Fig 1a and 1e were obtained under similar conditions. However, their tongue-like structures seem to differ in size. Can you explain that?

The size difference in the two cases is due to a longer immersion time for the specimen of figure 1e with respect to that of figure 1a.

Give extended comments on Figure 1b in the text.

Figure 1 has been further commented in the text. For example:

….as shown in the optical micrograph of Fig 1b, in the SEM micrograph of fig. 2a and in the EDS X-ray map of fig. 2b. Diffusion at high temperature, needed in order to produce alpha-alumina, increases the thickness of Fe₂Al₅, which in turn increases specimen hardness and brittleness.

Figure 2a: please, add phase designations: e.g. substrate, FeAl phase, α-alumina, and so on. As well as for Figure 6.

Phase designations have been added

It would be better if you added in Figures 3, 4 and 5 captions the samples to which the spectra relate.

The relations have been added

Table 2 shows the elemental analysis of coating layers of the samples shown in Figures 1c and 1d, isn't it? It would be better to separate these data in the Table.

Yes, the elemental analysis refers to the specimens of figure 1c and 1d. In table 2 it has been now specified to which specimen each phase belong.

Figure 4 demonstrates XRD spectrum of sample 1c. Where is α-Al₂O₃in Figure 1c?

α-Al₂O in Figure 1c cannot be detected because the diffusive process was conducted in an atmosphere without oxygen

We tried to improve the section and several changes has been done to the previous text.

Line 245 “This coating configuration possesses a high dislocation density at the interfaces, produced during the cooling process”. How the density of dislocations was estimated?

A high dislocation density is expected because of the lattice misfit at the boundary between the FaAl and Fe₂Al₅phases. In such a case, an interface with a high dislocation density is expected in order to accommodate the resulting stress. When the misfit is not more than 20% a semicoherent interface with high dislocation density is produced. On the other hand, if the two phases exibit a greater difference, an incoherent interface in produced, with even greater dislocation density. We do not measure in this work the dislocation density.

Reviewer 2 Report

This paper investigates the damping properties of different aluminium-based diffusion coatings on AISI 316 austenitic steel. The topic of investigation is very interesting. The paper is very well presented, follows a logical sequential order and is concise while complete because of the many experimental data and references provided. However, the paper lacks of sufficient scientific discussion and there are many significant mistakes and insufficient references on the part related to the coatings. I therefore suggest major revision.

Specific comments are given as follows:

Abstract

Line 17/18: aluminide coatings are NOT typically employed AS thermal barrier coatings. They are oxidation [e.g. Bouchaud et al. Oxid. Met. 69 (2008) 193-210] and corrosion [e.g. Fu et al. High Temp. Mater.Proc 36 (2017) 243-248] protective coatings (alone or combined with Cr, Si…). Otherwise, most often combined with Pt, they form the BOND COAT of the thermal barrier coating system [e.g. Boissonnet et al. Surf. Coatings Technol. 389 (2020), Art. No. 125566].

Introduction

Line 33: remove “s” to “subjects”

Lines 35/36: about the growing interest on combining thermal protection and damping capabilities. Please provide a supporting reference.

Line 55: replace “into” by “in”

Lines 58-68. There is no explanation why aluminide coatings are in particular studied. The authors should provide some supporting references on the damping behaviour of the aluminide coatings and therefore fully justify the current study. Similarly, the reasons for selecting AISI 316 steel are not given. Please cite some industrial applications where these aluminized AISI 316 steels could be employed.

Line 74: temperatures in the range 30-450°C. Why such temperatures? Again, which examples of application? Aluminide coatings are typically applied for temperatures higher than 450°C [e.g. Rouillard et al. Oxid. Met. 88 (2017) 221-233]. I thus believe it is key to justify why lower temperatures from both the scientific and the industrial perspectives.

Materials and Methods

Lines 93-96. It is unclear how the authors obtained two different coating thicknesses (200 and 130 µm) if all the treatments were equally performed (750°C/5 min)

Lines 97/98: why were the coatings oxidized precisely at 900°C/1h? Not more? Not less?

Line 103: replace “diffuse ion” by “diffusion”.

Line 123: remove “a”

Results and discussion

Line 139: X-ray do not produce spectra but diffractograms or patterns. The reason is simple: any spectroscopy has energy units (or equivalent) in the abscissas while in X-ray diffraction, one gets diffraction angles (in degrees).

Lines 142/143: the explanation of the tongue like features is not given [see e.g. Kepa et al. Surf. Coatings Technol. 397 (2020) 126011].

Line 154: replace “spectra” by “pattern”

Lines 158-169: the reasons for such results are not explained. References are needed to support such findings.

Line 176: replace “thermal barrier coating” by “appropriate coating system”

Figure 1: why are pore occur in Fig. 1f ? there is not explanation about them. Could their round morphology buffer the stresses upon damping?

Table 2: decimal points and not commas

Figure 3. It is impossible that the authors obtain the X-ray peaks of Al and Si alone [see e.g. Boulesteix et al. Oxid. Met. 87 (2017) 469-479].

Figure 6: the sample was excessively etched. Therefore, the microstructure of the outer and of the intermediate layers cannot be appreciated.

Figure 8: decimal points instead of commas.

Lines 245/246. The statement is not sufficiently demonstrated by experimental evidence. How do the authors know that there is a high dislocation density? TEM is needed to show the dislocations. Otherwise, an adequate reference to support that a high dislocation density forms during the cooling process, etc. I also believe that interdiffusion will produce dislocation climbing thereby annealing their potential presence in the coatings’ interfaces.

Line 283/284: the low ductility of aluminides occur in wet atmospheres and not in oxygen atmospheres !!!! This is clearly indicated in the introduction of the paper cited !!

Conclusions

Line 285: delete “a few results clearly stem from the experimental data” as the sentence has no clear meaning.

References

Homogenize the style of all the references (e.g. 2, 9, 10, 23…)

Author Response

Dear referee,

Finally, excuse me for the late response, due to access limitations to my University Department in August for the Covid epidemic.

Enrico G. Campari

Reviewer 2

Specific comments are given as follows:

Abstract

True. In fact, aluminides are the bond coat for surface protective ceramic layer. Accordingly, we modified the abstract and the first part of the introduction to better explain the situation. The relevant references you gave us were inserted into the reference list.

Introduction

Line 33: remove “s” to “subjects”

done

Lines 35/36: about the growing interest on combining thermal protection and damping capabilities. Please provide a supporting reference.

As written above, the introduction has been rewritten and the sentence without a supporting reference has been removed.

Line 55: replace “into” by “in”

done

The introduction was modified in order to try to explain why we study aluminide and used steel as a substrate. A suitable reference was added to this purpose.

“TBCs of ceramic nature may both increase thermal, chemical and mechanical resistance. Among them, aluminides are particularly interesting. Light, inexpensive, achievable in several layered configurations, their excellent chemical-physical properties must be coupled to a high adhesion resistance to substrate and between layers. Aluminization of stainless alloys such as AISI 316, followed by interdiffusion process, offers the possibility of building several multilayer configurations to assess the influence of the layers thickness, viscoelasticity, interface and elastic moduli [7].“

A temperature range up to 450°C has been set in order to assess the viscoelastic contribution of the metal layer in correlation with the contribution made by the interfaces between aluminide intermetallic layers. It is also close to the measure limit of the apparatus we used to measure the damping. The industrial outlook is partially considered in the responses to the lines 35/36. Finally, this work must be considered as indicating a route to achieve the desidered reductions in mechanical vibrations, suggesting which is the best contribution to damping between viscoelasticity, interfaces, thicknesses of the layers or elastic modulus variation between them.

Materials and Methods

Lines 93-96. It is unclear how the authors obtained two different coating thicknesses (200 and 130 µm) if all the treatments were equally performed (750°C/5 min)

The two thicknesses are due to a different time of immersion and precisely 5 and 3 minutes. This information has been added to the text.

Lines 97/98: why were the coatings oxidized precisely at 900°C/1h? Not more? Not less?

The paragraph Results and Discussion was modified in order to explain why that temperature was chosen. And the reason is that a temperature of at least 900°C or more is needed to form a thin film of alpha alumina (stable from 900°C) on the surface of the specimen. A one hour treatment time was used in order to hinder the growth of the brittle Fe₂Al₅ phase.

Line 103: replace “diffuse ion” by “diffusion”.

replaced

Line 123: remove “a”

removed

Results and discussion

The term “diffraction spectra” has been replaced by patterns, which is more precise.

Lines 142/143: the explanation of the tongue like features is not given [see e.g. Kepa et al. Surf. Coatings Technol. 397 (2020) 126011].

An explanation to the tongue like features has been added in the text.

Line 154: replace “spectra” by “pattern”

replaced

Line 176: replace “thermal barrier coating” by “appropriate coating system”

replaced

Figure 1: why are pore occur in Fig. 1f ? there is not explanation about them. Could their round morphology buffer the stresses upon damping?

The formation of pores in Figure 1f (now figure 1d) is the consequence of the Kirkendall effect, due to the different speeds of diffusion of the elements. Given their shape, they do not produce negative effects for damping

Table 2: decimal points and not commas

corrected

Figure 3. It is impossible that the authors obtain the X-ray peaks of Al and Si alone [see e.g. Boulesteix et al. Oxid. Met. 87 (2017) 469-479].

The metallographic cross sections of as coated samples show the presence of Fe₂Al₅ islands. These are detached from the continuous Fe₂Al₅ layer with tongue-like morphology and dispersed into the Al-Si hypoeutectic alloy matrix. Figure 3 shows diffraction peaks with the presence of the Fe2Al5.

Figure 6: the sample was excessively etched. Therefore, the microstructure of the outer and of the intermediate layers cannot be appreciated.

Unfortunately, it is like that!

Figure 8: decimal points instead of commas.

corrected

An brief explanation for the supposed high dislocation density has been added, e.g. in section 3.2. Damping behavior:

“A high dislocation density is expected because of the lattice misfit at the boundary between the FaAl and Fe₂Al₅phases. In such a case, an interface with a high dislocation density is expected in order to accommodate the resulting stress.”

Line 283/284: the low ductility of aluminides occur in wet atmospheres and not in oxygen atmospheres !!!! This is clearly indicated in the introduction of the paper cited !!

Corrected

Conclusions

Line 285: delete “a few results clearly stem from the experimental data” as the sentence has no clear meaning.

The beginning of the Conclusion section has been changed and the sentence deleted.

“A first result of this study is the absence, below 200 ° C, of a significant damping increase with respect to that of the substrate steel for all the tested multilayer coatings. Above that temperature…”

References

References has been checked and a number of imperfections has been corrected.

Reviewer 3 Report

The paper entitled „ Damping behavior of layered Aluminium and aluminide coatings on AISI 316 austenitic steel" concerns investigation of the damping behavior of the aluminide coatings. The results presented in the paper are interesting and, in my opinion, suitable for publication in the Coatings. However, before that, it should be major revision. Authors will find below general and detailed comments concerning the paper.

-P1 In the manuscript, in my opinion, authors just focused on one coating— aluminide coating but with different thickness and pre-treatment, the abstract is not well organized, it is not clear to describe the main methods, results and conclusions.

-P3 The author has to provide a compelling reason why did the author produce the six different coatings? As one of the traditional technique, the thickness of aluminized coating can be controlled in the process of hot dip. So the authors should give the detail process to get the different thickness of the aluminide coating.

-P3 In this manuscript, is the aluminium oxide layer same with alumina scale? If yes, that need to be unified, if not, please explain why.

-P5 The Fig. 1 needs to be revised, the magnification and resolution were different. In the Experimental, the sample 4 with diffusion annealing at 900 °C lasted for 4 h, but Fig. 1c is the sample with 3h?

-P4 Authors needs to reorder the Figures.

First Fig. 1, then Fig. 3 and 4, then back to Fig. 2? I don’t think it is a good expression.

- The abbreviation needs to be consistent, like “Figure 1a and Figure 1e” (Line 137), “fig. 2b” (Line 157), “figure 1.” (Line 209).

- “as shown in the optical micrograph of Fig 1c, in the XRD diffraction spectra of fig.4 and in the EDS analysis of Tab.2.”(Line 154-155), “1c and 1f) as aluminized and annealed at 900 °C for 3 h” (Line 187), “Figure 4. X-ray diffraction of diffusion aluminide coating: 900 °C for 3 and 4 h.” (Line 193). I don't think the data (like EDS, XRD) can support the author's results

-P6. In my opinion, for general metal materials, the penetration depth of X-ray is approximately 1-20 μm with Cu Ka radiation, but the thickness of the aluminised coatings is approximately 130-200 μm. So, the author uses XRD diffraction spectra to confirm that the intermetallic Fe₂Al₅ is unreasonable.

-P6. In the Table 2, “56, 2” should be rewritten as “56.2”, etc.

-P7 Why put the optical microstructure here? Same with Fig. 1d? If we don't get more detailed information, then this picture is useless.

-P 9 in my opinion, the Fig. 9 and 10 can be merged.

One General comments: For the effect of intermetallic layers such as NiAl, FeAl and Al-oxide on the damping behavior: Did the authors consider the influence of the preparation method on the damping performance?

Author Response

Dear referee,

Finally, excuse me for the late response, due to access limitations to my University Department in August for the Covid epidemic.

Enrico G. Campari

Reviewer 3

-P1 In the manuscript, in my opinion, authors just focused on one coating— aluminide coating but with different thickness and pre-treatment, the abstract is not well organized, it is not clear to

describe the main methods, results and conclusions.

We slightly modified the abstract trying to make it clearer, even if still concise as it should be.

The "introduction" and the "materials and methods" were modified in order to clarify the production process, adding further details on the specimens production, see text.

-P3 In this manuscript, is the aluminium oxide layer same with alumina scale? If yes, that need to be unified, if not, please explain why.

In the text it is now specified that the aluminum oxide is a-Al₂O₃.

-P4 Authors needs to reorder the Figures.

First Fig. 1, then Fig. 3 and 4, then back to Fig. 2? I don’t think it is a good expression.

As also suggested by the other referees, figures have been modified and reordered. Specimens were relabeled in order to make their description clearer. Figure 1d (now figure 1f) and figure 5 were merged.

- The abbreviation needs to be consistent, like “Figure 1a and Figure 1e” (Line 137), “fig. 2b” (Line 157), “figure 1.” (Line 209).

The term "figure" is now the only used in the text and figure citations are ordered.

It is certainly true that the diffraction has penetration limits; This further structural characterization has been conducted to certify that after interdiffusion treatments you get the layers that are identified with the other techniques

-P6. In the Table 2, “56, 2” should be rewritten as “56.2”, etc.

Table 2 is now corrected.

-P7 Why put the optical microstructure here? Same with Fig. 1d? If we don't get more detailed information, then this picture is useless.

Figure 5 has been deleted (see comment to P5)

-P 9 in my opinion, the Fig. 9 and 10 can be merged.

The plots get rather superposed merging figures 9 and 10. We suggest keeping them separated on the ground of a better data display.

It's definitely a good comment. The adopted layered configuration is inexpensive, simple and easy to prepare, especially when compared to other technologies. At this stage of the research, we do not jet care about optimizing the process, as it should be done for a patent or an industrial process, but only look for general answers that will be later improved.

Round 2

Reviewer 1 Report

The authors reply to the observations promoted and improved the paper following some suggestions. Thus, the manuscript can be published in the Journal now.

Reviewer 2 Report

The authors have adequately addressed the comments and queries I raised. Therefore, I can recommend this paper for publication in the journal "Coatings". Unfortunately, the quality of the images given in Fig. 6 is too low (excessive etching) and will likely lower the impact the paper may have in the coating's Community.

Reviewer 3 Report

I would like to suggest to accept for the modified version.

Article Menu

Damping Behavior of Layered Aluminium and Aluminide Coatings on AISI 316 Austenitic Steel

Further Information

Guidelines

MDPI Initiatives

Follow MDPI