The Preparation and Properties of Ni2Al3 Intermetallic Compound Coating
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThank you for sharing your draft with the journal, I have the following comments to improve the work:
-You can shorten the title by removing "and the high temperature oxidation performance for the coating" as that is expected to be studied in the work.
-Please rephrase in page 2 line 49 "the electroplating Ni process requires high requirements"
-Line 51 "that require thicker coatings", can you please clarify with some examples to emphasize the need for thicker coatings.
-Very good introduction with literature review.
-Please highlight the significance compared to previous research. You describe what you did in the work but what is the downside of previous methods?
-What do you mean by "This work would produce an enlightening significance" please clarify.
-Please specify the general outline of the paper at the end of the introduction.
-Does this method work on other types of steel or is it just specific for 45# steel?
-Is the coating you presented beneficial to other steel types?
-Section: preparation of coatings: why did you choose a distance of 15mm? is there a standard for the distance when coating?
-Results and analysis: how stable is this layer, as you mentioned diffusion can occur to generate different forms of Al:Ni is that an issue that will compromise the coating integrity? and how long does the diffusion process take?
-Great job with the figures, figures 6 and 7 clarify a variety of questions I had.
-Figure 11 is also very well presented.
-Its very interesting to see how this coating outperformed the Cr oxide films on the 15 CrMo steel.
Overall, great job. Please work on answering my questions.
Comments on the Quality of English LanguagePlease do a full grammatical review, there are some sentences such as "the electroplating Ni process requires high requirements" that need revising.
Author Response
Comment 1：
- You can shorten the title by removing "and the high temperature oxidation performance for the coating" as that is expected to be studied in the work.
Answer:Thank for your recommendation, the title has been simplified as:
Preparation and property of Ni2Al3 Intermetallic Compound Coating
Comment 2:
- Please rephrase in page 2 line 49 "the electroplating Ni process requires high requirements"
Answer: The rephrase has been simplified as: The electroplating Ni process, however, imposes stringent requirements and is limited to producing coatings with thicknesses around 10 micrometers[16]
Comment 3:
- Line 51 "that require thicker coatings", can you please clarify with some examples to emphasize the need for thicker coatings.
Answer: The electroplating Ni process, however, imposes stringent requirements and is limited to producing coatings with a few micrometers, rendering it unsuitable for applications that demand thicker coatings. Such as the high-temperature oxidation resistance coating for cast iron，which is 30~100μm[16].
Comment 4:
4)Very good introduction with literature review.
Answer: Thanks
Comment 5:
5)Please highlight the significance compared to previous research. You describe what you did in the work but what is the downside of previous methods?
Answer: We supplement the necessary why we do this work as follows:
At present, the preparation methods of Ni2Al3 coatings mostly use electroplating Ni firstly and then infiltration Al, in order to obtain Ni2Al3 coatings during the infiltration Al process[15]. The electroplating Ni process, however, imposes stringent requirements and is limited to producing coatings with thicknesses around 10 micrometers[16], rendering it unsuitable for applications that demand thicker coatings,such as the high-temperature oxidation resistance coating for cast iron，which is 30~100μm [17]. Patel et al. prepared a high temperature oxidation resistant coating on Ti6Al4V alloy by diffusion heat treatment after hot-dip aluminizing[18]. Relevant studies have shown that Ni and Al can form intergranular compounds at high temperatures, but the Ni2Al3 formed is only on the Ni/Al interface [19]. Therefore, if a mixed coating with uniform distribution of Ni and Al was formed before high temperature treatment, a full Ni2Al3 coating maybe formed after heat treatment. The key is how to form a mixed coating with uniform distribution of Ni and Al.
Cold spraying, also known as cold aerodynamic spraying method, is a spraying technology based on aerodynamic principles. It obtains high-speed airflow through the process of heating and pressurization, and impacts the substrate at a critical or supercritical speed, causing the sprayed powder particles to undergo thermal softening and plastic deformation, and deposit on the surface of the substrate. The raw material for cold spray is metal powers which means that powders can be flexibly selected[20], so, it is a promising way to obtain the mixed coating with uniform distribution of Ni and Al by cold spraying.
In this work，we used low-pressure cold spraying technology to prepare Ni-Al composite coating（mechanical mixture layer of Ni and Al）as pre-coating and then heat treatment the pre-coating to prepare a Ni-Al composite coating with Ni2Al3 as the main phase.
Comment 6:
6)What do you mean by "This work would produce an enlightening significance" please clarify.
Answer: "This work would produce an enlightening significance" refers to “This work will provide a new way to prepare high temperature protective coating for parts”.
Comment 7:
7)Please specify the general outline of the paper at the end of the introduction.
Answer: Thank for your recommendation, the general outline has been added as follows:
In this work, we firstly prepared Ni2Al3 composite coating on 45#steel by using low-pressure cold spraying technology and heat treatment process. Then, the surface and cross-section microstructure of the Ni2Al3 composite coating was characterized, and the phase composition for the coating was also analyzed. After that, the high-temperature oxidation performance of the composite coating was tested by isothermal oxidation tests in a high-temperature air environment at 600 ℃, and 15CrMo heat-resistant steel were used as a comparison sample. At the end, the high-temperature oxidation mechanism for Ni2Al3 composite coating was analyzed.
Comment 8
- Does this method work on other types of steel or is it just specific for 45# steel?
Answer: There are a range of substrates for cold sprayed process, such as low carbon steel. 45# steel was chosen because of its widely used in boiler.
Comment 9:
- Is the coating you presented beneficial to other steel types?
Answer：The coating preparation method is useful for other steels.
Comment 10:
- Section: preparation of coatings:why did you choose a distance of 15mm? is there a standard for the distance when coating?
Answer：Usually there is no standard spraying distance. The shorter distance, the stronger impact energy and powders is easy to rebound. However, the larger distance is difficult to obtain sufficient powder kinetic energy, which would affecting the binding force of the coating. We experiment a variety of different distances and finally determined that the optimal spraying distance was 15mm by evaluating the quality of the coating.
Comment 11:
11)Results and analysis: how stable is this layer, as you mentioned diffusion can occur to generate different forms of Al:Ni is that an issue that will compromise the coating integrity? and how long does the diffusion process take?
Answer：The Ni2Al3 intermetallic compound coating is very stable at 600℃. Actually, we heat treatment Ni-Al composite coating at 570℃ for 12h to transform the coating into an intermetallic compound coating with Ni2Al3 as the main phase, and the content of other phases is very low. In this experiment, the driving force of Ni and Al solid phase transformed into Ni-Al intermetallic compounds is heat energy provided by heat treatment and deformation energy of the powder after strong plastic deformation.
A small amount of NiAl phase generated during the diffusion process will not affect the high-temperature oxidation performance of the coating. At first, only a very small amount of NiAl phase will be geberated because the driving force of the transformation of Ni2Al3 into NiAl is only the heat energy provided by high temperature, It takes at least 594h to completely transform Ni2Al3 into NiAl at 650℃ argon. On the other hand, NiAl phase also has a strong high-temperature oxidation resistance as Ni2Al3.
Comment 12:
- Great job with the figures, figures 6 and 7 clarify a variety of questions I had.
Answers: Thanks.
Comment 13:
- Figure 11 is also very well presented.
Answers: Thanks.
Comment 14:
- Its very interesting to see how this coating outperformed the Cr oxide films on the 15 CrMo steel.
Answers: Thanks.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsComments for author File: Comments.pdf
Author Response
Comment 1:
1) Incorporate the key findings in the abstract.
Answer: The abstract has been revised as: In this work, a Ni2Al3 intermetallic compound coating was prepared on 45#steel by combining methods of low-pressure cold spray and heat treatment. Firstly, powders mixed with Ni powders, Al powders, and Al2O3 powders as a mass ratio of 20:6:4 were sprayed on surface of 45 steel by low-pressure cold spraying technology to prepare a Ni-Al pre-coating. Subsequently, the pre-coating was annealed at 570 ℃in an argon atmosphere for 12 h to obtain the Ni2Al3 intermetallic compound coating. The composite coating was characterized using TEM, SEM, and XRD. High Temperature Oxidation Performance of the composite coating was analyzed by isothermal oxidation tests conducted at 600 ℃ in air atmosphere for 96 h. The results show that the composite coating is composed of Ni2Al3 phase; Under high-temperature oxidation environment, a protective oxide film composed by Al2O3 and NiO was formed on the coating surface , which resulting in a superior high-temperature oxidation resistance compared to 15CrMo heat-resistant steel; The mechanism of the Ni2Al3 coating resistance to high-temperature oxidation is that an oxide film mainly composed of Al2O3 and NiO formed on the surface during the high-temperature oxidation process, this oxide film can effectively resist oxidation and protect the substrate material from oxidation at a high temperature of 600 ℃.
Comment 2:
2) what about cycic oxidation test?
Answer: In this work, we adopt static oxidation experiment at 600℃ to test the high temperature oxidation property of the Ni2Al3 coating. In order to survey the change of the coating during high temperature, the variation of coating weight in different time periods (every 24 hours) was monitored.
Comment 3:
3) how the elemental composition in wt% of the powders and substrates was measured
Answer: The substrates 45 # steel is purchased directly and the element content is shown in the table below. Powder used in this experiment was pure Ni, Al, and Al2O3 produced from Beijing Xingrongyuan Technology Co., Ltd. Before spraying, the three powders were uniformly mixed in a mass ratio of 20:6:4.
Tab 1 The chemical composition of 45# steel
|
The chemical composition |
C |
Si |
Mn |
Cr |
P |
Fe |
|
substrates（wt%） |
0.44 |
0.24 |
0.51 |
0.19 |
0.027 |
Bal. |
Comment 4:
4) How the temperatures ranges of the oxidation test were decided?
Answer: The temperature of oxidation test was decided by TAG analysis. From the TAG analysis of 15CrMo steel and Ni2Al3 intermetallic compound coating，it can be seen that the weight of 15CrMo steel, and Ni2Al3 coating began to increase when the temperature up to 500 ℃. Therefore, static oxidation tests were conducted at 600 ℃.
Comment 5:
5) check it, “ they have strongly long for the application pro-36 spects in high-temperature service occasions”
Answer: This was revised as follows: they have great application prospect in high-temperature field.
Comment 6:
6) its Cr steel, “15GrMo heat-resistant steel”
Answer: We are sorry for this mistake, 15CrMo is right.
Comment 7:
7) how the mass ratio “mass ratio of 20:6:4” is selected?
Answer: In the preliminary work，we found that the coating obtained by cold spraying with mixed powders (mass ratio of Ni, Al, Al2O3 is 20:6:4 ) has a superior high temperature wear resistance, in this work, we studied the high temperature oxidation property of the coating.
Comment 8:
- Show SEM image with average thickness of coatings.
Answer: The overall picture of the sectional coating has been added in Figure 2, and it can be easily seen that the average thickness of the coating is about 600μm.
Figure 2. SEM images of cross-sectional of the coating and EDS analysis of cross-sectional of the coating .
Comment 9:
- Types of bonding, mechanical or metallurgical, “the bonding force”
Answer: In the pre-cold spray coating, the bonding force of metal particles in the coating, and the force between the substrate and the coating is mechanical bonding. After heat treatment process, metallurgical bonding were occur due to the mutual diffusion of metal atom.
Comment 10:
- compare XRD before and after heat-treatment.
Answer: The XRD has been supplemented as follows:
Figure 3. The XRD of the pre-coating ((a)before heat treatment; (b)after heat treatment.)
Comment 11:
- section 2.4, the TEM characterisation part is missing.
Answer: The TEM characterisation was added as follows:
High-resolution images of the coating were obtained using field emission transmission electron microscopy(TEM, Talos F200, FEI, Brno, Czech Republic), enabling analysis of the coating's microstructure, crystal plane spacing, and electron diffraction patterns.
Comment 12:
12) Caption seems not correct, “Figure 7. the Ni2Al3 Intermetallic Compound Coating and 15CrMo oxidation kinetic curve”
Answer: The caption of Figure 7. is revised as : The oxidation kinetics curves of the Ni2Al3 coating and 15CrMo acquired at 600°C.
Comment 13:
13) Eq 1 what is the value of C to determine the value of Kp.
Answer: The Kp value is calculated using only the change in weight (ΔG), and the constant C was cancelled out during the calculation.
Comment 14:
- What is the Gibbs free energy for the formation of various oxides which oxide will form first (NiO and Al2O3)
Answer:
Through consulting the information, we can see that:
G(Al2O3)=-1681278.79-28.49T(ln T)+498.67T=-1414328.3 J/mol
G(NiO)= -239484-4.898T(ln T)+124.202T = -159999.2 J/mol
From the view of thermodynamic, the phase with low free energy will be preferentially generated, so Al2O3 should be the proformational phase.
Comment 15:
15) why test temp is 600 ℃.
Answer: From the TAG analysis of 15CrMo steel and Ni2Al3 intermetallic compound coating，it can be seen that the weight of 15CrMo steel, and Ni2Al3 coating began to increase when the temperature up to 500 ℃. Therefore, static oxidation tests were conducted at 600 ℃.
Comment 16:
16) Whether oxide layer thickness was measured after each time the samples were taken out.
Answer: We do not measure the oxide layer thickness after each time the samples were taken out. We mainly tested the weight change of coating after different oxidation time.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsI have carefully read your manuscript entitled "Two-step method preparation of Ni2Al3 Intermetallic Compound Coating and the High Temperature Oxidation Performance for the Coating" submitted to the Journal of Coatings. I appreciate the novelty and significance of your work, which aims to prepare a Ni2Al3 intermetallic compound coating on 45#steel by combining methods of low-pressure cold spray and heat treatment, and to evaluate its high temperature oxidation performance. I think your work is well-written, well-organized, and well-supported by experimental data and analysis. Therefore, I recommend that your manuscript be accepted for publication without any further revisions.
Author Response
Thank for your affirmation.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThank you for sending your corrections and answering all my comments. Great job with this work.
