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Peer-Review Record

Microstructure of a V-Containing Cobalt Based Alloy Prepared by Mechanical Alloying and Hot Pressed Sintering

Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Metals 2019, 9(4), 464; https://doi.org/10.3390/met9040464
Received: 8 March 2019 / Revised: 12 April 2019 / Accepted: 16 April 2019 / Published: 22 April 2019
(This article belongs to the Special Issue Metals Powders: Synthesis and Processing)

Round 1

Reviewer 1 Report

This manuscript concerns the synthesis of Co-alloy with high hardness and good toughness. The elaboration process is into steps: (a) ball-milled and (b) Heating under pressure. Despite the interesting mechanical behavior observed, several points should be more developed

1-      The synthesis method and particularly the second step must be more developed. Is this second step based on the HIP process? The holding time appears to be very short (20 min). Was this time varied and what is the influence on the as-obtained phases? Another point should be indicated: the heat rate to reach the holding temperature since diffusion reactions may be occurred before reaching the final temperature (1200°C)

 

2-      The qualitative X-ray diffraction study is insufficient to discuss more deeply the formation mechanism and factors governing the synthesis of such alloy.  A quantitative study must be undertaken using very good X-Ray data with high ratio Signal/Noise (this is not the case for the given pattern). This will allows by means of Programs such Rietveld or Maud to determine the amount of each phase in the final alloy.

      Furthermore the cell parameters of the obtained phases should be refined thanks to the cited programs

3-      This point is in relation with the second one. Is the amount of carbon used (0.6%) is sufficient to obtain all these carbides. Indeed the authors should check if carbon coming from ball and vial does not contribute to the formation of such carbides.

 

4-      SEAD diffraction patterns were given without any discussion in the manuscript. They must be discussed in the manuscript taking into account the space group and the cell parameters of each phase


Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

 

Thank you for your useful comments on our manuscript. The detailed corrections are listed below:

 

1- The synthesis method and particularly the second step must be more developed. Is this second step based on the HIP process? The holding time appears to be very short (20 min). Was this time varied and what is the influence on the as-obtained phases? Another point should be indicated: the heat rate to reach the holding temperature since diffusion reactions may be occurred before reaching the final temperature (1200°C)

 

We have described the mechanical alloying and sintering process in more detail in the revised manuscript. We also realized that the sintering parameters have much influence on the microstructure and properties of the obtained alloy and have started to investigate their influence.  

 

2- The qualitative X-ray diffraction study is insufficient to discuss more deeply the formation mechanism and factors governing the synthesis of such alloy.  A quantitative study must be undertaken using very good X-Ray data with high ratio Signal/Noise (this is not the case for the given pattern). This will allows by means of Programs such Rietveld or Maud to determine the amount of each phase in the final alloy.

 

We have again studied the X-ray diffraction results in more detail and corrected the results. We carried out a quantitative study to determine the volume faction of the phases by using quantitative metallography instead of using X-Ray data.   

 

      Furthermore the cell parameters of the obtained phases should be refined thanks to the cited programs

 

We have refined the cell parameters of the obtained phases in our revised manuscript.

 

3- This point is in relation with the second one. Is the amount of carbon used (0.6%) is sufficient to obtain all these carbides. Indeed the authors should check if carbon coming from ball and vial does not contribute to the formation of such carbides.

 

It is difficult to determine the amount of carbon used (0.6%) is sufficient to obtain all these carbides or not because of lack in density data of various phases.

The stainless steel vial and stainless steel balls were used to prepared the Co-based alloy powders in this work. According to the STEM-EDS results, small amount of Fe was indeed introduced into the sintered alloy. However, we dont think the carbon introduced from the stainless steel vial and stainless steel balls have much influence on the formation of carbides because the amount of introduced carbon was very small compared to the added 0.6 wt.% C.

  

4- SEAD diffraction patterns were given without any discussion in the manuscript. They must be discussed in the manuscript taking into account the space group and the cell parameters of each phase

 

The SEAD diffraction patterns were given to identify the phases. In relation to the XRD and STEM-EDS results, it is enough to confirm these phase. Therefore, we dont think it is necessary to further take into account the space group and the cell parameters of each phase.


Reviewer 2 Report

In this study, the V-containing cobalt-based alloy with high hardness and good toughness was prepared by the powder metallurgy technique, and the experimental part itself is considered to be demonstrated well. However, the objectives of this work is quite vague. If the purpose of this study is to investigate the effects of V on microstructure and mechanical properties of cobalt-based alloy, as described in the last paragraph in the introduction, The authors should prepare V-free sample at the same time, and these properties should be compared and discussed in detail. Or is the composition of the base alloy new and original? If so, the structure of the present manuscript is not appropriate and should be totally reconstructed to reflect the true novelty and achievement of this study including clear statement of the strategy leading to this composition.


Author Response

Dear Reviewer,

 

Thank you for your useful comments on our manuscript. 

 

In this study, the V-containing cobalt-based alloy with high hardness and good toughness was prepared by the powder metallurgy technique, and the experimental part itself is considered to be demonstrated well. However, the objectives of this work is quite vague. If the purpose of this study is to investigate the effects of V on microstructure and mechanical properties of cobalt-based alloy, as described in the last paragraph in the introduction, The authors should prepare V-free sample at the same time, and these properties should be compared and discussed in detail. Or is the composition of the base alloy new and original? If so, the structure of the present manuscript is not appropriate and should be totally reconstructed to reflect the true novelty and achievement of this study including clear statement of the strategy leading to this composition.

 

The work we are submitting is our preliminary results, systematic research including the wear property, effect of V content and process parameters on the microstructure and properties will start to be carried out in our lab.

 


Reviewer 3 Report

Dear authors,

The manuscript deals with the preparation process by mechanical alloying and hot pressing sintering, and microstructural characterization of a V-containing Co-base alloy. Also hardness and toughness are reported in the manuscript.

After reading the manuscript I consider the manuscript can be published after revising a series of changes indicated next.

 

-          Line 33-37. Authors make reference to Co alloys with good wear properties (also line 52 makes reference to wear), however, this does not seem to be related with their study, because no wear results are reported in the manuscript. Authors are measuring hardness and toughness, and the introduction should make emphasis on this properties on Co-base alloys, to make possible the comparison with the results of this manuscript.

-          Line 60. Purity of the used elements should be indicated.

-          Line 61. Regarding milling, the time interval used should be indicated in the methods section, as well as the total (or powders) mass of each milling process.

-          Line 67. Used radiation should be indicated, as well as XRD conditions (step, time for each step)

-          Line 70. Also the STEM equipment, or whether is the same as TEM, should be indicated.

-          Line 85. It is not clear the reason for not finding in the 0 h pattern the other peaks of certain elements, for instance, Co (in proportion of 32%) should have another peaks at about 52 and 76º under Cu radiation. Could it be due to the experimental conditions, (little detailed, too quick pattern)? Please check also the other elements. Also check that Figure 4 shows these other peaks.

-          Line 94. Indicate the abbreviation BSE the first time in the text.

-          Line 100. Indicate that gamma-Co is a FCC structure, and also that carbides are cubic structures.

-          Line 100. Also add something like JCPDS or ICDD card # before the number indicated in the text.

-          Line 100. This is a doubt of the reviewer: is it, for instance, the card number 22-597 a general card for M6C or specific of a particular carbide? Being of an specific metallic carbide should be indicated.

-          Line 103. Introduce the technique STEM and the meaning of STEM-HAADF in the Methods section.

-          Line 109. Any reason for not indicating that M6C is W-rich but also Cr-rich?

-          Line 108-110. When comparing the identification by colours given here with the identification in lines 99-101, there is something wrong.

-          Line 111-115. Phases sizes are indicated, but it is not clear where were they measured. Fig 3 or Fig 5? Please check the indicated values according to the appropriate figure.

-          Line 112. An average value is given. How was this average value obtained? Image analysis, line intercept… The technique should be indicated in the Methods section, making reference to the number of particles measured to reach the average value, also deviation should be indicated.

-          Line 120. Maybe indicating the phases in Figure as done in Figure 6, with the chemical composition instead of numbers, would make easier to follow the microstructure. The lower right corner of Figures b, d and e, indicating the phase is not clearly shown.

-          Line 123. Authors should comment on the presence of Fe in the EDS results, with a reported presence of up to 4.33.

-          Line 128. Number of measurement to reach the value 960 and deviation should be indicated somewhere. Please note that an adequate number of measurements have to be done to make the indicated value and acceptable measured property.

-          Line 133. Idem regarding toughness.

-          Line 137. Idem regarding crack length.

-          Line 142. Maybe the rectangle in fig a should be placed in the other side to make it coincident with the direction of the crack shown in Fig b.

-          Line 147. As-HPed must be defined, and indicated the first time used in the text.

-          Line 150. MX referring to carbonitride could be clarified indicating the definition of X. Also the meaning of M referring to Metal, although obvious, could be indicated at the manuscript beginning, the first time used.

-          Line 158. Please note that the structure is not totally amorphous after milling.

-          Line 162. It should be clarified the reason to say that M23C6 appears during cooling.

-          Line 179. Add ‘and cooling’ at the end of caption.

-          Line 180. Why do you indicate up to 960, is it a simple measurement or an average value?


Author Response

Dear Reviewer,

 

Thank you for your useful comments on our manuscript. The detailed corrections are listed below:

 

- Line 33-37. Authors make reference to Co alloys with good wear properties (also line 52 makes reference to wear), however, this does not seem to be related with their study, because no wear results are reported in the manuscript. Authors are measuring hardness and toughness, and the introduction should make emphasis on this properties on Co-base alloys, to make possible the comparison with the results of this manuscript.

 

The work we are submitting is our preliminary results, systematic research including the wear property, effect of V content and process parameters on the microstructure and properties will start to be carried out in our lab.

As to the hardness and toughness of Co-base alloys, we have reviewed in our revised manuscript.

 

- Line 60. Purity of the used elements should be indicated.

 

Purity of the used elements have been indicated in our revised manuscript.

 

-  Line 61. Regarding milling, the time interval used should be indicated in the methods section, as well as the total (or powders) mass of each milling process.

 

The mechanical alloying method has been indicated in more detail in our revised manuscript

 

-  Line 67. Used radiation should be indicated, as well as XRD conditions (step, time for each step)

 

The XRD analyses method has been indicated in more detail in our revised manuscript.

 

-  Line 70. Also the STEM equipment, or whether is the same as TEM, should be indicated.

 

The STEM and TEM are the same equipment and it has been indicated in more detail in our revised manuscript

 

-  Line 85. It is not clear the reason for not finding in the 0 h pattern the other peaks of certain elements, for instance, Co (in proportion of 32%) should have another peaks at about 52 and 76º under Cu radiation. Could it be due to the experimental conditions, (little detailed, too quick pattern)? Please check also the other elements. Also check that Figure 4 shows these other peaks.

 

The peaks at 52 and 76º are very weak but still visible as shown in Figure 1 and we have indexed these peaks in the revised manuscript. We have also checked the figure 4.  

-  Line 94. Indicate the abbreviation BSE the first time in the text.

 

We have indicated the abbreviation BSE in the revised manuscript.

.

-  Line 100. Indicate that gamma-Co is a FCC structure, and also that carbides are cubic structures.

 

We have indicated them in the revised manuscript

 

-  Line 100. Also add something like JCPDS or ICDD card # before the number indicated in the text.

 

We have added them in the revised manuscript

 

-  Line 100. This is a doubt of the reviewer: is it, for instance, the card number 22-597 a general card for M6C or specific of a particular carbide? Being of an specific metallic carbide should be indicated.

 

We have checked again the XRD results and found that the peaks are in accordence with that of Co6W6C carbide (JCPDS No 22-0597) . Therefore, the W-rich phase should be M12C-type carbide. According to the STEM-EDS results, the Co and W in Co6W6C carbide can be substituted by Cr and V as well as Fe but the lattice parameter do not change obviously.

 

-  Line 103. Introduce the technique STEM and the meaning of STEM-HAADF in the Methods section.

 

We have Introduced the technique STEM and the meaning of STEM-HAADF in the Methods section in the revised manuscript.

 

 -  Line 109. Any reason for not indicating that M6C is W-rich but also Cr-rich?

We have changed our description of M12C in the revised manuscript.

 

-   Line 108-110. When comparing the identification by colours given here with the identification in lines 99-101, there is something wrong.

 

Yes. I have corrected them in the revised manuscript   

 

-   Line 111-115. Phases sizes are indicated, but it is not clear where were they measured. Fig 3 or Fig 5? Please check the indicated values according to the appropriate figure.

The value of the phase sizes is measured in Fig 3 using line intercept method, which has been indicated in the revised manuscript.   

 

- Line 112. An average value is given. How was this average value obtained? Image analysis, line intercept… The technique should be indicated in the Methods section, making reference to the number of particles measured to reach the average value, also deviation should be indicated.

The value of the phase sizes is measured using line intercept method, and the technique has been indicated in the revised manuscript.   

 

- Line 120. Maybe indicating the phases in Figure as done in Figure 6, with the chemical composition instead of numbers, would make easier to follow the microstructure. The lower right corner of Figures b, d and e, indicating the phase is not clearly shown.

 

Yes, I agree. I have corrected them in the revised manuscript.

 

- Line 123. Authors should comment on the presence of Fe in the EDS results, with a reported presence of up to 4.33.

 

Fe should be introduced from stainless vial and balls during mechanical alloying process. We have comment on it in the in the revised manuscript.

 

-  Line 128. Number of measurement to reach the value 960 and deviation should be indicated somewhere. Please note that an adequate number of measurements have to be done to make the indicated value and acceptable measured property.

 

The value 960 is an average value of 5 measurements. Number of measurement and deviation has been indicated in the revised manuscript.

 

-  Line 133. Idem regarding toughness.

 

Number of measurement and deviation has been indicated in the revised manuscript.

 

- Line 137. Idem regarding crack length.

 

Number of measurement and deviation has been indicated in the revised manuscript.

 

-  Line 142. Maybe the rectangle in fig a should be placed in the other side to make it coincident with the direction of the crack shown in Fig b.

 

The crack shown in Fig b is located in the position of rectangle in fig a. Indeed, the crack has two propagation directions, one to indention core and the other away from indention.

 

- Line 147. As-HPed must be defined, and indicated the first time used in the text.

 

We have indicated it in the revised manuscript.

 

-   Line 150. MX referring to carbonitride could be clarified indicating the definition of X. Also the meaning of M referring to Metal, although obvious, could be indicated at the manuscript beginning, the first time used.

 

We have indicated them in the revised manuscript.

 

- Line 158. Please note that the structure is not totally amorphous after milling.

 

We have corrected it in the revised manuscript.

 

-  Line 162. It should be clarified the reason to say that M23C6 appears during cooling.

 

The microstructural formation mechanism is not clear yet. Thats only our speculation according to the microstructural characteristic. We have clarified it in more detail in the revised manuscript.

 

- Line 179. Add ‘and cooling’ at the end of caption.

 

‘and cooling’ has been added in the revised manuscript.

 

- Line 180. Why do you indicate up to 960, is it a simple measurement or an average value?

It is an average value. We have corrected the direction in the revised manuscript.

 

 


Round 2

Reviewer 1 Report

The authors should use XRD analysis to determine the amount of each present phases rather than metallography method. Furthermore this allows to obtain the cell parameters with accurrancy. The XRD data should be collected with longer time in order to obtain good quality pattern with high signal/noise. Very diffracttion peaks are not explained in the present version. 

On the other side chemical analysis of the final materials after HIP should be done. This result along with that obtained by XRD will enable to discuss the source of Carbon. Carbon can also come from the graphite mold

Author Response

Dear reviewer,

 

Thank you very much for your valuable comments!

 

The authors should use XRD analysis to determine the amount of each present phases rather than metallography method. Furthermore this allows to obtain the cell parameters with accuracy. The XRD data should be collected with longer time in order to obtain good quality pattern with high signal/noise. Very diffraction peaks are not explained in the present version.

 

Quantitave XRD analysis is not available now. We will do it and improve our research in the future.

 

On the other side chemical analysis of the final materials after HIP should be done. This result along with that obtained by XRD will enable to discuss the source of Carbon. Carbon can also come from the graphite mold.

 

Carbon content in the final materials after HIP was determined using carbon and sulphur analyzer. Indeed, carbon content was increased. And we have discussed the source of carbon in the revised manuscript.

 


Reviewer 2 Report

The manuscript has not been revised accordingly at all and the objectives of this study still remain quite vague as pointed before. This is very crucial point. If the research is on the way as mentioned in the response, after the objectives, novelty, benefits of this work, etc. become clear by further progress or completion of the future work, the paper should be totally reconstructed and then considered to be resubmitted in this journal or elsewhere.


Author Response

Dear reviewer,

 

Thank you very much for your valuable comments! We are sorry that we overlooked some of your valuable comments during the last revision.

 

The manuscript has not been revised accordingly at all and the objectives of this study still remain quite vague as pointed before. This is very crucial point. If the research is on the way as mentioned in the response, after the objectives, novelty, benefits of this work, etc. become clear by further progress or completion of the future work, the paper should be totally reconstructed and then considered to be resubmitted in this journal or elsewhere.

 

We studied this alloy to obtain a new material which has both good wear-resistant property and adequate toughness used for ultra-high speed rotating parts of aeroengine. Even though the wear-resistant property did not carry out yet, the high hardness and good toughness of the prepared alloy can be expected to have good wear-resistant property.


Reviewer 3 Report

Authors have atended most of the comments on my previous review, although some details should still be taken into account:

- Figure 4 still maintain M6C instead of M12C.

- Figure 5 is still not clear regarding the identification of the phases in the bottom right corner of the figures.

- In general, the resolution of figures in the pdf version of this review should be not aceptable for publication (check for instance Fig 7a). This should be improved in the final version.

- Author indicate that the cubis structure of matrix and carbides has been indicated in the text, I expected to find this when lattice parameters are indicated, but I think this information is still missing.

- Authors indicate in their response that the appearance of fine M23C6 carbides during cooling is discussed in this new version of the manuscript, but I was unable to find this discussion.  

Author Response

Dear reviewer,

 

Thank you very much for your valuable comments! We are sorry that we overlooked some of your valuable comments during the last revision.

 

 

Authors have attended most of the comments on my previous review, although some details should still be taken into account:

 

- Figure 4 still maintain M6C instead of M12C.

 

We have corrected them in the revised manuscript this time.

 

- Figure 5 is still not clear regarding the identification of the phases in the bottom right corner of the figures.

 

We have replaced them with clear Figures in the revised manuscript this time.

 

- In general, the resolution of figures in the pdf version of this review should be not acceptable for publication (check for instance Fig 7a). This should be improved in the final version.

 

We have improved them in the revised manuscript this time.

 

- Author indicate that the cubic structure of matrix and carbides has been indicated in the text, I expected to find this when lattice parameters are indicated, but I think this information is still missing.

 

We indicated this in Line 122-123 and 228-230 in the revised manuscript.

 

- Authors indicate in their response that the appearance of fine M23C6 carbides during cooling is discussed in this new version of the manuscript, but I was unable to find this discussion.  

 

We discussed in the revised version as follows:

The fine M23C6-type carbide particles within both the γ-Co matrix and M12C-type carbide particles are precipitated from the γ-Co matrix and M12C-type carbide during the furnace cooling process after hot pressed sintering because their size is much smaller than that of the striplike M23C6 carbide. M23C6 carbide precipitates usually along grain boundaries during cooling process in convention alloys, such as austenitic steels and Ni-based superalloys. While the fine M23C6 carbide precipitates within γ-Co matrix in the present V-containing alloy, we think the reason might be that the M23C6 carbide contains a lot of V element which has a larger atom size and lower diffusion coefficient than Cr element. 


Round 3

Reviewer 1 Report

Despite that paper still needs an accurate XRD quantification analysis, it can be  accepted for publication in its revised version

Reviewer 2 Report

The novelty of the composition has been stated in the revised manuscript, so it is now considered that this work is acceptable for publication.


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