Microstructure and Mechanical Properties of CoWB Based Composites Produced by Crystallization of Ni-Co-Zr-Ta-W-B Bulk Metallic Glass

Round 1

Reviewer 1 Report

The authors have prepared the CoWB matrix composites by annealing Ni33.6Co23.2Zr0.5Ta4W23.7B15 block Me-10 talc glass above the crystallization temperature.

The effect of annealing on the microstructure and mechanical properties of composites was studied. However, there are still some extensive mistakes in this manuscript that need to be addressed:

1. For the DSC test, it can be seen that the minimum crystallization temperature is 981K, but the author chose 1025K for annealing temperature, so why choosing high temperature instead of low temperature? Fig.1 is wrong. The authors labeled the melting temperature and crystallization temperature in the wrong order.

2. In Figure 3, there is mistake in font format. Figure 3b is missing original coordinates.

3. "3.3SEM analysis" mentions "The 50 min 154 annealed sample contains Ni-phase and CoWB", how to determine that the precipitated substances are Ni phase and CoWB? The authors must supply the corresponding SEM/EDS elemental mapping.

4. How does the author obtain the grain size quantification statistics? Was it only from Figure 4? Did the authors perform multiple SEM images to generate statistics?

5. In the "Discussion" section, the author mentioned that the microhardness of the composite material had not been improved, but remained unchanged. This is because the Ni phase has a phase transition to the Ni3Ta phase, and the Ni3Ta phase has a much lower microhardness value, about 500HV. Here, can the author supply the corresponding nanoindentation test to further prove the authors' point of view and make it convincing?

6. “The results revealed that volume fraction CoWB is ~0.4 in the composites obtained after annealing the amorphous alloy for 100 and 150 min (Table 2).” It was quantified from 2D not 3D and should be changed to area fraction.

7. How can the authors tell the reduction of fracture toughness from a single test? How can the authors tell it was the Ni3Ta instead of CoWB which reduce the fracture toughness?

8. The authors proposed the addition of Cu to replace Ni and reduce the negative effects of Ni3Ta. Have the authors done any experiments to support this? What is the role of Ta? What if reducing Ta instead of Cu?

9. “As the annealing time is increased, CoWB begins to precipitate as well as the nickel solid solution. If the annealing time is increased further, CoWB remains stable, while the nickel solid solution transforms into the Ni3Ta.” Is there any results to support this firm conclusion? It would be better not to draw such firm conclusions.

10. "There is no particular reason for choosing this temperature. Another temperature above the crystallization temperature could also be chosen as the annealing temperature. " Again, this kind of lose talking is not acceptable for scientific publications.

11. "The master alloy Ni33.6Co23.2Zr0.5Ta4W23.7B15 was prepared " Are they atmic percent or weight percent? It should be given clearly.

12. XRD should give the initial phase instead of just the final phase.

13. The procedure for calculating the phase fraction from XRD should be given.

14. “Because boron is not soluble in Ni and there exits only one phase containing boron, all of the boron atoms are expected to be in CoWB after completion of the crystallization.” The reference should be given.

15. The reference should be given in Table 3.

16. “Microhardness of Ni-25 at.% W solid solution with a grain size of 12 nm is about 1450 HV [34]. Because it is the majority phase in the composites obtained as a result of annealing for less than 50 min, the microhardness of the composites is about 1350 HV.” The logic is not right.

17. “Kc of the composite with the highest microhardness is quite low” The transformation from high hardness Ni phase into low hardness Ni3Ta phase should increase the Kc but the authors found the opposite. It should be clarified.

18. The English grammar should be double checked and the analysis of the results should be performed in details.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript reports on the study of microstructure and mechanical properties of CoWB based composites. The presented results will be of interest to scientists working with composites based on CoWB. The material under consideration requires further study. Thus, the manuscript can be recommended to be published in Metals after the authors address the following comments/concerns.

Introduction

• Please increase the relevance of the study in the introduction

Materials and Methods

• Line 27 - high-temperature?
• Line 63 - what caused the choice of annealing time? Is there a significant difference with materials with a different composition? For example, without tantalum addition?
• Lines 85 and 96 – Fig. 1 and Fig. 2 - the quality of the figures and signatures is not very good.

Results and Discussions

• Line 110 - Please indicate the error in determining the lattice parameters in Table 1.
• Line 176 - Please indicate the error in determining the microhardness values in Figure 5.

However, these comments do not reduce the relevance and importance of the results. The article is sufficiently novel and interesting to warrant publication. Results and discussion are reliable. References reflect the main publications on which the work is based.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript deals with novel CoWB materials produced via crystallization and further annealing Ni-Co-Zr-Ta-W-B systems. The challenge in  this field is to make tune the mechanic properties with simultaneous reproducibility of the contents and chemical structure of the metal glass composition. And I think the authors have resolved this problem for the case of CoWB based materials. For this purpose, they used a traditional set of the physicochemical techniques, including high-resolution microscopy and XRD studies.

I fing the results trustworthy and publishable. The manuscript clearly discuss the relations between the chemical and mechanical properties.

I recommend the manuscript for publication.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed only one third of the mistakes that we have pointed out. It should be revised again.

Author Response

Response to Reviewer 1 Comments

Point 1: The authors have addressed only one third of the mistakes that we have pointed out. It should be revised again.

Response 1: Unfortunately, we are unable to respond to this comment, because Reviewer 1 has not indicated which of our answers he/she still does not agree with.