Influence of Temperature on Mechanical Properties of AMCs
Round 1
Reviewer 1 Report
The authors attrition-milled Aluminium powder under three different atmosphere conditions (vacuum, ammonia gas and a combination of vacuum and ammonia gas flow). Powders were consolidated by cold uniaxial pressing and vacuum sintering. Microstructural and mechanical properties were investigated.
The authors suggest that some of the second phases decompose (very slowly) during a heat treatment at 400°C for 100h.
There are some questions: The second phases decompose into what (decomposition reaction?)? Where are the decomposition products? If no new peaks can be found in the XRD patterns, how did the decomposition products leave the sample.
The authors should write a few words for explanation.
Author Response
Reviewers' comments: Reviewer 1 1.There are some questions: The second phases decompose into what (decomposition reaction?)? Where are the decomposition products? If no new peaks can be found in the XRD patterns, how did the decomposition products leave the sample. The authors should write a few words for explanation. Regarding this point, it is known that aluminium forms hydrides, which are brittle, but they are easily removed by forming hydrogen which is evacuated during sintering [1,2].
[1] J. Cintas, J. M. Montes, F. G. Cuevas, and E. J. Herrera, “Heat-resistant bulk nanostructured P/M aluminium,” Journal of Alloys and Compounds, vol. 458, no. 1-2, pp. 282–285, 2008.
[2] J. Cintas, J. A. Rodr ́ıguez, J. M. Gallardo, and E. J. Herrera, “The impact of bulk nanostructured materials in modern research,” Revista de Metalurgia, vol. 37, no. 2, pp. 370–375, 2001.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The present work investigates the effect of heat treatment on the mechanical properties of aluminum matrix composites. Aluminum powders were produced in three different environments: vacuum, ammonia, and short duration flow of ammonia under vacuum. The work seems interesting and can be considered for publication after some minor revisions:
- In line 81, please specify what type of atomized powders are these? Is it gas atomized or water atomized etc.? Is there any atomization medium entrapment in the powders?
- On multiple occasions, it was mentioned in the manuscript that ammonia gas incorporation occurs during milling process (line 129, 197 etc.). There are no hydrogen based products observed in the present work. Also, only nitrogen diffused into the powders? Text should be corrected accordingly.
- I believe nitrogen is detrimental for the Al as it may go into interstitial sites of Al and results in severe embrittlement? This issue should also be discussed in the text.
- Pertaining to heat treatment word “heating” should be replaced by “annealing” throughout the text (e.g. line 192).
- Parameters of Rietveld refinement should be provided in the text, otherwise, the quantification data is not reliable. Please provide the Debye–Waller temperature factor, Site occupancy factor (SOF) for corresponding to element in each compound, fitting function, function to take care of texture (if any). Quality of refinement was determined using the statistical parameters such as weighted R-profile (Rwp) and Goodness of Fit. Also, please provide any other variable or assumptions considered during rietveld refinement.
- Please label the microstructural features (dimples, loose particles, pre-existing pores, etc) shown in figure 6 and 7.
Comments for author File: Comments.pdf
Author Response
Reviewer 2
1.In line 81, please specify what type of atomized powders are these? Is it gas atomized or water atomized etc.? Is there any atomization medium entrapment in the powders?
Authors agree with reviewer’s comment, and have changed the line 81: “The starting material consisted of atomized elemental aluminium powder (AS 61, Eckart)”
by the following one:
“The starting material consisted of gas atomized elemental aluminium powder (AS 61, Eckart)”
2. On multiple occasions, it was mentioned in the manuscript that ammonia gas incorporation occurs during milling process (line 129, 197 etc.). There are no hydrogen based products observed in the present work. Also, only nitrogen diffused into the powders? Text should be corrected accordingly.
Regarding hydrogen, authors have already answered this question to reviewer 1 as follow: it is known that aluminium forms hydrides, which are brittle, but they are easily removed by forming hydrogen which is evacuated during sintering [1,2].We would like to added that hydrogen as well as phases with hydrogen have not never detected by XRD neither before and after the sintering process.
3. I believe nitrogen is detrimental for the Al as it may go into interstitial sites of Al and results in severe embrittlement? This issue should also be discussed in the text.
Authors do not understand very well what the reviewer wants to say. Aluminium and nitrogen have a high reactivity which is used to form nitrogen-rich second phases. Due to ceramic nature of that phases the aluminium alloy can become more brittle. In fact, authors used the high reactivity between aluminium and nitrogen to synthetizing aluminium nitride (AlN) via a solid-gas direct reaction [3].
4. Pertaining to heat treatment word “heating” should be replaced by “annealing” throughout the text (e.g. line 192).
The reviewer is completely right in this comment, so that authors have replaced “heating” by “annealing” throughout the text, particularly in lines 21, 188, 190 and 192.
5. Parameters of Rietveld refinement should be provided in the text, otherwise, the quantification data is not reliable. Please provide the Debye–Waller temperature factor, Site occupancy factor (SOF) for corresponding to element in each compound, fitting function, function to take care of texture (if any). Quality of refinement was determined using the statistical parameters such as weighted R-profile (Rwp) and Goodness of Fit. Also, please provide any other variable or assumptions considered during rietveld refinement.
Authors agree with the reviewer, so to show the fitting goodness it has been included a new column in Tables 3 and 4 with the Rwp parameter.
6. Please label the microstructural features (dimples, loose particles, pre-existing pores, etc) shown in figure 6 and 7.
Authors have included labels in figure 6 and 7 to show the different microstructural features.
[1] J. Cintas, J. M. Montes, F. G. Cuevas, and E. J. Herrera, “Heat-resistant bulk nanostructured P/M aluminium,” Journal of Alloys and Compounds, 458(1-2), 282–285, 2008.
[2] J. Cintas, J. A. Rodr ́ıguez, J. M. Gallardo, and E. J. Herrera, “The impact of bulk nanostructured materials in modern research,” Revista de Metalurgia, 37(2), 370–375, 2001.
[3] E.S. Caballero, J. Cintas, F.G. Cuevas, J.M. Montes and J.M. Gallardo, “A new method for synthetizing nanocrystalline aluminium nitride via a solid–gas direct reaction”, 287, 341-345, 2016.
Author Response File: Author Response.pdf
