Improving the W Coating Uniformity by a COMSOL Model-Based CVD Parameter Study for Denser Wf/W Composites
, Jan Willem Coenen 1,3, Johann Riesch 4, Yiran Mao 1, Daniel Schwalenberg 1, Hanns Gietl 5, Christian Linsmeier 1 and Olivier Guillon 1,2,6Round 1
Reviewer 1 Report
The authors have done attempted to model the CVD process in creating Wf/W. This could be a very informative work, but without some form of validation of the models it should not be published. I think it really would benefit from some experimental data showing that the model set out is applicable to this system, and that by varying the parameters in the ways described give the expected results predicted by the model. Or at least show that with the optimised parameters chosen by the model a more homogenous structure is produced with no or few smaller pores.
Line 32, I was intrigued by the sentence “Wf/W is expected to provide longer lifetimes, especially after neutron irradiation [20]” So I went to look at Ref20 which does not have any neutron irradiation data in, this is misleading. I think it needs rewording to show the reference refers to the increased toughness rather than the neutron irradiation.
Line 34, why are they potassium doped?
Line 35, What’s the diameter range of the fibres? and how are the fibres coated?
Line 41/42, what is your definition of short or long fibres?
Figure 2, I’m a bit concerned about the assumptions going into the model, from the images the fibres are in layers, but the inter fibre distances within each layer are very variable, how is this taken account of in the model? It looks like you are assuming uniformity which does not look to be realistic.
Also from figure 2b, it seems that the pore density might increase with number of layers, which to me suggests that it may be a result of the fabric layers not being perfectly flat (which I assume is likely) which leads to different heights/gaps, thus depositing an even CVD layer will not fill all the gaps, and this will get exacerbated with more layers. Is this not the case? I don’t think modelling would solve this problem.
Line 67, what conditions were used to create the sample in Figure 2? And then later on you should say what your model predicts would happen when using these parameters.
Why did you go with 150um fibres, I think this adds to the problem, if you used finer fibres, then the variation would be smaller, and likely the pore sizes/density smaller, in the case of SiC composites I’ve worked with, the fibres are <10um diameter.
Line 190, I understand that the reaction surface area will get larger with deposition, but I don’t understand your reasoning for increasing the starting radius of the fibres. What is the justification for this, will this not affect your results in some way?
Line 409, I don’t think you can conclude this, without any evidence that these parameters are the optimised ones.
Line 424, similarly, how do you know the deposition duration per fabric layer can be predicted well?
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript is meaningful for improving the ductile of W component. It is reccomended to publication subject to some revisions.
(1) The title "Improving the relative density of Wf/W composites" let readers to thinck about density, while in the paper, only uniform of the layer is considered.
1 Is the format right for the journal METALs (submitted to Elsevier)?
2 The figure is not clear and is hard to understand. PLS use arrow to point what the author want to emphasize.
3 There are some typos and gramma erroneous needed to be corrected.
4 There needs a criterion to judge whether the convergence is proper or not for the calculation, since there are discontinuous result in Figure 7.
5 The details of gridding should be provided. And refers to the boundaries directly on each geometries. And what is the relation between the setup in figure 4 and figure 5?
6 PLS provide some typical contour maps of CVD depositing (including coatings, flow field and species concentrations) for better understanding of the readers.
7 Can the model be considered as 2D model?
8 Some of the expression should be more strictly, such as Rw1,2. It may be Rw2/RW1?
9 The remarks in the figure should be unified.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thank you to the authors for addressing my comments. However, I do think it's still a bit lacking, and would be a much stronger paper if the authors included a lot more experimental validation, showing the different morphologies formed by varying the parameters. As I'm still a little dubious as to how much the difference the "optimised" parameters are making, especially after seeing Figure 7.4 in the thesis where Figure 11 came from, I think there's a lot more to it than just these 4 parameters investigated in this work. As comparing Figure 2 with Figure 11, it does still seem that the most important thing is having uniform fibre distribution. Even in Figure 11 the higher pore densities seem to be around the fibres that aren't aligned well.
Also how does this work differ from that submitted to NME (Modeling and validation of the Wf/W-fabrication by chemical vapor deposition and infiltration)? From the title this seems like the paper I actually want to read.
line 102 mirco should be micro
Author Response
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Reviewer 2 Report
The manuscript are well revised. But there still has some questions to be verified.
1) The Abreviation for pressure is a capital letter "P" instead of the "p" in the text. In some places, it is appeared in the capital form such as "Ptot"
The hydrogen molecular format should be corrected in line 197, 201 and so on. H2 to H2
The reviewer still does find the definition for Rw,1+2 in the text.
COMSOL or Comsol?
There are also many ohter typos, grammar errors and format problems in the text. The authors should ammend them by theirself. It is recommended to use editing service if the author points out that they need the reviviewers to figure out them one by one.
2) It is still recommended to make an explanation for the descrete value of depositing rate, How does the author to judge that a descrete value is proper for a simulation result. Further more, is the gas really depleted? Why does there still have a much high depositing rate. The deposting rate should be zero if the reactant is depleted.
Author Response
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Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
The manuscript can be accepted for publication.
