In Situ Investigations on Stress and Microstructure Evolution in Polycrystalline Ti(C,N)/α-Al₂O₃ CVD Coatings under Thermal Cycling Loads

Round 1

Reviewer 1 Report

Review of "In-situ investigations on stress and microstructure evolution in polycrystalline Ti(C,N)/alpha-Al2O3 coatings under thermal cycling loads"
by Garcia, J., et al.

This paper describes the EDXRD, EM, and modelling work to understand the effect of thermal cycling on the coating material's behavior. The paper is nicely written with interesting analyses methods and interpretations of the data.

Below are some questions and comments that came up as I was reading the manuscript:
- Samples
What was the baseline substrate under the TiN?
What are the dimensions of the sample and different layers in the sample? Perhaps moving Figure 1 to the Sample section will be more informative.

How uniform are the coating layers?
A representative micrograph indicating these layers will be useful.

Residual stress analysis in the coating layers
While a tabulated summary of the experimental parameters are helpful, a figure indicating the coordinate system and angles used in this work will be quite useful for the readers to understand the paper without having to look up papers. Partiuclarly useful will be how the sample coordinate system is related to the instrument coordinate system.

Such figure will also help the readers understand what the authors mean by "which is why the residual stresses reported in this paper are volume averaged stresses".

How was the sample aligned with respect to the beam? For a material system with highly irregular boundaries, it seems like alignment will be key to acquiring good data?

What was the size of the gauge volume of the measurement setup?

What was the heating / cooling ramp rate?
Does Eq 1 imply that the assumed stress state is equi-biaxial in the plane of the coating? Has this been confirmed by measuring the other components of strain? How did you determine d0?

It will be good to clarify that sigma is the estimated in-plane stress component value based on the assumption in [22] and sigma_|| is the experimentally acquired in-plane stress values. As it is written from L167 - L175, it is unclear what the motivation is for Equation 2.

Lines 192 - 206.
What is beta^prime? How does one get beta_s and beta_D?

Eq 7.
Is E the fit energy?

Results
Figure 2. Is this sigma_|| averaged between the two hkls for each layer?

Figure 2b. Is it reasonable that the Al2O3 layer is now substantially in the compressive stress for the component presented and the Ti(C,N) layer virtually did not change at all? How does the system stay in equilibrium?

Figure 4: if it is due to micro-cracking? shouldn't the discrepancy get worse with heat-cool cycle as more cracks are introduced? It does not appear to be the case based on this figure. is is possible that the modulus or CTE is slightly off or d0 is off? Afterall, the stresses presented here (as well as other works) depend on the reference and the modulus and the red lines can move up and down in Figure 4's Y axis. Is it more reasonable to compare in strain (since the strain measured here are elastic and the model in [22] assumes elastic strains)?

Figure 8. What is sigma_11?

Minor comments:
Line 186
E-module ==> elastic modulus?

Line 486 - due to ???.

Author Response

Please see attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Dear author,

your work is interesting on the study of the stresses according to the heat treatments and the conditions of elaboration, for my part before the publication it would be necessary to bring some precision to your study:
- Can give the purity of the basic products for the synthesis of films in CVD? is it commercial mix or not?
- During shot blasting is the top layer polluted by the balls or not? you are not talking about roughness it is affected or not?
- During your tests according to the temperature, can you tell us the heating speed? You mentioned that your measurements take 10 minutes did you maintain the set temperature? if so, what is the time? have you observed changes over time?
- line 169, you mark that your film is 5 µm and that the substrate is 5000 µm. I don't agree with you, each layer is about 5 µm. the film you are showing is at least 8 µm
- on the SEM observation, we can see the presence of a TiN and BL layer between Ti (C, N) and Alumina, Can you tell us the interest of having such accommodation layers? Why not put the characteristics of its layers in table 3 because they influence the measurements? What is the impact of its layers on the results? What are their thicknesses?
- during thermal cycles, have you observed any effects on the composition of the films? have you observed any diffusion phenomena? How does grain size change? The quality of the interfaces?

In addition to your measurements, why didn't you carry out mechanical tests such as hardness, Poisson's ratio, coefficient of friction?
Can you tell us what is the advantage of choosing WC-Co as a substrate? because it presents an important mismatch with your coating

Best regards

reviewer

Author Response

Please see attachment

Author Response File: Author Response.docx

Reviewer 3 Report

The authors investigated Ti(C,N)/a-Al₂O₃ coatings deposited to WC-6%Co substrate by CVD method.

The results of the investigation are very well presented. However, there are a few suggestions and comments for the authors:

I would like to suggest inserting the "CVD" term to the title; e.g. "…polycrystalline Ti(C,N)/a-Al₂O₃ CVD coatings…".

How many samples were used in total? Did the authors use more samples for the same experimental conditions, i.e. replications?

The contribution of the results of investigation to the industrial applicability should be highlighted in the Conclusion.

The authors stated: "The insert geometry was selected with a flat surface to avoid geometry effects on stress analysis.". How would a different geometry of the insert affect the directions of the investigation?

The authors should use uniformly [13,14] or [15-16]. The authors should use space between number and unit of measurement. 

Author Response

See attached response.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear

I thank you for having taken into account my remarks and for having answered my questions, for my part the article can be published

Best regards