Structural Transformations on the Surface of Al-Ti Cathodes Subjected to Vacuum Arc Heating

Сomment

Response

1. Details for preparation of at least cathodes No.1, 2 and 4 should be added.

The cathodes 2,3,4 are the purchased goods. The providers do not disclose the manufacturing technologies. So, mode of the cathodes manufacturing we have determined on the base of microstructural studies. Additional preparation details concerning to cathode No. 1 are appended to the text.

2. Description of XRD results requires some structure and relation to the sequence of the XRD patterns on Fig. 1.

The sequence of the description was changed, line 104-108.

3. Improvement of Fig. 1 is needed: (i) labels are not readable; (ii) formula of phases is written in different manner, e.g. AlTi3 on pattern 1 and Ti3Al on pattern 2 (Fig. 1a); (iii) Intensity is usually labelled as "I" and not "J"; (iv) the same scaling and font will make figure less confusing (e.g., a,c,d - 15-90 deg. 2 Theta and b - 30-145 deg. 2 Theta).

The most of the reviewer remarks are taken into account.

4. Why weights of different phases were estimated only for cathodes No.1 and 2??? Background for 3 and 4 are not worth as No.2.

The weights of different phases were estimated for cathodes No. 3 and 4. Additional date are added to the Table 2.

5. Discussion of ring structure on page 4 and together with optical images is confusing, since it is not visible from Fig. 2

The phases of the ring structure are specified on the Figure 2. The figure 3 (EDS) together with the notes in the text provide more elucidation about the structure.

6. How exactly XRD was performed? It is not clear the explanation about the absence of TiAl3 reflections due to the capsulation (line 117). More details are needed.

There was a wrong text. XRD description was corrected.

7. Tables with EDXS results are overloaded with raw numerical data as well as Fig. 3 with labels of analysis points. It is better to sign the phases on Fig. 3 and give the average composition (together with deviations!) for different phases in Table 3.

The phases were signed on the Fig 3. The average compositions (together with deviations) are given on the tables.

8. Description in lines 155-162 is related to wrong Figure.

Wrong notations are corrected. Line 163.

9. How TiH0.71 phase was determined in the cathode? From where it is?

A probable reason of hydride phase occurrence in the modified layer is a reaction of titanium with impurities in the vacuum media.

10. Thermal conductivity values should be presented using IUPAC units

“grad” was substituted to “K”.

11. The presented cathodes look very inhomogeneous and different from each other. Can these layers be reproduced (in terms of composition, porosity, etc.) to retain the mechanical properties?

According to XRD (Table 2) all the cathodes are multiphase and have porosity in the different extent. As there are no increased requirements to the mechanical properties of the cathodes the porosity do not influence on the working capacity of the cathodes. On the other hand, surface melting of cathodes converted multiphase and porous structure into compact layer. So, the porosity is not expect to influence considerably on the structure of the modified layer.

12. Labels for scales on Fig. 2-7 should be "μm".

The notation was changed.

13. The text and figures should be "synchronized".

Figures and the tables are inserted on the page followed after the page with first reference of the figure or of the table.

Сomment

Response

1. In the introduction, please highlight where such electrodes are used

A destination of the cathodes is pointed in the beginning of the introduction: “Vacuum arc evaporation of metal and metallic alloys cathodes in the reactive gas media is widely used for deposition of wear resistant coatings on the surfaces of metal-working tools [1–3]”.

2. Why this topic is so important?

Phase composition and microstructure of the cathode can influence on the modified surface layer, that is a source of plasma flows and microparticles deposited on the substrate to form the coating. So, in our work we investigated modified layers emerging on the cathodes of different phase composition and structure.

3. Why modify ready-made electrodes?

Layer, modified with vacuum arc, emerges on the cathodes surface independently of the cathode composition and structure.

4. Whether the authors would be able to make their own electrodes from scratch?

We used for the investigation cathodes of four kinds. One of them was produced in our laboratory by vacuum sintering   of TiAl₃ and Ti powder mixtures, the rest cathodes were purchased.

Сomment

Response

1. The abstract section is good, unfortunately, it does not contain any numerical results, therefore, it is recommended to add such numerical results which will encourage the reader to continue reading the research articles.

Addition regarding to thickness of the modified layer introduced into the abstract.

2. The introduction is based on documentation from old articles 1981-2017, only 4 articles are current from a total of 26 articles. Therefore, this part can be considerably improved by making a bridge between existing applications and the novelty of the work.

The problem of the surface modification with vacuum arc have raised when multicomponent composite cathodes were introduced into practice in the 2000. Surface modification of the cathodes, differing in elemental or phase composition, in the constituent configuration and so on have been studied (see reference list). A novelty of our work is that comparative investigation cathodes of identical elemental composition, but differing in structure and phase composition was conducted to offer recommendations to practical using of the cathodes.

3. The Materials and Experimental Technique section can be enhanced by providing complete experimental details including vacuum arc method, material properties, preparation before and after of the surface exposed to vacuum arc technology and other features.

Vacuum arc technology of the coating deposition, including materials used is described in the papers, presented in the reference list.

4. In the Results part the authors are recommended to provide additional methods of characterization of the surface exposed to the vacuum arc like SEM, TEM as well as FTIR analyses. In Fig. 1, the dimensions of the graphics are changed, thus the details inside the images are indecipherable (especially Fig. 1c). From Fig. 2 to Fig. 7 all the images have the measurement unit µ, I recommend to change in µm being more internationally used.

1) On our opinion XRD, optical and SEM microscopy methods are enough to characterize structure and phase composition of the cathodes. There is no need to use TEM and FTIR.

2) Additional notation of the phases added on the Figure 1a.

3)  µ notation was changed to µm.

5. In The discussion of the results section add more interpretations/opinions related to the implementation of the results in practical applications.

 Comparison of the cathodes relative to practical using added to “Discussion of the results” section.

6. The conclusion part, it too short and additional results might be added to conclude the work significantly.

Recommendation to practical using of the cathodes added to the “Conclustions” section.

7. The References are adequate to the subject, but most of them are not of latest studies. References 9, 13, 15 have different Font and dimenssions.

Reference list was corrected.