Thermal Fatigue Resistance Studies of Multilayer CrN and AlTiN Coatings Deposited on Plasma Nitrided H-13 Hot Work Steel

Round 1

Reviewer 1 Report

In this work, the authors studied the structure, tribology, corrosion and mechanical properties of the duplex-treated samples of H-13 steel compared to the untreated H-13 and only PVD-coated H-13 for die-casting applications. The results found that the duplex-treated samples showed better wear resistance and thermal fatigue properties compared to the untreated and only coated samples. This is a system work and the obtained results may help for guiding the optimization of the wear resistance of H-13 steel surface. However, the following points should be considered.

(1)   In Table 1, the average roughness data of the plasma nitrided H-13 samples with and without m-CrN and m-AlTiN coatings (6 materials, including four coatings) are not supported by detailed data, such as AFM or SEM morphology comparison. Secondly, what method did be used to measure the roughness?

(2)   The author conducted EDS element analysis in Figure 2. How to measure, point, line or surface scanning method? However, only the table of element composition analysis is seen here, and experimental measurement data is not displayed.

(3)   In the case of m-CrN coating (Fig. 3.a, b), the adhesive Cr layer, CrN/Cr multilayer (14/14 layer), and the final layer of CrN were clearly visible under an optical microscope. However, there are no detailed notes in the figure, so the reader cannot clearly distinguish these different layers of materials (Only two different layers can be distinguished). The same problems also exist in Fig. 3.c and d of m-AlTiN coating structures.

(4)   The coating thickness measurement of individual layer thicknesses was done using the Calo-test instrument. Similarly, Figure 4 also only shows the schematic diagram without the support of actual experimental data.

(5)   Fig. 8 (a), (b) and (c) should be compared in one diagram instead of being divided into three diagrams, so as to compare the changes of coating XRD curve more intuitively.

(6)   A thermal fatigue test was carried out on the samples for 100 cycles (TF100), 300 cycles (TF300), and 500 cycles (TF500), the wear rate also increases with the increase in the TF cycle due to the increase of surface oxide layer. But it is impossible to judge the formation and thickness increase of the oxide layer from the optical microscope in Figure 9. Is there any other experimental characterization data?

(7)   Grammar and format problems exist in this manuscript, author should check carefully.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

This paper investigated that H-13 steel surface was duplex-treated using Plasma Nitriding (PN) and PVD coatings to solve the thermal fatigue problem faced in die-casting applications by depositing Chromium-based multilayer CrN/Cr (m-CrN) coatings and multi-component aluminium-titanium-based AlTiN (m-AlTiN) coatings  after plasma nitriding H-13 steel surface. The structural, tribological, corrosion, and mechanical properties of the duplex-treated samples were discussed.

This paper is a valuable paper with detailed experiments. On the other hand, the discussion seems to be not sufficient.

For example, the samples on plasma nitrided H-13 with 200 μm case depth have superior properties than that of  50 μm case.

Author should consider the reason why the 200 μm case depth is better for the properties. In particular, it is necessary to discuss how the mechanism of thickness of the nitrided layer affects on the PVD coating failure in the scratch adhesion tests after thermal fatigue with TF500.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

No comment.