Near-Surface and Bulk Dissolution Behavior of γ′ Precipitates in Nickel-Based VDM^® Alloy 780 Studied with In-Situ Lab-Source and Synchrotron X-ray Diffraction

Round 1

Reviewer 1 Report

Considering the Section "Metal Failure Analysis", also the title of the Special Issue that mentions "Deformation", I feel that the submitted paper is out of the scope content to be published in the Journal, although the subject is very interesting in my view, but to a Special Issue linked to nanometallurgy, or something like that.   I have already responded it in the day after I received the review request.

Author Response

Dear reviewer,

The editor writes in the information, "Advances in superalloys involving microstructure evolution and deformation behaviour fall within the scope of this special issue" and "The results or methods that improve microstructure stability and temperature resistance are generally welcomed."

We have concluded that it is not mandatory to present results that include both microstructural and mechanical studies. Therefore, we consider our study to be suitable, in which the microstructural changes during heat treatment, especially the dissolution of the g' hardening phase, is intensively investigated at the surface and in the bulk.

The precise knowledge of the microstructure at the surface and in the bulk is very important for a long service life of components. On the one hand, the microstructure in the bulk is responsible for sufficient load tolerance of the component to minimize plastic deformation under load, since the microstructure in this area makes up a large part of the component cross-section. On the other hand, typical failure criteria are crack initiation during fatigue or critical oxidation, which both typically starts at the surface of the material. These two failure mechanisms are strongly related to the phases that are present at the surface. This fact is directly addressed in the introduction and conclusion part.

To make the relevance of the contribution to the special issue clearer we have modified the abstract and conclusion. With the connection to the long service life respectively possible failure mechanism the relation of the study is better seen.  

Reviewer 2 Report

The manuscript entitled “Near surface and bulk dissolution behavior of γ’ precipitates in Nickel-based VDM Alloy 780 studied with in-site lab source and synchrotron X-ray diffraction” has investigated the dissolution behavior of VDM alloy 780 at different temperature. The demonstration of this article is clear and this article may have significant advancement in the understanding of dissolution behavior of VDM alloy. While, before the manuscript can be accepted, a few concerns need to be addressed:

1. Incomplete information in the title, abstract and text. E.g., symbol’γ’are missing in the title and abstract. “Error! Reference source not found” in the text. Please proofread and revise carefully.
2. The significance of this research is not clear. It is suggested to supplement the significance of the research in the last paragraph of the Introduction to show the necessity of the article.
3. Irregular fonts and formats. E.g., “Page 2 Line 95-96 and Page 3 Line 97-100”. “Page 14 Figure 1 and Page 17 Figure 12”. Please proofread and revise carefully.
4. Note that the authors used two methods (lab source XRD and synchrotron XRD) for in-site heating XRD to investigate the alloy, what is the fundamental difference between them?
5. According to the Introduction (Page 2 Line 50 and 70), the microstructure of the VDM alloy 780 consists of NiC-high-temperature phases. Why could be the NbC phase observed in the results (Page 5 Line 201)? How to accurately identify NiC and NbC by XRD only?
6. Note that all XRD pattern expressed as an Intensity-Q relationship, what does the abscissa Q represent? It is suggested to label the crystal plane parameters and phases directly on the corresponding diffraction peaks, instead of sheets (Figure 2).
7. It would be ideal if the authors involve briefly the latest literatures (e.g., ACS Appl. Mater. Interfaces 2021, 13, 55712-55725; Friction (2022). https://doi.org/10.1007/s40544-021-0581-6) in the manuscript.
8. Note that the phase of near-surface can be identified by using lab source XRD, while using synchrotron XRD can identified the phase of near-surface and bulk. Why can γ-2 phase near-surface not be detected by synchrotron XRD?

Author Response

Dear reviewer,

thank you very much for your valuable comments. You find a detailed response to your comments in the attached document.

Author Response File: Author Response.pdf

Reviewer 3 Report

This is an original study on the phase evolution of Ni-based VDM Alloy 780 mainly by X-ray diffraction methods. The topic is interesting and valuable. However, the current version is not well-organized. There are a lot of cross-reference errors and displaying problems that stopped me from reading. Even the title could not be displayed correctly. It's suggested to correct all the layout and formatting problems before a proper review can be made.

Author Response

Dear reviewer,

We are sorry that these problems have occurred. Unfortunately, formatting problems occurred during the preparation of the manuscript by the journal. These errors have now been corrected. Also, the references as well as display problems are now fixed.

Round 2

Reviewer 1 Report

The authors inserted a new paragraph in the revised text (lines 77-91) mentioning the relation of the scope of their work to failure and deformation, which are the topics of the section and special issue of the journal, but there is no any demonstration of how the dissolution of nanoprecipitates in the metallic matrix so identified by XRD can act towards both phenomena. Clear link to the focus of the journal section is missing.

Author Response

It is known from a large number of publications that the g' volume fraction and the g/g' lattice mismatch are two key parameters for the mechanical strength of nickel-based superalloys. Therefore, an accurate knowledge of these two parameters is a crucial criterion for component design at different temperatures. The XRD investigations carried out in this study now provide a unique opportunity to measure both the g' volume fraction and the g/g' lattice misfit as a function of temperature, and therefore to estimate the suitability of the investigated nickel-base superalloy for different temperature ranges. 

See for example the following literature:

• Murakumo, T. Kobayashi, Y. Koizumi, H. Harada: Creep behaviour of Ni-base single-crystal superalloys with various γ′ volume fraction, Acta Materialia, Volume 52, Issue 12, 2004, Pages 3737-3744, ISSN 1359-6454, https://doi.org/10.1016/j.actamat.2004.04.028.D.
• Mukherji and J. Rösler, Joachim. "Effect of the γ’ volume fraction on the creep strength of Ni-base superalloys" International Journal of Materials Research, vol. 94, no. 5, 2003, pp. 478-484. https://doi.org/10.1515/ijmr-2003-0086
• Torster, G. Baumeister, J. Albrecht, G. Lütjering, D. Helm, M.A. Daeubler: Influence of grain size and heat treatment on the microstructure and mechanical properties of the nickel-base superalloy U 720 LI, Materials Science and Engineering: A,Volumes 234–236,1997,Pages 189-192, ISSN 0921-5093, https://doi.org/10.1016/S0921-5093(97)00161-5.

Reviewer 3 Report

The current manuscript deals with the phase identification of Ni-based alloy 780 via X-ray diffraction methods. Intensive studies have been conducted with both lab sources and synchrotron sources.  The precipitates dissolution behavior was a focus in this work. The presented results can be a food reference for researchers in the relevant field.

A suggestion for Fig.11: the authors can mark the differences in the peaks and the indexed results to highlight the conclusions.

Author Response

Dear reviewer,

thank you very much for your valueable commets. The figure was changed according to your suggestion.

 

Round 3

Reviewer 1 Report

Thanks to all the authors for the efforts to clarifying the correspondence to the scope of the special issue of the journal.