Improvement of the Fatigue Resistance of Super Duplex Stainless-Steel (SDSS) Components Fabricated by Wire Arc Additive Manufacturing (WAAM)

Round 1

Reviewer 1 Report

The article reports an experimental investigation conducted to improve fatigue Property of Super Duplex Stain- Steel components 3D printed by WAAM.

The experimental work omits the rationalization of the selection of applied process parameters and their levels.

Also, the proper explanation of the results is missing.

The authors need to highlight the novelty of the work.

Author Response

Response to Reviewers

The authors would like to thank the editor and the reviewers for their time and valuable comments which have helped to improve the quality of the manuscript.

Reviewer 1

The article reports an experimental investigation conducted to improve fatigue Property of Super Duplex Stain- Steel components 3D printed by WAAM.

• The experimental work omits the rationalization of the selection of applied process parameters and their levels.
• Also, the proper explanation of the results is missing.
• The authors need to highlight the novelty of the work.

Many thanks for the comments. The reviewer is correct; the process parameters have been selected based on the consistency and stability of the deposition largely using the trial and error method as there are currently no guidelines for the selection of the process parameters of the WAAM method and specifically for SSDS consumables. This issue was also discussed in the manuscript.

We significantly enhanced the discussion of the results in the new version of the manuscript and, in particular, provided the link between microscopic examinations (defects) and the observed fatigue limits using the concept of the stress intensity factor threshold. We also discussed the observed anisotropy in the fatigue resistance and many other aspects of mechanical behaviour of materials fabricated with WAAM.

Regarding the novelty – the application of the Micro-CT 3D reconstruction to relatively large metal volumes can be viewed as innovative development in the micro-examination/characterisation methods. The fatigue results, comparison and the investigation of the interpass temperature effect are all innovative for the area of WAAM, which is also highlighted by Reviewer 2

Reviewer 2 Report

The paper “Improvement of the Fatigue Property of Super Duplex Stainless Steel Components Fabricated by Wire Arc Additive Manufacturing (WAAM)” presents analysis of the interpass temperature on the mechanical properties and fatigue life of structural components fabricated with WAAM. From my point of view, the article is of great interest and its publication would have great impact and interest, only a few minor changes could improve the holistic vision of the topic:

·        Abstract make reference to previous works while information about them is still not presented I suggest not to open with this statement.

·        Refer to the the ISO/ASTM 52900 standard "directed energy deposition" and latest classification of WAAM as part of it.

·        Explain some new contributions on different strategies to improve mechanical properties and interpass strategies:

o   https://doi.org/10.1007/s40194-020-00921-3

o   https://doi.org/10.1016/j.jmatprotec.2021.117271

·        Figure 2 could be enriched by adding a part a) with the scheme of the trajectories used or with the location of the extracted specimens, and also by adding the wall measurements. As in:

o   https://doi.org/10.1016/j.jmrt.2020.11.012

·        In Figure 4 improve the presentation of the scale.

·        In point 3.1 please add a summary of the number and size of pores found.

·        “For TW1, the longitudinal specimens obtained 670-672 MPa for yield and 871-875 MPa for 210 the tensile stress in comparison with the transverse specimens of 836-850 MPA and 645-650 MPa, respectively.”. I think this sentence is the wrong way round, the values are not placed in the correct order.

·        Please add a graph or table with the values obtained from the mechanical tensile test.

·        In the conclusions, from my perspective bulleting conclusions are better.

These are suggestions for paper publication.

Author Response

Response to Reviewers

The authors would like to thank the editor and the reviewers for their time and valuable comments which have helped to improve the quality of the manuscript.

Reviewer 2

The paper “Improvement of the Fatigue Property of Super Duplex Stainless Steel Components Fabricated by Wire Arc Additive Manufacturing (WAAM)” presents analysis of the interpass temperature on the mechanical properties and fatigue life of structural components fabricated with WAAM. From my point of view, the article is of great interest and its publication would have great impact and interest, only a few minor changes could improve the holistic vision of the topic:

Thank you for positive comments.

• Abstract make reference to previous works while information about them is still not presented I suggest not to open with this statement. Noted and reference in abstract is removed as suggested.
• Refer to the ISO/ASTM 52900 standard "directed energy deposition" and latest classification of WAAM as part of it. Noted and included
• Explain some new contributions on different strategies to improve mechanical properties and interpass strategies:

  https://doi.org/10.1007/s40194-020-00921-3

https://doi.org/10.1016/j.jmatprotec.2021.117271

Thank you, these important and closely related to our work references have been missed; and now have been added to the reference list. Amendments have been also made to improve abstract and explain innovations of this work.

• Figure 2 could be enriched by adding a part a) with the scheme of the trajectories used or with the location of the extracted specimens, and also by adding the wall measurements.

These suggestions are included, scale bar added and figure description updated indicating thickness.

• In Figure 4 improve the presentation of the scale.

Scale bar increased.

• In point 3.1 please add a summary of the number and size of pores found.

Noted and this is explained in details.

• “For TW1, the longitudinal specimens obtained 670-672 MPa for yield and 871-875 MPa for 210 the tensile stress in comparison with the transverse specimens of 836-850 MPA and 645-650 MPa, respectively.”. I think this sentence is the wrong way round, the values are not placed in the correct order.

This sentence has been changed.

• Please add a graph or table with the values obtained from the mechanical tensile test.

We do not think that 3 values (elongation and yield strengths) needs to be tabled. We left these values embedded in the text.

In the conclusions, from my perspective bulleting conclusions are better.

The bullet format is now used.

These are suggestions for paper publication.

Thank you for valuable comments.

Reviewer 3 Report

This paper mainly focuses on improving the mechanical properties of the WAAM fabricated SDSS by adjusting the processing parameters. The results are interesting and the paper can be acceptted if the following points are properly addressed.

1. The authors mentioned that the approach to improve the fatigue properties of the material by selecting the deposition direction along the maximum principal cyclic stress will not be applicable when the structure is working under changing load. But in the fatigue test of this study, the achieved specimen is not subjected to the changing load.

2. Please indicate the longitudinal and transverse directions in the CT images.

3. The fractures of the mechanical tested samples need to be analysed.

Author Response

Response to Reviewers

The authors would like to thank the editor and the reviewers for their time and valuable comments which have helped to improve the quality of the manuscript.

Reviewer 3

This paper mainly focuses on improving the mechanical properties of the WAAM fabricated SDSS by adjusting the processing parameters. The results are interesting and the paper can be accepted if the following points are properly addressed.

1. The authors mentioned that the approach to improve the fatigue properties of the material by selecting the deposition direction along the maximum principal cyclic stress will not be applicable when the structure is working under changing load. But in the fatigue test of this study, the achieved specimen is not subjected to the changing load.

Thanks for the comment and the specimens have been subjected to cyclic (changing) loading conditions. The text was modified to avoid confusion as follows “However, this approach has its limitations and becomes much less effective for structures working under stress states with a relatively small difference in principal cyclic stresses or for structures in which the direction of principal stresses also changes over time.”

We addressed this issue by improving the fatigue resistance, specifically, in the weakest (transverse) direction.

2. Please indicate the longitudinal and transverse directions in the CT images.

Noted and included following “X direction represents the longitudinal bead layering direction, Y represents the transverse bead direction”.

3. The fractures of the mechanical tested samples need to be analysed.

Description is now included.

Round 2

Reviewer 1 Report

The authors claimed that they addressed the reviewer comments without indicating precisely where changes were made. The authors are asked to support their claim with detailed info of what has been addressed and where to find these changes in the papers starting from line XX to line YY.

Author Response

Reviewer 1

The article reports an experimental investigation conducted to improve fatigue Property of Super Duplex Stain- Steel components 3D printed by WAAM.

• The experimental work omits the rationalization of the selection of applied process parameters and their levels.

The manuscript has been updated in lines [111-118], which are reproduced below:

“Two test walls were fabricated by WAAM with the same welding parameters, but different interpass temperatures to alter the cooling rates and are summarised in Table 2. Heat input and cooling rates were selected based on standard welding methods to achieve stable characteristics of the deposition and additionally achieve an industry acceptable phase balance of 30%-70% ferrite-austenite based on various literature [2, 14, 16, 21]. An interpass dwell time between layers was set at 150 °C for Test Wall 1 and 100 °C for Test Wall 2, which would allow a variance of the final phase balance. The interpass temperature was measured with a pyrometer by the readings taken immediately prior to the proceeding bead to be deposited”

• Also, the proper explanation of the results is missing.

As we mentioned in the previous respond, we have significantly revised the manuscript, and in particular, included new text, lines [183-190], [215-220], [234-246], which better explain the obtained results.   However, we do not fully understand what exactly the reviewer means?

• The authors need to highlight the novelty of the work.

Regarding the novelty – the application of the Micro-CT 3D reconstruction to relatively large metal volumes can be viewed as innovative development in the micro-examination/characterisation methods. The fatigue results, comparison and the investigation of the interpass temperature effect are all innovative for the area of WAAM, which is also highlighted by other reviewers.

We added lines [290-292] into the conclusion to further highlight these innovations.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper has improved significantly. The work seems interesting and publishable. I would like to thank the editor for allowing me to review this type of work and the authors for their research efforts.

Author Response

Many thanks for your comments and positive attitude.

Round 3

Reviewer 1 Report

The authors addressed the reviewers' comment and the manuscript can be accepted as is.