Abstract

PurposeLithium disilicate glass-ceramics (LS2 GC) are widely used as dental prosthetics and dental restorations. Based LS2 GC have hardness and translucency similar to that of natural teeth. This study aims to investigate the tribological features of LS2 GC with crystalline volume fraction of 64% and different crystal sizes from 8 mu m to 34 mu m for different counterparts.Design/methodology/approachThe tribological behavior was investigated using a pin-on-disc tribometer with alumina and tungsten carbide (WC) spheres, applied load of 5 N and sliding speed of 5 cm/s at normal conditions. The coefficient of friction was measured continuously up to 10,000 sliding cycles. The specific wear rate was calculated from tribological and profile measurements. The wear mechanism was investigated by surface morphology analysis.FindingsThe coefficient of friction during running-in varied from 0.8 to 1.0 for the alumina counterpart, because of severe wear. Afterwards, it reduced and reached a stationary regime, characterized by a mild wear regime and the formation of a tribolayer formed by the debris. For the WC counterpart, the coefficient of friction curves increased initially with sliding cycles up to a stationary regime. The samples tested against WC presented the lowest specific wear rate (k), and no variation of wear rate with crystal size was observed. For samples tested against the alumina, crystallization and crystal size increased the wear resistance.Originality/valueThis study evaluated the effect of different counterfaces on the tribological properties of the LS2 GC, an important glass-ceramic base for many dental prosthetics and dental restorations, discussing results in light of the contact mechanics. Different specific wear rates, wear regimes and dependence on the glass-ceramic microstructure were observed depending on the counterpart.Peer reviewThe peer review history for this article is available at:


Authors

da Cruz, Crislaine;  Mathias, Ivan;  Senk, Mariza Veiga;  de Souza, Gelson Biscaia;  Serbena, Francisco Carlos

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  • pre-publication peer review (FINAL ROUND)
    Decision Letter
    2020/04/21

    21-Apr-2020

    Dear da Cruz, Crislaine; Mathias, Ivan; Senk, Mariza; de Souza, Gelson; Serbena, Francisco

    It is a pleasure to accept your manuscript ilt-08-2019-0352.R3, entitled "Effect of crystal size on tribological properties of lithium disilicate glass-ceramics sliding against alumina and tungsten carbide spheres" in its current form for publication in Industrial Lubrication and Tribology. Please note, no further changes can be made to your manuscript.

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    Thank you for your contribution. On behalf of the Editors of Industrial Lubrication and Tribology, we look forward to your continued contributions to the Journal.

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    Prof. Henara Costa
    Guest Editor, Industrial Lubrication and Tribology
    ltm-henara@ufu.br, henara.costa@gmail.com

    Decision letter by
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    Reviewer report
    2020/04/15

    Paper was corrected accordingly and is ready to be published.

    Reviewed by
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    Author Response
    2020/04/13

    Dear Editor,

    Follows the updated version of our manuscript. Thank you again for the suggestions and valuable comments.

    Please, let us know if any other changes are necessary.

    Best regards,
    The authors.



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  • pre-publication peer review (ROUND 3)
    Decision Letter
    2020/03/27

    27-Mar-2020

    Dear Ms. da Cruz:

    Manuscript ID ilt-08-2019-0352.R2 entitled "Effect of crystal size on tribological properties of lithium disilicate glass-ceramics sliding against alumina and tungsten carbide spheres" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

    The reviewer(s) have recommended revisions to the submitted manuscript, before it can be considered for publication. Therefore, I invite you to respond to the reviewer(s)' comments and revise your manuscript.

    To revise your manuscript, log into https://mc.manuscriptcentral.com/ilt and enter your Author Centre, where you will find your manuscript title listed under "Manuscripts with Decisions." Under "Actions," click on "Create a Revision." Your manuscript number has been appended to denote a revision.

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    Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

    Sincerely,
    Prof. Henara Costa
    Guest Editor, Industrial Lubrication and Tribology
    ltm-henara@ufu.br, henara.costa@gmail.com

    Reviewer(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    Some minor correction still needed:
    pg3 ln50 - Please, revise the paragraph. It seems grammatically incorrect.

    fig 2 - Please include the diffraction planes in the XRD spectra. Also, the Intensity (y-axis) is not an arbitrary unit. Depending on the experiment is measured as "counts" or "cps".

    pg7 - I guess that when you say "though lowly" you mean "slightly"

    Reviewer: 2

    Comments to the Author
    Thanks for your nice contribution, the requirements were well incorporated.
    Reviewer: 1

    Recommendation: Minor Revision

    Comments:
    Some minor correction still needed:
    pg3 ln50 - Please, revise the paragraph. It seems grammatically incorrect.

    fig 2 - Please include the diffraction planes in the XRD spectra. Also, the Intensity (y-axis) is not an arbitrary unit. Depending on the experiment is measured as "counts" or "cps".

    pg7 - I guess that when you say "though lowly" you mean "slightly"

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: yes

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Literature citation is adequate

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Yes. The experimental methodology is adequate.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Results and conclusions are adequate,

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: All the implications are consistent with the conclusions.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Language was improved, and it is ok.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: Yes

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: Yes, I would like my name to appear with my report on Publons

    Reviewer: 2

    Recommendation: Accept

    Comments:
    Thanks for your nice contribution, the requirements were well incorporated.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: It is ok.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: It is well described.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Yes,

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: Yes,

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: It is well written

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: Yes, I would like my name to appear with my report on Publons

    Decision letter by
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    Reviewer report
    2020/03/26

    Thanks for your nice contribution, the requirements were well incorporated.

    Cite this review
    Reviewer report
    2020/03/04

    Some minor correction still needed:
    pg3 ln50 - Please, revise the paragraph. It seems grammatically incorrect.

    fig 2 - Please include the diffraction planes in the XRD spectra. Also, the Intensity (y-axis) is not an arbitrary unit. Depending on the experiment is measured as "counts" or "cps".

    pg7 - I guess that when you say "though lowly" you mean "slightly"

    Reviewed by
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    Author Response
    2020/03/02

    Ponta Grossa, 02.Mar.2020

    Dear Prof. Henara Costa
    Guest Editor, Industrial Lubrication and Tribology

    Regarding your comment: "Please reduce the maximum number of figures of this manuscript. This can be done by grouping some of them together. "

    We group the figures 3 and 4, 5 and 6, and 7 and 8. Such that, our manuscript has now 7 figures.

    We thank again the revision process and all the reviewers comments that have improved our manuscript. Please let us know if any other adjustment/modification is required.

    With our best regards,
    The authors.



    Cite this author response
  • pre-publication peer review (ROUND 2)
    Decision Letter
    2020/02/03

    03-Feb-2020

    Dear Ms. da Cruz:

    Manuscript ID ilt-08-2019-0352.R1 entitled "Effect of crystal size on tribological properties of lithium disilicate glass-ceramics sliding against alumina and tungsten carbide spheres" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

    Editorial comments:

    Please reduce the maximum number of figures of this manuscript. This can be done by grouping some of them together.

    To revise your manuscript, log into https://mc.manuscriptcentral.com/ilt and enter your Author Centre, where you will find your manuscript title listed under "Manuscripts with Decisions." Under "Actions," click on "Create a Revision." Your manuscript number has been appended to denote a revision.

    You will be unable to make your revisions on the originally submitted version of the manuscript. Instead, revise your manuscript using a word processing program and save it on your computer. Please also highlight the changes to your manuscript within the document by using the track changes mode in MS Word or by using bold or coloured text.

    Once the revised manuscript is prepared, you can upload it and submit it through your Author Centre. The deadline for uploading a revised manuscript is 04-Mar-2020 from receiving this email. If it is not possible for you to resubmit your revision within this timeframe, we may have to consider your paper as a new submission.

    When submitting your revised manuscript, you will be able to respond to the comments made by the reviewer(s) in the space provided. You can use this space to document any changes you make to the original manuscript. In order to expedite the processing of the revised manuscript, please be as specific as possible in your response to the reviewer(s).

    IMPORTANT: Your original files are available to you when you upload your revised manuscript. Please delete any redundant files before completing the submission.

    Please note that Emerald requires you to clear permission to re-use any material not created by you. If there are permissions outstanding, please send these to Emerald as soon as possible. Emerald is unable to publish your paper with permissions outstanding.

    Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

    Sincerely,
    Prof. Henara Costa
    Guest Editor, Industrial Lubrication and Tribology
    ltm-henara@ufu.br, henara.costa@gmail.com

    Reviewer(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    Thank you for your revision, all requirements were attended.

    Reviewer: 2

    Comments to the Author
    (There are no comments.)
    Reviewer: 1

    Recommendation: Accept

    Comments:
    Thank you for your revision, all requirements were attended.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Yes, the citations are adequate.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Yes.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Yes, well organized.

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: Yes, the implications are now well pointed out.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: The manuscript is clear.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: Yes, I would like my name to appear with my report on Publons

    Reviewer: 2

    Recommendation: Accept

    Comments:
    (There are no comments.)

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: yes

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: yes

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: yes

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: yes

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: yes

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: yes

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: yes

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: Yes, I would like my name to appear with my report on Publons

    Decision letter by
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    Reviewer report
    2020/01/28

    Thank you for your revision, all requirements were attended.

    Cite this review
    Author Response
    2020/01/18

    Madri, 18.Jan.2020

    Dear Prof. Henara Costa
    Guest Editor, Industrial Lubrication and Tribology

    We would like to thank the reviewers for the careful reading of the manuscript. We are thankful for the suggestions that improved the new version of the text. We carefully revised our manuscript taking into account the referees comments and suggestions.
    In the following, we comment each point arisen by the referees and the modifications made.

    With our best regards,

    The authors

    Response to the first reviewer:
    1- Please correct et. al. to et al.
    Thank you. We made this correction in the text.

    2 - Aim is clear, but not justified. Justify why 64% of crystalline fraction, and why compare WC with alumina counterpart?
    We chose to compare WC and alumina spheres because both of them are used as counterparts for tribology tests in ceramics and indeed we found differences between them.
    We used the parameters of the study that used WC spheres in glass-ceramics reported in “Buchner, et al. (2013), “Comparison of the mechanical and tribological properties of a sintered low expansion Li_2O – Al_2O_3 – SiO_2 glass-ceramic and a commercial cooktop plate”, European Journal of Glass Science and Technology, Vol. 54, pp. 211-217.” to compare with our results. However, as we did not find a significant difference in wear for the WC sphere, we chose to test with the alumina sphere, which is used to test lithium disilicate based glass-ceramics for dental applications (Peng, Z., Rahman, M. I. A. , and Zhang, V. (2015), “Wear behavior of pressable lithium disilicate glass ceramic”, Journal of Biomedical Materials Research B, Vol. 104B, pp. 968-978).
    The selection of 64% of crystallized volume fraction is because this is approximately the crystallized volume fraction of the commercial LS2 based glass-ceramics (Villas‐Boas, M. O. C., Serbena, F. C., Soares, V. O., Mathias, I., and Zanotto, E. D. (2019), “Residual stress effect on the fracture toughness of lithium disilicate glass‐ceramics”, Journal of the American Ceramic Society, Vol, 103, pp. 465-479).

    We added the following text in the article:
    The chosen crystalline volume fraction of 64% is because this is approximately the crystallized volume fraction of commercial LS2 based glass-ceramics (Villas-Boas et al., 2019) The counterparts investigated are alumina, used to investigate dental glass-ceramics, and WC spheres, used to investigate ceramics such as alumina due to its higher hardness.

    Villas‐Boas, M. O. C., Serbena, F. C., Soares, V. O., Mathias, I., and Zanotto, E. D. (2019), “Residual stress effect on the fracture toughness of lithium disilicate glass‐ceramics”, Journal of the American Ceramic Society, Vol, 103, pp. 465-479.

    3 - Experimental procedure: language should be revised: "poured three times in an electric furnace"... usually glass melt is poured between two metallic plates for fast cooling.
    Thank you for point that out. We revised the text.

    The new text is:
    The mixture was melted in a Pt crucible in an electric furnace and poured three times for good homogenization of the glass.

    4 - Crystallization temperatures are missing. What is the nucleation and growth temperatures, what is each treatment time? How the temperatures were chosen?
    The nucleation and growth temperatures were chosen according to differential scanning calorimeter (DSC) measurements. The nucleation temperature was 460ºC, near the transition glass temperature (455°C). The growth temperature was 538ºC and it was lower than the temperature for the onset of crystallization (635ºC) to allow for better control of the crystal size. We included Table 1 in the text with the details of the heat treatments.

    The added text is:
    The samples were subsequently submitted to a double stage heat treatment for nucleation and growth of crystals according to Table 1 (added in the new version of the manuscript).

    5 - All the works citing tribological properties of LS2 glass-ceramics refers to lubricated conditions. Why did you use unlubricated? Does it make any sense once these materials will always be worn differently when in aqueous environment? Please, justify.
    This is an on-going project where the measurements in dry conditions will be compared with those in artificial saliva. This article reports on measurements performed in dry conditions. The measurements in lubricated conditions will be the next step of this research.

    6 - Information about nanoindentation tests should be more detailed. What was the applied load, number of load/unload cycles, number of indentations, was the indenter calibrated and how? Probably you used the Oliver and Pharr method to calculate the H and E values, and thus should be mentioned.
    We included the following text:
    Hardness (H) and elastic modulus (E) were measured by the same instrumented indentation facility (UNAT\Asmec) using a diamond Berkovich-type indenter. For each sample, a matrix of 25 indentations was performed. The maximum applied load was 400 mN using the quasi-continuous stiffness method (QCSM). The values of H and E were calculated following the Oliver and Pharr method (Oliver and Pharr, 1992). The indenter area function was calibrated with silica and sapphire standards.

    Oliver, W. C. and Pharr, G. M. (1992), “An improved technique for determing hardness and elastic modulus using load and displacement sensing indentations experiments”, Journal of Materials Research, Vol. 7, pp. 1564-1583.

    7 - Please, inform which type of tribological test was used. reciprocating or circular, and if circular what is the diameter, if reciprocating the stroke length?
    We already described in the text the type of tribological test – “The tribological behavior was investigated by a pin-on-disc tribometer (High-temperature – CSEM instruments) at unlubricated conditions…”

    We added the following text:
    The radius of the wear tracks was 2 mm.

    8 - Results: How the crystal sizes were measured (how many crystals were count?) Please present images of sample showing the crystals. Also, include XRD results to prove that the crystalline phases are LS2.
    The crystal sizes were measured using the ImageJ software. The crystal sizes were determined by average of the largest crystals and are the measurement of the longest axis since the crystals are ellipsoids with a 1.6 long/short axis ratio. The largest crystals were chosen because these are the crystals that the surface cut them at the longest axis and are suitable for measurements. The size was the average of 10 to 15 crystals.
    We added figures 1 and 2 of the images showing the microstructures consisting of crystals and the glassy phase and a typical XRD of the crystallized phase, respectively.

    We added the following text:
    The crystallized volume fractions and the crystal sizes were measured using the ImageJ software (Schneider, Rasband, and Eliceiri 2012).

    The crystalline phases were verified by X-ray difraction using a Rigaku Ultima IV diffractometer in theta-theta configuration and using Cu Kalpha radiation. The scan were performed in continuous mode from 5º to 70º at a speed of 1º/min and step of 0.02º.

    Figures 1(a), 1(b) and 1(c) (added in the new version of the manuscript) show the microstructure of the samples consisting of the LS2 crystals sizes of 8 mum, 13 mum and 34 mum, respectively, uniformly dispersed in a glassy matrix. Figure 2 (added in the new version of the manuscript) shows a typical XRD pattern of the LS2 sample with an 8 mum crystal size. All diffraction peaks are of the Li_2Si_2O_5 phase, identified according to the JCPDS 82-2396 card.

    Schneider, C. A., Rasband, W. S. and Eliceiri, K. W. (2012) “NIH Image to ImageJ: 25 years of image analysis”, Nature Methods, Vol. 9, pp. 671-675.

    9 - Figure 1 - You can use the smoothing tool in the Tribox software, so that we can see clearly the differences on COF for alumina ball.
    We smoothed the COF curves for the alumina ball in figure 1.

    10 - Why the running-in behavior is different for both ball materials? For alumina there is a decrease of COF while for WC there is an increase.
    This might be related with the severity of the wear. For alumina spheres, the high initial friction coefficient is related with a severe wear regime in the initial part of the test. As the test progress, the regime changes to a less severe regime with a decrease in the COF. For the WC spheres, the regime is moderate with a continuous increase in COF. We can speculate at this stage this might be related to the larger hardness of the WC sphere and/or the different chemical bonds of the spheres. Alumina has mainly ionic bonds and has a hardness of 13 GPa while WC has mainly covalent bonds and is harder, with a hardness of 19 GPa. Their interactions with the LS2 glass-ceramics, which has both ionic and covalent bonds and has a lower hardness, might be different mechanically and chemically. We are currently investigating this.

    12 - Figure 4. Please correct the numbers in the Y axis - use dot as decimal notation.
    Error bars for k is notably different when comparing results for alumina and WC balls. Please, explain.
    Thank you. We corrected figure 4. The relative errors varied from 12% to 33% to the WC sphere and from 5% to 19% to the alumina sphere. The difference of the error bars might be related with the severity of the wear. For the WC sphere, the wear is mild and produced a large uncertainty. We are currently investigating this at different stages of the test in more detail.

    13 - Figure 7a. Please correct the numbers in the Y axis - use dot as decimal notation.
    As your glass-ceramic is not fully crystalline, how did you choose the indentation values, considering that you can indent a glassy region or a crystalline region. Could this explain the larger error bars for GC results? Please, comment.
    Thank you. We corrected figure 7a. The indentations were distributed randomly on the sample surface. Therefore, the indentations could be on the crystal, on the glass or on the interface (crystal/glass) regions. The glass has the lowest error bars and as the crystal size increases, the error bars become larger. This is related with the size of the microstructure (crystal size) in relation to the impression size. The smaller the crystal, the more homogenous is the structure in relation to the indentation size. This leads to smaller error bars of H and E.

    We added the following text:
    The glass has the lowest error bars and as the crystal size increases, the error bars become larger. This is related with the size of the microstructure (crystal size) in relation to the impression size. The smaller the crystal, the more homogenous is the structure in relation to the indentation size. This leads to smaller error bars of H and E.

    14 - In the discussion section, I was expecting to see an explanation of why the wear severity using alumina ball is higher than for WC ball. It is still not clear once the hardness of the two ball materials is quite different. Have you analysed the wear on the counterpart?
    We are currently investigating this. We are looking in more detail the wear mechanisms in the initial stages of the tests. At present, the causes of the wear severity is unclear. We can only speculate the difference is related to the differences in hardness and/or the nature of the chemical bonds of the WC and alumina spheres. Both are harder than the LS2 GCs. We have not analyzed the wear of the counterpart and this is an interesting measurement to be made,but would be the subject of another paper.

    15 - Results should be better discussed, correlating the mechanical properties of the glass and glass-ceramics with wear. Also, what is the effect of residual stress around crystals on the tribological behavior?
    We added a text and a new figure in the discussion. Regarding the effect of residual stresses on the tribological behavior, this is an open topic. In LS2 glass-ceramics, the residual stresses in the crystals are compressive while in the glass, the average stress is tensile. Residual stresses might affect microcracking. As the main mechanism for material removal is by fracture, tensile stresses in the glass may help to promote fracture and increase wear rate.

    The added text is:
    Two questions arise from these findings: how would crystal sizes influence abrasion, and why does the material´s counterpart cause such an enormous variation in wear rates? Regarding the first query: because wear mechanisms depend on both plastic and elastic strains, the modest variations in k were somehow expected based on the overall hardness and elastic modulus measured for these samples, as shown in Figure 10. The plasticity index H/E_r can be a useful parameter to investigate it further, since, as demonstrated for a wide range of single-phase materials (Pintaude, 2013), the work dissipated as plastic deformation decreases as such ratio increases (Cheng and Cheng, 2004). E_r is the reduced elastic modulus, given by (equation added in the new version of the manuscript), where the first term in the right-hand side regards to the sample, and the last one to the diamond indenter. The calculated H/Er were about 0.07 for glass and 0.06 for the crystallized conditions. These values are in the same magnitude found for materials such as sapphire; they are higher than those for ductile metals (~0.02) but are lower than fused silica (~0.14) (Cheng and Cheng, 2004). Moreover, the parameter clearly decreased with crystal sizes (Fig. 10(a)) (figure added in the new version of the manuscript); however, the concomitant behavior, the expected depreciation of abrasion resistance, was not verified in this study, as seen in Figure 10(b) (figure added in the new version of the manuscript). The reason for that lack of coherency is not clear. Perhaps, it reflects limitations of the plasticity index to be a universal parameter. Glass-ceramics are composed of crystalline and amorphous phases, in which the correlation between abrasion and crystal sizes is a complex matter involving fracture toughness as an important property (Serbena et al., 2015). Another important factor is the residual stresses due to the different thermal expansion coefficients between the glass and the crystals that arise from cooling from Tg. In LS2 glass-ceramics, the residual stresses in the crystals are compressive while in the glass, the average stress is tensile. Residual stresses might produce microcracking (Serbena and Zanotto, 2012). As the main mechanism for material removal is by fracture, tensile stresses in the glass may help to promote fracture and increase wear rate. Of course, these subjects are not exhausted and demands further and more detailed investigation.

    The influence of the sphere material on k values is understood based on the contact mechanics.

    Cheng, Y., and Cheng, C. (2004), “Scaling, dimensional analysis, and indentation measurements”, Mater. Sci. Eng. R, Vol. 44, pp. 91–149.

    Serbena, F. C., and Zanotto, E. D, (2012), “Internal residual stresses in glass-ceramics: A review”, Journal of Non-Crystalline Solids. Vol. 358, pp. 975–984.

    Response to the second reviewer:
    1. The choose of two counterbodies should be justified and correlated to a practical problem, in this case, probably for biomaterials.
    Thank you for point that out.

    We have added the following text:
    The chosen crystalline volume fraction of 64% is because this approximately the crystallized volume fraction of the commercial LS2 based glass-ceramics (Villas-Boas et al., 2019). The counterparts investigated are alumina, used to investigate dental glass-ceramics, and WC spheres, a used to investigated ceramics such as alumina due to its higher hardness.

    Villas‐Boas, M. O. C., Serbena, F. C., Soares, V. O., Mathias, I., and Zanotto, E. D. (2019), “Residual stress effect on the fracture toughness of lithium disilicate glass‐ceramics”, Journal of the American Ceramic Society, Vol, 103, pp. 465-479.

    1. The discussion should correlate the mechanical properties to wear performance. I recommend to consider the properties of counterbodies. Please, see the approach given in "Giuseppe Pintaude (May 22nd 2013). Introduction of the Ratio of the Hardness to the Reduced Elastic Modulus for Abrasion, Tribology - Fundamentals and Advancements, Jürgen Gegner, IntechOpen, DOI: 10.5772/55470. Available from: https://www.intechopen.com/books/tribology-fundamentals-and-advancements/introduction-of-the-ratio-of-the-hardness-to-the-reduced-elastic-modulus-for-abrasion". In this chapter, the raio E/H is explored in terms of wear performance, considering the equivalent elastic modulus.
      We added in the discussion the following text:
      Two questions arise from these findings: how would crystal sizes influence abrasion, and why does the material´s counterpart cause such an enormous variation in wear rates? Regarding the first query: because wear mechanisms depend on both plastic and elastic strains, the modest variations in k were somehow expected based on the overall hardness and elastic modulus measured for these samples, as shown in Figure 10. The plasticity index H/E_r can be a useful parameter to investigate it further, since, as demonstrated for a wide range of single-phase materials (Pintaude, 2013), the work dissipated as plastic deformation decreases as such ratio increases (Cheng and Cheng, 2004). E_r is the reduced elastic modulus, given by (equation added in the new version of the manuscript), where the first term in the right-hand side regards to the sample, and the last one to the diamond indenter. The calculated H/Er were about 0.07 for glass and 0.06 for the crystallized conditions. These values are in the same magnitude found for materials such as sapphire; they are higher than those for ductile metals (~0.02) but are lower than fused silica (~0.14) (Cheng and Cheng, 2004). Moreover, the parameter clearly decreased with crystal sizes (Fig. 10(a)) (figure added in the new version of the manuscript); however, the concomitant behavior, the expected depreciation of abrasion resistance, was not verified in this study, as seen in Figure 10(b) (figure added in the new version of the manuscript). The reason for that lack of coherency is not clear. Perhaps, it reflects limitations of the plasticity index to be a universal parameter. Glass-ceramics are composed of crystalline and amorphous phases, in which the correlation between abrasion and crystal sizes is a complex matter involving fracture toughness as an important property (Serbena et al., 2015). Another important factor is the residual stresses due to the different thermal expansion coefficients between the glass and the crystals that arise from cooling from Tg. In LS2 glass-ceramics, the residual stresses in the crystals are compressive while in the glass, the average stress is tensile. Residual stresses might produce microcracking (Serbena and Zanotto, 2012). As the main mechanism for material removal is by fracture, tensile stresses in the glass may help to promote fracture and increase wear rate. Of course, these subjects are not exhausted and demands further and more detailed investigation.

    The influence of the sphere material on k values is understood based on the contact mechanics.

    Cheng, Y., and Cheng, C. (2004), “Scaling, dimensional analysis, and indentation measurements”, Mater. Sci. Eng. R, Vol. 44, pp. 91–149.

    Serbena, F. C., and Zanotto, E. D, (2012), “Internal residual stresses in glass-ceramics: A review”, Journal of Non-Crystalline Solids. Vol. 358, pp. 975–984.



    Cite this author response
  • pre-publication peer review (ROUND 1)
    Decision Letter
    2019/10/26

    26-Oct-2019

    Dear Ms. da Cruz:

    Manuscript ID ilt-08-2019-0352 entitled "Effect of crystal size on tribological properties of lithium disilicate glass-ceramics sliding against alumina and tungsten carbide spheres" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

    The reviewer(s) have recommended major revisions to the submitted manuscript, before it can be considered for publication. Therefore, I invite you to respond to the reviewer(s)' comments and revise your manuscript.

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    Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

    Sincerely,
    Prof. Henara Costa
    Guest Editor, Industrial Lubrication and Tribology
    ltm-henara@ufu.br, henara.costa@gmail.com

    Reviewer(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    1- Please correct et. al. to et al.

    2 - Aim is clear, but not justified. Justify why 64% of crystalline fraction, and why compare WC with alumina counterpart?

    3 - Experimental procedure: language should be revised: "poured three times in an electric furnace"... usually glass melt is poured between two metallic plates for fast cooling.

    4 - Crystallization temperatures are missing. What is the nucleation and growth temperatures, what is each treatment time? How the temperatures were chosen?

    5 - All the works citing tribological properties of LS2 glass-ceramics refers to lubricated conditions. Why did you use unlubricated? Does it make any sense once these materials will always be worn differently when in aqueous environment? Please, justify.

    6 - Information about nanoindentation tests should be more detailed. What was the applied load, number of load/unload cycles, number of indentations, was the indenter calibrated and how? Probably you used the Oliver and Pharr method to calculate the H and E values, and thus should be mentioned.

    7 - Please, inform which type of tribological test was used. reciprocating or circular, and if circular what is the diameter, if reciprocating the stroke length?

    8 - Results: How the crystal sizes were measured (how many crystals were count?) Please present images of sample showing the crystals. Also, include XRD results to prove that the crystalline phases are LS2.

    9 - Figure 1 - You can use the smoothing tool in the Tribox software, so that we can see clearly the differences on COF for alumina ball.

    10 - Why the running-in behavior is different for both ball materials? For alumina there is a decrease of COF while for WC there is an increase.

    11- Figure 3 should be plotted using the same scale (X and Y axis), and use a inset for WC.

    12 - Figure 4. Please correct the numbers in the Y axis - use dot as decimal notation.
    Error bars for k is notably different when comparing results for alumina and WC balls. Please, explain.

    13 - Figure 7a. Please correct the numbers in the Y axis - use dot as decimal notation.
    As your glass-ceramic is not fully crystalline, how did you choose the indentation values, considering that you can indent a glassy region or a crystalline region. Could this explain the larger error bars for GC results? Please, comment.

    14 - In the discussion section, I was expecting to see an explanation of why the wear severity using alumina ball is higher than for WC ball. It is still not clear once the hardness of the two ball materials is quite different. Have you analysed the wear on the counterpart?

    15 - Results should be better discussed, correlating the mechanical properties of the glass and glass-ceramics with wear. Also, what is the effect of residual stress around crystals on the tribological behavior?

    Reviewer: 2

    Comments to the Author
    Please, pay attention for two points:
    1. The choose of two counterbodies should be justified and correlated to a practical problem, in this case, probably for biomaterials.
    2. The discussion should correlate the mechanical properties to wear performance. I recommend to consider the properties of counterbodies. Please, see the approach given in "Giuseppe Pintaude (May 22nd 2013). Introduction of the Ratio of the Hardness to the Reduced Elastic Modulus for Abrasion, Tribology - Fundamentals and Advancements, Jürgen Gegner, IntechOpen, DOI: 10.5772/55470. Available from: https://www.intechopen.com/books/tribology-fundamentals-and-advancements/introduction-of-the-ratio-of-the-hardness-to-the-reduced-elastic-modulus-for-abrasion". In this chapter, the raio E/H is explored in terms of wear performance, considering the equivalent elastic modulus.
    Reviewer: 1

    Recommendation: Major Revision

    Comments:
    1- Please correct et. al. to et al.

    2 - Aim is clear, but not justified. Justify why 64% of crystalline fraction, and why compare WC with alumina counterpart?

    3 - Experimental procedure: language should be revised: "poured three times in an electric furnace"... usually glass melt is poured between two metallic plates for fast cooling.

    4 - Crystallization temperatures are missing. What is the nucleation and growth temperatures, what is each treatment time? How the temperatures were chosen?

    5 - All the works citing tribological properties of LS2 glass-ceramics refers to lubricated conditions. Why did you use unlubricated? Does it make any sense once these materials will always be worn differently when in aqueous environment? Please, justify.

    6 - Information about nanoindentation tests should be more detailed. What was the applied load, number of load/unload cycles, number of indentations, was the indenter calibrated and how? Probably you used the Oliver and Pharr method to calculate the H and E values, and thus should be mentioned.

    7 - Please, inform which type of tribological test was used. reciprocating or circular, and if circular what is the diameter, if reciprocating the stroke length?

    8 - Results: How the crystal sizes were measured (how many crystals were count?) Please present images of sample showing the crystals. Also, include XRD results to prove that the crystalline phases are LS2.

    9 - Figure 1 - You can use the smoothing tool in the Tribox software, so that we can see clearly the differences on COF for alumina ball.

    10 - Why the running-in behavior is different for both ball materials? For alumina there is a decrease of COF while for WC there is an increase.

    11- Figure 3 should be plotted using the same scale (X and Y axis), and use a inset for WC.

    12 - Figure 4. Please correct the numbers in the Y axis - use dot as decimal notation.
    Error bars for k is notably different when comparing results for alumina and WC balls. Please, explain.

    13 - Figure 7a. Please correct the numbers in the Y axis - use dot as decimal notation.
    As your glass-ceramic is not fully crystalline, how did you choose the indentation values, considering that you can indent a glassy region or a crystalline region. Could this explain the larger error bars for GC results? Please, comment.

    14 - In the discussion section, I was expecting to see an explanation of why the wear severity using alumina ball is higher than for WC ball. It is still not clear once the hardness of the two ball materials is quite different. Have you analysed the wear on the counterpart?

    15 - Results should be better discussed, correlating the mechanical properties of the glass and glass-ceramics with wear. Also, what is the effect of residual stress around crystals on the tribological behavior?

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes, there are few works related to the crystallization effect on the wear of a LS2 glass.

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Yes. Literature citation is adequate.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Authors should explain why they decided to study unlubricated wear once these materials will always be used in lubricated conditions.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Some graphics should be improved, figures of crystals on samples included. Conclusions are adequate and answer the objectives of the work.

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: All the implications are consistent with the conclusions.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Language should be revised by a native speaker.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: Some experimental details are missing.

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: Yes, I would like my name to appear with my report on Publons

    Reviewer: 2

    Recommendation: Minor Revision

    Comments:
    Please, pay attention for two points:
    1. The choose of two counterbodies should be justified and correlated to a practical problem, in this case, probably for biomaterials.
    2. The discussion should correlate the mechanical properties to wear performance. I recommend to consider the properties of counterbodies. Please, see the approach given in "Giuseppe Pintaude (May 22nd 2013). Introduction of the Ratio of the Hardness to the Reduced Elastic Modulus for Abrasion, Tribology - Fundamentals and Advancements, Jürgen Gegner, IntechOpen, DOI: 10.5772/55470. Available from: https://www.intechopen.com/books/tribology-fundamentals-and-advancements/introduction-of-the-ratio-of-the-hardness-to-the-reduced-elastic-modulus-for-abrasion". In this chapter, the raio E/H is explored in terms of wear performance, considering the equivalent elastic modulus.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes, it does.

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: The relationship to the literature is almost ok, only a connection between mechanical properties and wear would be completed.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Any problem here.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Please, complete the relationship between mechanical properties and wear.

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: This is the weak point of manuscript. The selection of different counterbodies should be related to practical implications in biomedical applications.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Any problem here.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: Yes, I would like my name to appear with my report on Publons

    Decision letter by
    Cite this decision letter
    Reviewer report
    2019/10/26

    Please, pay attention for two points:
    1. The choose of two counterbodies should be justified and correlated to a practical problem, in this case, probably for biomaterials.
    2. The discussion should correlate the mechanical properties to wear performance. I recommend to consider the properties of counterbodies. Please, see the approach given in "Giuseppe Pintaude (May 22nd 2013). Introduction of the Ratio of the Hardness to the Reduced Elastic Modulus for Abrasion, Tribology - Fundamentals and Advancements, Jürgen Gegner, IntechOpen, DOI: 10.5772/55470. Available from: https://www.intechopen.com/books/tribology-fundamentals-and-advancements/introduction-of-the-ratio-of-the-hardness-to-the-reduced-elastic-modulus-for-abrasion". In this chapter, the raio E/H is explored in terms of wear performance, considering the equivalent elastic modulus.

    Cite this review
    Reviewer report
    2019/10/08

    1- Please correct et. al. to et al.

    2 - Aim is clear, but not justified. Justify why 64% of crystalline fraction, and why compare WC with alumina counterpart?

    3 - Experimental procedure: language should be revised: "poured three times in an electric furnace"... usually glass melt is poured between two metallic plates for fast cooling.

    4 - Crystallization temperatures are missing. What is the nucleation and growth temperatures, what is each treatment time? How the temperatures were chosen?

    5 - All the works citing tribological properties of LS2 glass-ceramics refers to lubricated conditions. Why did you use unlubricated? Does it make any sense once these materials will always be worn differently when in aqueous environment? Please, justify.

    6 - Information about nanoindentation tests should be more detailed. What was the applied load, number of load/unload cycles, number of indentations, was the indenter calibrated and how? Probably you used the Oliver and Pharr method to calculate the H and E values, and thus should be mentioned.

    7 - Please, inform which type of tribological test was used. reciprocating or circular, and if circular what is the diameter, if reciprocating the stroke length?

    8 - Results: How the crystal sizes were measured (how many crystals were count?) Please present images of sample showing the crystals. Also, include XRD results to prove that the crystalline phases are LS2.

    9 - Figure 1 - You can use the smoothing tool in the Tribox software, so that we can see clearly the differences on COF for alumina ball.

    10 - Why the running-in behavior is different for both ball materials? For alumina there is a decrease of COF while for WC there is an increase.

    11- Figure 3 should be plotted using the same scale (X and Y axis), and use a inset for WC.

    12 - Figure 4. Please correct the numbers in the Y axis - use dot as decimal notation.
    Error bars for k is notably different when comparing results for alumina and WC balls. Please, explain.

    13 - Figure 7a. Please correct the numbers in the Y axis - use dot as decimal notation.
    As your glass-ceramic is not fully crystalline, how did you choose the indentation values, considering that you can indent a glassy region or a crystalline region. Could this explain the larger error bars for GC results? Please, comment.

    14 - In the discussion section, I was expecting to see an explanation of why the wear severity using alumina ball is higher than for WC ball. It is still not clear once the hardness of the two ball materials is quite different. Have you analysed the wear on the counterpart?

    15 - Results should be better discussed, correlating the mechanical properties of the glass and glass-ceramics with wear. Also, what is the effect of residual stress around crystals on the tribological behavior?

    Reviewed by
    Cite this review
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