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Peer-Review Record

Dynamics of Radiation Damage in AlN Ceramics under High-Dose Irradiation, Typical for the Processes of Swelling and Hydrogenation

Crystals 2020, 10(6), 546; https://doi.org/10.3390/cryst10060546
by Artem L. Kozlovskiy 1,2,*, Dmitriy. I. Shlimas 1,2, Inesh E. Kenzhina 1,2, Daryn B. Borgekov 1,2 and Maxim V. Zdorovets 1,2,3
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Crystals 2020, 10(6), 546; https://doi.org/10.3390/cryst10060546
Submission received: 30 May 2020 / Revised: 17 June 2020 / Accepted: 22 June 2020 / Published: 26 June 2020

Round 1

Reviewer 1 Report

The current manuscript carries useful information of structural ceramics (AlN) for their potential usage as radiation protection. However, it needs to have clear benchmarking with the current state-of-the-art materials being used. Else it is captured as the  mere collection few experimental facts. The results should be connected more with materials point of view. Author should also mention the overall all novelty of this work. Last but not least, the overall English should be improved in the revised manuscript.  

Author Response

The authors are grateful to the referee for the submitted comments. The following corrections and additions have been made to the text of the article.

 

Introduction

 

The choice of aluminum nitride from a large number of other nitride materials (Si3N4, TiN, BN) as the object of study is due to its high resistance to most aggressive acids, including aqua regia, HF, good thermal conductivity, high rates of mechanical strength and insulating properties. Great interest in this type of ceramics was shown by material scientists involved in the development of materials for the new generation of Gen IV nuclear reactors [Onoda, Yusuke, et al. "Thermally stimulated luminescence properties of Eu-doped AlN ceramic." Optik 181 (2019): 50-56.; Patino, M. I., R. P. Doerner, and G. R. Tynan. "Exposure of AlN and Al2O3 to low energy D and He plasmas." Nuclear Materials and Energy (2020): 100753.; Sall, M., et al. "Electronic excitations induced climb of dislocations in swift heavy ion irradiated AlN and AlxGa1− xN." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 435 (2018): 116-120. ]. The high stability of aluminum nitride to the effects of heavy ions, the absence of latent ion tracks in it after irradiation, as well as the low mobility of grains as a result of the accumulation of defects, makes this material one of the promising materials for use as the basis of the first wall of high-temperature nuclear reactors.

 The novelty of the scientific work consists in obtaining new data on the radiation resistance of AlN ceramics to high-dose irradiation with protons and helium ions and subsequent aging, as well as changes in properties due to external influences. As a rule, irradiation with doses higher than 1-3Ñ…1017 ion/cm2 is considered as the initial dose of the initialization of the processes of blister formation and swelling of ceramic materials, which leads to an acceleration of degradation processes.

 

Results and Discussion

 

The data obtained are in good agreement with the previously presented studies on the radiation resistance to helium embrittlement and swelling of nitride materials. For example, data on resistance to the formation of blisters and helium bubbles have a good correlation with similar results for thin-film multilayer coatings based on ZrN, CrN, and AlN [Uglov, V. V., et al. "Blistering in Helium-Ion-Irradiated Zirconium, Aluminum, and Chromium Nitride Films." Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques 14 (2020): 359-365., Uglov, V. V., et al. "Surface blistering in ZrSiN nanocomposite films irradiated with He ions." Surface and Coatings Technology (2020): 125654.]. The authors of these works found that the degradation of nitride materials as a result of the accumulation of implanted helium occurs as a result of the formation of porous inclusions and deformations of the structure of the surface layer at low irradiation fluences. An increase in the irradiation fluence leads to the filling of these cavities with poorly soluble helium ions, followed by the formation of helium bubbles. Moreover, for different samples, the dose loads necessary to start the nucleation of bubbles are different. In the case of proton irradiation with nitride ceramics, the structural changes resulting from the irradiation are in good agreement with the works [Ives, Nathan E., et al. "Effects of proton-induced displacement damage on gallium nitride HEMTs in RF power amplifier applications." IEEE Transactions on Nuclear Science 62.6 (2015): 2417-2422.; Kim, Hong Yeol, et al. "Characterization of AlGaN/GaN HEMT irradiated at 5 keV and 25 MeV proton energies." J. Ceramic Process. Res. 9.2 (2008): 155-157.; Gan, Jian, et al. "Proton irradiation study of GFR candidate ceramics." Journal of nuclear materials 389.2 (2009): 317-325.], according to which it was found that in the case of large-dose irradiation, the main structural changes are associated with the formation of microcracks and disordering regions. In this case, the presence of impurities of other elements in the structure of nitride ceramics leads to the formation of additional disordering regions and accumulations of defects.

Author Response File: Author Response.doc

Reviewer 2 Report

This manuscript provides some experimental results on the effects of protons and helium ions irradiation on the performance of nitride ceramics. The research in this study is not very detailed, but it may still provide some useful data for the development of this field. I have the following comments on the manuscript:

1) Why investigating the influence of irradiation on the dielectric properties? For the heat-conducting properties, it is understandable that the reduction of which can have a negative impact on the performance of reactors. What effect does the dielectric properties of the material have on the performance of the reactor?

2) The kinetics of the degradation of ceramics were investigated under accelerated degradation. It is claimed that 1 hour of treatment with water vapor at a temperature of 150 degree C and a pressure of 2.2-2.3 atm is 1.5-2.0 years of aging in vivo. However, the theoretical background of this estimate is not provided. The authors should detail the estimate or provide related references.

3) At the end of the conclusion, it is said that the mechanisms of degradation are different for ceramics irradiated by protons and by helium ions. Figure 8 illustrated the different morphologies of ceramics irradiated with different particles. However, the discussion about the degradation mechanism is insufficient (if not completely absent).

4) There are some formatting errors. For example, line 65, N2 without subscript; equation (1), the sentence above the right arrow should be formatted; line 84, it is not a new paragraph and there should be no first line indent; Fig. 4, 6, and 7, the outermost wireframe deviates from the position of the figures.

Author Response

1. The study of the dielectric properties of ceramics exposed to radiation is due to the fact that these ceramics can be used not only as materials for the first wall of nuclear reactors for which heat conductivity and crack resistance are one of the most important characteristics, but also as the basis for substrates or printed circuit boards of microelectronic circuits working in conditions of increased radiation background.

2. The technique of low-temperature aging under the influence of water vapor under pressure is one of the common methods capable of simulating the effect of aging of ceramics. This technique has established itself as one of the most effective and accurate methods of artificial aging of materials due to external influences [Zhigachev, Andrey O., et al. "Low-temperature aging of baddeleyite-based Ca-TZP ceramics." Journal of the American Ceramic Society100.7 (2017): 3283-3292., Pereira, G. K. R., et al. "Low-temperature degradation of Y-TZP ceramics: a systematic review and meta-analysis." Journal of the mechanical behavior of biomedical materials 55 (2016): 151-163., Pereira, G. K. R., et al. "Mechanical behavior of a Y-TZP ceramic for monolithic restorations: effect of grinding and low-temperature aging." Materials Science and Engineering: C 63 (2016): 70-77.].

3. To describe the effects of irradiation and aging, one can propose the following mechanism of surface layer degradation. When irradiated with helium ions or protons, regions with a high degree of disorder are formed in the structure of the surface layer at various depths, which arise both as a result of elastic and inelastic collisions of incident particles with electron shells (elastic interactions) and target nuclei (inelastic interactions), and as a result the formation of cascading effects of the migration of point defects and initially knocked out atoms. Moreover, in the case of proton irradiation, the probability of the formation of initially knocked out atoms is small due to the small size of the incident particles, as well as large energy losses on the electron shells with the subsequent formation of cascades of knocked out electrons. In the case of irradiation with low-energy helium ions, inelastic collisions predominate, which can lead to the displacement of atoms from the lattice sites, and thereby significantly increase the degree of deformation of the crystal structure. Also, due to the high penetrating ability of protons in ceramics and a significantly larger mean free path (4 μm), the density of defects in the near-surface layer 300-500 nm thick is much lower than when irradiated with helium ions. In this regard, for samples irradiated with helium ions, the surface layer (300-500 nm) is subject to great deformation not only due to the large number of defects formed, but also helium bubbles that form at high doses of radiation, inside which additional pressure accumulates, leading to bloating bubble. When modeling the effects of aging of ceramics irradiated with protons, the surface layer of which contains fewer defects than a similar layer of ceramics irradiated with helium ions, the degradation of the layer occurs due to the destruction of the disordering regions and partial cracking of the irradiated layer with the formation of a porous structure, which indicates the presence of irradiated samples gas-filled inclusions of small size (5-15 nm). For samples irradiated with helium ions, in the surface layer of which, at high radiation doses, strongly distorted defective regions and blisters are formed, explosive destruction of gas-filled bubbles occurs with increasing exposure time of the vapor, with the formation of microcracks along the grain boundaries that serve as defect sinks. 

Thus, it was found that at an irradiation dose of 5x1017 ion/cm2 characteristic of a displacement of 50 dpa, the degradation of the surface layer of ceramics is catastrophic in nature, which can have a significant impact on the performance characteristics of structural materials.

The data obtained are in good agreement with the previously presented studies on the radiation resistance to helium embrittlement and swelling of nitride materials. For example, data on resistance to the formation of blisters and helium bubbles have a good correlation with similar results for thin-film multilayer coatings based on ZrN, CrN, and AlN [Uglov, V. V., et al. "Blistering in Helium-Ion-Irradiated Zirconium, Aluminum, and Chromium Nitride Films." Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques 14 (2020): 359-365., Uglov, V. V., et al. "Surface blistering in ZrSiN nanocomposite films irradiated with He ions." Surface and Coatings Technology (2020): 125654.]. The authors of these works found that the degradation of nitride materials as a result of the accumulation of implanted helium occurs as a result of the formation of porous inclusions and deformations of the structure of the surface layer at low irradiation fluences. An increase in the irradiation fluence leads to the filling of these cavities with poorly soluble helium ions, followed by the formation of helium bubbles. Moreover, for different samples, the dose loads necessary to start the nucleation of bubbles are different. In the case of proton irradiation with nitride ceramics, the structural changes resulting from the irradiation are in good agreement with the works [Ives, Nathan E., et al. "Effects of proton-induced displacement damage on gallium nitride HEMTs in RF power amplifier applications." IEEE Transactions on Nuclear Science 62.6 (2015): 2417-2422.; Kim, Hong Yeol, et al. "Characterization of AlGaN/GaN HEMT irradiated at 5 keV and 25 MeV proton energies." J. Ceramic Process. Res. 9.2 (2008): 155-157.; Gan, Jian, et al. "Proton irradiation study of GFR candidate ceramics." Journal of nuclear materials 389.2 (2009): 317-325.], according to which it was found that in the case of large-dose irradiation, the main structural changes are associated with the formation of microcracks and disordering regions. In this case, the presence of impurities of other elements in the structure of nitride ceramics leads to the formation of additional disordering regions and accumulations of defects.

 

4. All corrections are made according to the comment of the reviewer.

Author Response File: Author Response.doc

Reviewer 3 Report

This paper reports on the radiation damage in AlN ceramics under high-dose irradiation of proton or He ions.

The comparative results of the influence of large-dose irradiation with protons and helium ions on the properties of AlN ceramics, as well as the kinetics of degradation due to aging by pressurized water vapor at 150 degree C.

My comments are follows:

 

Comment 1

Page 2, Equation 1:

The AlN used in this study was fabricated by reaction bonding or using sintering aids such as Y2O3?

Since the simple annealing in N2 (ambient pressure) could not afford dense AlN bulk ceramics up to 1800 degree C. More details including the N2 pressure, and the density of the resulting AlN ceramics should be reported.

 

Comment 2: Thermal conductivity

Thermal conductivity depends on the measurement temperature (range).

The Tc1 and Tc2 applied in this study should be reported.

Also, there is no information on the number of data for each point.

The data variation should be shown using Error bar for each bar in Fig. 5.

 

Comment 3: Crack resistance

The evaluation method is missing in the experimental method.

Again, there is no information on the number of data for each point.

The data variation should be shown using error bar for each point in Fig. 6. Then, Figure 7 will be able to be discussed.

Author Response

2. The range of tc1 and tc2 as a result of thermal conductivity tests ranged from 300 to 1000 K. The number of measurements for each test sample was 10 independent measurements.

 

Figure 5.  Diagram of the dependence of the coefficient of thermal conductivity on the dose and type of exposure

 

3. The results of studying the kinetics of ceramic degradation under accelerated aging of initial and irradiated samples are presented below (see Figure 6). Kinetics was determined by measuring the crack resistance of ceramics after a certain time. According to the data obtained, for the initial sample, there is a slight decrease in crack resistance in the range of 5-7 % for the entire test period, which is comparable in time to 50-60 years. The technique of low-temperature aging under the influence of water vapor under pressure is one of the common methods capable of simulating the effect of aging of ceramics. This technique has established itself as one of the most effective and accurate methods of artificial aging of materials due to external influences [Zhigachev, Andrey O., et al. "Low-temperature aging of baddeleyite-based Ca-TZP ceramics." Journal of the American Ceramic Society100.7 (2017): 3283-3292., Pereira, G. K. R., et al. "Low-temperature degradation of Y-TZP ceramics: a systematic review and meta-analysis." Journal of the mechanical behavior of biomedical materials 55 (2016): 151-163., Pereira, G. K. R., et al. "Mechanical behavior of a Y-TZP ceramic for monolithic restorations: effect of grinding and low-temperature aging." Materials Science and Engineering: C 63 (2016): 70-77.]. The number of measurements for each test sample was 10 measurements.

   

a)

b)

Figure 6. The graph of the dependence of the crack resistance on the aging time of the samples: a) Proton irradiation; b) Helium ion irradiation

 

The small value of sample degradation in the initial state indicates a high resistance of ceramics to aging and embrittlement. For proton-irradiated samples, a decrease in crack resistance by 15-19 % is observed compared with the initial sample, however, an increase in fluence does not lead to significant differences in a decrease in crack resistance. During aging tests, a decrease in crack resistance for proton-irradiated samples is of a two-stage nature of change. The first stage is characterized by a gradual decrease in crack resistance for cases of irradiation of 1Ñ…1017 – 3Ñ…1017 ion/cm2. The second stage is characterized by an almost constant value of crack resistance, which indicates the stabilization of the crack resistance and the absence of mechanisms for further destruction of the structure. However, for irradiated samples with a fluence of 5x1017 ion / cm2, the decrease in crack resistance is constant over the course of the test time. In the case of ceramics irradiated with helium ions, for fluxes of irradiation of 1Ñ…1017 – 3Ñ…1017 ion/cm2, a decrease in the crack resistance is observed comparable with irradiation with protons, and an increase in fluence to 5x1017 ion/cm2 leads to a decrease in the value by 35-37% from the initial value. In this case, in contrast to proton irradiation, for which the decrease in crack resistance over time is from 25 to 45 % depending on the dose, for samples irradiated with helium ions, the decrease in crack resistance after the test time is from 25 to 87 % depending on the dose exposure (see chart data in Figure 7).

 

   

a)

b)

Figure 7. The diagram of the dependence of changes in the degree of resistance to cracking: a) Proton irradiation; b) Helium ion irradiation

 

 

To describe the effects of irradiation and aging, one can propose the following mechanism of surface layer degradation. When irradiated with helium ions or protons, regions with a high degree of disorder are formed in the structure of the surface layer at various depths, which arise both as a result of elastic and inelastic collisions of incident particles with electron shells (elastic interactions) and target nuclei (inelastic interactions), and as a result the formation of cascading effects of the migration of point defects and initially knocked out atoms. Moreover, in the case of proton irradiation, the probability of the formation of initially knocked out atoms is small due to the small size of the incident particles, as well as large energy losses on the electron shells with the subsequent formation of cascades of knocked out electrons. In the case of irradiation with low-energy helium ions, inelastic collisions predominate, which can lead to the displacement of atoms from the lattice sites, and thereby significantly increase the degree of deformation of the crystal structure. Also, due to the high penetrating ability of protons in ceramics and a significantly larger mean free path (4 μm), the density of defects in the near-surface layer 300-500 nm thick is much lower than when irradiated with helium ions. In this regard, for samples irradiated with helium ions, the surface layer (300-500 nm) is subject to great deformation not only due to the large number of defects formed, but also helium bubbles that form at high doses of radiation, inside which additional pressure accumulates, leading to bloating bubble. When modeling the effects of aging of ceramics irradiated with protons, the surface layer of which contains fewer defects than a similar layer of ceramics irradiated with helium ions, the degradation of the layer occurs due to the destruction of the disordering regions and partial cracking of the irradiated layer with the formation of a porous structure, which indicates the presence of irradiated samples gas-filled inclusions of small size (5-15 nm). For samples irradiated with helium ions, in the surface layer of which, at high radiation doses, strongly distorted defective regions and blisters are formed, explosive destruction of gas-filled bubbles occurs with increasing exposure time of the vapor, with the formation of microcracks along the grain boundaries that serve as defect sinks. 

Thus, it was found that at an irradiation dose of 5x1017 ion/cm2 characteristic of a displacement of 50 dpa, the degradation of the surface layer of ceramics is catastrophic in nature, which can have a significant impact on the performance characteristics of structural materials.

The data obtained are in good agreement with the previously presented studies on the radiation resistance to helium embrittlement and swelling of nitride materials. For example, data on resistance to the formation of blisters and helium bubbles have a good correlation with similar results for thin-film multilayer coatings based on ZrN, CrN, and AlN [Uglov, V. V., et al. "Blistering in Helium-Ion-Irradiated Zirconium, Aluminum, and Chromium Nitride Films." Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques 14 (2020): 359-365., Uglov, V. V., et al. "Surface blistering in ZrSiN nanocomposite films irradiated with He ions." Surface and Coatings Technology (2020): 125654.]. The authors of these works found that the degradation of nitride materials as a result of the accumulation of implanted helium occurs as a result of the formation of porous inclusions and deformations of the structure of the surface layer at low irradiation fluences. An increase in the irradiation fluence leads to the filling of these cavities with poorly soluble helium ions, followed by the formation of helium bubbles. Moreover, for different samples, the dose loads necessary to start the nucleation of bubbles are different. In the case of proton irradiation with nitride ceramics, the structural changes resulting from the irradiation are in good agreement with the works [Ives, Nathan E., et al. "Effects of proton-induced displacement damage on gallium nitride HEMTs in RF power amplifier applications." IEEE Transactions on Nuclear Science 62.6 (2015): 2417-2422.; Kim, Hong Yeol, et al. "Characterization of AlGaN/GaN HEMT irradiated at 5 keV and 25 MeV proton energies." J. Ceramic Process. Res. 9.2 (2008): 155-157.; Gan, Jian, et al. "Proton irradiation study of GFR candidate ceramics." Journal of nuclear materials 389.2 (2009): 317-325.], according to which it was found that in the case of large-dose irradiation, the main structural changes are associated with the formation of microcracks and disordering regions. In this case, the presence of impurities of other elements in the structure of nitride ceramics leads to the formation of additional disordering regions and accumulations of defects.

 

Author Response File: Author Response.doc

Round 2

Reviewer 2 Report

The authors have responded quite well to the last comments. The manuscript has been significantly improved in quality and can be published.

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