rus
Issue #5/2025
E.V.Bobruk
MANIFESTATION OF LOW-TEMPERATURE SUPERPLASTICITY IN NANOSTRUCTURED ALUMINUM ALLOYS
MANIFESTATION OF LOW-TEMPERATURE SUPERPLASTICITY IN NANOSTRUCTURED ALUMINUM ALLOYS
The presented paper gives an overview of nanostructured state formation accompanied by the decomposition of supersaturated solid solution with forming the Zn, Mg, Cu segregations and secondary phases in alloys of Al–Zn, Al–Zn–Mg, Al–Mg–Mn, Al–Mg–Si and Al–Cu–Mg systems to achieve the effect of low-temperature superplasticity.
INTRODUCTION
Superplastic (SP) behaviour is usually described by relation (1):
, (1)
where according to [1] D is the diffusion coefficient, G is the shear modulus, b is the Burgers vector, K is the Boltzmann constant, T is the absolute temperature, d is the average grain size, σ is the applied stress (flow stress), p is the degree exponent usually equal to 2, n is the inverse of the velocity sensitivity coefficient of the flow stress m, and A is the dimensionless coefficient.
This equation shows the relationship between the external deformation conditions and the internal structure of materials. It implies that a decrease in grain size should lead to an increase in the strain rate and a decrease in the deformation temperature at which the SP behaviour is observed.
To date, it is known that during alloys transition with grain size less than 10 μm to the SP state, a change of deformation mechanism from intra-grain dislocation slip (IDS) controlled by bulk diffusion to grain boundary slip (GBS) controlled by grain boundary diffusion (GBD) is observed [2–4].
Many researchers [3–5] have noted unusual properties of GB in nanostructured metals produced by severe plastic deformation (SPD). In addition to the structure of the GB, the type and concentration of impurities and segregation [6, 7] have a significant influence on the development of grain boundary processes, which is important in the manifestation of SP behaviour at reduced temperatures.
The aim of this work was to summarise the results of recent studies on realisation of low temperature SP (LTSP) established on model and industrial Al alloys of such alloying systems as Al–Zn, Al–Zn–Mg, Al–Mg–Mn, Al–Mg–Si and Al–Cu–Mg. In these studies, special attention has been paid to identification of the physical nature of LTSPs, where along with the ultrafine grain size in aluminium alloys formed during the SPD process, a prominent role is played by the GB state associated with the presence of grain boundary segregations, as well as nanoscale particles of second phases, which inhibit the migration of GBs and thus limit grain growth [8–15].
RESEARCH METHODS
The alloys selected for the study were Al-30%Zn, Al-4.8%Zn-1.2%Mg-0.14%Zr, Al-5.7Zn-2.2Mg-1.6Cu-0.25Cr, Al-5.66Mg-0.81Mn-0.67Zn-0.09Zr, Al-0.60Mg-0.60Si-0.10Cu-0.10Mn-0.15Zn-0.50Cr and Al-4.98Cu-1.49Mg-0.73Mn-0.04Si-0.07Fe (weight %). To form the nanostructured (NS) state, a solid solution was obtained after processing, from billets of the study materials were made in the form of discs of 20 mm diameter were subjected to SPD by by high pressure torsion (HPT) at room temperature (RT) and applied pressure of 6 GPa.
For structural studies, a JEOL JEM 2100 transmission electron microscope, JEOL®-ARM200F scanning electron microscopes (SPEM) with JEOL® JED-2300 detector for energy dispersive (EDS) analysis and Titan Themis G2 200 with EDS Super-X detector, FEI Quanta 600 field emission scanning electron microscope (SEM) equipped with TSL OIMTM software were used. The methods are described in more detail in [8–16].
Mechanical tests were performed on an INSTRON-5982 universal testing unit equipped with a thermal chamber with Bluehill 3 software to determine the flow stress and relative elongation to rupture. The value of the velocity sensitivity coefficient m was determined by formula (2):
, (2)
where σ is the flow stress at a strain rate of 100%;
έ is the strain rate.
RESULTS
During the process of HPT at RT, a homogeneous UMZ structure was formed in the binary model alloy Al-30Zn (Fig.1a) [8–10]. Formation of the UMZ structure is accompanied by disintegration of the supersaturated solid solution leading to the nucleation of Zn particles both in the body and at the grain boundaries of aluminium (Fig.1b). The size of aluminium grains is 410±30 nm, the size of Zn precipitates inside aluminium grains is 10±4 nm. Large Zn particles larger than 100 nm are formed in the triple junctions of these grains. Formation of interlayers of Zn atoms with a width of about 5 nm is noted at the boundary of most grains.
Formation of NS state in Al-30Zn alloy possessing the above mentioned features led to the manifestation of LTSP features [8, 10]. In the NS state Al-30Zn alloy demonstrates unusually high elongation to failure – 235% at RT and strain rate of 10–4 s–1. At the same time, the velocity sensitivity coefficient m is 0.32. Increasing the test temperature to 100 °C allowed to achieve an elongation of 265% at a strain rate of 10–4 s–1. The value of m is 0.45.
Based on the binary alloy studies, it was found that Zn alloying can fundamentally restructure the state of high-angle GBs in ultrafine grain aluminium alloys. As a result of accelerated diffusion processes, Zn atoms are redistributed during deformation and form segregations along the grain boundaries of aluminium grains, facilitating GBS – the main mechanism of SP [8].
Another common alloying element of aluminium alloys is Mg, which, as it was shown in studies [5, 11, 12], in the process of ultrafine or nanosized grains formation, forming segregations along the grain boundaries of aluminium and nanosized particles of second phases, increases their resistance to deformation and thermal effects by reducing the GB energy, and reducing their mobility, which also has a positive effect on achieving increased values of ductility.
The influence of complementary elements Zn and Mg on the features of the structural-phase state and the LTSP effect was presented in [11, 12] on the example of high-strength NS alloys of the Al-Zn-Mg system. Processing of Al-4.8Zn-1.2Mg-0.14Zr (wt.%) alloy samples by HPT at RT resulted in formation of a nanostructured state (NS) with a grain size of about 100 nm and formation of particles of metastable secondary η´-phase MgZn2 up to 5 nm in size near the grain boundaries of aluminium (Fig.2). EDS analysis has shown that as a result of HPT, Mg and/or Zn atoms are abundant along aluminium grain boundaries, with the ratio of Zn and Mg varying along the boundary (Fig.2b).
In NS state the Al–Zn–Mg–Zr alloy exhibits the LTSP effect. Elongation to failure of 500% is achieved at a temperature of 170 °C and a strain rate of 10–2 s–1, and the value of m is 0.37. At 200 °C, the maximum elongation is 700% at a strain rate of 5 ∙ 10–4 s–1. The m value increases markedly (up to 0.73). According to the results of studies [11, 12], LTSP is carried out mainly due to realisation of ZGP, the course of which is facilitated by the presence of Zn atoms along the GBS, while IDS is suppressed by Mg segregations and intra-grained nanosized particles of the MgZn2 phase.
Aluminium alloys exhibiting SP behaviour that do not contain Zn as the main alloying element, such as non-thermally hardenable alloys of the Al–Mg–Mn system, are also known.
During HPT process at RT, NS state with a grain size of 95±3 nm and a regulated particle distribution of secondary phases such as Al3Mg2 (predominantly in GB), Al6Mn and Al3Zr (wt.%) was formed in the alloy Al-5.66Mg-0.81Mn-0.67Zn-0.09Zr (alloy 1565h) [13]. The use of HTP also ensured the formation of Mg segregations along the Al grain boundaries (Fig.3). Formation of such state allowed to realise in the alloy the effect of high-speed LTSP at temperatures of 250 and 300 °C and strain rate of 5 ∙ 10–3 s–1. At these temperature and velocity conditions, maximum elongations of 300 and 500% were achieved, and m was 0.35 and 0.28, respectively [13, 14].
A precision study of deformation topography after SP deformation showed that strain-rate SP at 300 °C is carried out by a combination of cooperative GBS (CGBS) and IDS [14]. Nanoscale particles of Al3Mg2 phase and Mg segregations along the GB during deformation improve grain enlargement stability by reducing both the GB energy and limiting their mobility, which has a positive effect on ductility.
Another representative of aluminium alloys alloyed with Mg are low-alloyed alloys of Al-Mg-Si system widely used in Russia and abroad. In the process of HPT at RT in the alloy Al-0.60Mg-0.60Si-0.10Cu-0.10Mn-0.15Zn-0.50Cr (wt.%) (alloy 6060) NS state with an average grain size of 180 nm was formed. Nanoscale particles of the secondary phase Mg2Si, as well as segregations of Mg and Si atoms along the HS were found in the structure [15]. According to the results of mechanical tests, the NS alloy shows signs of LTSP at temperatures of 150 and 180 °C in NS Al-Mg-Si alloy. The maximum values of elongation to fracture (240%) are observed at strain rate of 10–4 s–1 and temperature of 200 °C. The value of m is 0.32 [15]. The pole figure for NS alloy after HPT (Fig.4b), shows the features of deformation texture with moderate intensity of maximum pole density (texture index, denoting the deviation from random texture, was 2.47). SP deformation at 150 °C resulted in a noticeable texture scattering visible in the pole figures (Fig.4c), the texture index decreased to 1.22 [15]. SP deformation leads to reorientation of grains towards random texture. This process is caused by intensified non-crystallographic deformation modes such as sliding or rotation of grain boundaries. Analyses of the microstructure of NS alloy after deformation at 150 and 180 °C have shown that GBS and IDS with formation of subgrain boundaries contribute significantly to SP flow [15].
Another of the most popular Al-based alloys is the Al–Cu–Mn system. As a result of HPT treatment at RT, the NS state in the alloy Al-4.98Cu-1.49Mg-0.73Mn-0.04Si-0.07Fe (wt.%) (alloy 2024) with an average grain size of 100±7 nm was obtained. Single globular particles of ϑ(CuAl2) phase up to 5 nm in size are observed in the body of aluminium grains [16]. In alloys of the Al-Cu system Cu segregations are formed along the Al grain boundaries [1]. As a result of tests at 240 °C (0.56Tm), the maximum elongations (280%) were achieved at strain rates of 10-3 s-1 and the parameter m was 0.32. Increasing test temperature to 270 °C (0.60Tm) resulted in the achievement of maximum elongation (400%) at a strain rate of 10–3 s–1, parameter m 0.33. Nanosized particles of ϑ(CuAl2) phase and Cu segregations along the GB during deformation, as well as Mg, improve the stability of grains to enlargement by reducing both the GB energy and limiting their mobility, which has a positive effect on ductility.
It is worth noting that alloy 2024 of the Al–Cu–Mn system, as well as alloy 6060 of the Al–Mg–Si system in the fine-grained state, do not tend to exhibit SP.
DISCUSSION
Fig.6 presents a summary analysis of experimental results of the influence of structural-phase states, including the presence of Zn, Mg, Cu segregations on the LTSP effect in Al–Zn–Mg–Zr, Al–Zn–Mg–Cu and Al–Mg–Mn, Al–Mg–Si, Al–Cu–Mg alloys with grain size 100–400 nm in the form of a map of temperature-strain rate conditions of the LTSP effect. It can be concluded that in NS aluminium alloys, Zn alloying contributes to a significant decrease in the temperature range of low-temperature SP manifestation to 20 (RT) – 200 °C, with a velocity range of 10–4 to 10–3 s–1, while Mg contributes to the manifestation of high-velocity deformation of 5 ∙ 10–3 to 10–2 s–1. The maximum temperature of 250–300 °C of transition to the SP state was exhibited by aluminium alloy with Mg content of more than 5 weight.%.
Through their interaction with crystal defects, solute atoms play a crucial role in the evolution of the microstructure of aluminium alloys during deformation. The role of alloying elements in the manifestation of LTSP has been determined: zinc alloying of aluminium alloys with ultrafine grains allows significant rearrangement of large-angle boundaries. This is achieved by accelerated diffusion processes that redistribute Zn atoms during deformation and lead to formation of segregations or nanolayers along the GB, facilitating GBP. At the same time, segregations of Mg and Cu anchor aluminium grain boundaries and impede their migration during deformation, while the formed second phase particles suppress IDS.
CONCLUSIONS
The conditions and criteria of manifestation of low-temperature superplasticity or its signs by nanostructured alloys of Al–Zn, Al–Zn–Mg–Zr, Al–Zn–Mg–Cu, Al–Mg–Mn, Al–Cu–Mg and Al-Mg-Si systems at relatively low temperatures from room temperature to 300 °C, which are characterised by strain rate sensitivity sensitivity m (0.31...0.77), have been analysed.
ACKNOWLEDGEMENTS
The research was performed under RSF grant No. 24-19-00819, https://rscf.ru/project/24-19-00819/. All studies were performed at the Nanotech Collective Use Centre of the Ufa University of Science and Technology.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Superplastic (SP) behaviour is usually described by relation (1):
, (1)
where according to [1] D is the diffusion coefficient, G is the shear modulus, b is the Burgers vector, K is the Boltzmann constant, T is the absolute temperature, d is the average grain size, σ is the applied stress (flow stress), p is the degree exponent usually equal to 2, n is the inverse of the velocity sensitivity coefficient of the flow stress m, and A is the dimensionless coefficient.
This equation shows the relationship between the external deformation conditions and the internal structure of materials. It implies that a decrease in grain size should lead to an increase in the strain rate and a decrease in the deformation temperature at which the SP behaviour is observed.
To date, it is known that during alloys transition with grain size less than 10 μm to the SP state, a change of deformation mechanism from intra-grain dislocation slip (IDS) controlled by bulk diffusion to grain boundary slip (GBS) controlled by grain boundary diffusion (GBD) is observed [2–4].
Many researchers [3–5] have noted unusual properties of GB in nanostructured metals produced by severe plastic deformation (SPD). In addition to the structure of the GB, the type and concentration of impurities and segregation [6, 7] have a significant influence on the development of grain boundary processes, which is important in the manifestation of SP behaviour at reduced temperatures.
The aim of this work was to summarise the results of recent studies on realisation of low temperature SP (LTSP) established on model and industrial Al alloys of such alloying systems as Al–Zn, Al–Zn–Mg, Al–Mg–Mn, Al–Mg–Si and Al–Cu–Mg. In these studies, special attention has been paid to identification of the physical nature of LTSPs, where along with the ultrafine grain size in aluminium alloys formed during the SPD process, a prominent role is played by the GB state associated with the presence of grain boundary segregations, as well as nanoscale particles of second phases, which inhibit the migration of GBs and thus limit grain growth [8–15].
RESEARCH METHODS
The alloys selected for the study were Al-30%Zn, Al-4.8%Zn-1.2%Mg-0.14%Zr, Al-5.7Zn-2.2Mg-1.6Cu-0.25Cr, Al-5.66Mg-0.81Mn-0.67Zn-0.09Zr, Al-0.60Mg-0.60Si-0.10Cu-0.10Mn-0.15Zn-0.50Cr and Al-4.98Cu-1.49Mg-0.73Mn-0.04Si-0.07Fe (weight %). To form the nanostructured (NS) state, a solid solution was obtained after processing, from billets of the study materials were made in the form of discs of 20 mm diameter were subjected to SPD by by high pressure torsion (HPT) at room temperature (RT) and applied pressure of 6 GPa.
For structural studies, a JEOL JEM 2100 transmission electron microscope, JEOL®-ARM200F scanning electron microscopes (SPEM) with JEOL® JED-2300 detector for energy dispersive (EDS) analysis and Titan Themis G2 200 with EDS Super-X detector, FEI Quanta 600 field emission scanning electron microscope (SEM) equipped with TSL OIMTM software were used. The methods are described in more detail in [8–16].
Mechanical tests were performed on an INSTRON-5982 universal testing unit equipped with a thermal chamber with Bluehill 3 software to determine the flow stress and relative elongation to rupture. The value of the velocity sensitivity coefficient m was determined by formula (2):
, (2)
where σ is the flow stress at a strain rate of 100%;
έ is the strain rate.
RESULTS
During the process of HPT at RT, a homogeneous UMZ structure was formed in the binary model alloy Al-30Zn (Fig.1a) [8–10]. Formation of the UMZ structure is accompanied by disintegration of the supersaturated solid solution leading to the nucleation of Zn particles both in the body and at the grain boundaries of aluminium (Fig.1b). The size of aluminium grains is 410±30 nm, the size of Zn precipitates inside aluminium grains is 10±4 nm. Large Zn particles larger than 100 nm are formed in the triple junctions of these grains. Formation of interlayers of Zn atoms with a width of about 5 nm is noted at the boundary of most grains.
Formation of NS state in Al-30Zn alloy possessing the above mentioned features led to the manifestation of LTSP features [8, 10]. In the NS state Al-30Zn alloy demonstrates unusually high elongation to failure – 235% at RT and strain rate of 10–4 s–1. At the same time, the velocity sensitivity coefficient m is 0.32. Increasing the test temperature to 100 °C allowed to achieve an elongation of 265% at a strain rate of 10–4 s–1. The value of m is 0.45.
Based on the binary alloy studies, it was found that Zn alloying can fundamentally restructure the state of high-angle GBs in ultrafine grain aluminium alloys. As a result of accelerated diffusion processes, Zn atoms are redistributed during deformation and form segregations along the grain boundaries of aluminium grains, facilitating GBS – the main mechanism of SP [8].
Another common alloying element of aluminium alloys is Mg, which, as it was shown in studies [5, 11, 12], in the process of ultrafine or nanosized grains formation, forming segregations along the grain boundaries of aluminium and nanosized particles of second phases, increases their resistance to deformation and thermal effects by reducing the GB energy, and reducing their mobility, which also has a positive effect on achieving increased values of ductility.
The influence of complementary elements Zn and Mg on the features of the structural-phase state and the LTSP effect was presented in [11, 12] on the example of high-strength NS alloys of the Al-Zn-Mg system. Processing of Al-4.8Zn-1.2Mg-0.14Zr (wt.%) alloy samples by HPT at RT resulted in formation of a nanostructured state (NS) with a grain size of about 100 nm and formation of particles of metastable secondary η´-phase MgZn2 up to 5 nm in size near the grain boundaries of aluminium (Fig.2). EDS analysis has shown that as a result of HPT, Mg and/or Zn atoms are abundant along aluminium grain boundaries, with the ratio of Zn and Mg varying along the boundary (Fig.2b).
In NS state the Al–Zn–Mg–Zr alloy exhibits the LTSP effect. Elongation to failure of 500% is achieved at a temperature of 170 °C and a strain rate of 10–2 s–1, and the value of m is 0.37. At 200 °C, the maximum elongation is 700% at a strain rate of 5 ∙ 10–4 s–1. The m value increases markedly (up to 0.73). According to the results of studies [11, 12], LTSP is carried out mainly due to realisation of ZGP, the course of which is facilitated by the presence of Zn atoms along the GBS, while IDS is suppressed by Mg segregations and intra-grained nanosized particles of the MgZn2 phase.
Aluminium alloys exhibiting SP behaviour that do not contain Zn as the main alloying element, such as non-thermally hardenable alloys of the Al–Mg–Mn system, are also known.
During HPT process at RT, NS state with a grain size of 95±3 nm and a regulated particle distribution of secondary phases such as Al3Mg2 (predominantly in GB), Al6Mn and Al3Zr (wt.%) was formed in the alloy Al-5.66Mg-0.81Mn-0.67Zn-0.09Zr (alloy 1565h) [13]. The use of HTP also ensured the formation of Mg segregations along the Al grain boundaries (Fig.3). Formation of such state allowed to realise in the alloy the effect of high-speed LTSP at temperatures of 250 and 300 °C and strain rate of 5 ∙ 10–3 s–1. At these temperature and velocity conditions, maximum elongations of 300 and 500% were achieved, and m was 0.35 and 0.28, respectively [13, 14].
A precision study of deformation topography after SP deformation showed that strain-rate SP at 300 °C is carried out by a combination of cooperative GBS (CGBS) and IDS [14]. Nanoscale particles of Al3Mg2 phase and Mg segregations along the GB during deformation improve grain enlargement stability by reducing both the GB energy and limiting their mobility, which has a positive effect on ductility.
Another representative of aluminium alloys alloyed with Mg are low-alloyed alloys of Al-Mg-Si system widely used in Russia and abroad. In the process of HPT at RT in the alloy Al-0.60Mg-0.60Si-0.10Cu-0.10Mn-0.15Zn-0.50Cr (wt.%) (alloy 6060) NS state with an average grain size of 180 nm was formed. Nanoscale particles of the secondary phase Mg2Si, as well as segregations of Mg and Si atoms along the HS were found in the structure [15]. According to the results of mechanical tests, the NS alloy shows signs of LTSP at temperatures of 150 and 180 °C in NS Al-Mg-Si alloy. The maximum values of elongation to fracture (240%) are observed at strain rate of 10–4 s–1 and temperature of 200 °C. The value of m is 0.32 [15]. The pole figure for NS alloy after HPT (Fig.4b), shows the features of deformation texture with moderate intensity of maximum pole density (texture index, denoting the deviation from random texture, was 2.47). SP deformation at 150 °C resulted in a noticeable texture scattering visible in the pole figures (Fig.4c), the texture index decreased to 1.22 [15]. SP deformation leads to reorientation of grains towards random texture. This process is caused by intensified non-crystallographic deformation modes such as sliding or rotation of grain boundaries. Analyses of the microstructure of NS alloy after deformation at 150 and 180 °C have shown that GBS and IDS with formation of subgrain boundaries contribute significantly to SP flow [15].
Another of the most popular Al-based alloys is the Al–Cu–Mn system. As a result of HPT treatment at RT, the NS state in the alloy Al-4.98Cu-1.49Mg-0.73Mn-0.04Si-0.07Fe (wt.%) (alloy 2024) with an average grain size of 100±7 nm was obtained. Single globular particles of ϑ(CuAl2) phase up to 5 nm in size are observed in the body of aluminium grains [16]. In alloys of the Al-Cu system Cu segregations are formed along the Al grain boundaries [1]. As a result of tests at 240 °C (0.56Tm), the maximum elongations (280%) were achieved at strain rates of 10-3 s-1 and the parameter m was 0.32. Increasing test temperature to 270 °C (0.60Tm) resulted in the achievement of maximum elongation (400%) at a strain rate of 10–3 s–1, parameter m 0.33. Nanosized particles of ϑ(CuAl2) phase and Cu segregations along the GB during deformation, as well as Mg, improve the stability of grains to enlargement by reducing both the GB energy and limiting their mobility, which has a positive effect on ductility.
It is worth noting that alloy 2024 of the Al–Cu–Mn system, as well as alloy 6060 of the Al–Mg–Si system in the fine-grained state, do not tend to exhibit SP.
DISCUSSION
Fig.6 presents a summary analysis of experimental results of the influence of structural-phase states, including the presence of Zn, Mg, Cu segregations on the LTSP effect in Al–Zn–Mg–Zr, Al–Zn–Mg–Cu and Al–Mg–Mn, Al–Mg–Si, Al–Cu–Mg alloys with grain size 100–400 nm in the form of a map of temperature-strain rate conditions of the LTSP effect. It can be concluded that in NS aluminium alloys, Zn alloying contributes to a significant decrease in the temperature range of low-temperature SP manifestation to 20 (RT) – 200 °C, with a velocity range of 10–4 to 10–3 s–1, while Mg contributes to the manifestation of high-velocity deformation of 5 ∙ 10–3 to 10–2 s–1. The maximum temperature of 250–300 °C of transition to the SP state was exhibited by aluminium alloy with Mg content of more than 5 weight.%.
Through their interaction with crystal defects, solute atoms play a crucial role in the evolution of the microstructure of aluminium alloys during deformation. The role of alloying elements in the manifestation of LTSP has been determined: zinc alloying of aluminium alloys with ultrafine grains allows significant rearrangement of large-angle boundaries. This is achieved by accelerated diffusion processes that redistribute Zn atoms during deformation and lead to formation of segregations or nanolayers along the GB, facilitating GBP. At the same time, segregations of Mg and Cu anchor aluminium grain boundaries and impede their migration during deformation, while the formed second phase particles suppress IDS.
CONCLUSIONS
The conditions and criteria of manifestation of low-temperature superplasticity or its signs by nanostructured alloys of Al–Zn, Al–Zn–Mg–Zr, Al–Zn–Mg–Cu, Al–Mg–Mn, Al–Cu–Mg and Al-Mg-Si systems at relatively low temperatures from room temperature to 300 °C, which are characterised by strain rate sensitivity sensitivity m (0.31...0.77), have been analysed.
ACKNOWLEDGEMENTS
The research was performed under RSF grant No. 24-19-00819, https://rscf.ru/project/24-19-00819/. All studies were performed at the Nanotech Collective Use Centre of the Ufa University of Science and Technology.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Readers feedback
