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DOI: https://doi.org/10.22184/1993-8578.2023.16.3-4.204.207
Strong fine-grained ceramics (about 1 μm) based on yttrium oxide nanopowder was prepared using spark plasma sintering (SPS) method. It has microhardness of 2.1 GPa.
Strong fine-grained ceramics (about 1 μm) based on yttrium oxide nanopowder was prepared using spark plasma sintering (SPS) method. It has microhardness of 2.1 GPa.
Теги: ceramics nanopowder spark plasma sintering yttrium oxide керамика нанопорошок оксид иттрия электроискровое спекание
INTRODUCTION
The differences between nanocrystalline and coarse grained materials in elastic, damping, strength, thermal, electrical, magnetic and diffusion properties are not only due to the small grain size in nanocrystalline materials, but also to the special surface state or their grain boundaries [1].
One of the future paths of nanotechnology is development of ceramics produced from nanoscale powders in which very small grain sizes can be retained. It is expected that nanoceramics will not only have the ceramics properties obtained from coarse-grained materials, but also some unique ones (such as superplasticity [2]).
It is known that the smaller grain size of ceramics and the more developed grain structure, the stronger and harder ceramics are. At the same time, in nanopowders used for production of ceramics, there are stable agglomerates of nanoparticles which are difficult to break [3], which requires the use of non-standard methods of compaction (for example, hot pressing method).
The current state of research on nanoceramics made from different nanopowders is well documented in [4–6] and others, including the author [7–10].
This work is to study ceramics made of yttrium oxide nanopowder.
The application field of materials based on yttrium oxide and other rare-earth elements is constantly expanding, and in the areas that determine technical progress (alloys with unique properties, nuclear energy, electronics, etc.).
The aim of this work was to use the SPS method to produce dense and hard yttrium oxide nanodisperse powders with a fine-grained (micron-sized) structure.
DESCRIPTION OF EXPERIMENTAL CONDITIONS
Yttrium oxide powder with an average particle size of 32 nm and chemical purity of 99%, obtained by evaporation of raw materials in an electron accelerator, followed by condensation of the substance in the form of nanodispersed particles [11], was used as a starting point.
Figure 1 shows the results of transmission electron microscopy of yttrium oxide powder.
For this powder sintering was carried out on Labox "Sinter Land" facility of IGIL SB RAS by the spark plasma sintering method (hot pressing with the use of sintering spark plasma) (Spark Plasma Sintering, SPS), when electric current pulses pass through the pre-compressed powder (in these experiments the current strength reached 2 kA at a voltage of 3–4 V). The main difference of SPS from conventional pressing (successive pressing and sintering) is introduction of pulsed electric current directly on the sample, which results in rapid heating of the powder and largely preservation of its microstructural parameters in the consolidated material. The pressing was carried out at a maximum temperature of 1400 °C and a pressure of 40 MPa. The heating rate was typically 100 °C/min and there was no holding time at the maximum temperature.
Microhardness of all ceramic samples was examined with a PMT-3 microhardness tester.
On an electron scanning microscope ZEISS EVO-50WDS-XVP-BU ITPM SB RAS chips of ceramics after gold layer sputtering on them were investigated.
RESULTS AND DISCUSSION
The diameter and thickness of the obtained ceramic specimens were 9.6 and 3.2 mm.
Figure 2 shows an electron microscopy of the ceramic chip. It can be seen that the grain size of the obtained ceramics is about 1 micron, i.e. using SPS method a fine-grained dense ceramic was created.
Microhardness of obtained ceramics was high enough: Hv = 18.1 GPa. For comparison, microhardness of ceramics obtained by in [12] by traditional way (by successive pressing and sintering) from the same nanopowder at maximum sintering temperature 1500 °С, was equal to 11 GPa.
CONCLUSIONS
Thus, using the electrospark sintering method (ESM) based on nano-sized yttrium oxide powder, a fine-grained (about 1 micron), dense, strong ceramic with microhardness up to 18 GPa was developed.
ACKNOWLEDGMENTS
The authors thank A.G.Anisimov, V.I.Mali, V.A.Emelkin and G.A.Pozdnyakov for their help and support in this work.
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.
The differences between nanocrystalline and coarse grained materials in elastic, damping, strength, thermal, electrical, magnetic and diffusion properties are not only due to the small grain size in nanocrystalline materials, but also to the special surface state or their grain boundaries [1].
One of the future paths of nanotechnology is development of ceramics produced from nanoscale powders in which very small grain sizes can be retained. It is expected that nanoceramics will not only have the ceramics properties obtained from coarse-grained materials, but also some unique ones (such as superplasticity [2]).
It is known that the smaller grain size of ceramics and the more developed grain structure, the stronger and harder ceramics are. At the same time, in nanopowders used for production of ceramics, there are stable agglomerates of nanoparticles which are difficult to break [3], which requires the use of non-standard methods of compaction (for example, hot pressing method).
The current state of research on nanoceramics made from different nanopowders is well documented in [4–6] and others, including the author [7–10].
This work is to study ceramics made of yttrium oxide nanopowder.
The application field of materials based on yttrium oxide and other rare-earth elements is constantly expanding, and in the areas that determine technical progress (alloys with unique properties, nuclear energy, electronics, etc.).
The aim of this work was to use the SPS method to produce dense and hard yttrium oxide nanodisperse powders with a fine-grained (micron-sized) structure.
DESCRIPTION OF EXPERIMENTAL CONDITIONS
Yttrium oxide powder with an average particle size of 32 nm and chemical purity of 99%, obtained by evaporation of raw materials in an electron accelerator, followed by condensation of the substance in the form of nanodispersed particles [11], was used as a starting point.
Figure 1 shows the results of transmission electron microscopy of yttrium oxide powder.
For this powder sintering was carried out on Labox "Sinter Land" facility of IGIL SB RAS by the spark plasma sintering method (hot pressing with the use of sintering spark plasma) (Spark Plasma Sintering, SPS), when electric current pulses pass through the pre-compressed powder (in these experiments the current strength reached 2 kA at a voltage of 3–4 V). The main difference of SPS from conventional pressing (successive pressing and sintering) is introduction of pulsed electric current directly on the sample, which results in rapid heating of the powder and largely preservation of its microstructural parameters in the consolidated material. The pressing was carried out at a maximum temperature of 1400 °C and a pressure of 40 MPa. The heating rate was typically 100 °C/min and there was no holding time at the maximum temperature.
Microhardness of all ceramic samples was examined with a PMT-3 microhardness tester.
On an electron scanning microscope ZEISS EVO-50WDS-XVP-BU ITPM SB RAS chips of ceramics after gold layer sputtering on them were investigated.
RESULTS AND DISCUSSION
The diameter and thickness of the obtained ceramic specimens were 9.6 and 3.2 mm.
Figure 2 shows an electron microscopy of the ceramic chip. It can be seen that the grain size of the obtained ceramics is about 1 micron, i.e. using SPS method a fine-grained dense ceramic was created.
Microhardness of obtained ceramics was high enough: Hv = 18.1 GPa. For comparison, microhardness of ceramics obtained by in [12] by traditional way (by successive pressing and sintering) from the same nanopowder at maximum sintering temperature 1500 °С, was equal to 11 GPa.
CONCLUSIONS
Thus, using the electrospark sintering method (ESM) based on nano-sized yttrium oxide powder, a fine-grained (about 1 micron), dense, strong ceramic with microhardness up to 18 GPa was developed.
ACKNOWLEDGMENTS
The authors thank A.G.Anisimov, V.I.Mali, V.A.Emelkin and G.A.Pozdnyakov for their help and support in this work.
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.
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