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The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering Yuri Pristinskiy a,⇑, Nestor Washington Solis Pinargote a, Anton Smirnov a a
Moscow State University of Technology ‘‘STANKIN”, Vadkovsky Lane 3a, Moscow 127055, Russia
a r t i c l e
i n f o
Article history: Received 10 May 2019 Accepted 2 July 2019 Available online xxxx Keywords: Spark plasma sintering Alumina oxide Magnesium oxide Hardness Fracture toughness Flexural strength
a b s t r a c t Spark plasma sintering (SPS) is a method of powder consolidation through uniaxial pressing accompanied by high heating and cooling rates. Short holding time that provides completely dense samples while preserving the structure and dimensions of the initial material is one the key features of the technology. Within the project samples based on Al2O3 with 1 wt% MgO were obtained by SPS. It was anticipated that MgO additions in alumina based composite would improve mechanical performance. However, the obtained mechanical properties remained at the same level compared to bulk ceramic and ceramic composites except for the hardness (increased 21%). Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Modern Trends in Manufacturing Technologies and Equipment 2019.
1. Introduction Due to the excellent properties of alumina (Al2O3), such as high heat resistance, hardness, excellent dielectric properties, resistance to corrosion and wear at high temperatures, this material is the most used in the manufacture of ceramic cutting tools [1]. Alumina in its pure form has a high chemical stability, which is a very important characteristic for its choice as a tool material for the machining of metals and cast iron [2]. In addition, when alumina is heated, its hardness decreases significantly less compared with other tool materials. This effect allows alumina to work 200– 400 °C higher than the maximum cutting temperature of carbide tools. The main drawback of alumina is the poor fracture toughness of the material and resulting low flexural strength. In order to reduce brittleness and increase the strength, various reinforcement phases are incorporated into ceramic matrix, for example, magnesia (MgO) [3]. Cutting tools based on Al2O3 can contain up to 1 wt%. MgO. Magnesium oxide inhibits grain growth and increases the strength of aluminum oxide [4]. The incorporation of magnesia has a great influence on the nature of nucleation and interaction of cracks, as the addition of MgO to the ceramic matrix forms thin layers of MgAl2O4 spinel, creating areas of compressive stresses
around the grains. These areas of compressive stresses prevent the propagation of cracks, inhibits Al2O3 grain growth and, therefore, strengthens the material [5]. Traditional sintering methods of ceramic cutting tools are cold pressing followed by sintering and hot pressing. However, these methods have some disadvantages, among which the most significant are the slow heating rate and consequently long sintering process. Long sintering time results in significant growth of Al2O3 ceramic grains and can decrease its mechanical properties. In this regard, the use of new technology, such as spark plasma sintering (SPS), is a promising method to obtain materials with high density and less grain growth for ceramic cutting tools [6–9]. Spark plasma sintering is a method of consolidating powder material that uses uniaxial pressing in combination with high heating rates (up to 1000 °C/min) and cooling, leading to a drastic reduction in sintering time [10]. Heating in the SPS is carried out by DC pulses that flow through a graphite matrix containing the ceramic material. The unique features of this method makes it possible to use a very short dwell time (up to several minutes) to obtain completely dense samples while preserving the structure and dimensions of the starting material. The purpose of this paper was to study the effects of SPS temperature on the mechanical properties of Al2O3 – based ceramic composites reinforced with 1 wt% MgO.
⇑ Corresponding author. E-mail address: [email protected] (Y. Pristinskiy). https://doi.org/10.1016/j.matpr.2019.07.058 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Modern Trends in Manufacturing Technologies and Equipment 2019.
Please cite this article as: Y. Pristinskiy, N. Washington Solis Pinargote and A. Smirnov, The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.058
2
Y. Pristinskiy et al. / Materials Today: Proceedings xxx (xxxx) xxx
2. Materials and characterization 2.1. Raw materials Commercially available powders were used as raw materials: (1) Al2O3 (Taimei Chem. Co. Ltd., Tokyo, Japan) with an average particle size d50 = 50 ± 17 nm, and (2) MgO (Probus, Badalona, Spain) with an average particle size d50 = 45 ± 15 nm. 2.2. Powder processing and sintering Al2O3-1wt%MgO mixture was prepared using distilled water as liquid media via ball milling (ML-1, Kaluga, Russia), with alumina balls in polyethylene container at 150 rpm during 24 h. Then the suspension was dried in a FreeZone2.5 freeze-drying system (LabConco, Kansas, MO, USA). The collector temperature is continuously set at 50 ± 2 °C. Furthermore, the shell temperature and the chamber pressure were kept at +23 ± 2 °C and 0.02 ± 0.01 mbar, respectively, during the entire process. Powder densification was performed by SPS H-HP-D25-SD (FCT Systeme GmbH, Rauenstein, Germany) at a maximum temperature of 1200–1600 °C (increments of 50 °C), reached under vacuum at a heating rate of 100 °C/min, and an applied pressure of 50 MPa. The final temperature and pressure were maintained for 3 min. The sintered specimens had diameters of 20 mm and thicknesses of 3 mm. For comparison purposes Al2O3 powder was SPSed following the same sintering cycles. 2.3. Microstructural and mechanical characterization XRD analyses (Empyrean diffractometer, PANalytical, Almelo, Netherlands, Cu-Ka radiation, wavelength 1.5405981 Å, accelerating voltage 60 kV, beam current 30 mA) of the sintered samples were conducted in a step scanning mode at diffraction angles 2h ranging from 20° to 70° (step size 0.05°). Scanning electron microscopy characterization was carried out on polished down to 1 mm surfaces by VEGA 3 LMH (SEM Tescan, Brno, Czech Republic). The density (q) of the sintered samples was measured in distilled water using Archimedes’ principle and was compared with the theoretical value, calculated according to the rule of mixtures. In order to quantify the Al2O3 average grain size, the sintered and polished samples were thermally etched in vacuum oven (Thermionic T1, Podolsk, Russia) for 30 min at a temperature of 25% lower than the sintering temperature. Vickers hardness, Hv, was measured on polished surfaces using a Vickers diamond indenter (QNess A10 Microhardness Tester, Salzburg, Austria), applying a load of 1 kg and an indentation time of 10 s. The hardness results were averaged over 10 indentations per specimen. Fracture toughness (K1c) was determined from Vickers indentations obtained with a load of 10 kg for 10 s. The sizes of the corresponding indentations and crack lengths were measured using SEM. The HV and K1c of reference materials were measured using the same equipment and under the same testing conditions. The method and formulas for calculating Hv and K1c have been reported elsewhere [11]. 3. Results and discussion 3.1. XRD analyses Fig. 1 shows the XRD of alumina oxide with the addition of magnesium oxide, sintered in the following modes: sintering temperature-1400 °C, holding time – 3 min, pressure – 50 MPa.
Fig. 1. XRD patterns of SPS sintered (1400 °C/3 min/50 MPa) ceramic composite.
X-ray diffraction indicated that only the a-alumina peaks without any impurities were detected. Whereas peaks of magnesium oxide were not observed, due to the low content [12]. 3.2. Microstructure characterization Typical thermally etched microstructures of the SPSed ceramics are shown in Fig. 2. The average grain size of produced samples was 0.6 ± 0.2 lm, 2.9 ± 0.2 lm and 2 ± 0.2 lm for samples sintered at 1400 °C, 1600 °C and 1400 °C for ceramic composite and alumina, respectively. A grain growth was observed with increasing sintering temperature. 3.3. Mechanical properties The influence of sintering temperature on density, hardness, fracture toughness and flexural strength of sintered composites presented on Figs. 3–6. Fig. 3 shows a density of the sintered samples with addiction to the sintering temperature. Maximum density of the samples is achieved at a sintering temperature of 1400 °C. With further increase of sintering temperature, changes in density are practically not observed. The increase of the density of the samples along with the increase in the sintering temperature is due to the fact that with an increase in the sintering temperature in the samples, the number of pores decreases. It is worth noting that this graph is constructed for samples from the material Al2O3-1 wt% MgO, however, a similar situation occurs during the sintering of pure aluminum. The biaxial flexural strength (rf) was measured by using the piston-on-3-ball method (ISO 6872 standard). Specimens (diameter 20 mm, thickness 1.3–1.9 mm) were placed on three balls located 120° apart on a 10-mm-diameter circle with the polished surface as the tensile side. A piston positioned above the center of the three-ball support directly applies the load to the unpolished side producing a biaxial flexural loading condition. The tests were performed at room temperature with the 5 kN testing machine applying a piston speed of 1 mm/min until failure occurred [13]. To obtain the average strength and elastic modulus, 12 specimens were tested. Details of the data collection and calculation procedures were reported elsewhere [14]. The Fig. 4 shows that the maximum bending strength for the Al2O3-1 wt% MgO composites achieved at a sintering temperature of 1400 °C (491 MPa). The maximum bending strength for the monolithic Al2O3 was reached at a sintering temperature of
Please cite this article as: Y. Pristinskiy, N. Washington Solis Pinargote and A. Smirnov, The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.058
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Y. Pristinskiy et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 2. SEM images of polished and thermally etched sections of ceramic composite (a, b) sintered at 1400 °C and 1600 °C, respectively and monolithic alumina (c) sintered at 1400 °C.
Fig. 5. The dependence of hardness of Al2O3-1 wt% MgO ( the sintering temperature.
) and Al2O3 (
) on
Fig. 3. The dependence of the density of the sintered samples on the sintering temperature.
Fig. 4. The dependence of the flexural strength of Al2O3-1 wt% MgO ( Al2O3 ( ) on the sintering temperature.
) and
1450 °C (499 MPa). However, the strength significantly decreased at higher temperature. Fig. 5 exhibits a graph of the hardness of the samples obtained on the temperature during sintering. The effect of the sintering temperature on the hardness is presented in Fig. 5. The maximum hardness value (23 GPa and 18 GPa) was obtained at the sintering temperature of 1400 °C for the Al2O3-1 wt% MgO composites and reference material,
Fig. 6. The dependence of the fracture toughness of Al2O3-1 wt% MgO ( Al2O3 ( ) on the sintering temperature.
) and
respectively. A decrease in hardness with further increase in temperature was observed. The hardness and flexural strength decreased when sintering temperature rose from 1400 °C to 1600 °C. This behavior can be explained in the terms of average grain size of alumina (higher temperature leads to higher grain size) that was experimentally determined by using the intercept technique (Fig. 2).
Please cite this article as: Y. Pristinskiy, N. Washington Solis Pinargote and A. Smirnov, The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.058
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Y. Pristinskiy et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 6 shows the change in fracture toughness with the sintering temperature. This figure demonstrates that there is no definite relationship between the sintering temperature and the fracture toughness of the samples.
4. Conclusion Al2O3-1 wt% MgO composites have been successfully fabricated by combining a wet processing route and Spark Plasma Sintering. The optimal sintering conditions (T – 1400 °C, P – 50 MPa, dwelling time – 3 min) were found. Results showed that the addition of low magnesium oxide content to an Al2O3 – ceramic matrix improved mechanical properties of composites, especially hardness, due to alumina grain refinement which is provided by the presence of MgO in the composite.
Acknowledgements We would like to thank the Ministry of Science and Higher Education of the Russian Federation for supporting this work under the grant № 074-11-2018-011 implement in the framework of the of the Decree of the RF Government No 218 dd. 09.04.2010.
References [1] P. Ramakrishnan, Trans. Indian Ceram. Soc. 31 (issue 4) (1972), https://doi.org/ 10.1080/0371750X.1972.10840811. [2] P.K. Mehrotra, Key Eng. Mater. 1–24 (1998) 138–140. [3] K. Hayder, A.S. Rashid Mohammed, Industrial Khudher, Eng. Lett. 9 (2019), https://doi.org/10.7176/IEL. [4] Makmwod O.C. b lp. Codpeveyyse repavbxecrbe bycnpyveynakmyse vanepbaks. Texyokoubz bpuonodkeybz b 'aaernbdyocnm gpbveyeybz. Maibyocnpobnekmyoe gpobpdolcndo. Cepbz: Texyokoubz b o,opylodaybe o,pa,onrb venakkod pepaybev. M.: BHBBT”PM, 1989. (In Russian). [5] M. Demuyncka, J.P. Erauw, O. Van der Biest, F. Delannay, F. Cambier, J. Eur. Ceram. Soc. 32 (2012) 1957–1964. [6] D.I. Yushin, A.V. Smirnov, N. Solis Pinargote, P.Yu. Peretyagin, V.A. Kuznetsov, R. Torrecillas, Russian Eng. Res. 36 (5) (2016) 410–413, https://doi.org/ 10.3103/S1068798X16050233. [7] C.F. Gutiérrez-González, S. Pozhidaev, S. Rivera, P. Peretyagin, W. Solís, L.A. Díaz, A. Fernandez, R. Torrecillas, Int. J. Appl. Ceram. Technol. 14 (3) (2017), https://doi.org/10.1111/ijac.12647. [8] S. Pozhidaev, A. Seleznev, N.W. Solis Pinargote, P. Peretyagin, Mech. Industry 16 (7) (2015) 710, https://doi.org/10.1051/meca/2015084. [9] Y. Pristinskiy, N.W. Solis Pinargote, A. Smirnov, MATEC Web Conf. 224 (2018) 01055. [10] A. Smirnov, H.D. Kurland, J. Grabow, F.A. Müller, J.F. Bartolomé, J. Eur. Ceram. So. 35 (2015) 2685. [11] M. Farooq, A. Ramli, Published in national Postgraduate Conference, 2011. [12] A. Smirnov, J.F. Bartolome, H.D. Kurland, J. Grabow, F.A. Muller, J. Am. Ceram. Soc. 99 (10) (2016) 3205–3209. [13] A. Smirnov, J.F. Bartolome, J. Eur. Ceram. Soc. 32 (15) (2012) 3899–3904. [14] Y. Pristinskiy, N. Peretyagin, N.W. Solis Pinargote, MATEC Web Conf. 129 (2017) 02028.
Please cite this article as: Y. Pristinskiy, N. Washington Solis Pinargote and A. Smirnov, The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.058
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering Yuri Pristinskiy a,⇑, Nestor Washington Solis Pinargote a, Anton Smirnov a a
Moscow State University of Technology ‘‘STANKIN”, Vadkovsky Lane 3a, Moscow 127055, Russia
a r t i c l e
i n f o
Article history: Received 10 May 2019 Accepted 2 July 2019 Available online xxxx Keywords: Spark plasma sintering Alumina oxide Magnesium oxide Hardness Fracture toughness Flexural strength
a b s t r a c t Spark plasma sintering (SPS) is a method of powder consolidation through uniaxial pressing accompanied by high heating and cooling rates. Short holding time that provides completely dense samples while preserving the structure and dimensions of the initial material is one the key features of the technology. Within the project samples based on Al2O3 with 1 wt% MgO were obtained by SPS. It was anticipated that MgO additions in alumina based composite would improve mechanical performance. However, the obtained mechanical properties remained at the same level compared to bulk ceramic and ceramic composites except for the hardness (increased 21%). Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Modern Trends in Manufacturing Technologies and Equipment 2019.
1. Introduction Due to the excellent properties of alumina (Al2O3), such as high heat resistance, hardness, excellent dielectric properties, resistance to corrosion and wear at high temperatures, this material is the most used in the manufacture of ceramic cutting tools [1]. Alumina in its pure form has a high chemical stability, which is a very important characteristic for its choice as a tool material for the machining of metals and cast iron [2]. In addition, when alumina is heated, its hardness decreases significantly less compared with other tool materials. This effect allows alumina to work 200– 400 °C higher than the maximum cutting temperature of carbide tools. The main drawback of alumina is the poor fracture toughness of the material and resulting low flexural strength. In order to reduce brittleness and increase the strength, various reinforcement phases are incorporated into ceramic matrix, for example, magnesia (MgO) [3]. Cutting tools based on Al2O3 can contain up to 1 wt%. MgO. Magnesium oxide inhibits grain growth and increases the strength of aluminum oxide [4]. The incorporation of magnesia has a great influence on the nature of nucleation and interaction of cracks, as the addition of MgO to the ceramic matrix forms thin layers of MgAl2O4 spinel, creating areas of compressive stresses
around the grains. These areas of compressive stresses prevent the propagation of cracks, inhibits Al2O3 grain growth and, therefore, strengthens the material [5]. Traditional sintering methods of ceramic cutting tools are cold pressing followed by sintering and hot pressing. However, these methods have some disadvantages, among which the most significant are the slow heating rate and consequently long sintering process. Long sintering time results in significant growth of Al2O3 ceramic grains and can decrease its mechanical properties. In this regard, the use of new technology, such as spark plasma sintering (SPS), is a promising method to obtain materials with high density and less grain growth for ceramic cutting tools [6–9]. Spark plasma sintering is a method of consolidating powder material that uses uniaxial pressing in combination with high heating rates (up to 1000 °C/min) and cooling, leading to a drastic reduction in sintering time [10]. Heating in the SPS is carried out by DC pulses that flow through a graphite matrix containing the ceramic material. The unique features of this method makes it possible to use a very short dwell time (up to several minutes) to obtain completely dense samples while preserving the structure and dimensions of the starting material. The purpose of this paper was to study the effects of SPS temperature on the mechanical properties of Al2O3 – based ceramic composites reinforced with 1 wt% MgO.
⇑ Corresponding author. E-mail address: [email protected] (Y. Pristinskiy). https://doi.org/10.1016/j.matpr.2019.07.058 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Modern Trends in Manufacturing Technologies and Equipment 2019.
Please cite this article as: Y. Pristinskiy, N. Washington Solis Pinargote and A. Smirnov, The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.058
2
Y. Pristinskiy et al. / Materials Today: Proceedings xxx (xxxx) xxx
2. Materials and characterization 2.1. Raw materials Commercially available powders were used as raw materials: (1) Al2O3 (Taimei Chem. Co. Ltd., Tokyo, Japan) with an average particle size d50 = 50 ± 17 nm, and (2) MgO (Probus, Badalona, Spain) with an average particle size d50 = 45 ± 15 nm. 2.2. Powder processing and sintering Al2O3-1wt%MgO mixture was prepared using distilled water as liquid media via ball milling (ML-1, Kaluga, Russia), with alumina balls in polyethylene container at 150 rpm during 24 h. Then the suspension was dried in a FreeZone2.5 freeze-drying system (LabConco, Kansas, MO, USA). The collector temperature is continuously set at 50 ± 2 °C. Furthermore, the shell temperature and the chamber pressure were kept at +23 ± 2 °C and 0.02 ± 0.01 mbar, respectively, during the entire process. Powder densification was performed by SPS H-HP-D25-SD (FCT Systeme GmbH, Rauenstein, Germany) at a maximum temperature of 1200–1600 °C (increments of 50 °C), reached under vacuum at a heating rate of 100 °C/min, and an applied pressure of 50 MPa. The final temperature and pressure were maintained for 3 min. The sintered specimens had diameters of 20 mm and thicknesses of 3 mm. For comparison purposes Al2O3 powder was SPSed following the same sintering cycles. 2.3. Microstructural and mechanical characterization XRD analyses (Empyrean diffractometer, PANalytical, Almelo, Netherlands, Cu-Ka radiation, wavelength 1.5405981 Å, accelerating voltage 60 kV, beam current 30 mA) of the sintered samples were conducted in a step scanning mode at diffraction angles 2h ranging from 20° to 70° (step size 0.05°). Scanning electron microscopy characterization was carried out on polished down to 1 mm surfaces by VEGA 3 LMH (SEM Tescan, Brno, Czech Republic). The density (q) of the sintered samples was measured in distilled water using Archimedes’ principle and was compared with the theoretical value, calculated according to the rule of mixtures. In order to quantify the Al2O3 average grain size, the sintered and polished samples were thermally etched in vacuum oven (Thermionic T1, Podolsk, Russia) for 30 min at a temperature of 25% lower than the sintering temperature. Vickers hardness, Hv, was measured on polished surfaces using a Vickers diamond indenter (QNess A10 Microhardness Tester, Salzburg, Austria), applying a load of 1 kg and an indentation time of 10 s. The hardness results were averaged over 10 indentations per specimen. Fracture toughness (K1c) was determined from Vickers indentations obtained with a load of 10 kg for 10 s. The sizes of the corresponding indentations and crack lengths were measured using SEM. The HV and K1c of reference materials were measured using the same equipment and under the same testing conditions. The method and formulas for calculating Hv and K1c have been reported elsewhere [11]. 3. Results and discussion 3.1. XRD analyses Fig. 1 shows the XRD of alumina oxide with the addition of magnesium oxide, sintered in the following modes: sintering temperature-1400 °C, holding time – 3 min, pressure – 50 MPa.
Fig. 1. XRD patterns of SPS sintered (1400 °C/3 min/50 MPa) ceramic composite.
X-ray diffraction indicated that only the a-alumina peaks without any impurities were detected. Whereas peaks of magnesium oxide were not observed, due to the low content [12]. 3.2. Microstructure characterization Typical thermally etched microstructures of the SPSed ceramics are shown in Fig. 2. The average grain size of produced samples was 0.6 ± 0.2 lm, 2.9 ± 0.2 lm and 2 ± 0.2 lm for samples sintered at 1400 °C, 1600 °C and 1400 °C for ceramic composite and alumina, respectively. A grain growth was observed with increasing sintering temperature. 3.3. Mechanical properties The influence of sintering temperature on density, hardness, fracture toughness and flexural strength of sintered composites presented on Figs. 3–6. Fig. 3 shows a density of the sintered samples with addiction to the sintering temperature. Maximum density of the samples is achieved at a sintering temperature of 1400 °C. With further increase of sintering temperature, changes in density are practically not observed. The increase of the density of the samples along with the increase in the sintering temperature is due to the fact that with an increase in the sintering temperature in the samples, the number of pores decreases. It is worth noting that this graph is constructed for samples from the material Al2O3-1 wt% MgO, however, a similar situation occurs during the sintering of pure aluminum. The biaxial flexural strength (rf) was measured by using the piston-on-3-ball method (ISO 6872 standard). Specimens (diameter 20 mm, thickness 1.3–1.9 mm) were placed on three balls located 120° apart on a 10-mm-diameter circle with the polished surface as the tensile side. A piston positioned above the center of the three-ball support directly applies the load to the unpolished side producing a biaxial flexural loading condition. The tests were performed at room temperature with the 5 kN testing machine applying a piston speed of 1 mm/min until failure occurred [13]. To obtain the average strength and elastic modulus, 12 specimens were tested. Details of the data collection and calculation procedures were reported elsewhere [14]. The Fig. 4 shows that the maximum bending strength for the Al2O3-1 wt% MgO composites achieved at a sintering temperature of 1400 °C (491 MPa). The maximum bending strength for the monolithic Al2O3 was reached at a sintering temperature of
Please cite this article as: Y. Pristinskiy, N. Washington Solis Pinargote and A. Smirnov, The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.058
3
Y. Pristinskiy et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 2. SEM images of polished and thermally etched sections of ceramic composite (a, b) sintered at 1400 °C and 1600 °C, respectively and monolithic alumina (c) sintered at 1400 °C.
Fig. 5. The dependence of hardness of Al2O3-1 wt% MgO ( the sintering temperature.
) and Al2O3 (
) on
Fig. 3. The dependence of the density of the sintered samples on the sintering temperature.
Fig. 4. The dependence of the flexural strength of Al2O3-1 wt% MgO ( Al2O3 ( ) on the sintering temperature.
) and
1450 °C (499 MPa). However, the strength significantly decreased at higher temperature. Fig. 5 exhibits a graph of the hardness of the samples obtained on the temperature during sintering. The effect of the sintering temperature on the hardness is presented in Fig. 5. The maximum hardness value (23 GPa and 18 GPa) was obtained at the sintering temperature of 1400 °C for the Al2O3-1 wt% MgO composites and reference material,
Fig. 6. The dependence of the fracture toughness of Al2O3-1 wt% MgO ( Al2O3 ( ) on the sintering temperature.
) and
respectively. A decrease in hardness with further increase in temperature was observed. The hardness and flexural strength decreased when sintering temperature rose from 1400 °C to 1600 °C. This behavior can be explained in the terms of average grain size of alumina (higher temperature leads to higher grain size) that was experimentally determined by using the intercept technique (Fig. 2).
Please cite this article as: Y. Pristinskiy, N. Washington Solis Pinargote and A. Smirnov, The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.058
4
Y. Pristinskiy et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 6 shows the change in fracture toughness with the sintering temperature. This figure demonstrates that there is no definite relationship between the sintering temperature and the fracture toughness of the samples.
4. Conclusion Al2O3-1 wt% MgO composites have been successfully fabricated by combining a wet processing route and Spark Plasma Sintering. The optimal sintering conditions (T – 1400 °C, P – 50 MPa, dwelling time – 3 min) were found. Results showed that the addition of low magnesium oxide content to an Al2O3 – ceramic matrix improved mechanical properties of composites, especially hardness, due to alumina grain refinement which is provided by the presence of MgO in the composite.
Acknowledgements We would like to thank the Ministry of Science and Higher Education of the Russian Federation for supporting this work under the grant № 074-11-2018-011 implement in the framework of the of the Decree of the RF Government No 218 dd. 09.04.2010.
References [1] P. Ramakrishnan, Trans. Indian Ceram. Soc. 31 (issue 4) (1972), https://doi.org/ 10.1080/0371750X.1972.10840811. [2] P.K. Mehrotra, Key Eng. Mater. 1–24 (1998) 138–140. [3] K. Hayder, A.S. Rashid Mohammed, Industrial Khudher, Eng. Lett. 9 (2019), https://doi.org/10.7176/IEL. [4] Makmwod O.C. b lp. Codpeveyyse repavbxecrbe bycnpyveynakmyse vanepbaks. Texyokoubz bpuonodkeybz b 'aaernbdyocnm gpbveyeybz. Maibyocnpobnekmyoe gpobpdolcndo. Cepbz: Texyokoubz b o,opylodaybe o,pa,onrb venakkod pepaybev. M.: BHBBT”PM, 1989. (In Russian). [5] M. Demuyncka, J.P. Erauw, O. Van der Biest, F. Delannay, F. Cambier, J. Eur. Ceram. Soc. 32 (2012) 1957–1964. [6] D.I. Yushin, A.V. Smirnov, N. Solis Pinargote, P.Yu. Peretyagin, V.A. Kuznetsov, R. Torrecillas, Russian Eng. Res. 36 (5) (2016) 410–413, https://doi.org/ 10.3103/S1068798X16050233. [7] C.F. Gutiérrez-González, S. Pozhidaev, S. Rivera, P. Peretyagin, W. Solís, L.A. Díaz, A. Fernandez, R. Torrecillas, Int. J. Appl. Ceram. Technol. 14 (3) (2017), https://doi.org/10.1111/ijac.12647. [8] S. Pozhidaev, A. Seleznev, N.W. Solis Pinargote, P. Peretyagin, Mech. Industry 16 (7) (2015) 710, https://doi.org/10.1051/meca/2015084. [9] Y. Pristinskiy, N.W. Solis Pinargote, A. Smirnov, MATEC Web Conf. 224 (2018) 01055. [10] A. Smirnov, H.D. Kurland, J. Grabow, F.A. Müller, J.F. Bartolomé, J. Eur. Ceram. So. 35 (2015) 2685. [11] M. Farooq, A. Ramli, Published in national Postgraduate Conference, 2011. [12] A. Smirnov, J.F. Bartolome, H.D. Kurland, J. Grabow, F.A. Muller, J. Am. Ceram. Soc. 99 (10) (2016) 3205–3209. [13] A. Smirnov, J.F. Bartolome, J. Eur. Ceram. Soc. 32 (15) (2012) 3899–3904. [14] Y. Pristinskiy, N. Peretyagin, N.W. Solis Pinargote, MATEC Web Conf. 129 (2017) 02028.
Please cite this article as: Y. Pristinskiy, N. Washington Solis Pinargote and A. Smirnov, The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.07.058