mechanical properties of zro2–lamgal11o19 ceramics
TRANSCRIPT
Mechanical Properties of ZrO2-LaMgAl11O19 Ceramics
Min Xin1, a, Fang Minghao1, 2, b, Liu Yangai1, Huang Zhaohui1, Liu Fengjiao1
and Tang Chao1 1 School of Materials Science and Technology, China University of Geosciences (Beijing), Beijing
100083, P.R. China
2 Department of Materials Science and Engineering, University of Michigan, Ann Arbor MI 48109,
USA
Keywords: ZrO2-LaMgAl11O19 ceramics; Mechanical properties
Abstract. ZrO2 ceramics have been widely used in many fields with its excellent physical and chemical properties, but the mechanical properties of YSZ ceramics, especially the fracture toughness, decline caused by the failure of the phase transformation toughening at high temperature. In this investigation, plate-like LaMgAl11O19 toughened ZrO2 ceramics were prepared by pressureless sintering at 1550 °C for 3 h in air . The bulk density of the sintered samples are between 5.5 to 6.0 g/cm3, and the relative density are above 93%. The mechanical properties of the ZrO2-LaMgAl11O19 ceramics were studied systematically at room temperature. The flexure strength and fracture toughness of ZrO2-LaMgAl11O19 ceramic are 811.8 MPa and 13.9 MPa·m½ with the LMA addition of 2 wt%.
Introduction
ZrO2 ceramics are widely used in many fields with its excellent physical and chemical properties, such as high fracture toughness, high strength, high melting point, low thermal conductivity, high thermal expansion coefficient, high chemical stability andcorrosion resistance [1,2]. But the mechanical properties of YSZ ceramics, especially the fracture toughness, decline caused by the failure of the phase transformation toughening at high temperature, which caused the concerns of researchers recent decades. Transformation toughening, microcrack toughening and the second phase particle toughening are the main ZrO2 ceramics toughening ways in recently study . The second phase particle toughening is to bring in the second phase enhanced particles into the ZrO2 ceramics, which can be divided into particles, chips and whisker [3]. The investigations on the plate-like crystal are increasing in recent years as its remarkable toughening effect and well characteristics such as low cost, easy to mix and good thermal reliability [4]. According to the study on SiCpl/ZrO2 ceramics by M. Poorteman [5], the plate-like SiC can improve the flexure strength and the fracture toughness.
Lanthanum magnesium hexaluminate (LaMgAl11O19, LMA) with its high melting point, high-temperature thermal stability, low thermal conductivity and the plate-like hexagonal crystal morphology has been extensively studied as a potential candidate material for a number of applications in industry, military and scientific research [6,7].
In this paper, we added plate-like LMA powders to 3YSZ in order to improve strength and fracture toughness. The mechanical properties of the ZrO2-LaMgAl11O19 ceramics were studied systematically.
Experimental
LaMgAl11O19 was synthesized by solid-state reaction, using Al(OH)3 (99.9%), La2O3 (99.95%) and Mg(OH)2 (99.9%) as raw materials. The La2O3 was heated at1100 °C for 5 h previously, considering that La2O3 could absorb water from atmosphere rapidly. The stoichiometric mixtures were mixed and ball-milled in ethanol for 3 h to homogenize, and then dried at 75 °C. The mixtures were calcined at 1500 °C for 4 h and then crushed into powders.
Key Engineering Materials Vols. 512-515 (2012) pp 455-458Online available since 2012/Jun/04 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/KEM.512-515.455
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Subsequently, ZrO2-LaMgAl11O19 ceramics with different LMA addition(0 wt%, 2 wt% 4 wt%, 6 wt% 8 wt% and 10 wt%) were prepared using 3YSZ (99.5 wt% pure, grain size 1µm, Orient Zirconic Ind Sci & Tech Co., Ltd., China)as raw materials. After ball-milling in ethanol for 6 h, the as-prepared slurries were dried at 100 °C for 24 h, and then sifting with 100 mesh. the powders were molded to 4.5 mm×5 mm×40 mm green by uniaxial pressing at 30 MPa and then were further compacted by cold isostatic pressing at 200 MPa. The samples were finally pressureless sintered at 1550 °C for 3 h in air atmosphere.
The bulk density of the sintered samples was measured by the Archimedes method. Crystal-phase identification of the synthesized samples was made by X-ray diffraction (XRD, D8 Advance diffractometer, Bruker Corporation Germany) with Cu-Kα radiation (λ=1.5406Å). The microstructure of the sintered samples was examined by the scanning electron microscope (SEM, JSM-6460LV, JEOL Corporation Japan ). The flexure strength was determined using a three-point bending method, and the fracture toughness was tested by the three-point single-edge notched bending (SENB) method according to ASTM standard (C1421- 01b(R2007)).
Results and Discussion
Synthesis of the LMA powders. The XRD pattern of LMA powders synthesized at 1500 °C for 4 h is showed in Fig. 1. It presents that the diffraction peaks of the powders in the XRD pattern matches well with the standard PDF card of the LaMgAl11O19 [JCPDS 78-1854]. The SEM micrograph of LMA powders was showed in Fig. 2. As can be seen from Fig.2, LMA with plate-like morphology was observable. The thickness of platelet is 2-3 µm. The XRD and SEM results reveal that the plate-like LMA powders can be synthesized at 1500 °C for 4 h.
Fig. 1 XRD pattern of the LMA powders synthesized at1500 °C for 4 h in air
Fig. 2 SEM micrograph of LMA powders Fig. 3 XRD patterns of ZrO2–LaMgAl11O19
ceramics calcined at 1550 °C for 3 h
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Phase analysis of the ZrO2-LaMgAl11O19 ceramics. Fig. 3 shows the XRD results of ZrO2-LaMgAl11O19 ceramics sintered at 1550 °C for 3 h. It is clear that no new phase were formed . It indicates that ZrO2 and LaMgAl11O19 can coexist stably with each other.
Mechanical properties of the ZrO2-LaMgAl11O19 ceramics. Fig. 4 shows the bulk density and the relative density of the ZrO2-LaMgAl11O19 ceramics with different LMA addition . It can be seen that the bulk density and the relative density of the products are decreasing with the increasing of LMA addition. The bulk density of the sintered samples are between 6.0 to 5.5 g/cm3, and the relative density are all above 93%.
Fig. 4 Bulk density and relative density of ZrO2-LaMgAl11O19 ceramics with different LMA addition
Fig. 5 Flexural strength and fracture toughness of ZrO2-LaMgAl11O19 ceramics with different LMA
addition
Fig. 5 shows the flexural strength and fracture toughness of the ZrO2-LaMgAl11O19 ceramics. It can be seen that the flexural strength and fracture toughness of the 3YSZ is 701.3 MPa and 12.6 MPa·m½ respectively. The flexural strength and fracture toughness increase to 811.8 MPa and 13.9 MPa·m½ with LMA addition to 2 wt%. Then the flexural strength and fracture toughness of the samples decrease with the increasing of LMA addition.
Microstructure of ZrO2-LaMgAl11O19 ceramics. Fig.6 shows the SEM micrograph of the fracture surface of the ZrO2-LaMgAl11O19 samples. It presents that the quantity of the pores increase with the increasing of LMA addition amounts. It also can be seen that the fracture surface of
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ZrO2-LaMgAl11O19 samples are mostly due to transgranular fracture, and the plate-like morphology of LMA appears in the ZrO2 gains randomly to bond with each other strongly. The presence of LMA plate-like grains may play an important role in improving the flexural strength, fracture toughness and crack growth resistance effectively.
Fig. 6 SEM photographs of surface morphology of ZrO2–LaMgAl11O19 ceramic with different LMA addition amounts prepared at 1550 °C for 3 h ((a) 0 wt%, (b) 2 wt%, (c) 4 wt%, (d) 6 wt%, (e) 8 wt%,
(f) 10 wt%)
Conclusions
In this paper, ZrO2-LaMgAl11O19 ceramics were prepared by pressureless sintering at 1550 °C for 3 h in air atmosphere. The bulk density of the sintered samples are between 5.5 to 6.0 g/cm3. The flexural strength and fracture toughness of ZrO2-LaMgAl11O19 were increasing to 811.8 MPa and 13.9 MPa·m½ at the LMA addition of 2 wt%.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (NSFC Grant Nos.50802091 and 51172216) and the Fundamental Research Funds for the Central Universities (Grant Nos. 2010ZY31and 2011YXL001).
References
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458 High-Performance Ceramics VII
High-Performance Ceramics VII 10.4028/www.scientific.net/KEM.512-515 Mechanical Properties of ZrO2–LaMgAl11O19 Ceramics 10.4028/www.scientific.net/KEM.512-515.455
DOI References
[1] D. Casellas, F. L. Cumbrera, On the Transformation Toughening of Y-ZrO2 Ceramics with Mixed Y-
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http://dx.doi.org/10.1016/0955-2219(95)91297-2 [5] M. Poorteman, P. Descamps, F. Cambier, Cambier Hot Isostatic Pressing of SiC-platelets/Y-TZP
Composites, J. Eur. Ceram. Soc. Vol. 12 (1993) 103-109.
http://dx.doi.org/10.1016/0955-2219(93)90129-F [6] N. P. BANSAL, D. M. ZHU, Thermal properties of oxides with magneto-plumbite structure for advanced
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http://dx.doi.org/10.1016/j.surfcoat.2007.09.048 [7] X. Q. CAO, Y. F. ZHANG, J. F. ZHANG, et al., Failure of the plasma-sprayed coating of lanthanum
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http://dx.doi.org/10.1016/j.jeurceramsoc.2008.01.023