High-temperature strength of a thermally conductive silicon carbide ceramic sintered with yttria and scandia
Introduction
Silicon carbide (SiC) is an important material due to its excellent thermal conductivity, wear resistance, oxidation resistance, and high-temperature mechanical properties [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. SiC ceramics have been used for several industrial applications. Capsule materials for nuclear fuel, burner nozzles, rocket nozzles, heater and heater plates, and other high-temperature applications all take advantage of its excellent high-temperature mechanical properties as well as its excellent thermal conductivity.
Thermal conductivity of liquid-phase sintered SiC (LPS-SiC) ceramics has been intensively investigated over the past three decades [11], [12], [13], [14], [15], [16]. Polycrystalline SiC ceramics demonstrate a wide range of thermal conductivity values, from 30 W (m K)−1 to 270 W (m K)−1, depending on the specific chemistry of sintering additives and post-heat treatment conditions. For example, hot-pressed SiC sintered with BeO yielded a thermal conductivity of 270 W (m K)−1 [11]. A SiC ceramic sintered with Al2O3–Y2O3 had a conductivity of 55–90 W (m K)−1 [12], [13], whereas a SiC ceramic sintered with Al2O3–C had a conductivity of 30–45 W (m K)−1 [14]. Hot-pressed SiC ceramic sintered with Al2O3–Y2O3–CaO additives at 1750 °C for 40 min at a pressure of 25 MPa yielded a conductivity of 32 W (m K)−1. Post annealing of the hot-pressed SiC ceramic at 1850 °C for 4 h increased its thermal conductivity to 106 W (m K)−1 [15]. Hot-pressed SiC ceramic with 5 vol% Y2O3–La2O3 had a thermal conductivity of 167 W (m K)−1 [16]. When the SiC ceramic was further annealed at 2000 °C for 4 h in an argon atmosphere, the thermal conductivity increased from 167 W (m K)−1 to 211 W (m K)−1. Unfortunately, mechanical properties of the above ceramics were not reported simultaneously with thermal conductivity data.
The flexural strength of SiC ceramics sintered with various additives has also been studied at high temperatures [2], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26]. SiC ceramics sintered with Al2O3–Y2O3 exhibited rapid degradation in flexural strength at temperatures above 1300 °C, with strength values of 200–300 MPa at 1300 °C [2], [17]. A SiC ceramic with 5.6 wt% Al–B–C also demonstrated severe degradation in flexural strength at high temperatures, with a strength of ∼100 MPa at 1300 °C [18]. Higher strength values were obtained in SiC ceramics sintered with AlN–RE2O3 (RE = Lu, Yb, Er, Y): ∼400 MPa at 1400 °C in SiC with 10 vol% AlN–Y2O3 [19], ∼500 MPa at 1400 °C in SiC with 10 vol% AlN–Yb2O3 [20], ∼500 MPa at 1500 °C in SiC with 10 vol% equimolar AlN–Lu2O3 [21], and ∼550 MPa at 1600 °C in SiC with 10 vol% AlN–Er2O3 in a 3:2 molar ratio [22]. Improved strength values were obtained in SiC ceramics sintered with 10 vol% AlN–Lu2O3 in a 2:3 molar ratio (∼600 MPa at 1600 °C) [23] and SiC ceramics with 10 vol% AlN–Sc2O3 in a 1:4 molar ratio (∼620 MPa at 1600 °C) [24]. However, the additive content in the above investigations was greater than 5 wt%. High-temperature strength data of SiC ceramics with a small amount of additives (<2 wt%) was quite limited. Lim et al. [25] reported 100% retention of room temperature strength (∼630 MPa) at 1600 °C in SiC sintered with 1 wt% AlN–Lu2O3 in a 3:2 molar ratio. All of the above SiC ceramics contained Al or Al-compounds as sintering additives. We were unable to find any reports regarding high-temperature strength of SiC ceramics sintered without Al or Al-compounds.
Recently, a highly thermally conductive LPS-SiC ceramic with a thermal conductivity of 234 W (m K)−1 was successfully fabricated by hot-pressing a SiC powder mixture containing Y2O3–Sc2O3 as sintering additives [26]. The high thermal conductivity was attributed to (i) the reduction of oxygen content in SiC surface and/or lattice by forming (Sc,Y)2Si2O7 phase, (ii) the lack of solubility of Y and Sc in SiC lattice, (iii) forming clean or crystallized SiC–SiC boundaries, and (iv) growth of nitrogen-doped SiC grains. In semiconductors, the conduction electrons can also contribute to thermal conduction as well as phonons [27]. In the present study, the highly thermally conductive SiC ceramic with 1 vol% (1.37 wt%) Y2O3–Sc2O3 was fabricated using a hot-pressing technique. Its grain boundary structure was characterized using high resolution transmission electron microscopy (HRTEM), and the high-temperature strength of the ceramic was examined at temperatures up to 1800 °C in a nitrogen atmosphere.
Section snippets
Experimental procedure
To prepare SiC with 1 vol% Y2O3–Sc2O3 additives (Y2O3:Sc2O3 = 1:1 in molar ratio), 98.63 wt% β-SiC (∼0.5 μm, Grade BF-17, H. C. Starck, Berlin, Germany), 0.85 wt% Y2O3 (99.99% pure, Kojundo Chemical Lab Co., Ltd., Sakado-shi, Japan), and 0.52 wt% Sc2O3 (99.99% pure, Kojundo Chemical Lab Co., Ltd.) were mixed by ball milling using SiC media in a plastic jar for 24 h in ethanol. The mixture was dried, sieved, and hot pressed at 2050 °C for 6 h under an applied pressure of 40 MPa in a nitrogen atmosphere.
The
Results and discussion
The relative density of the hot-pressed specimen was 99.9%. This result suggests that a small amount (1 vol%) of Y2O3–Sc2O3 was sufficient to densify SiC to a relative density greater than 99% by conventional hot-pressing at 2050 °C for 6 h under 40 MPa in a nitrogen atmosphere. XRD analyses of the starting SiC powder, the sintered specimen, and the specimen tested at 1800 °C are shown in Fig. 1. Quantitative phase analyses of SiC polytypes (using the Rietveld refinement method) showed that: (1) the
Conclusions
A small amount (1 vol%) of Y2O3–Sc2O3 was sufficient to yield a SiC ceramic with a relative density greater than 99% by conventional hot-pressing at 2050 °C for 6 h under 40 MPa in a nitrogen atmosphere. High-temperature strengths of the thermally conductive SiC ceramic (thermal conductivity = 234 W (m K)−1) were examined up to 1800 °C. Flexural strengths of the ceramic were 536 MPa, 501 MPa, and 345 MPa at RT, 1600 °C, and 1800 °C, respectively.
Although the microstructure of the SiC ceramic was completely
Acknowledgments
This work was supported by a grant from the National Research Foundation of Korea (NRF) funded by the Korea Government (MSIP) (No. 2015R1A2A2A01004860).
References (32)
SiC and Si3N4 materials with improved fracture resistance
J. Eur. Ceram. Soc.
(1992)- et al.
Improved high temperature properties of SiC-ceramics sintered with Lu2O3-containing additives
J. Eur. Ceram. Soc.
(2003) - et al.
Effect of AlN-content on the microstructure and fracture toughness of hot-pressed and heat-treated LPS-SiC ceramics
J. Eur. Ceram. Soc.
(2005) - et al.
Nano-versus macro-hardness of liquid phase sintered SiC
J. Eur. Ceram. Soc.
(2005) - et al.
Anomalous oxidation behavior of pressureless liquid-phase-sintered SiC
J. Eur. Ceram. Soc.
(2011) - et al.
Electrochemical corrosion of silicon carbide ceramics in H2SO4
J. Eur. Ceram. Soc.
(2014) - et al.
Pressureless fabrication of dense monolithic SiC ceramics from a polycarbosilane
J. Eur. Ceram. Soc.
(2014) - et al.
Effect of grain growth on electrical properties of silicon carbide ceramics sintered with gadolinia and yttria
J. Eur. Ceram. Soc.
(2015) - et al.
Thermal conductivity in hot-pressed silicon carbide
Ceram. Int.
(1996) - et al.
Electrical and thermal conductivity of liquid phase sintered SiC
J. Eur. Ceram. Soc.
(2001)
Flexural strength and tougthness of liquid phase sintered silicon carbide
Ceram. Int.
Role of the grain boundarey phase on the elevated-temperature strength toughness, fatigue and creep resistance of silicon carbide sintered with Al, B and C
Acta Mater.
High-temperature effects in the fracture mechanical behaviour of silicon carbide liquid-phase sintered with AlN–Y2O3 additives
J. Eur. Ceram. Soc.
Gas pressure sintering of SiC sintered with rare-earth-(III)-oxides and their mechanical properties
Ceram. Int.
High-temperature strength of silicon carbide ceramics sintered with rare-earth oxide and aluminum nitride
Acta Mater.
Heat-resistant silicon carbide with aluminum nitride and scandium oxide
Acta Mater.
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