Abstract
ABSTRACT SiC-4 vol% BN composites were hot-pressed at 2050°C for 4 h at 40 MPa in a N2 atmosphere using micron-sized β-SiC and h-BN starting powders with 1 vol% sintering additives. Four batches were prepared using four different types of additive systems, i.e. Y2O3-Sc2O3, Yb2O3-CaO, Yb2O3-MgO, and Al2O3-AlN-Y2O3. The electrical, thermal, and mechanical properties of the SiC-4 vol% BN composites, which are primarily limited by the intrinsic weakness of h-BN and by the point defects (BC and AlSi) created by the dissolution of B and Al in the SiC lattice, were successfully tuned with the use of different additive systems. The electrical conductivity of SiC-4 vol% BN composites improved ~fivefold, i.e. from 2.6 (Ω·cm)−1 for the Al2O3-AlN-Y2O3-containing specimen to 13.9 (Ω·cm)−1 for the Y2O3-Sc2O3-containing specimen, owing to grain-growth-assisted N-doping and the elimination of Al-derived acceptors. Thermal conductivity was altered by 16% with the use of different additive systems. Fracture toughness dramatically increased from 4.3 MPa∙m1/2 in Yb2O3-CaO-containing specimens to 7.3 MPa∙m1/2 in Y2O3-Sc2O3-containing specimens. The electrical conductivity, thermal conductivity, flexural strength, and fracture toughness of SiC-4 vol% BN composite sintered with 1 vol% Y2O3-Sc2O3 were 13.9 (Ω·cm)−1, 82.0 W·m−1 K−1, 505 MPa, and 7.3 MPa∙m1/2, respectively.
Highlights
Boron nitride (BN)-reinforced silicon carbide (SiC) is an important particulate-reinforced ceramic matrix composite owing to its interesting engineering properties, such as high thermal conductivity, high thermal shock resistance, high-temperature strength, high oxidation resistance, and excellent electrical properties [1,2,3,4,5,6,7,8]
The oxide melt was transformed to a Y/Yb-Sc/Al/Mg/Ca-B-Si-OCN melt with the dissolution of SiC, BN, and N2 from the atmosphere
The high density obtained in binary additive systems is attributed to the high densification rate obtained with the less viscous silica-based melt modified with Y, Yb, Ca, Mg, and Sc as opposed to the highly viscous Almodified silica melt formed in the ternary additive system
Summary
Boron nitride (BN)-reinforced silicon carbide (SiC) is an important particulate-reinforced ceramic matrix composite owing to its interesting engineering properties, such as high thermal conductivity, high thermal shock resistance, high-temperature strength, high oxidation resistance, and excellent electrical properties [1,2,3,4,5,6,7,8]. A brief literature review is as follows: the electrical resistivity of SiC-BN composites could be successfully adjusted in the range of 8.1 × 10−3 to 1.0 × 1012 Ω·cm by varying the BN content, sintering atmosphere, and processing route. Owing to the more homogeneous distribution of insulating BN throughout the matrix, chemically synthesized SiC-10 vol% BN composite sintered in an Ar atmosphere exhibited higher electrical resistivity (1.0 × 1012 Ω·cm) [7] than that (9.3 × 105 Ω·cm) [9] reported for the powderprocessed composites. Compared with the chemically processed composites, powder-processed SiC-BN composites exhibited higher fracture toughness with equivalent BN content owing to the increased crack deflection by the large plate-shaped BN grains.
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