Microstructure and Mechanical Properties of SiC/zirconia-toughened Mullite Nanocomposites Prepared from Mixtures of Mull
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SiC/ZTM (zirconia-toughened mullite) nanocomposites were prepared by hot pressing mixtures of mullite gel, 2Y-TZP, and SiC nanopowders. The intimate mixing of Al2O3 and SiO2 components in the starting powder prevented intermediate ZrSiO4 phase formation during sintering. Addition of nano-sized SiC significantly retarded the matrix grain growth, making the microstructure much finer and more uniform. Transmission electron microscopy and high-resolution transmission electron microscopy revealed that many SiC nanoparticles were found in mullite and ZrO2 grains, and low-energy grain boundaries and mullite–liquid interfaces parallel to the {110} planes of rodlike mullite grains were formed. It is deduced that the formation of rodlike mullite grains is the result of the preferential development of these low-energy grain boundaries and mullite–liquid interfaces. The mechanical properties of the SiC/ZTM nanocomposite showed significant improvement over those of ZTM, and further enhancement in the mechanical properties was achieved by combinative strengthening with nano- and micro-sized SiC.
I. INTRODUCTION
During recent decades, much attention has been concentrated on nanocomposites due to their extraordinarily improved mechanical properties.1–14 Niihara and coworkers reported that the strength of Al2O3 increased from 450 to 1500 MPa by producing an Al2O3/SiC nanocomposite,1,2 along with great enhancement in the creep resistance.6 Similar results were also found in MgO/SiC, Al2O3/ WC, Al2O3/TiC, and Si3N4/SiC nanocomposites.2,11–14 Mullite is a promising high-temperature engineering ceramic, due to its excellent high-temperature strength, good creep resistance, and thermochemical stability.15 However, the poor ambient properties of the material have become a bottleneck to restrict its structural applications. In this paper, SiC/ZTM nanocomposites were prepared to improve the mechanical properties of mullite through the strengthening and toughening effects of ZrO2 and SiC particles.
Chemistry Metallurgy) was ultrasonically dispersed in distilled water, and tetraethyl orthosilicate (TEOS) was prehydrolyzed overnight at room temperature in an alcohol–water solution before mixing with AlCl3 ⭈ 6H2O. Then the TEOS/AlCl3 solution and 4 N ammoniated water were added simultaneously into the SiC suspension under vigorous stirring with an electromagnetic stirrer. The resulting precipitate was washed free of Cl − ions with distilled water, followed by rinsing with hot ethanol. Dried SiC/mullite gel mixture was calcined at 600 °C for 1 h to remove absorbed water and organic contaminants. SiC/ZTM nanocomposite powders were prepared by ball-milling a 2Y-TZP (50 nm, self-prepared), nanosized SiC, and mullite gel mixture in ethanol for 24 h. For some of them, both nano- and micro-sized SiC (0.97 m) were used to investigate the combinative effects of the bimodal SiC particles. The designed compositions of these powders are listed in Table I.
II. EXPERIMENTAL
B. Sintering and characterization
A. Powder preparation
Sintering was conducte
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