Abstract
This work aims to evaluate the influence of a Li2O-ZrO2-SiO2-Al2O3 (LZSA) glass-ceramic on the mechanical behavior of alumina. Composites were prepared from alumina with three different particle sizes and 7 to 21 vol% of an LZSA glass-ceramic composition (11.6Li2O-16.8ZrO2-68.2SiO2-3.4Al2O3,). Specimens were obtained by uniaxial pressing. The optimum sintering temperature and holding time were found to be different for each composite. Structural characterization (bulk density and crystalline phases); mechanical characterization (flexure strength, elastic modulus, fracture toughness, and fracture energy); and microstructural analyses were carried out. Fine-grained alumina-based composite containing 21 vol% of glass-ceramic (1470 oC and 3 h holding time, 2.0% porosity) showed a fracture toughness of 4.93 MPa·m0.5, an elastic modulus of 210 GPa, a fracture energy of 57 J·m-2, and a flexural strength of 170 MPa, in very good agreement with values reported by the literature. An increase of 37-177% in the fracture energy due to 21 vol% LZSA addition in the alumina was achieved for the range of grain size obtained in this work. Even though the final composition included a glassy component, the observed mechanical properties confirmed the effectiveness of the crystalline phases that were formed from LZSA glass-ceramic in reducing the propagation of cracks. The results showed that the addition of the LZSA glass-ceramic improved the mechanical properties of alumina.
Highlights
Ceramic materials have been used to meet engineering requirements[1], such as high wear-resistance in the power generation and aerospace industry[2,3], because of their essential characteristics, such as chemical stability, fairly high hardness[1,2,3], lower density when compared to metals[2], high mechanical strength[1,3], good refractory properties[1,2,3,4], and high corrosion resistance[2]
Part I of this work demonstrated the effect of an LZSA glass-ceramic on the grain growth of alumina[25], since the grain size is one of the most important microstructural features that must be controlled in order to obtain high performance alumina
Suppression of grain growth plays a crucial role. In this Part II, LZSA glass-ceramic was added to alumina to cause suppression of grain growth; crystalline phases were formed during heating in the range of 640-820 °C19
Summary
Ceramic materials have been used to meet engineering requirements[1], such as high wear-resistance in the power generation and aerospace industry[2,3], because of their essential characteristics, such as chemical stability, fairly high hardness[1,2,3], lower density when compared to metals[2], high mechanical strength[1,3], good refractory properties[1,2,3,4], and high corrosion resistance[2]. A fine-grained microstructure[3,10,11] and narrow range of particle size distribution often result in an improvement of the mechanical behavior of alumina[10,11]. The mechanical strength of alumina may be improved when the microstructure shows fine grainsize and residual porosity less than 0.05%15. A reduction of the residual glassy phase can improve the mechanical behavior of alumina obtained by LPS. The formed glass-ceramic must have a low coefficient of thermal expansion (CTE) in order to generate compressive residual stress at the interfaces with the alumina. This stress should strengthen the structure, hampering the stripping of. Part II of this work aims to evaluate the effect on the mechanical behavior of alumina caused by the addition of an LZSA glass-ceramic
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