Effect of LZSA Glass-Ceramic Addition on Pressureless Sintered Alumina. Part II: Mechanical Behavior

Abstract

This work aims to evaluate the influence of a Li 2 O-ZrO 2 -SiO 2 -Al 2 O 3 (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 (11.6Li 2 O-16.8ZrO 2 -68.2SiO 2 -3.4Al 2 O 3 ,). 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·m 0.5 , 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.

Desempenho balístico de estruturas multicamadas à base de alumina/epóxi

“…Pelo fato de não terem sido observadas variações significativas do módulo de elasticidade e da tenacidade à fratura, a variação foi atribuída ao aumento do tamanho do defeito natural com a redução da espessura. Valores de tamanho de defeito natural de aproximadamente 90 µm foram medidos em [27] para a mesma alumina empregada neste trabalho, porém com espessura de 5 mm. Atribuiu-se este resultado principalmente à etapa de conformação por prensagem.…”

Effect of LZSA glass-ceramic addition on the erosive wear of pressureless sintered alumina

“…The composition A M 15 refers to the center point and was used in triplicate. The same experimental design was also used in previous studies (Montedo et al, 2017;Montedo et al, 2018). Thus, results of these studies, especially porosity and average grain size, are going to be used to understand the results obtained presented herein.…”

“…LZSA glass-ceramic composition shows high Na 2 O and B 2 O 3 contents, respectively 3.7 and 4.6 wt%•Na 2 O and B 2 O 3 are flux agents and were used to de-crease the sintering temperature (Montedo et al, 2015). More than an energetic gain, the main objective was to avoid the excessive growing of alumina grain (Montedo et al, 2017;Montedo et al, 2018) although this addition promotes an increase of the residual glassy phase, which causes damage to the mechanical properties. Table 2 shows the experimental design used in this study.…”

“…In fact, previous works (Montedo et al, 2017;Montedo et al, 2018) investigated the addition of 21 vol% of a 11.6Li 2 O-16.8ZrO 2 -68.2SiO 2 -3.4Al 2 O 3 (mol%) glass-ceramic to a fine grain alumina, sintered at 1470 ºC and 3 h holding time (2% porosity). They observed that the glass-ceramic addition caused a much more significant effect on the mechanical properties than the initial particle size of alumina.…”

“…Considering these works (Montedo et al, 2017;Montedo et al, 2018) involving the addition of a LZSA glassceramic to a fine grain alumina, we hypothesize that such composite could present a low wear rate related to pure alumina, refining the microstructure and improving the erosive wear resistance of alumina.…”