Hardness and Indentation Fracture Toughness of Slip Cast Alumina and Alumina-Zirconia Ceramics

Abstract

Alumina (Al2O3) and zirconia (ZrO2) have good overall properties and thus are widely used oxide technical ceramics. The biggest drawback of Al2O3 is its low fracture toughness. In contrast, ZrO2 is relatively tough, but is also much more expensive. In order to improve the alumina toughness, composite ceramics are being developed. Slip casting technology has economic advantages over the conventional hot isostatic pressure technology, but problems may arise when preparing stable highly-concentrated suspensions (slip) for filling the mold. The purpose of this study is to prepare aqueous suspensions using 70 wt. % α-Al2O3, with 0, 1, 5 and 10 wt. % of added t-ZrO2. Suspensions were electrosterically stabilized using the ammonium salt of polymethylacrylic acid, an alkali-free anionic polyelectrolyte dispersant. Also, magnesium oxide in form of magnesium aluminate spinel (MgAl2O4) was used to inhibit the abnormal alumina grain growth during the sintering process. Minimum viscosities were used as stability estimators, where an increase in ZrO2 content required adding more dispersant. After sintering, the Vickers indentation test was used to determine the hardness and the indentation fracture toughness from the measurement of the crack length. Also, the brittleness index (Bi, μm−1/2) was calculated from values of Vickers hardness and the Vickers indentation fracture toughness. It was found that with increasing ZrO2 content the fracture toughness increased, while the hardness as well as the brittleness index decreased. Zirconia loading reduces the crystallite sizes of alumina, as confirmed by the X-ray diffraction analysis. SEM/EDS analysis showed that ZrO2 grains are distributed in the Al2O3 matrix, forming some agglomerates of ZrO2 and some pores, with ZrO2 having a smaller grain size than Al2O3.

Characterization of Al2O3 Samples and NiAl–Al2O3 Composite Consolidated by Pulse Plasma Sintering

“…The value calculated with the Anstis equation was in the range 5.2–5.4 MPa·m 0.5 , while in the following work, the values of K IC calculated in the same way reached the value above 10 MPa·m 0.5 . In the study of Žmak et al [ 49 ], where solid Al 2 O 3 samples were fabricated by slip casting and sintered at 1650 °C, the calculated K IC values from the Niihara and Lankford equations remain in good correlation with the results derived in this paper, with K IC values of 4.89 MPa·m 0.5 and 5.29 MPa·m 0.5 , respectively. According to Chakravarty et al [ 50 ], Al 2 O 3 ceramic specimens were fabricated by the SPS method at 1300 °C, K IC values ranging from 3.25 MPa·m 0.5 to 3.45 MPa·m 0.5 were derived based on the Chantikul equation.…”

Optimization of Alumina Ceramics Corrosion Resistance in Nitric Acid

“…Therefore, it may be applied as an advanced material in electronics, metallurgy, catalysis, wear protection, refractories, as a composite, etc. [ 5 , 6 , 7 ]. Nevertheless, the issue of ceramic corrosion is considered and investigated in many fields, such as geochemical research, nuclear waste disposal, art history and archaeological research—including industrial applications [ 8 , 9 ].…”

Effects of flake-shape and content of nano-mullite on mechanical properties and fracture process of corundum composite ceramics

“…Relative density is used to characterize densification of the samples. Theoretical densities of mullite ceramics [23][24][25] and alumina ceramics [28,29] are 2.8 g/ cm 3 and 3.6 g/cm 3 , respectively. Figure 5 shows relative densities of the samples with different contents of mullite after sintering at different temperatures.…”

“…The mechanical properties of alumina ceramics are dependent on various factors, such as particle size of raw materials [28][29][30][31], sintering method [-32-35] and grain size of the final ceramics [35][36][37][38]. Hu et al studied the relationship between sample grain size and fracture toughness from mechanics point of view [39,40].…”