Evaluation of the reliability of Si3N4-Al2O3 -CTR2O3 ceramics through Weibull analysis

Abstract

The objective of this work has been to compare the reliability of two Si3N4 ceramics, with Y2O3/Al2O3 or CTR2O3/Al2O3 mixtures as additives, in regard to their 4-point bending strength and to confirm the potential of the rare earth oxide mixture, CTR2O3, produced at FAENQUIL, as an alternative, low cost sinter additive for pure Y2O3 in the sintering of Si3N4 ceramics. The oxide mixture CTR2O3 is a solid solution formed mainly by Y2O3, Er2O3, Yb2O3 and Dy2O3 with other minor constituents and is obtained at a cost of only 20% of pure Y2O3. Samples were sintered by a gas pressure sintering process at 1900 °C under a nitrogen pressure of 1.5 MPa and an isothermal holding time of 2 h. The obtained materials were characterized by their relative density, phase composition and bending strength. The Weibull analysis was used to describe the reliability of these materials. Both materials produced presented relative densities higher than 99.5%t.d., b-Si3N4 and Y3Al5O12 (YAG) as cristalline phases and bending strengths higher than 650 MPa, thus demonstrating similar behaviors regarding their physical, chemical and mechanical characteristics. The statistical analysis of their strength also showed similar results for both materials, with Weibull moduli m of about 15 and characteristic stress values s o of about 700 MPa. These results confirmed the possibility of using the rare earth oxide mixture, CTR2O3, as sinter additive for high performance Si3N4 ceramics, without prejudice of the mechanical properties when compared to Si3N4 ceramics sintered with pure Y2O3

Unified nano-mechanics based probabilistic theory of quasibrittle and brittle structures: I. Strength, static crack growth, lifetime and scaling

“…The testing of concrete, engineering ceramics and fiber composites, revealed systematic deviations of the strength histograms from the two-parameter Weibull distribution, even though the number of test repetitions ð o100Þ did not suffice to reveal the tails (Weibull, 1939;Lohbauer et al, 2002;Munz and Fett, 1999;Salem et al, 1996;Santos et al, 2003;Schwartz, 1987;Tinschert et al, 2000). As a remedy, a switch to the three-parameter Weibull distribution, which has a finite threshold, has recently been widely adopted to achieve better fits (Duffy et al, 1993;Gross, 1996;Stanley and Inanc, 1985).…”

“…For decades, tremendous efforts have been devoted to experimentally study the strength and lifetime distributions of structures made of quasibrittle materials such as concrete (Weibull, 1939), fiber composites (Chiao et al, 1977;Wanger et al, 1984;Wagner et al, 1986;Wagner, 1989) and industrial or dental ceramics (Weibull, 1939;Stanley and Inanc, 1985;Okabe and Hirata, 1995;Salem et al, 1996;Munz and Fett, 1999;Tinschert et al, 2000;Lohbauer et al, 2002;Santos et al, 2003). The two-parameter Weibull distribution (having zero threshold) has been widely used to fit these histograms.…”

“…(b) Silicon nitride with sintering additive (Si 3 N 4 -Al 2 , O 3 -Y 2 O 3 ), which enhances the bending strength and fracture toughness. Four-point bending tests were carried out on 27 specimens with dimensions 3 Â 4 Â 40 mm (Santos et al, 2003). (c) Dicor dental ceramic (tetrasilicic fluoromica glass ceramic), tested by four-point-bend beams (Tinschert et al, 2000).…”

Activation energy based extreme value statistics and size effect in brittle and quasibrittle fracture

“…For concrete specimens, as it appears, statistical samples with N eq 4500 do not exist. However, test data for fine-grained ceramics cover this kind of size, and they show a distinctly Weibull cdf (e.g., Weibull, 1939;Bansal et al 1976a, b;Ito et al, 1981;Katayama and Hattori, 1982;Matsusue et al, 1982;Soma et al, 1985;Ohji, 1988;Amar et al, 1989;Hattori et al, 1989;Bru¨hner-Foit and Munz, 1989;Quinn, 1990;Quinn and Morrell, 1991;Katz et al, 1993;Gehrke et al, 1993;Danzer and Lube, 1996;Sato et al, 1996;Lu et al, 2002a;Santos et al, 2003). This justifies Hypothesis II.…”

Size effect on strength and lifetime probability distributions of quasibrittle structures

“…Extensive experimental data showed that the strength histograms of various quasibrittle materials, such as concrete, industrial and dental ceramics (Salem et al 1996;Munz & Fett 1999;Tinschert et al 2000;Lohbauer et al 2002;dos Santos et al 2003), and fiber composites (Wagner et al 1986;Wagner 1989), consistently deviate from the two-parameter Weibull distribution. Recently, the three-parameter Weibull distribution with a non-zero threshold has been adopted as a remedy (Stanley & Inanc 1985;Duffy et al 1993;Gross 1996).…”