NIST Standard Reference Database 30
Last Update to Data Content: 2002
"Effects of Ceramic Microstructures on Strength and Fracture Surface Energy," G.K. Bansal, Proceedings of the Sixth International Materials Symposium, pp. 860-871 (1976), edited by R.M. Fulrath and J.A. Pask, published by Westview Press (Boulder Colorado).Language: English
"...commercial polycrystalline ceramics, a sintered alumina, a hot pressed alumina, and a hot pressed silicon nitride, were investigated. ... The sintered alumina is made by isostatic pressing and sintering of spray-dried powder granules. The final product contains about 96% Al2O3, and is 95% dense. The grain size of the material is 5 µm. The hot-pressed alumina is 99.5% dense and contains about 99.8% Al2O3 and 0.2% of a grain growth inhibitor. The grain size of the material is about 2 µm. The hot pressed silicon nitride is prepared by hot pressing of high α-phase Si3N4 powder with about 2% MgO used as a densification aid. The material is pressed to nearly full density and possesses an average grain size of 1 µm to 2µm. Some SiO2 in the initial powder is believed to react with MgO to form a glassy grain boundary phase."
"Strengths were measured using 3-point bend tests on specimens having dimensions (2.54 mm x 5.08 mm x 38.1 mm = 0.1 x 0.2 x 1.5 in.). Specimens' surfaces were finish ground parallel to the tensile axis using a 320-grit (25-40 µm) diamond wheel. All tests were conducted on a (3.175 cm =1.25-in.) span, and in dry nitrogen at a stress rate of 100 MNm-2s-1 to restrict moisture-assisted subcritical crack growth. More than 10 specimens were tested for each material. Strengths of hot pressed Al2O3 specimens were measured in two directions: in each case, the fracture plane contained the hot pressing direction. In one, flaws propagated parallel to the pressing direction and, in the other, perpendicular to it. Strengths of the hot pressed Si3N4 specimens were measured with flaws moving parallel to the pressing direction only. The glass-ceramic and the sintered Al2O3 were found to be isotropic."Toughness test
The author sites D.P. Williams et al., J. Testing and Evaluation, Vol. 1 (4) 264-270 (1973) and R.W. Davidge et al., Proc. Br. Ceram. Soc., Vol. 15, 47-60 (1970), and summarizes the procedure as follows. "Fracture surface energies were measured using two techniques: double torsion and notch bend. Four specimens of each material were used for determination by each technique."Stress-strain measurement
"Young's moduli were determined both in uniaxial compression from measurements of strain as a function of applied load, and from 4-point bend tests. In the bend test, axial strains were measured as a function of applied moment using resistance strain gages on both the tension and the compression surfaces."
| Amount of Element ( formula units ) |
Element ( no unit ) |
|---|---|
| 2 | Al |
| 3 | O |
| Temperature ( °C ) |
Elastic Modulus ( GPa ) |
|---|---|
| 22 | 318 |
| Temperature ( °C ) |
Flaw Direction |
Flexural Strength ( MPa ) |
|---|---|---|
| 22 | -- | 408 ± 12 |
| Temperature ( °C ) |
Flaw Direction |
Fracture Energy ( J m-2 ) |
|---|---|---|
| 22 | -- | 23.2 ± 1.2 |
| Amount of Element ( formula units ) |
Element ( no unit ) |
|---|---|
| 2 | Al |
| 3 | O |
| Temperature ( °C ) |
Elastic Modulus ( GPa ) |
|---|---|
| 22 | 413 |
| Temperature ( °C ) |
Flaw Direction |
Flexural Strength ( MPa ) |
|---|---|---|
| 22 | parallel | 915 ± 50 |
| 22 | normal | 843 ± 54 |
| Temperature ( °C ) |
Flaw Direction |
Fracture Energy ( J m-2 ) |
|---|---|---|
| 22 | Parallel | 42.2 ± 6.0 |
| 22 | Normal | 21.2 ± 2.1 |
| Amount of Element ( formula units ) |
Element ( no unit ) |
|---|---|
| 3 | Si |
| 4 | N |
| Sintering Aid Mass Fraction ( % ) |
Sintering Aid ( no unit ) |
|---|---|
| 2 | MgO |
| Temperature ( °C ) |
Elastic Modulus ( GPa ) |
|---|---|
| 22 | 310 |
| Temperature ( °C ) |
Flaw Direction |
Flexural Strength ( MPa ) |
|---|---|---|
| 22 | parallel | 960 ± 35 |
| Temperature ( °C ) |
Flaw Direction |
Fracture Energy ( J m-2 ) |
|---|---|---|
| 22 | Parallel | 61.3 ± 5.3 |
| 22 | Normal | 42.2 ± 1.8 |