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Displaying 51 - 66 of 66

Low Angle Grain Boundary Dewetting in Sapphire

August 1, 2001
Author(s)
B Hockey, M K. Kang, Sheldon M. Wiederhorn, J Blendell
The structure and composition of low angle grainboundaries produced in sapphire by a liquid phase sintering process were investigated by conventional and high resolution transmission electron microscopy (CTEM and HRTEM, respectively). Considering the

Silicon Nitride for Gas Turbines

August 1, 2001
Author(s)
Sheldon M. Wiederhorn, M Ferber
Silicon nitride is a material with a high-temperature potential and, hence, an excellent candidate for gas turbines. The incentive to use silicon nitride is substantial, as higher operating temperatures can be translated directly into higher engine

Misalignment-Induced Bending in Pin-Loaded Tensile-Creep Specimens

January 1, 2001
Author(s)
Ralph Krause, Sheldon M. Wiederhorn, J J. Kuebler
In this paper, we examined the possibility that elastic bending induced by load misalignment can affect creep measurements on pin-loaded tension specimens of silicon nitride(Si 3N 4). We have shown that elastic bending ato room temperature can be as great

Tensile Creep in the Next Generation Silicon Nitride

January 1, 2001
Author(s)
F Lofaj, Sheldon M. Wiederhorn, Gabrielle G. Long, P R. Jemian
The tensile creep behavior of a Lu-containing silicon nitride (SN 281) was characterized in the temperature range of 1350oC to 1550oC for test periods up to 10000h. For the same test conditions, the minimum strain rates were several orders of magnitude

Comparison of Tensile and Compressive Creep Behavior in Silicon Nitride

January 1, 2000
Author(s)
K J. Yoon, Sheldon M. Wiederhorn, William E. Luecke
The creep behavior of most commercial grade of Si 3N 4 was studied at 1350 and 1400 C. Stresses ranged from 10 to 200 Mpa in tension and from 30 to 300 Mpa in compression. In tension, the creep rate increased linearly with stress at low stresses and

Tensile Properties of Ti 3 SiC 2 in the 25-1300 {degrees} C Temperature Range

January 1, 2000
Author(s)
M Radovic, M W. Barsoum, T El-Raghy, J Seidensticker, Sheldon M. Wiederhorn
Although significant progress has been achieved in understanding the mechanical behavior of bulk, polycrystalline Ti 3SiC 2 in compression and flexure, as far as we are aware there are no reports in the literature dealing with its mechanical response under

High Temperature Deformation of Silicon Nitride

December 1, 1999
Author(s)
Sheldon M. Wiederhorn
Three mechanisms for the creep of silicon nitride are discussed with regard to the microstructural variables that control creep. During the initial stages of creep, the amorphous silicate layer that coats all grains of silicon nitride is displaced from

High-Temperature Properties of Liquid-Phase-Sintered A-Sic

November 1, 1999
Author(s)
R P. Jensen, William E. Luecke, N P. Padture, Sheldon M. Wiederhorn
We have characterized the high-temperature subcritical crack growth and oxidation resistance of a liquid-phase-sintered (LPS) SiC with 20% volume fraction yttrium aluminum garnet (YAG) second phase. Constant stress rate testing in air in the temperature

A new model for tensile creep of silicon nitride

October 1, 1999
Author(s)
William E. Luecke, Sheldon M. Wiederhorn
The tensile creep rate of most commercial grades of Si3N4 increases strongly with stress. Although the usual power-law functions can represent the creep data, the data often show curvature and systematic variations of slope with temperature and stress. In

Tensile Creep and Rupture of Silicon Nitride

May 1, 1999
Author(s)
Ralph Krause, William E. Luecke, J French, B Hockey, Sheldon M. Wiederhorn
We have characterized the tensile creep, rupture lifetime, and cavitation behavior of a commercial, gas-pressure-sintered silicon nitride in the temperature range 1150 to 1400 C and stress range 70 to 400 MPa. Individual creep curves generally show primary

A Strain-Based Methodology for High Temperature Lifetime Prediction

September 1, 1998
Author(s)
Sheldon M. Wiederhorn, William E. Luecke, Ralph Krause
In structural materials, lifetime is often strain-determined. Once a part exceeds its allowable strain, its functional integrity is lost. Although most ceramics are designed to a brittle failure criterion, silicon nitride at the temperatures expected in

Interlaboratory verification of silicon nitride tensile creep properties

April 1, 1997
Author(s)
William E. Luecke, Sheldon M. Wiederhorn
Five laboratories tested NIST-supplied, pin-loaded, 76-mm-long tensile creep specimens at 1400 degrees C under a 150 MPa load using flag-based, laser extensometry, The laboratories reported failure time and strain and supplied the individual creep curves

CAVITATION CONTRIBUTES SUBSTANTIALLY TO TENSILE CREEP IN SILICON NITRIDE

August 1, 1995
Author(s)
William E. Luecke, Sheldon M. Wiederhorn, B Hockey, Ralph Krause, Gabrielle G. Long
During tensile creep of a hot isostatically pressed (HIPed) silicon nitride, the volume fraction of cavities increases linearly with strain; these cavities produce nearly all of the measured strain. In contrast, compressive creep in the same stress and