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Displaying 1 - 25 of 66

Cavitation Creep in the Next Generation Silicon Nitride

October 12, 2021
Author(s)
F Lofaj, Sheldon M. Wiederhorn, Gabrielle G. Long, P R. Jemian, M Ferber
X-ray scattering (A-USAXS). Failure strains were around 0.5 %. The creep resistance of this grade was found to be up to two orders of magnitude better than that of other silicon nitrides. The corresponding stress exponents were higher than 6. Creep damage

Ring-on-Ring Strength Measurements on Rectangular Glass Slides

October 12, 2021
Author(s)
Theo Fett, G Rizzi, J -. Guin, Sheldon M. Wiederhorn
The ring-on-ring test has been standardized and used extensively for strength measurements on glasses and ceramics. The specimen is especially useful to avoid edge defects that often dominate the failure of flexure bars. In this paper, we extend the

Secondary Phase Evolution in Silicon Nitride During Creep and Heat Treatment

October 12, 2021
Author(s)
F Lofaj, H Gu, A Okada, Sheldon M. Wiederhorn, H Kawamoto
The microstructure of a ytterbia- and yttria-containing grade of silicon nitride, SN 88, was investigated after it had been annealed in nitrogen, in air and crept in air. We were particularly interested in phase transformation within the secondary silicate

Viscous Flow Creep in Ceramics Containing Secondary Crystalline Phases

October 12, 2021
Author(s)
Q Jin, D S. Wilkinson, G C. Weatherly, William E. Luecke, Sheldon M. Wiederhorn
Experimental observations of the creep response of a Y 2 0 3 -fluxed Si 3 N 4 containing secondary crystalline phases(SP)are presented.The widths of grain-boundary amorphous films before and after creep have been characterized by using transmission

Diffusion of water in silica: Influence of moderate stresses

August 29, 2017
Author(s)
Sheldon M. Wiederhorn, Susanne Wagner, Gabriele Rizzi, Michael J. Hoffmann, Theo Fett
Here we study the diffusive transfer of water into silica glass in the presence of externally applied stresses, and stresses caused by water induced swelling of the glass. By considering the simultaneous action of water penetration into the surface of

Diffusion of water in silica in the absence of stresses

April 21, 2017
Author(s)
Sheldon M. Wiederhorn
In this paper we consider the diffusion of water vapour into silica glass at relatively low temperatures, 25°C to ≈500°C. Extensive studies of such diffusion by others have shown that water diffusion from inert gases behaves differently than diffusion from

Characterization of the Mirror Region With Atomic Force Microscopy

February 19, 2017
Author(s)
Sheldon M. Wiederhorn, Jose Lopez-Cepero, Jay S. Wallace, Jean-Pierre Guin, Theo Fett
In this paper we use atomic force microscopy to investigate the roughness of the mirror region in silica glass. We demonstrate a decrease in surface RMS Roughness from about 0.5 nm to about 0.4 nm with increasing stress intensity factor (0.5KIc to about 0

Effects of Polarity on Grain Boundary Migration in ZnO

February 19, 2017
Author(s)
Jong S. Lee, Sheldon M. Wiederhorn
Boundary migration of ZnO has been investigated using single crystals with defined crystallographic orientations. The migration rate of the basal C planes depended on the crystallographic polarity: Zn-terminated positive (0001)-planes. The migration in the

Lifetime Prediction for Silicon Nitride

February 19, 2017
Author(s)
Sheldon M. Wiederhorn
This paper reviews lifetime prediction methodologies for high-temperature structural ceramics. The methodologies consider failure from subcritical crack growth at low temperatures, 800 C to 1000 C, and creep, or creep-rupture at high temperatures. The

Measurement Methods for Materials Properties: Elasticity

February 19, 2017
Author(s)
Sheldon M. Wiederhorn, Richard J. Fields
Elastic constants must be obtained by experiment methods. Materials are too complicated and theory of solids insufficiently sophisticated to obtain accurate theoretic determinations of elastic constants. Usually, simple static mechanical tests are used to

Particulate Ceramic Composites: Their High-Temperature Creep Behavior

February 19, 2017
Author(s)
Sheldon M. Wiederhorn
Particulate composites, such as liquid-phase sintered silicon nitride and reaction-bonded silicon carbide, are being considered for use in applications where superior chemical and mechanical behavior at high temperatures are essential. Superior strength

Cell Adhesion to Borate Glasses by Colloidal Probe Microscopy

August 1, 2011
Author(s)
Sheldon M. Wiederhorn, Carl G. Simon Jr., Young-Hun Chae
The adhesion of Osteoblast-like cells to silicate and borate glasses was measured using colloidal probe microscopy in a cell growth medium. The probe consisted of silicate and borate glass spheres, 25 µm to 50 µm in diameter, attached to the tip of an

Fracture of Silicate Glasses: Ductile or Brittle?

October 16, 2008
Author(s)
J -. Guin, Sheldon M. Wiederhorn
Atomic force microscopy is used to investigate the possibility of crack tip cavitation during crack growth in silicate glasses. Matching areas on both surfaces of a crack were mapped and then compared for soda-lime silicate glass and for silica glass. For

Glass Pocket Evolution in Vitreous Bonded Sapphire

October 16, 2008
Author(s)
Jong S. Lee, M K. Kang, Sheldon M. Wiederhorn, B Hockey, J Blendell
This paper discusses the evolution of glass filled pockets formed by the growth of sapphire through polycrystalline aluminum oxide bonded by anorthite glass. During growth, excess glass is entrapped within the sapphire as channels, which, upon annealing

Report of the Workshop: Nanometrology of Materials

October 16, 2008
Author(s)
P M. McGuiggan, Sheldon M. Wiederhorn
Probe microscopy is a class of techniques used worldwide to characterize properties and structures of materials. The techniques are especially good for examining materials locally for a wide range of material properties, including surface topology, surface

Structural Behavior of Ceramics

October 16, 2008
Author(s)
Sheldon M. Wiederhorn, Lin-Sien H. Lum
In this chapter, we discussed ceramic materials, materials that by and large do not deform plastically when subjected to high stresses. Consequently, ceramics have a low toughness and are very flaw sensitive. Methods of toughening ceramics involve grain or

Subcritical Crack Growth in Brittle Materials: Mechanics

October 16, 2008
Author(s)
Sheldon M. Wiederhorn
The fracture of ceramic materials is often preceded by subcritical crack growth originating from flaws or cracks contained in these materials. Subcritical crack growth usually results from a stress-enhanced chemical interaction between the solid and