Grain-Boundary Films in A Silicon Nitride Ceramic at High Temperatures

The thickness distribution of grain-boundary films during the superplastic deformation of fine-grained β–silicon nitride was investigated by high-resolution electron microscopy. In particular, grain-boundary thickness was considered with respect to the stress axis in two orientations; namely, parallel and perpendicular to the direction of applied stress. The results showed that the thickness distribution in boundaries perpendicular to the direction of applied stress was unimodal, whereas in parallel boundaries it was bimodal. Moreover, it was found that the majority of film-free boundaries were parallel to the direction of applied stress in the extremely deformed sample. The variation in spacing reflects distribution of stresses within the material due to irregular shape of the grains and the existence of percolating load-bearing paths through the microstructure.

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High-Resolution Electron Microscopy Observations of Grain-Boundary Films in Silicon Nitride Ceramics

MRS Proceedings ◽

10.1557/proc-287-65 ◽

1992 ◽

Vol 287 ◽

Cited By ~ 13

Author(s):

H.-J. Kleebe ◽

M. K. Cinibulk ◽

I. Tanaka ◽

J. Bruley ◽

R. M. Cannon ◽

...

Keyword(s):

Electron Microscopy ◽

Silicon Nitride ◽

High Resolution ◽

Grain Boundary ◽

Film Thickness ◽

High Resolution Electron Microscopy ◽

Resolution Electron ◽

Nitride Ceramics ◽

Boundary Films ◽

Repulsive Forces

ABSTRACTCharacterization of silicon nitride ceramics by transmission electron microscopy (TEM) provides structural and compositional information on intergranular phases necessary to elucidate the factors that can influence the presence and thickness of grain-boundary films. Different TEM techniques can be used for the detection and determination of intergranular-film thickness, however, the most accurate results are obtained by high-resolution electron microscopy (HREM). HREM studies were applied, in conjunction with analytical electron microscopy, to investigate the correlation between intergranular-phase composition and film thickness. Statistical analyses of a number of grain-boundary films provided experimental verification of a theoretical equilibrium film thickness. Model experiments on a high-purity Si3N4 material, doped with low amounts of Ca, suggest the presence of two repulsive forces, a steric force and a force produced by an electrical double layer, that may act to balance the attractive van der Waals force necessary to establish an equilibrium film thickness.

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Effect of Heat-Treatment on Thermal and Mechanical Properties of Silicon Nitride Ceramic at Room and High Temperatures

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.352.35 ◽

2007 ◽

Vol 352 ◽

pp. 35-39 ◽

Cited By ~ 1

Author(s):

Yuki Sekimoto ◽

Thanakorn Wasanapiarnpong ◽

Masamitsu Imai ◽

Keiichi Katayama ◽

Toyohiko Yano

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Silicon Nitride ◽

High Temperatures ◽

Thermal And Mechanical Properties ◽

Silicon Nitride Ceramic

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Silicon Nitride Ceramics with Sodium Ion Conductive Grain Boundary Phase

Journal of Materials Research ◽

10.1557/jmr.2003.0383 ◽

2003 ◽

Vol 18 (12) ◽

pp. 2752-2755 ◽

Cited By ~ 13

Author(s):

Hirokazu Kawaoka ◽

Tohru Sekino ◽

Takafumi Kusunose ◽

Koichi Niihara

Keyword(s):

Electrical Conductivity ◽

Silicon Nitride ◽

Ionic Conductivity ◽

Grain Boundary ◽

Sodium Ion ◽

Boundary Phase ◽

Structural Ceramics ◽

Silicon Nitride Ceramic ◽

Nitride Ceramics ◽

Conductive Particles

Sodium ion-conductive silicon nitride ceramic with Na2O–Al2O3–SiO2 glass as the grain boundary phase was fabricated by adding Na2CO3, Al2O3, and SiO2 as sintering additives. The electrical conductivity was two and four orders of magnitude higher than that of Si3N4 ceramic with Y2O3 and Al2O3 additives at 100 and 1000°C, respectively. This result clearly indicates that ionic conductivity can be provided to insulating structural ceramics by modification of the grain boundary phase without dispersion of conductive particles.

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Compositions and Thicknesses of Grain Boundary Films in Ca-Doped Silicon Nitride Ceramics

Tailoring of Mechanical Properties of Si3N4 Ceramics ◽

10.1007/978-94-011-0992-5_20 ◽

1994 ◽

pp. 275-289 ◽

Cited By ~ 8

Author(s):

I. Tanaka ◽

J. Bruley ◽

H. Gu ◽

M. J. Hoffmann ◽

H.-J. Kleebe ◽

...

Keyword(s):

Silicon Nitride ◽

Grain Boundary ◽

Nitride Ceramics ◽

Doped Silicon ◽

Boundary Films

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Effect of Heat-Treatment on Thermal and Mechanical Properties of Silicon Nitride Ceramic at Room and High Temperatures

Innovation in Ceramic Science and Engineering - Key Engineering Materials ◽

10.4028/0-87849-454-5.35 ◽

2007 ◽

pp. 35-39

Author(s):

Yuki Sekimoto ◽

Thanakorn Wasanapiarnpong ◽

Masamitsu Imai ◽

Keiichi Katayama ◽

Toyohiko Yano

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Silicon Nitride ◽

High Temperatures ◽

Thermal And Mechanical Properties ◽

Silicon Nitride Ceramic

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On the Effect of Local Grain-Boundary Chemistry on the Macroscopic Mechanical Properties of a High Purity Y2O3-Al2O3-Containing Silicon Nitride Ceramic

MRS Proceedings ◽

10.1557/proc-839-p3.14 ◽

2004 ◽

Vol 839 ◽

Author(s):

A. Ziegler ◽

J.M. McNaney ◽

M. J. Hoffmann ◽

R. O. Ritchie

Keyword(s):

Mechanical Properties ◽

Silicon Nitride ◽

Grain Boundary ◽

Oxygen Content ◽

High Purity ◽

Interfacial Structure ◽

Crack Advance ◽

Transgranular Fracture ◽

Boundary Films ◽

Boundary Chemistry

ABSTRACTThe effects of grain-boundary chemistry on the mechanical properties of a high-purity silicon nitride ceramics were investigated, with specific emphasis on the role of oxygen. Variations in the grain-boundary oxygen content, through control of oxidizing heat treatments and sintering additives, was found to result in a transition in fracture mechanism from transgranular to intergranular fracture, with an associated increase in fracture toughness. This phenomenon is correlated to an oxygen-induced change in grain-boundary chemistry that appears to affect fracture by “weakening” the interface, facilitating debonding and crack advance along the boundaries, thereby enhancing the toughness by grain bridging. It is concluded that if the oxygen content in the thin grain-boundary films exceeds a lower limit, which is ∼0.87 equiv% oxygen content, then the interfacial structure and bonding characteristics favor intergranular debonding during crack propagation; otherwise, transgranular fracture ensues, with consequent low toughness.

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