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

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.

TEM Studies of Grain Boundary Films in Si3N4 Ceramics

1991 ◽  
Vol 49 ◽  
pp. 930-931
Author(s):  
H.-J. Kleebe ◽  
J.S. Vetrano ◽  
J. Bruley ◽  
M. Rühle
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Hot Isostatic Pressing ◽  
Amorphous Film ◽  
Liquid Phase Sintering ◽  
Second Phase ◽  
High Temperature Mechanical Properties ◽  
Triple Points ◽  
Boundary Films

It is expected that silicon nitride based ceramics will be used as high-temperature structural components. Though much progress has been made in both processing techniques and microstructural control, the mechanical properties required have not yet been achieved. It is thought that the high-temperature mechanical properties of Si3N4 are limited largely by the secondary glassy phases present at triple points. These are due to various oxide additives used to promote liquid-phase sintering. Therefore, many attempts have been performed to crystallize these second phase glassy pockets in order to improve high temperature properties. In addition to the glassy or crystallized second phases at triple points a thin amorphous film exists at two-grain junctions. This thin film is found even in silicon nitride formed by hot isostatic pressing (HIPing) without additives. It has been proposed by Clarke that an amorphous film can exist at two-grain junctions with an equilibrium thickness.

ChemInform Abstract: Dopant Distribution in Grain-Boundary Films in Calcia-Doped Silicon Nitride Ceramics.

ChemInform ◽  
2010 ◽  
Vol 30 (13) ◽  
pp. no-no
Author(s):  
Hui Gu ◽  
Xiaoqing Pan ◽  
Rowland M. Cannon ◽  
Manfred Ruehle
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Dopant Distribution ◽  
Nitride Ceramics ◽  
Doped Silicon ◽  
Boundary Films

High-resolution Electron Microscopy Observation of Grain-boundary Films in Superplastically Deformed Silicon Nitride

2000 ◽  
Vol 15 (7) ◽  
pp. 1551-1555 ◽  
Author(s):  
Guo-Dong Zhan ◽  
Mamoru Mitomo ◽  
Yuichi Ikuhara ◽  
Taketo Sakuma
Keyword(s):  
Electron Microscopy ◽  
Silicon Nitride ◽  
High Resolution ◽  
Grain Boundary ◽  
Applied Stress ◽  
Thickness Distribution ◽  
High Resolution Electron Microscopy ◽  
Stress Axis ◽  
Resolution Electron ◽  
Boundary Films

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.

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

1992 ◽  
Vol 287 ◽  
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.

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

1994 ◽  
pp. 275-289 ◽  
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

Microstructure and grain-boundary characterization of HIP'ed high-purity silicon nitride

1993 ◽  
Vol 28 (15) ◽  
pp. 4217-4222 ◽  
Author(s):  
P. Lu ◽  
S. C. Danforth ◽  
W. T. Symons
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
High Purity ◽  
High Purity Silicon

The Effect of Grain Boundary Chemistry on the Slip Transmission Process Through Grain Boundaries in Ni3Al

1991 ◽  
Vol 238 ◽  
Author(s):  
I. M. Robertson ◽  
T. C. Lee ◽  
Raja Subramanian ◽  
H. K. Birnbaum
Keyword(s):  
Stress Concentration ◽  
Grain Boundary ◽  
Slip System ◽  
Grain Boundaries ◽  
Local Stress ◽  
Crack Advance ◽  
Boron Doped ◽  
Show Evidence ◽  
Fcc Alloy ◽  
Boundary Chemistry

ABSTRACTThe conditions established in disordered FCC systems for predicting the slip system that will be activated by a grain boundary to relieve a local stress concentration have been applied to the ordered FCC alloy Ni3Al. The slip transfer behavior in hypo-stoichiometric Ni3Al with (0.2 at. %B) and without boron was directly observed by performing the deformation experiments in situ in the transmission electron microscope. In the boron-free and boron-doped alloys, lattice dislocations were incorporated in the grain boundary, but did not show evidence of dissociation to grain boundary dislocations or of movement in the grain boundary plane. The stress concentration associated with the dislocation pileup at the grain boundary was relieved by the emission of dislocations from the grain boundary in the boron-doped alloy. The slip system initiated in the adjoining grain obeyed the conditions established for disordered FCC systems. In the boron-free alloy, the primary stress relief mechanism was grain-boundary cracking, although dislocation emission from the grain boundary also occurred and accompanied intergranular crack advance. Because of the importance of the grain boundary chemistry in the models for explaining the boron-induced ductility in hypo-stoichiometric Ni3Al, the chemistry of grain boundaries in well-annealed boron-doped and boron-free alloys was determined by using EDS. No Ni enrichment was found at the grain boundaries examined. These observations are discussed in terms of the different models proposed to explain the ductility improvement in the boron-doped, hypo-stoichiometric alloy.

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