Grain Boundary Films in Boron Steels

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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Grain boundary films in Al–Zn alloys after high pressure torsion

Scripta Materialia ◽

10.1016/j.scriptamat.2013.09.019 ◽

2014 ◽

Vol 70 ◽

pp. 59-62 ◽

Cited By ~ 90

Author(s):

B.B. Straumal ◽

X. Sauvage ◽

B. Baretzky ◽

A.A. Mazilkin ◽

R.Z. Valiev

Keyword(s):

High Pressure ◽

Grain Boundary ◽

High Pressure Torsion ◽

Boundary Films ◽

Zn Alloys

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The selection of grain-growth control additives for the sintering of ceramics

Mineralogical Magazine ◽

10.1180/minmag.1970.037.291.08 ◽

1970 ◽

Vol 37 (291) ◽

pp. 833-838 ◽

Cited By ~ 12

Author(s):

D. W. Budworth

Keyword(s):

Grain Boundary ◽

Grain Growth ◽

Growth Control ◽

Boundary Films ◽

Selection Of

SummaryThe close interrelation between sintering and grain growth is discussed critically, and the necessity for control, but not suppression, of grain growth is established. A distinction between discontinuous and exaggerated grain growth is drawn, and the superiority of grain boundary films as grain-growth control agents is demonstrated. Work on the establishment of tentative criteria for the selection of grain-growth control additives for alumina is reviewed and discussed, and the extension of these ideas to the selection of NaF as a successful aid for magnesia is described.

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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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Analytical Electron Microscopy And High-Resolution Electron Microscopy Studies Of Grain-Boundary Films In Silicon Nitride-Based Ceramics

MRS Proceedings ◽

10.1557/proc-238-859 ◽

1991 ◽

Vol 238 ◽

Cited By ~ 8

Author(s):

H.-J. Kleebe ◽

M. Rühle

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Grain Boundary ◽

Film Thickness ◽

Grain Boundaries ◽

Liquid Phase Sintering ◽

Chemical Compositions ◽

Phase Boundaries ◽

Intergranular Films ◽

Boundary Films

ABSTRACTThe microstructures of post-sintered reaction-bonded Si3N4 materials (SRBSN) were investigated. The materials consist of large elongated β-Si3N4 grains embedded in a finegrained matrix. Amorphous secondary phases exist at triple grain junctions owing to the liquid phase sintering involved during densificacition. Those amorphous phases can be crystallized (nearly completely) by post-sintering heat treatment. Apart from these crystalline grain pockets the grains of all materials are covered with thin (<l-2 nm) amorphous intergranular films on both Si3N4/Si3N4 grain boundaries as well as on secondary-phase/Si3N4 phase boundaries. A control of the intergranular films is most desirable since they limit the high-temperature mechanical properties of Si3N4-based ceramics. Therefore, the required characterization was performed by analytical and high-resolution transmission electron microscopy (AEM/HREM). Si3N4 materials with different rare-earth and transition-element oxide additions were studied. AEM and HREM investigations revealed marked differences in thicknesses and chemical compositions of the different intergranular films depending on the system analyzed indicating a strong dependence of film thickness on chemical composition. However, a given composition of each investigated material showed a characteristic intergranular film thickness, independent of grain misorientation, with the only exception of low-energy grain boundaries. The thickness of the intergranular films was constant within 0.2 nm. In addition, the film thickness of phase boundaries was always greater (by 1–2 nm) compared to grain-boundary films.

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Crystalline-amorphous interfaces and their relation to grain boundary films

10.2172/5738322 ◽

1992 ◽

Author(s):

C.B. Carter

Keyword(s):

Grain Boundary ◽

Boundary Films

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Quantitative Characterization of Grain Boundary Films In Si3n4 by Eels and Z-Contrast Imaging

Microscopy and Microanalysis ◽

10.1017/s1431927600010199 ◽

1997 ◽

Vol 3 (S2) ◽

pp. 661-662

Author(s):

H. Gu

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Surface Oxidation ◽

Force Balance ◽

Contrast Imaging ◽

Full Spectrum ◽

High Temperature Mechanical Properties ◽

Boundary Films ◽

Z Contrast

High temperature mechanical properties of structural ceramics Si3N4 are controlled by ∼1 nm thick silicate amorphous films covering all grain boundaries. The composition of the film dictates the equilibrium film thickness resulted from a force balance at grain boundary. Many efforts arc brought to alter film chemistry and thickness, and this system offers ideal model materials to understand grain boundary and property relationship. Using a dedicated STEM (VG HB601) with high spatial resolution EELS analysis and high resolution Z-contrast imaging, various novel quantification data of the grain boundary in Si3N4 can be obtained. The methods described here can also be applied to other types of grain boundaries.EELS profiling was performed to acquire a full spectrum from each position at a lateral increment of 1Å across a boundary in a pure Si3N4 sample with only SiO2 impurities from surface oxidation. It gives directly elemental distributions near the boundary such as Si, N and O profiles shown in Fig. 1.

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