PROCESSING, MICROSTRUCTURE AND CREEP BEHAVIOR OF Mo-Si-B-BASED INTERMETALLIC ALLOYS FOR VERY HIGH TEMPERATURE STRUCTURAL APPLICATIONS

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

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Use of LaB6 for a High Quality, Small Energy Spread Beam in an Electron Velocity Spectrometer

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100092633 ◽

1976 ◽

Vol 34 ◽

pp. 534-535 ◽

Cited By ~ 1

Author(s):

P. E. Batson ◽

C. H. Chen ◽

J. Silcox

Keyword(s):

High Temperature ◽

Energy Resolution ◽

Electron Velocity ◽

Electronic Excitations ◽

Small Energy ◽

Small Intensity ◽

Good Energy ◽

Spectrometer System ◽

Electron Energy Loss ◽

Very High

Electron energy loss experiments combined with microscopy have proven to be a valuable tool for the exploration of the structure of electronic excitations in materials. These types of excitations, however, are difficult to measure because of their small intensity. In a usual situation, the filament of the microscope is run at a very high temperature in order to present as much intensity as possible at the specimen. This results in a degradation of the ultimate energy resolution of the instrument due to thermal broadening of the electron beam.We report here observations and measurements on a new LaB filament in a microscope-velocity spectrometer system. We have found that, in general, we may retain a good energy resolution with intensities comparable to or greater than those available with the very high temperature tungsten filament. We have also explored the energy distribution of this filament.

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TEM study of boron additions to cobalt aluminide

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100104790 ◽

1988 ◽

Vol 46 ◽

pp. 546-547

Author(s):

Gerald B. Feldewerth

Keyword(s):

High Temperature ◽

Turbine Engines ◽

Major Drawback ◽

University Of Missouri ◽

Specific Strength ◽

Aerospace Applications ◽

Wide Range ◽

Ordered Alloys ◽

The University ◽

Very High

In recent years an increasing emphasis has been placed on the study of high temperature intermetallic compounds for possible aerospace applications. One group of interest is the B2 aiuminides. This group of intermetaliics has a very high melting temperature, good high temperature, and excellent specific strength. These qualities make it a candidate for applications such as turbine engines. The B2 aiuminides exist over a wide range of compositions and also have a large solubility for third element substitutional additions, which may allow alloying additions to overcome their major drawback, their brittle nature.One B2 aluminide currently being studied is cobalt aluminide. Optical microscopy of CoAl alloys produced at the University of Missouri-Rolla showed a dramatic decrease in the grain size which affects the yield strength and flow stress of long range ordered alloys, and a change in the grain shape with the addition of 0.5 % boron.

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Crystallization sequence of an A1N-Y2O3-SiO2 glass-ceramic

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100143808 ◽

1986 ◽

Vol 44 ◽

pp. 446-447

Author(s):

T.R. Dinger ◽

G. Thomas

Keyword(s):

High Temperature ◽

Glass Ceramic ◽

Crystallization Behavior ◽

High Stress ◽

Crystallization Sequence ◽

Sio2 Glass ◽

Structural Applications ◽

Ceramic Precursors

The use of Si3N4, alloys for high temperature, high stress structural applications has prompted numerous studies of the oxynitride glasses which exist as intergranular phases in their microstructures. Oxynitride glasses have been investigated recently in their bulk form in order to understand their crystallization behavior for subsequent Si3N4 applications and to investigate their worth as glass-ceramic precursors. This research investigates the crystallization sequence of a glass having a normalized composition of Y26Si30Al11 ON11 and lying in the A1N-Y2O3-SiO2 section of the Y-Si-Al-O-N system. Such glasses exist as intergranular phases in the technologically important Y2O3/Al2O3-fluxed Si3N4 alloys.

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