Electron Microscopy Study of the Effect of Iron in Reaction-Sintered Silicoa Nitride |
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Authors: | S SHINOZAKP M E MILBERG |
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Affiliation: | Engineering and Research Staff, Ford Motor Company, Dearborn, Michigan 48121 |
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Abstract: | The microstructure, crystal structure, and chemical composition of reaction-sintered Si3N4 containing iron were studied using conventional and scanning transmission electron microscopy. It was found that the grains of β -Si3N4 were large and blocklike with well-developed facets, a series of voids along some grain boundaries, a subgrain of iron silicide near the periphery, and penetration of iron silicide into the three-grain junctions and grain boundaries. At some distance from each β -Si3N4 grain was a region of small α-Si3N4 grains, with no evidence of iron silicide. Between this region and the β -Si3N4 grain was a zone containing both α- and β -Si3N4 and iron silicide. These observations suggest that the large β -Si3N4 grains grow in liquid iron silicide, that the smaller α-Si3N4 grains grow from the vapor, and that the latter are converted to the β form by solution in, and reprecipitation from, liquid iron silicide. |
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