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The Effect of High Temperature Soaking on the Microstructure and Properties of a Sintered Silicon Nitride

2010; Wiley; Linguagem: Inglês

10.1002/9780470294499.ch1

1940-6339

Q. Wei, Jag Sankar, Varun Vijayrao, J. Narayan,

Boron and Carbon Nanomaterials Research

An investigation was carried out to study the effect of high temperature soaking in air on the microstructure and mechanical properties of an AlliedSignal sintered silicon nitride using optical and scanning electron microscopy, energy dispersive spectroscopy and microhardness testing. The Si3N4 samples were soaked in air at 1275°C for different periods of time ranging from 16–40 hours. The cross section of the samples were then studied using optical microscope and microhardness measurements. It was found that two distinct white annular rings were formed during thermal soaking. While the outer annular ring stayed relatively stationary with respect to the surface, the inner one advanced towards the center of the sample and expanded simultaneously with time. The position of the inner diameter of the inner ring is roughly a linear function of the time of soaking. Vickers hardness measurements showed strength degradation in both of the annular rings. The results are discussed in combination with the oxygen attacks on the material through fast diffusion along the amorphous grain boundary phases, surface diffusion in the micropores and lattice diffusion of oxygen in silicon nitride grains as revealed by EDS at the edge and in the center of the samples. This would contribute to a better understanding of the high temperature behavior of sintered Si3N4.