Etude par Sonde Atomique Tomographique de la formation de nano ...
Etude par Sonde Atomique Tomographique de la formation de nano ...
Etude par Sonde Atomique Tomographique de la formation de nano ...
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tel-00751814, version 1 - 14 Nov 2012<br />
Chapter 4. Nitri<strong>de</strong> Dispersion Strengthened Steels<br />
APT reveals that different families of <strong>nano</strong><strong>par</strong>ticles with different morphologies are<br />
present. As expected, <strong>nano</strong>metre scale p<strong>la</strong>telet shape and spherical Ti-N rich <strong>par</strong>ticles are<br />
formed, but elongated Cr-rich <strong>par</strong>ticles are also found. These <strong>par</strong>ticles could be formed in<br />
areas containing high level of nitrogen, even after the homogenisation treatment (small<br />
pow<strong>de</strong>r grains). In these regions, Cr-N <strong>formation</strong> could occur during hot extrusion pre-<br />
heating. Their final morphology could be the results of extrusion induced <strong>de</strong><strong>formation</strong> of<br />
p<strong>la</strong>te-shape <strong>par</strong>ticles.<br />
Thus, it seems that further optimisation of nitriding process is necessary to get an<br />
homogeneous microstructure. As a solution, it may be suggested to control homogeneity of<br />
nitrogen distribution before consolidation of the pow<strong>de</strong>r by using a smaller size distribution<br />
of pow<strong>de</strong>r grain for nitriding.<br />
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