J. Phys. IV France
Volume 124, Mai 2005
Page(s) 9 - 15

J. Phys. IV France 124 (2005) 9-15

DOI: 10.1051/jp4:2005124002

The effects of milling conditions on the subsequent oxidation behaviour of mechanically alloyed Fe$_{\bf 3}$Al-based powders

J. Ritherdon1, H. Al-Badairy1, A.R. Jones1, G.J. Tatlock1 and I.G. Wright2

1  Department of Engineering, University of Liverpool, Liverpool L69 3GH, UK
2  Oak Ridge National Laboratory, Oak Ridge, Tennessee, TN37831, USA

Mechanically alloyed, Fe3Al-based, oxide dispersion strengthened alloys form a surface oxide scale during powder processing. This scale becomes entrained in the consolidated alloy, and may have a significant effect on subsequent recrystallisation behaviour. The high oxidation rates found in these alloys are mainly due to the bulk alloy composition. However, batch-to-batch differences in oxidation mass gain occur in powders with ostensibly identical compositions. Batches PMWY2 and PMWY3 were studied and parameters such as alloy composition and homogeneity, powder surface area to volume ratios and scale thickening rates considered. Batch PMWY2 showed 20-90% faster weight gain than PMWY3 and reached the onset of breakaway oxidation approximately twice as quickly. PMWY2 was found to contain aluminium-depleted regions, whereas PMWY3 is much more homogeneous. The surface area to volume ratio for PMWY2 was 44% higher than that of PMWY3, and batch PMWY2 was found to contain extremely fine powder particles. The scale on batch PMWY2 thickened more quickly than that on batch PMWY3, with rates 20-40% higher at different stages in the oxidation. The major contributory factor to the difference in oxidation mass gain between the two alloy batches is scale thickening rate and factors influencing thickening rates are discussed.

Key words: Fe3Al powder, oxidation, mass gain, mechanical alloying, inhomogeneity.

© EDP Sciences 2005