FeAl-Al2o3 And NiAl-Al2O3 Composite Powders Formed By Mechanical Alloying
Dariusz Oleszak Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa
Annals 1 No. 1, 2001 pages 76-78
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abstract The milling processes were performed for starting powder mixtures of compositions Fe2O3+4Al and 3NiO+5Al in order to study the phase transformations leading to the in situ formation of composites 2FeAl+Al2O3 and 3NiAl+Al2O3. A Fritsch planetary ball mill was applied for the experiments. The reduction reaction of hematite took place after 20 h of processing, however, the reaction product, beside Al2O3, was not ordered FeAl intermetallic compound, but disordered bcc Fe(Al) solid solution, characterized by mean crystallites size of 10 nm and lattice parameter of 0.2931 nm. Heating the sample up to 700oC resulted in the ordering process and formation of FeAl. In the case of the reduction of NiO, NiAl intermetallic compound was formed directly during the milling, after 1.5 h of processing only. This phase was characterized by average crystallite size of 15 nm and lattice parameter of 0.2884 nm. Simultaneously, the crystallites of Al2O3 were considerably bigger (about 65 nm). Prolonged milling up to 40 h led to further refinement of the microstructure and decreasing of crystallites size of NiAl and Al2O3 down to 10 and 25 nm, respectively.