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Experiments have been performed to test the efficiency with which a novel fluidised bed technique could separate different metallic powders in terms of size and density. The overall aim was to assess the potential of this technique for the commercial separation of defective powder fractions from mechanically alloyed (MA), iron based powders. Separation in terms of size was readily achieved, with the largest powder particles sinking to the bottom of the fluidised bed. In a simulated commercial process, density separation of defective Fe3Al powder could not be demonstrated as any differences in density were overshadowed by size and morphology differences. However, from a batch of iron based powder (ρ=8·02 g cm-3), seeded with six other metallic powders, aluminium powder (ρ=2·70 g cm-3) segregated strongly to the top of the bed from where samples containing 93 vol.-%Al were taken. The process is thought to be sensitive to differences in density of a factor of 1.1–3. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened (ODS) alloys prepared by mechanical alloying (MA) and subsequent consolidation are usually subjected to a series of heat treatments during production, typically comprising a degassing process at ≊600°C and a preconsolidation high temperature 'soak' at ≊1000°C, both under vacuum. In the current work, the oxidation behaviour of a prototype ODS Fe[sub 3]Al alloy and a commercial FeCrAl alloy has been studied during simulation of these temperature and pressure regimes. After the high temperature 'soak' simulation, oxidation had taken place on both alloys with a significantly thicker scale forming on the ODS Fe[sub 3]Al. This scale is believed to be the source of much of the high alumina content found in fully consolidated ODS Fe[sub 3]Al. Variation in the amount of particulate alumina found in different batches of commercially consolidated powder is discussed. Novel processes involving hydrogen purging and powder precompaction have been employed to decrease oxidation and thereby increase sintering efficiency. [ABSTRACT FROM AUTHOR]