Oxidation of mechanically alloyed powders during processing: origins and control

Abstract

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 Fe₃Al 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 Fe₃Al. This scale is believed to be the source of much of the high alumina content found in fully consolidated ODS Fe₃Al. 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.