Structure of Fe40AI Iron Aluminides Sintered Under Cyclic Loading

摘要

Many conventional P/M (powder metallurgy) processing methods utilize mostly the prealloyed powders as starting materials and consolidation is achieved by sintering, hot isostatic pressing or hot extrusion. However, these methods involve many complex-processing steps and are rather costly. Recently, we developed a P/M process termed sintering under cyclic loading, as an alternative fabrication method, by which dense Fe40AI intermetallics have been produced successfully from elemental powder mixtures. Two stages technological process of Fe40AI sinter manufacturing was presented in this work. The first stage (presintering) was realised at two temperatures 620°C and 670°C under static and dynamic loading with frequency 20, 40, 60Hz during 1 hour at air atmosphere. The second stage consisted in pressureless sintering at temperature 1250°C under protective argon atmosphere during 1 hour. Suitable selection of presintering parameters (temperature, type and frequency of pressing) enabled around five times grain size reduction of Fe40AI phase in comparison with particle size of raw Fe and Al powder material (40-60μm) as well as effective fragmentation of oxide layers. Sinters obtained after full heat treatment possess fine-grained and chemically homogeneous FeAl phase with uniformly distributed AI_2O_3 spherical particles along Fe40AI grain boundaries. It was found that temperature and frequency of loading during presintering process also effected consolidation level of Fe-AI powder mixture, which increases with temperature and frequency. For optimal presintering parameters three percent of porosity of sinters after full cycle of heat treatment was obtained. This value is around twice smaller then presented by other authors.