The Structure of FeAl Sinters Fabricated Using Cyclic Loading

A two stage process including a sintering under a cyclic loading is proposed as an alternative fabrication method of dense FeAl intermetallics from elemental powder mixtures. The first stage (pre-sintering) is conducted at two temperature values (620 °C and 670 °C, respectively) under a static and a cyclic loading with a frequency of 20, 40 and 60 Hz. The second one includes a pressureless sintering at temperature of 1250 °C, under a protective argon atmosphere. A suitable selection of pre-sintering parameters (temperature, type and frequency of pressing) allows approximately five times grain size reduction of FeAl phase in comparison to particle size of raw Fe and Al powder material (40-60 µm), as well as induces an effective fragmentation of oxide layers. For the sinters obtained using 60 Hz loading frequency an oxide particle size of 4.0 or 4.5 µm (smaller for sintering with liquid phase) is observed. Material obtained after the full heat treatment are characterized by a fine-grained structure of chemically homogeneous FeAl phase with uniformly distributed Al₂O₃ spherical particles along grain boundaries. Moreover, it was found that temperature and frequency of loading during the presintering process also affect a consolidation level of the Fe-Al powder mixture, which increases with rising both temperature and frequency.