Control of FeAl Composition Produced by SPS Reactive Sintering from Mechanically Activated Powder Mixture

Abstract

The effects of mechanically activated powder mixture (Fe + Al) on the microstructure and the chemical composition of FeAl compound produced by reactive sintering implying an exothermic reaction were studied. Firstly, the characteristics of Fe/Al mechanically activated powder mixtures were investigated in terms of their phase composition and microstructure. The high-energy milling allowed the formation of micrometric agglomerates composed of nanometric crystallites of iron and aluminum. Three aggregate sizes class A:ϕ<125 µm, class B:125 µm≤ϕ<250 µm, and class C:ϕ≥250 µm were considered. The latter class enhanced the reactivity of powder mixtures due to an increase of interfaces in contact as an analogy to nanostructured multilayer systems. Interrupted SPS experiments were performed on these mixtures to understand the origin of chemical heterogeneities observed after the reactive sintering. Formation of the intermediate phase Fe2Al5at ~510°C was accompanied by an exothermic reaction and a linear expansion and followed by the formation of small amount of FeAl. The conversion to FeAl was complete at temperatures higher than the melting point of Fe2Al5(1170°C). Finally, a phase evolution between Fe and Al versus the temperature during the reactive sintering is suggested.