On the in situ synthesis of (Fe,Cr)Al and (Fe,Cr)Al-Al₂O₃ nanostructured materials

In the present work, FeAl, (Fe,Cr)Al and (Fe,Cr)Al-Al₂O₃ intermetallic compounds were synthesized by mechanical alloying (MA), in which the intermetallic compounds were formed in one step at room temperature, and the nanocrystalline structure led to significant improvements of strength and ductility. Specifically, MA of a Fe₅₀Al₅₀ powder mixture led to the formation of the FeAl compound in 30 h with a grain size of about 80 nm. Increasing milling time to 100 h decreased the grain size to about 50 nm. In the next step, a Fe₄₀Cr₁₀Al₅₀ power mixture was converted into a solid solution and then an intermetallic compound with a grain size of about 30 nm after 100 h of MA. Finally, the synthesis of nanocomposites with (Fe,Cr)Al intermetallic compound containing Al₂O₃ as the reinforcing phase was investigated. For this purpose, two different methods, the reduction of chromium oxide (Cr₂O₃) and hematite (Fe₂O₃), were examined. In the first method, a mixture of Fe-Al-Cr₂O₃ powder aluminum was milled and alumina phase was formed, but after 100 h of MA, the Cr₂O₃ phase was still observed. In the second method, a Cr-Al-Fe₂O₃ mixture was milled, and the heat of reaction immediately resulted in the formation of (Fe,Cr)Al nanoparticles with a grain size of about 29 nm, along with Al₂O₃ crystalline particles. The results of nanoindentation tests on these particles revealed that their hardness increases by chromium addition as well as Al₂O₃ reinforcing nanoparticles.