Observation of Reaction Mechanisms for Combustion Synthesis of Co-Al Intermetallic Compounds by Dipping Experiment of Co Wire into Al Melt

Abstract

In order to analyze the combustion synthesis reactions of Co-Al intermetallic compounds, Co/Al premixed compacts were quenched during the combustion synthesis. Additionally, Co wires were dipped into molten Al, and the compound formation reactions between Co and molten Al were investigated.
From microstructure observation, SEM-EDX analysis and X-ray analysis of the quenched compacts, molten Al phase, un-reacted Co phase, and CoAl₃ intermetallic compound phase were found. The CoAl₃ compound phase was also found in the Co wire dipped into the molten Al. The thickness of the CoAl₃ compound layer in the dipped wire depended on dipping temperature and dipping time. Therefore, Co-Al intermetallic compounds were formed via CoAl₃ formation reaction during the combustion synthesis. Form above results and Co-Al phase diagram, the following reaction equations were suggested in the combustion synthesis of Co-Al intermetallic compound.
Al(s)→Al(l) (933 K)
Co(s)+Al(l)→CoAl₃(s) (933∼1408 K)
CoAl₃(s)→Co₂Al₅+(Al-Co) Liq. (1)→CoAl+(Al-Co) Liq. (1) (1408 K∼1453 K)
Co(s)+(Al-Co) Liq. (1)+CoAl(s) (1453 K∼)