Effect of Si addition to Fe on the formation and growth of intermetallic compounds in Fe/Al composites

The effects of Si addition to Fe on the formation and growth of intermetallic compounds (IMC) in Fe/Al composites were studied by Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and electron backscatter diffraction (EBSD) techniques. The results showed that: when annealing time was 1 h, the critical IMC formation temperature of Pure Al/Pure Fe, Pure Al/Fe+0.82Si, Al+0.88Si/Pure Fe and Al+0.88Si/Fe+0.82Si were 440 degrees C, 480 degrees C, 520 degrees C and 620 degrees C, respectively. The major IMC phase formed in the four composites after heat treatments at 640 degrees C/1h and 640 degrees C/24h was the eta phase (Fe2Al5), and a large number of theta phase (Fe4Al13) particles were present in the eta phase for the Pure Al/Pure Fe sample. When Si element was added to Fe and Al, Fe3Al2Si3 phase and FeAl2Si phase were observed in the eta phase. The thickness of the formed IMC layer in the four composites after heat treatment at 640 degrees C/1h was in the order: Pure Al/Pure Fe approximate to Pure Al/Fe+0.88Si > Al+0.888Si/Pure Fe approximate to Al+0.888Si/Fe+0.88Si. The growth activation energies of the IMC layer in the Pure Al/Pure Fe, Pure Al/Fe+0.82Si, Al+0.88Si/Pure Fe, Al+0.88Si/Fe+0.82Si samples were 76.1 kJ/mol, 276 kJ/mol, 349 kJ/mol and 519.6 kJ/mol, respectively. The effect of Si atoms on the formation of IMC was mainly by the interfacial enrichment mechanism and the new phase inhibition mechanism of FexAlySiz. The enrichment of Si at the interface of Al and Fe increased the growth activation energy and reduce the growth rate of IMC layer thickness. The formation of new FexAlySiz phase can inhibit the rapid growth of IMC phase along the C axis.