Interface study by dual-beam FIB-TEM in a pressureless infiltrated Al(Mg)-Al2O3 interpenetrating composite

This paper considers the microstructures of an Al(Mg)-Al(2)O(3) interpenetrating composite produced by a pressureless infiltration technique. It is well known that the governing principle in pressureless infiltration in Al-Al(2)O(3) system is the wettability between the molten metal and the ceramic phase; however, the infiltration mechanism is still not well understood. The objective of this research was to observe the metal-ceramic interface to understand the infiltration mechanism better. The composite was produced using an Al-8 wt% Mg alloy and 15% dense alumina foams at 915 degrees C in a flowing N(2) atmosphere. After infiltration, the composite was characterized by a series of techniques. Thin-film samples, specifically produced across the Al(Mg)-Al(2)O(3) interface, were prepared using a dual-beam focussed ion beam and subsequently observed using transmission electron microscopy. XRD scan analysis shows that Mg(3)N(2) formed in the foam at the molten alloy-ceramic infiltration front, whereas transmission electron microscopy analysis revealed that fine AlN grains formed at the metal-ceramic interface and MgAl(2)O(4) and MgSi(2) grains formed at specific points. It is concluded that it is the reactions between Al, Mg and the N(2) atmosphere that improve the wettability between molten Al and Al(2)O(3) and induce spontaneous infiltration.