Effect of Applied Pressure on the Joining of Combustion Synthesized Ni3Al Intermetallics with Al Alloy

We focused on the surface reinforcement of ligth weight casting alloys with Ni-AI intermetallic compounds by in-situ combustion reaction to improve the surface properties of non-ferrous casting components.In our previous works,green compact of elemental Ni and Al powders were reacted to form Ni3Al intermetallic compound by SHS (Self-propagating high temperature synthesis) reaction with the heat of molten Al alloy and simultaneously bonded with Al casting alloy.But some defects such as tiny cracks and porosities were remained in the reacted compact.So we applied pressure to prevent thermal cracks and fill up the pores with liquid Al alloy by squeeze casting process.The compressed Al alloy bonded with the Ni3Al intermetallic compound was sectioned and observed by optical microscopy and scanning electron microscopy (SEM).The stoichiometric compositions of the intermetallics formed around the bonded interface and in the reacted compact were identified by energy dispersive spectroscopy (EDS) and electron probe micro analysis (EPMA). Si rich layer was formed on the Al alloy side near the bonded interface by the sequential solidification of Al alloy.The porosities observed in the reacted Ni3Al compact were filled up with the liquid AI alloy.The Si particles from the molten Al alloy were detected in the pores of reacted Ni3Al intermetallic compact.The Al casting alloy and Ni3Al intermetallic compound were joined very soundly by applying pressure to the liquid Al alloy.