Microwave-Assisted Combustion Synthesis of intermetallic composites from recycled powders

This work deals with the synthesis of in situ intermetallic matrix composites using spent powders from additive manufacturing as raw materials and microwave energy for ignition of combustion synthesis reactions between aluminum and 3d transition metals (nickel and titanium). The powders derived from selective laser melting manufacturing of components for automotive in nickel-based super alloys (Inconel 625) and lightweight aluminum (AlSi10Mg) and titanium (Ti6Al4V) alloys. The powders were combined in the pseudo-binary systems NiAl (30-70 at.% aluminum) and TiAl (50-70 at.% aluminum). Minor additional metals (Cr, Mo, Nb and Fe, V, Mg) and metalloids (Si) were introduced from the recycled powders themselves giving the possibility to obtain interesting multi-phase microstructures and microalloying of the main nickel and titanium aluminides. Microstructural investigations were performed by X-ray diffraction (XRD) and scanning electron microscopy imaging coupled with energydispersive X-ray spectroscopy (SEM-EDS). It is shown that the NiAl-based system mainly results in near to equiaxed grains of B2 NiAl surrounded by a complex intergranular region with a fine microstructure. Main phases in this region are microalloyed chromium silicides, Laves C14 NbSi2 and tetragonal s-phase (in Ni-rich samples). In compositions with highest amount of Al, more complex nickel aluminides are formed (Al3Ni2, Al3Ni). The TiAl-system contains the titanium aluminides predicted from phase diagrams in addition to Si3Ti5. The use of recycled alloy powders and energetically efficient ignition by microwaves has high potential for obtaining sustainable intermetallic composites without the need for additional alloying.