Process control of reactive rapid prototyping for nickel aluminides

A new freeform fabrication method for intermetallics named Reactive Rapid Prototyping (RRP), which combines combustion synthesis and rapid prototyping, has been developed. Small droplets of molten aluminum ejected onto the nickel powder bed on the moving x–y–z stage form and simultaneously join hot nickel aluminide beads eventually building up the 3-D object. The RRP is systematically controlled by computer. The process control was investigated because the formation and joining of beads are influenced by temperature and volume of aluminum droplets, time and space intervals of their ejection, thickness of the nickel powder bed, and reaction control agents. The addition of fine alumina particles to the nickel powder bed effectively controlled the spreading of the bead formation. Joinings between adjacent beads and between layers were successfully performed without cracks and pores. The boundary region between layers was composed of NiAl phase, but the interior in each layer shifted from the stoichiometric composition.