Particle penetration during spray forming and Co-injection of Ni3Al + B/Al2O3 intermetallic matrix composite

Intermetallic matrix Ni3Al + B/Al2O3 composite, with 11 vol pct of Al2O3 particles incorporated into the matrix, was synthesized using a spray atomization and coinjection method. The penetration behavior of ceramic particles into atomized droplets during spray atomization and coinjection of Ni3Al + B/Al2O3 composite was investigated experimentally and numerically. It was found that the extent of incorporation of Al2O3 into Ni3Al + B droplets depends on the solidification condition of the droplets at the time of droplet/particle interaction. Penetration was observed only in fully liquid droplets or partially solidified droplets. No penetration was observed for droplets smaller than ∼40 µm, because droplets in this size range were fully solidified at the point of coinjection, and penetration was not possible for fully solidified droplets. The distribution of penetrated Al2O3 in the Ni3Al + B droplets was, in general, uniform, with no trends of segregation observed. However, it was noted that most Al2O3 particles were located at the grain boundaries inside the droplets, while some Al2O3 particles were trapped inside the droplets by primary dendrite arms resulting from a fast moving solidification front typically associated with rapid solidification processes such as spray atomization. Finally, it was believed that the Al2O3 particles facilitated nucleation upon penetration of the Ni3Al + B droplets either by means of thermal gradients or compatibility of preferred growth planes.