Combustion synthesis of rounded Ni-Al intermetallic powders

Spherical powders based on Ni-Al intermetallic compounds are of significant importance for the additive manufacturing of high-temperature structures used in the energy and aerospace industries. This article presents a novel, energy-efficient approach to producing finely dispersed (≤ 63 μm) rounded granules of Ni-(13.6–17.0)wt.%Al alloys. These alloys consist of L1₂Ni₃Al, B2NiAl, and L1₀NiAl phases, and are synthesized via combustion synthesis in a Ni-Al reaction mixture with CaCO₃ and Ca(OH)₂ as modifying additives. The synthesis and spheroidization of the materials occur simultaneously within the reaction wave. We have demonstrated that the formation of the granules is a consequence of the capillary fusion of the Ni-Al melts into isolated droplets, followed by rapid crystallization within the pulsating hot-spot combustion. This process occurs over a period of approximately 10–100 ms. The effect of the additives on the reaction temperature and product morphology was investigated. Compared to combustion products without additives, rounded granules synthesized with CaCO₃ and Ca(OH)₂ exhibit increased flowability and a reduced concentration of O and N impurities. Their characteristics are similar to those of spherical NiAl-Cr-Co-Hf powder, which was previously produced through a two-step process: combustion synthesis and plasma spheroidization.