Microstructural characterization of NiAl-Al2O3 composite materials obtained by in situ aluminothermic reduction of NiO for potential coating applications

Aluminothermic reactions between Al microparticles and preoxidized Ni particles were carried out to fabricate mixed compounds of NixAly containing in situ generated Al2O3. The mixed composites were obtained by applying a thermal treatment to either a mixture of NiO and Al powders or to a stacking of powders. The effects of the particle size, thickness of oxide, heating ramp and temperature on the microstructure of the NiAl-Al2O3 coating are discussed. The results indicate that Ni3Al forms first during the synthesis, followed by NiAl and Al3Ni2 while Al3Ni forms on cooling. Moreover, the alumina was observed to form a continuous network surrounding NixAly intermetallic compounds. It derives that these composites have a potential to form self-healing coatings.