Microscale thermal propagation characteristics and intermetallic compound formation in Al/Ni multilayer powders during quasi-static heating processes

Abstract To investigate the heat conduction behavior during the self-propagating exothermic reaction of Al/Ni multilayer powders, microscale temperature response measurements were conducted on annealed and as-prepared Al/Ni multilayer powders using the thermoreflectance method and the intermetallic compounds were identified through X-ray diffraction analysis. Temperature response measurements from the initial to intermediate reaction stages revealed significant inhomogeneity in thermal propagation at the microscale because of the contrasting thermal conductivities of Al and Ni. In particular, the Ni layer in the Al/Ni lamellar structure likely contributes to thermal resistance. As the temperature increases, Ni diffuses into Al, promoting the formation of Ni–Al intermetallic compounds such as Al₃Ni, ultimately leading NiAl formation. Although thermal propagation became spatially uniform, the overall conductivity decreased because of the intrinsically low conductivities of the intermetallic compounds, further limiting thermal propagation. These results indicate that reaction inhibition occurs through different mechanisms at each stage of the exothermic reaction.