Chemical reactions of Ni/Al multilayers upon ultrahigh compressive load at ambient temperature

Energetic multilayers are peculiarized by their self-propagation reactions when giving them a thermal pulse. This work reports the chemical reactions of Ni/Al energetic multilayers can be triggered upon ultrahigh compressive load (stress >1 GPa) at ambient temperature, which is realized by micro-compressions of Ni/Al micropillars with equal molar ratio. Detailed microscopic characterizations evidence monolayer reactions of Ni20Al30 and Ni110Al140 (NixAly: x and y are average thickness of individual layers in nanometer) are triggered, forming a stoichiometric NiAl phase after micropillar compression. The as-observed reactions must be triggered by ultra -high compressive loads, which aid for nucleation of NiAl grains at atomic intermixing zones of Ni-Al interfaces. Once occurrence, the grain growth is self-sustained by the released heat during NiAl formation. The grain textures depend strongly on the deformation extent. The self-sustained process is terminated until the whole micropillar is reacted. Analogous chemical reactions are not observed in the thickest Ni450Al620 micropillar where atomic intermixing is absent. The comparison highlights the critical role of ultrahigh compressive load to trigger monolayer reactions of Ni/Al multilayers, and could forward the advance of Ni/Al energetic multilayers for diffusion welding purpose.

Automated summary

This study reveals that the chemical reactions of Ni/Al energetic multilayers can be triggered by ultrahigh compressive loads, leading to the formation of a stoichiometric NiAl phase. The key to trigger these reactions lies in the nucleation of NiAl grains at the atomic intermixing zones of Ni-Al interfaces, which is facilitated by the ultrahigh compressive loads.