Analysis of Ni/Al nanolaminate microstructure offers guidance for customizing ignition

Nickel/aluminum nanolaminates are layered composite materials, capable of customizable combustion reactions. These materials are used for soldering microelectronic components and other energetic heat release applications. Scientists are investigating the connection between microstructure and macroscale heat release so that combustion characteristics can be better predicted.

Brandon Witbeck and Douglas Spearot studied how changes in grain boundary structure affect the atomic diffusion that generates combustion reactions in Ni/Al nanolaminates. They used molecular dynamics simulations to observe combustion in nanolaminate bicrystal models with different symmetric tilt grain boundaries. For comparison, the authors also studied a Ni/Al nanolaminate model without grain boundaries.

“Understanding the connection between microstructure and macroscale heat release can guide design and fabrication decisions,” said Spearot. “Thus, nanometer-scale modifications to system microstructure can precisely tune combustion characteristics to join materials or focus energetic release toward an intended effect.”

The authors found that ignition temperature depends on grain size and grain boundary structure in nanolaminates. Understanding this relationship allows for customization of the microstructure to tune ignition sensitivity. For example, microstructural engineering can be used to decrease ignition sensitivity, so that self-sustaining combustion in Ni/Al nanolaminates is prevented without a corresponding increase in external stimulus.

“By fabricating Ni/Al nanolaminates with microstructures that contain higher energy grain boundaries, Ni/Al nanolaminates can be designed to be more sensitive to energetic stimulus,” said Spearot. “Conversely, nanolaminates that contain lower energy grain boundaries will be less sensitive.”

The authors expect future research on the topic will include better evaluation of the initial stages of the reaction and their influence on combustion as well as an increased understanding of an identified transition period between early combustion stages.

Source: “Role of grain boundary structure on diffusion and dissolution during Ni/Al nanolaminate combustion,” by Brandon Witbeck and Douglas E. Spearot, Journal of Applied Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0002036 .