Novel high-temperature materials reveal a new parameter for designing self-propagating multilayers

Materials that exhibit high temperature, self-propagating reactions after an initial ignition have a variety of current and prospective applications, ranging from high-performance ceramics to microscale soldering. While certain arrangements of binary metallic multilayers can develop these extremely hot reactions and are well known, little is known about the properties of multilayers that include three or more types of metals. One group is beginning to explore what factors should be considered when designing ternary multilayers.

Pauly et al. report the effects of stacking sequence as a new parameter when designing ternary layered self-propagating reactive materials. Using magnetron sputter deposition with nanoscale control, the authors started with ruthenium/aluminum binary systems to add either nickel, platinum or hafnium to create the ternary systems.

In most of today’s binary systems, bilayer thickness serves as the main design parameter.

Using electron microscopy, they found that the ignition temperature was controlled primarily by the exothermic solid state reactions at the layer interfaces and grain boundaries. The stacking sequence determined how much these reactions contributed to ignition by determining the specific volume density of phase boundaries.

Hot plate ignition experiments showed that incorporating nickel and platinum into the systems reduced the ignition temperatures by to 150 °C and 230 °C, respectively. The authors attribute this to the fact that nickel and platinum form various compounds with aluminum exothermically at lower temperatures than ruthenium does, which drives the binary system. This was supported by calorimetry experiments combined with x-ray diffraction. Addition of hafnium produced little or no effect.

The authors hope their work provides a deeper understanding of ignition mechanisms and can be transferred to other reactive multilayers.

Source: “Ignition in ternary Ru/Al-based reactive multilayers–Effects of chemistry and stacking sequence,” by C. Pauly, K. Woll, I. Gallino, M. Stüber, H. Leiste, R. Busch, and F. Mücklich, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5046452 .