Ternary reactive Ru/Al/X multilayers – How morphology design controls ignition, propagation and microstructure evolution
To date, self-propagating reactions in PVD multilayers have been extensively studied regarding their underlying mechanisms and applications. Adjusting the reaction behavior to meet the demands of an application requires a fundamental understanding of the mechanisms and transformations on the micro- and nanoscale. To this end, a comprehensive description not only of the microstructure but also on a morphological level is necessary. This is expressed by the “morphological signature” of the sample. We demonstrate its role for understanding the reaction by extending the conventional design comprising alternating layers of two metals to a three-layer approach. Introducing a third component makes the stacking sequence a design parameter that allows use to define type and density of interfaces.
In this study, we designed ternary reactive multilayers based on Ru/Al by partially substituting either Ru or Al for selected elements which allows us to retain the B2-structure of the product phase. The system Ru/Al shows a heat of formation and propagation velocity comparable to that of Ni/Al, however, its temperature of reaction and ignition are higher. We present how stacking sequence and ternary additions affect the properties of the self-propagating reaction. The role of interfacial solid state reactions on ignition is discussed and how this can be used to modify ignition temperatures. Strong effects of composition and stacking sequence on net propagation velocity are observed and discussed with the help of microstructural analysis of quenched reaction fronts.