Understanding the Role of Intermetallic Interface Contributions in Al – Ni Layered Systems

Nanometallic multilayer systems with designed micro- and nanostructures offer great potential to sustain extreme conditions, such as high temperature, corrosive environments, or radiation. The internal interfaces of such material systems include grain boundaries and interphase boundaries and can be tailored with respect to composition and morphology to achieve properties that cannot be achieved by conventional materials. Understanding the role and behaviors of the different interfaces is thus critical to developing materials suitable for extreme conditions. Most studies of layered systems focused on elements with a positive enthalpy of mixing to create almost atomically sharp interfaces. By contrast, only few studies investigated the interface morphology for systems with negative enthalpy of mixing, which offers additional degrees of freedom regarding materials design.<br/>We investigated the Ni-Al multilayer system with varying layer thicknesses between 5 and 250 nm to understand the effects of the layer structure on the mechanical behavior and the stability of the microstructures not only at elevated temperatures but also after severe deformation. The microstructure characterization with TEM and STEM-EELS indicates wide interdiffusion at Al/Ni interface and formation of intermetallic bonding at interfaces and grain boundaries in Al/Ni multilayer. We measured a peak hardness of 9.03 ± 0.14 GPa, which is the highest measured so far for fcc-fcc layered systems and shows the potential of this interface engineering route. Our findings demonstrate that the intermetallic formed at Al/Ni multilayers contributes to a strong interface strengthening effect and compensates the weakening from interface diffusion. In this presentation we will discuss the role and potential of the interfaces and interphase boundaries for materials under extreme conditions.