Nanocomposites are a class of composite materials where the size of the base or constituent materials are on the nanometer length scale - one nanometer being one-billionth of a meter. They can offer unprecedented properties beyond those currently studied and used. The goal of this fellowship proposal is to augment the advantages of a multilayered design in a metal-ceramic nanocomposite that is hypothesized to exhibit tunable strength and toughness, by the selective activation of deformation mechanisms at the nanoscale. The metal-ceramic multilayered nanocomposite is composed of alternating metallic and MAX phase layers with a lamellar thickness reduced to the nanoscale. Because of the ideal, highly oriented structure that prevails across the film, each film contains thousands of "like layers", and a high density of interfaces. MAX phases are a family of ceramic materials consisting of laminated ternary carbide or nitride materials, and they represent a novel class of layered solids, where Mn+1Xn layers are interleaved with pure A-group element layers. These metal-MAX multilayered nanocomposite thin films show uniform interface spacing (~2 to 100â€™s of nm apart) and uniform interface plane and crystallography throughout the film. MAX phases have applications in multiple technological fields, including high temperature structural applications, protective coatings, sensors, tunable damping films for microelectromechanical systems, etc., along with potential applications in cladding materials for nuclear use. The ability to have a strong yet ductile metal-MAX composite with improved mechanical behavior to satisfy the demands of such applications will provide considerable technological and economic benefits. This research is an integrated collaboration planned between the principal investigator (PI) and the Center for Integrated Nanotechnologies, Sandia National Laboratories (CINT-SNL), which will support a postdoctoral researcher, and enable extended collaborative visits and infrastructure development opportunities at the nationâ€™s premier national laboratory at CINT-SNL. Undergraduate education in the capstone senior design projects in the Materials department at the PIâ€™s university will particularly benefit from this collaboration by having mentors (and possible visitations to CINT-SNL) from both national laboratory and university.
The objectives of this fellowship project are to leverage a fundamental understanding of the activation and confinement of deformation mechanisms directly linked to the hierarchical structure at the nanoscale in multilayered nanocomposite materials, to potentially enable tunable strength and toughness. Unlike other various multilayered systems that have been pursued in the past, the metal-MAX nanocomposites studied here are composed of a unique hierarchical topology - as interfaces between the layers are in direct competition with the internal interfaces within the MAX layers to drive the tunable macroscopic mechanical behavior. Guided by experimental synthesis and novel nanomechanical testing capabilities of the PI, computational modeling at CINT-SNL will complement the experimental component to study the fundamental mechanisms (e.g., dislocations and ripplocations) within the metal-MAX hierarchical structure. Outcomes from the fellowship project will include the development of correlations between the metal-MAX hierarchical structure, its fundamental deformation mechanisms and the resulting mechanical properties, namely strength and toughness.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.