FRG: M_n+1AX_n Phase Solid Solutions: Unique Opportunities at Engineering Bulk and Surface Properties

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NON-TECHNICAL DESCRIPTION: The properties of an emerging family of inorganic, nano-laminate engineered compounds will be investigated by a focused research group (FRG) of investigators from Drexel and Rowan Universities. These materials with the general formula Mn+1AXn (where n = 1 to 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element and X is either C and/or N) and their solid solution alloys known as the so-called MAX phases feature unique chemical, physical, electronic and mechanical properties. They possess superb machinability and extremely low friction coefficients despite being extremely stiff materials. This combination of properties bridges some of the outstanding properties of metals and ceramics within one class of material, the MAX phases. These properties make MAX phases an ideal choice in many areas, for example those requiring low-wear, high-temperature application in aerospace, electronics, tools and consumer goods. The efforts in this program encompass a broad range of experimental and theoretical simulation tools and resources for the characterization, modeling, prediction and manipulation of properties. This program represents a partnership of Drexel, a Ph.D.-granting university, with Rowan, a four-year undergraduate university with a strong tradition of undergraduate research excellence. The linking of students, faculty and resources from both institutions will bring undergraduates and graduate students together in an interdisciplinary environment to provide broader educational and research experiences, to develop important analytical skills, to reinforce their knowledge of the materials through direct interactions, and to further stimulate interest among actively participating and talented undergraduates to pursue graduate studies in a science and engineering discipline.TECHNICAL DETAILS: The MAX phases are among the few polycrystalline solids that deform by a combination of kink and shear band formation, together with delaminations within individual grains. The unusual combination of properties is traceable to their layered structure, the metallic-covalent nature of the MX bonds that are exceptionally strong, together with M-A bonds that are relatively weak, especially in shear. While the potential of select Mn+1AXn phases for high temperature structural applications is beginning to be realized, little is understood about how their thermal, electronic and mechanical properties can be effectively tuned to produce new and unexpected combination of properties in their solid solutions. Herein we propose to explore new materials using combinatorial materials synthesis along with first-principles calculations of electronic properties and lattice dynamical calculations of MAX-phase solid solutions. With bulk and thin-film analytic experimental techniques that have proven to be successful in characterizing these phases, efficient coverage of the compositional and synthetic processing parameter space will enable rapid identification of solid solutions with attractive, and quite possibly novel, combinations of properties. Characterization will include nano-tribological measurements such as local friction and surface energy dissipation via variable temperature scanning probe microscopy; local stress-strain analysis via nanoindentation; linkage of lattice dynamics with mechanical properties via in situ Raman scattering; and probing of electronic, optical and magnetic properties in bulk and thin films.