Linking Fundamental Structural and Physical Properties of the MAX Phases at Finite Temperatures through Synergetic Experimental and Computational Research

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NON-TECHNICAL DESCRIPTION: Recently, a new class of nanolayered carbides and nitrides, commonly referred to as MAX phases, has attracted considerable attention as potential multi-functional/structural materials for harsh environments since they combine some of the best attributes of ceramics (high-temperature stability and strength) and metals (high thermal conductivity and resistance to fracture). MAX phases are an exciting, and technologically important class of high-temperature materials but much remains to be understood, especially about the influence of chemistry on their properties, and their transition from brittle to ductile behavior (at elevated temperatures). This project addresses this challenge by synergistically combining experiments and computer simulations. A better understanding of the relationship between chemistry and mechanical stability may enable the faster deployment of MAX phases in technologies that benefit from higher operating temperatures, making it possible to develop more reliable and efficient power generation (and propulsion) systems. In addition to contributions to the science and technology of MAX phases, the project supports activities related to curriculum development, K-12 outreach, high school teacher training, mentoring and contributing to the professional training and development of undergraduate and graduate student researchers.TECHINCAL DETAILS: The overall goal of this project is to investigate the finite-temperature structural and thermo-mechanical properties of MAX phases (comprised of an early transition metal (M), an A-group element and X which is either carbon and/or nitrogen) and their solid solutions through high-throughput experimental and computational approaches. Computations are being used for the rapid screening of materials while high-throughput synthesis allows the fine exploration of alloying effects on the thermal, mechanical and structural properties of a wide range of MAX structures. The project's major scientific goal is to elucidate the microscopic mechanisms responsible for the ductile-to-brittle transition in these materials under the hypothesis that the anharmonic nature of the motion of the M and A layers in the structures drives the onset of mechanical instability. Conventional electronic structure calculations and ab initio molecular dynamics will be used to investigate the ground state and anharmonic properties of MAX phases while spark plasma sintering will be used for the high-throughput synthesis of compositional variants of MAX compounds pre-screened by computations. The project addresses fundamental questions related to the compositional stability of MAX phases, the effect of composition and structure on their finite-temperature mechanical properties as well as the microscopic basis for the brittle-to-ductile transition. Understanding of the influence of chemistry on thermo-mechanical stability of these materials will enable their faster deployment in important technologies.