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

非技术描述：最近，一类新的纳米碳化物和氮化物，通常被称为MAX相，由于它们结合了陶瓷(高温稳定性和强度)和金属(高导热系数和抗断裂)的一些最佳属性，作为潜在的多功能/结构材料而引起了人们的极大关注。MAX相是一类令人兴奋的、具有重要技术意义的高温材料，但仍有许多需要了解，特别是关于化学对其性能的影响，以及它们从脆性行为到延性行为的转变(在高温下)。该项目通过协同结合实验和计算机模拟来解决这一挑战。更好地了解化学和机械稳定性之间的关系，可能会使MAX阶段更快地部署在受益于更高运行温度的技术中，从而有可能开发出更可靠、更高效的发电(和推进)系统。除了对MAX阶段的科学和技术做出贡献外，该项目还支持与课程开发、K-12推广、高中教师培训、指导和促进本科生和研究生研究人员的专业培训和发展有关的活动。技术细节：该项目的总体目标是通过高通量实验和计算方法研究MAX阶段(由早期过渡金属(M)、A族元素和碳和/或氮的X组成)及其固溶体的有限温度结构和热力学性质。计算用于快速筛选材料，而高通量合成允许精细探索合金对各种MAX结构的热、机械和结构性能的影响。该项目的主要科学目标是在假设结构中M层和A层运动的非谐性驱动机械不稳定的开始的情况下，阐明导致这些材料从韧性到脆性转变的微观机制。传统的电子结构计算和从头算分子动力学将用于研究MAX相的基态和非谐性质，而放电等离子烧结将用于高通量合成通过计算预先筛选的MAX化合物的组成变体。该项目解决了与MAX相的成分稳定性、成分和结构对其有限温度力学性能的影响以及脆性-延性转变的微观基础相关的基本问题。了解化学对这些材料热机械稳定性的影响，将使它们能够更快地应用于重要技术。

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.