CAREER: Mesoscopic Scale Phase Separation in Alloys under Sustained External Forcing

9733582 Bellon这项职业补助金用于研究和教育项目，这些项目以材料的非平衡加工为中心。研究部分检验了在持续外力作用下合金中相分离可能发生在介观尺度上的新观点，即既不是原子尺度，也不是宏观尺度，这些介观结构在稳态下是稳定的。所提出的研究目标是：(a)在受控条件下，对稳态正混合热合金在球磨过程中的成分场进行详细表征；(b)阐明合金在持续剪切作用下介观相分离稳定化的原因；(c)测试这些介观结构的现有实验结果是否可以通过具有竞争动力学的动力学模型来合理化，其中位错滑动将是迫使不混相元素混合的动力学。所选择的方法包括在受控条件下铣削Fe-Cu和Cu-Ag粉末，并使用可以解决纳米成分不均匀性的分析技术，包括首次使用原子探针和三维原子探针技术对球磨材料进行研究。原子计算机模拟和建模应该有助于理解这些强制系统。该提案的教育部分包括为研究生课程开发计算机辅助材料，使用CyberProf （Urbana Beckman Institute开发的人机界面）研究辐照下的材料；重组本科材料科学实验室，激发学生的主动性。最近，通过原子模拟在持续剪切作用下发现了正混合热金属合金中的介观相分离现象。这些发现与最近发表的实验结果一致，表明在球磨过程中，具有正混合热的合金具有复杂的动态相平衡和强的化学非均质性。本研究的动机是非平衡系统领域的快速发展，并在过去二十年中受到了广泛的关注。事实上，在许多应用中，材料在制备过程中（例如，通过球磨）或在使用过程中（例如，通过辐照），会被一些外部作用力使其偏离平衡。＊＊＊

9733582 Bellon This CAREER grant addresses research and educational programs which are centered on non-equilibrium processing of materials. The research component examines the new idea that in alloys under sustained external forcing phase separation may take place on a mesoscopic scale, i.e. a scale which is neither atomic, nor macroscopic, and these meso-structures can be stable at steady-state. The objectives of the proposed research are: (a) to perform a detailed characterization of the composition field in alloys with positive heat of mixing at steady-state during by ball milling under controlled conditions; (b) to elucidate the origin of the stabilization of mesoscopic phase separation in alloys under sustained shearing; and (c) to test whether the available experimental results on these mesostructures can be rationalized by a kinetic model with competing dynamics, where dislocation glide would be the dynamics forcing the mixing of immiscible elements. The approach chosen involves the milling of Fe-Cu and Cu-Ag powders under controlled conditions and the use of analytical techniques that can resolve nanometric composition heterogeneity, including for the first time for ball milled materials the use of atom probe and three-dimensional atom probe techniques. Atomistic computer simulations and modeling should assist in understanding of these forced systems. The educational component of the proposal consists in developing a computer-assisted material for a graduate course on materials under irradiation using CyberProf, a human- computer interface developed at the Beckman Institute in Urbana; and in reorganizing an undergraduate materials science laboratory to stimulate initiatives from the students. %%% Mesoscopic phase separations have been recently identified in metal alloys with positive heats of mixing under sustained shearing by atomistic computer simulations. These findings are consistent with the latest published experiments showing complex dy namical phase equilibria and strong chemical heterogeneity in alloys with positive heat of mixing when submitted to ball milling. This research is motivated by the fact that the field of nonequilibrium systems is in rapid development and has received much attention in the last two decades. Indeed in many applications, materials are driven away from equilibrium by some external forcing, either during their preparation (e.g., by ball milling) or during their use (e.g., by irradiation). ***