Quantitative Study of Nonequilibrium Phase Formation by Mechanical Attrition

9902435这是一个关于球磨金属粉末中非平衡相形成和稳定性的实验和模拟研究程序。最近的实验表明，相的演化和力学行为的影响之间的耦合导致了复杂的行为。为了更好地了解这一问题，定量研究了样品硬度和球磨参数对亚稳态合金有效热力学的影响。本研究选用的主要合金为镍-银。表征方法包括X射线衍射法、量热法、纳米压痕硬度测量和透射电子显微镜。利用最先进的设备，结合分析和高分辨率电子显微镜来研究纳米级成分的变化。实验结果与基于(1)有效热力学和塑性应变增强扩散模型以及(2)元素铁球磨过程中晶粒度演化的定量数据的预测结果进行了比较。这项研究对外力系统这一广泛领域的基础知识做出了贡献，与材料科学、物理、化学和其他学科相重叠。在理解球磨形成相的原子学方面有望取得重大进展。虽然球磨过程的复杂性使这一基础研究变得困难，但从相和微结构设计方面获得的知识应该会产生显著的实际效益。

9902435AtzmonThis is an experimental and modeling research program on nonequilibrium phase formation and stability in ball-milled metal powders. Recent experiments demonstrate the complex behavior that results from a coupling between the evolution of phases and effects of mechanical behavior. In order to gain greater understanding of this subject the influence of sample hardness and milling parameters on the effective thermodynamics of metastable alloys is investigated quantitatively. The main alloy selected for this study is nickel-silver. Characterization methods include x-ray diffraction, calorimetry, nanoindentation hardness measurements, and transmission electron microscopy. Nanoscale composition variations are investigated by a combination of analytical and high-resolution electron microscopy, taking advantage of state-of-the-art facilities. The experimental results are compared with predictions based on (1) models of effective thermodynamics and diffusion enhancement by plastic strain, and (2) quantitative data on grain size evolution during ball milling of elemental iron. %%%This research contributes to basic knowledge in the broad field of externally forced systems, overlapping with materials science, physics, chemistry and other disciplines. Significant progress is anticipated in understanding the atomistic aspects of phase formation by ball milling. Although the complexity of the ball milling process makes this fundamental study difficult, the knowledge derived on phase and microstructure design should result in significant practical benefit.***