Twinning Studies via Experiments and DFT-Mesoscale Formulation

技术支持：该项目旨在开发一种先进材料设计的分层方法，利用最先进的工具，联合实验和理论方法。它带来了新的和清晰的洞察溶质的故障能量和孪晶成核应力的计算，不能收集从单独的介观或原子的角度来看的作用。PI已经确定，为了确定孪生的成核应力，需要评估实际原子位移所需的能量。PI计划重点关注低堆垛层错能合金、Fe-X和Fe-X-N（X=Mn、Cr、Ni）钢、Cu-Al系统，以开发顺序多尺度设计方法。这些合金的变形行为的特点是显着的孪生活动，在形核应力的变化与合金化可以是相当复杂的，需要进一步的询问。PI将基于第一性原理计算开发多组分面心立方合金的连续孪晶（异质）形核模型。PI将解决与孪晶边界相关的位置对称性的重要问题，并获得作为稳定和不稳定故障能量的函数的广义表达式。PI将决定合金化如何通过内在和/或不稳定的能量影响所得的孪晶成核应力水平。通过对具有选定取向的单晶进行实验，并结合局部应变测量，PI将以高精度建立孪生开始时的应力。这项工作的智力价值是，PI是第一个建立一个定量的孪晶应力和能量障碍之间的相关性，涉及的情况下，变形孪晶从一个理论，是植根于量子力学和介观位错理论。与以前的研究不同，PI将专注于单晶，并开发具有多尺度测量的新型数字成像技术，以通过局部应变测量来揭示孪生的细节。在过去的研究中，还没有解决复杂合金系统（如Fe-X）中的氮效应，并且通过实验PI确认理论将开发实验/理论工具，以实现该领域的重大进步，提供预测设计能力。非技术性：PI的一般方法是独特的，适用于各种各样的研究和技术兴趣的材料，而不受通常的实验和理论的限制。该项目将通过避免大型测试矩阵方法和优化试验来加速先进材料的设计。总体而言，该策略是通过连接底层物理和连续尺度而无需半经验（拟合）常数来推进一种新的材料设计建模/实验方法。该方法在材料和机械科学家的设计、教育和教学方面具有深远的影响。

TECHNICAL: This project is aimed at developing a hierarchical methodology for advanced materials design utilizing the most advanced tools in a joint experimental and theoretical approach. It brings new and clear insight into the role of solute on the fault energies and twin nucleation stress calculations that cannot be gleaned from solely mesoscopic or atomistic perspectives. PIs have established that in order to determine the nucleation stress for twinning, the energy required for the actual atom displacements needs to be evaluated. PIs plan to focus on low stacking fault energy alloys, Fe-X and Fe-X-N (X=Mn,Cr,Ni) steels, Cu-Al systems, to develop sequential multiscale design approach. The deformation behavior of these alloys is characterized by significant twinning activity, and the changes in nucleation stress with alloying can be rather complex and require further interrogation. PI will develop a continuum twin (heterogeneous) nucleation model for multicomponent fcc alloys based on first-principle calculations. PIs will address the important issues of positional symmetries associated with twin boundaries, and obtain generalized expressions as a function of stable and unstable fault energies. PIs will determine how alloying influences the resultant twin nucleation stress levels, through intrinsic and/or unstable energies. By conducting experiments on single crystals with selected orientations, and in conjunction with local strain measurements, PIs will establish the stress at the onset of twinning with a high level of precision. The intellectual merit of the work is that PIs are the first to establish a quantitative correlation between the twinning stress and energy barriers involved in case of deformation twinning from a theory that is rooted in quantum mechanics and mesoscale dislocation theory. Unlike previous studies, PIs will focus on single crystals and develop novel digital imaging techniques with multiscale measurements to unravel the details of twinning via local strain measurements. Incorporating the nitrogen effects in complex alloy systems, such as Fe-X, have not been addressed in past studies, and with confirmation of theory with experiment PIs will develop the experimental/theoretical tools for significant advancement in the field, offering predictive design abilities. NON-TECHNICAL: PIs general methodology is unique and applicable to a wide variety of materials of research and technological interest, while not suffering from usual limitations in experiment and theory. The project will accelerate the design of advanced materials by avoiding the large test matrix approach and optimization trials. Overall, the strategy is to advance a new modeling/experiment approach for design of materials by connecting the underlying physics and continuum scales without the semi-empirical (fitting) constants. The approach has far outreaching implications in design, education, and teaching of materials and mechanical scientists.