Twinning Studies via Experiments and DFT-Mesoscale Formulation

技术：该项目旨在开发先进材料设计的分层方法，利用最先进的工具，结合实验和理论方法。它对溶质在断层能和孪核应力计算中的作用提供了新的和清晰的认识，这些计算不能从单一的介观或原子的角度来收集。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计划将重点放在低层错能合金、Fe-X和Fe-X- n （X=Mn,Cr,Ni）钢、Cu-Al体系上，以开发顺序多尺度设计方法。这些合金的变形行为以显著的孪生活性为特征，而形核应力随合金化的变化可能相当复杂，需要进一步研究。PI将开发基于第一性原理计算的多组分fcc合金的连续孪晶（非均相）形核模型。pi将解决与孪生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函数的广义表达式。pi将决定合金如何通过固有能量和/或不稳定能量影响最终的孪核应力水平。通过对选定方向的单晶进行实验，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在于，pi是第一个从植根于量子力学和中尺度位错理论的理论中建立变形孪晶中涉及的孪晶应力和能量势垒之间的定量相关性的理论。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，通过局部应变测量来揭示孪生的细节。将氮效应纳入复杂合金体系，如Fe-X，在过去的研究中尚未得到解决，并且通过实验验证理论，pi将开发实验/理论工具，在该领域取得重大进展，提供预测设计能力。非技术：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材料，而不受通常在实验和理论方面的限制。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不需要半经验（拟合）常数，为材料设计提出一种新的建模/实验方法。该方法对材料和机械科学家的设计、教育和教学具有深远的影响。

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.