Deformation Mechanisms of Gradient Steels with High Strength and Ductility

梯度金属被设计成使得物理性质随着位置而稳定地变化。这有许多好处，但没有比同时实现增强的强度和延展性的能力更多。关于造成这一现象的机制，存在着不同的观点，但其中许多观点尚未得到证实和调和。该奖项将使用各种长度尺度的新型原位力学测试和建模相结合，以区分梯度钢微观结构中的各种变形机制。高强度高韧性梯度结构钢在核工业、石油化工和汽车工业中有着广泛的应用。本研究所获得的基本知识可普遍应用于其他强韧性结构金属材料的设计。该奖项还将支持一项广泛的教育和推广计划，包括研究生有机会在国家实验室与合作者合作，招募少数民族本科生作为实习生，并在科学博览会上指导初中和高中学生。结合剧烈塑性变形、原位微观力学测试和晶体塑性模拟，研究了显微组织梯度对钢力学行为的影响。目标是设计具有显著改善的机械强度和延展性的异质材料。该假设是，显着的晶粒粗化的细长晶粒形态来自动态再结晶和/或应力驱动的晶界迁移，这两种机制之间的切换应该是温度依赖性的。进一步的假设是，在变形机制和梯度微观结构演变的综合影响下，局部剪切软化的抑制导致强度和延展性的增加。为了验证这些假设，位错塑性为基础的理论框架相结合的塑性变形，动态再结晶，和应力驱动的晶界迁移将被开发来研究梯度微观结构。该模型将补充调查的基本变形机制，在现场张力显微镜研究在不同的温度和长度scales.This奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

Gradient metals are designed such that the physical properties change steadily with position. This has many benefits but none more than the ability to achieve enhanced strength and ductility at the same time. There are competing views regarding the mechanisms responsible for this phenomenon, but many of these views have not been validated and reconciled. This award will use a combination of novel in situ mechanical testing and modeling at various length scales to distinguish the various deformation mechanisms in gradient steel microstructures. Structurally gradient steels with high strength and ductility have broad applications in nuclear, petrochemical and automobile industries. The fundamental knowledge derived from this study may be generally applicable for the design of other strong and ductile structural metallic materials. The award will also support an extensive education and outreach plan, including the opportunity for graduate students to work with collaborators at a national laboratory, recruitment of minority undergraduate students as interns, and mentoring of middle and high school students in science fairs.The objective of this grant is to investigate, at a fundamental level, the influence of microstructure gradient on mechanical behavior of steels by integrating severe plastic deformation, in situ micromechanical testing, and crystal plasticity simulations. The goal is to design heterogeneous materials with significantly improved mechanical strength and ductility. The hypothesis is that significant grain coarsening of the elongated grain morphology arises from dynamic recrystallization and/or stress-driven grain boundary migration, and the switching between the two mechanisms should be temperature dependent. A further hypothesis is that the suppression of localized shear softening under the combined influence of deformation mechanisms and gradient microstructure evolution leads to increased strength and ductility. To test these hypotheses, a dislocation plasticity based theoretical framework combining plastic deformation, dynamic recrystallization, and stress-driven grain boundary migration will be developed to study gradient microstructures. The modeling will complement the investigation of the fundamental deformation mechanisms by in situ tension microscopy studies at various temperatures and length scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.