Non-Isothermal Viscoplasticity in Metals

在高温下，金属在恒定的机械应力下往往会蠕变或永久变形，从而导致失效。根据在高温但恒定的温度下进行的材料测试获得的数据，通常认为工作温度越高，金属应用的寿命越短。该奖项支持基础研究，以了解随着时间的推移，温度向更高的值变化如何提高金属的蠕变性能。这些新知识将满足航空航天和发电等关键工业部门提高工作温度的需求，以提高效率并减少对环境的影响，同时不影响安全性。从这个项目的见解将最终被用于设计材料，更好地适合更高的热机械负荷。该奖项还支持一个有吸引力的教育平台，为高中，本科和研究生，包括女性和少数民族学生，通过接触STEM主题和参与实验室研究。该项目的基本假设是，在某些非等温载荷下，镍基高温合金中相之间的晶格失配在提高高温蠕变性能方面起着至关重要的作用。因此，该项目依赖于“更热可以更长”的变革范式，这取决于相干应力如何演变。为了验证这一假设，晶格失配的演变将跟踪在新的温度/应力制度下，在同步辐射下的原位X射线衍射。原位结果将被用来关联，在宏观尺度上，非等温机械响应。此外，离散位错动力学模拟将进行进一步了解位错/沉淀物的相互作用取决于微观结构状态和晶格失配。这些模拟将有助于识别和量化竞争机制，例如，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Metals tend to creep or deform permanently under constant mechanical stress at elevated temperatures leading to failure. Based on data obtained from material testing at elevated but constant temperatures, it has been generally assumed that the higher the operating temperatures the shorter the lifetime of metallic applications. This award supports fundamental research to understand how varying temperature with time towards higher values could enhance creep performance of metals. This new knowledge will address the need to increase operating temperatures in key industrial sectors, such as aerospace and electricity generation, to improve efficiency and reduce environmental impact, without compromising safety. Insights from this project will ultimately be used by metallurgists to design materials that are better suited for higher thermo-mechanical loading. This award also supports an attractive educational platform for a diverse group of high school, undergraduate and graduate students, including female and minority students, through exposure to STEM topics and participation in laboratory research.The underlying hypothesis of this project is that the lattice misfit between phases in Nickel-based superalloys under certain non-isothermal loadings plays an essential role in enhancing creep performance at elevated temperatures. The project, therefore, rests on the transformative paradigm that “hotter can be longer” depending on how the coherency stresses evolve. To test this hypothesis, the lattice misfit evolution will be tracked in new temperature/stress regimes by in situ X-ray diffraction under synchrotron radiation. In situ results will be used to correlate, at the macroscale, the non-isothermal mechanical responses. Furthermore, discrete dislocation dynamics simulations will be carried out to gain further insight into dislocation/precipitate interactions depending on the microstructural state and lattice misfit. These simulations will help identify and quantify competing mechanisms, e.g., climb/glide and self-interaction/precipitate hardening effects, which will qualitatively help explain experimental results.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.