Micromechanical behavior of nanostructured oxides at Very High Temperature – Experimental investigations and virtual multiscale material design

HoTMiX学术研究项目的目的是深入了解氧化物材料在极高温度下的非线性力学响应与其纳米级微观结构之间的关系。在加工或操作条件下，与高度各向异性弹性行为和热膨胀相关的固态相变（SPT）引起复杂的机械响应，仍然有待研究（并最终定制）。通过SPT的热应力的松弛导致通常涉及从晶体到晶粒尺寸跨越至少三个数量级的长度尺度的微结构的形成。实际上，相干衍射域具有几十纳米的典型尺寸，并且它们是通常几十微米的较大结晶区域的一部分。这些氧化物材料的显著特征在于相干畴内的局部应力（nm尺度）（其在GPa范围内）与本体的拉伸强度（即cm尺度）（通常仅为几十MPa）之间的巨大（三个数量级）差异。最重要的是，发生相关现象（应力积累、微裂纹和SPT）的温度范围从室温到2000 °C，因此覆盖了三个数量级。因此，我们想要解决的一般问题需要沿着三个主轴进行多尺度分析：温度，应力，尺寸。结合塑性在微观结构尺度与非常规的弹性行为，与尺寸效应，一些本质上脆性氧化物材料表现出意想不到的高顺应性。虽然这是在微观尺度上观察到的，但其起源在于纳米尺度。在纳米尺度上理解这种机械行为是HotTMiX项目的中心目标。使用几种基于X射线的先进技术（散射，衍射，折射，断层扫描）在同步辐射光束线，我们将确定这些“活氧化物材料”的微观结构演变（在非常高的温度和/或施加的应力下原位）。这是我们将在HoTMix项目中解决的主要实验挑战。微观结构和力学性能之间的关系将通过结合在非常高的温度和/或在施加的应力下的原位定量实验测量与精确的微观结构建模的基础上提交的温度和外部应力的演变虚拟但现实的微观结构进行探索。

The aim of the HoTMiX academic research project is to provide a deep understanding of the relationships between the nonlinear mechanical response of oxide materials at very high temperature and their microstructure at the nanoscale. During elaboration, or operando conditions, solid-state phase transitions (SPTs) associated with highly anisotropic elastic behavior and thermal expansion induce a complex mechanical response that still remains to be studied (and eventually tailored). Relaxation of thermal stresses through SPTs results in the formation of microstructures that usually involve length scales spanning at least three orders of magnitude from the crystal to the grain size. Indeed, coherently diffracting domains have a typical size of few tens of nanometers and they are part of larger crystalline areas of usually a few tens of micrometers. A striking feature of these oxide materials lies in the huge (three orders of magnitude) difference between local stresses within coherent domains (nm scale), which are in the GPa range, and the tensile strength of the bulk (i.e. cm scale), usually of only a few tens of MPa. On top of that, the temperature range in which relevant phenomena take place (stress build-up, microcracking, and SPTs) span from room temperature to 2000 °C, thereby covering three orders of magnitude. Therefore, the general question that we want to address requires a multiscale analysis along three main axes: temperature, stress, size. Combining plasticity at the microstructural scale with unconventional elastic behavior, related to size effects, some intrinsically brittle oxide materials exhibit an unexpected high compliance. Although this is observed at the microscale, its origin lies at the nanoscale. The understanding at the nanoscale of this mechanical behavior, is the central objective of the HoTMiX project. Using several X-ray based advanced techniques (scattering, diffraction, refraction, tomography) at synchrotron radiation beamlines, we will determine the microstructure evolution (in situ at very high temperatures and/or under applied stresses) of these “living oxide materials”. This is the main experimental challenges that we will address in the HoTMiX project. The relationship between microstructure and mechanical properties will be explored by combining in situ quantitative experimental measurements at very high temperature and/or under applied stresses with accurate microstructural modelling based on virtual but realistic microstructures submitted to temperature and external stresses evolutions.