通过原位EBSD和TEM加热关联揭示超细晶粒Al-Mg-Si合金中的再结晶现象
Recrystallisation phenomena in an ultrafine-grained Al-Mg-Si alloy revealed by correlative in situ EBSD and TEM heating
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中文总结 AI 辅助
研究超细晶粒Al-Mg-Si合金热稳定性，通过原位EBSD和TEM加热对比及多种方法辅助，确定再结晶起始温度，揭示晶粒细化对析出的影响，表明再结晶中晶界汇强度下降，建立原位EBSD加热为确定微观结构不稳定性的原位方法。
中文摘要 AI 辅助
超细晶粒铝合金是有前景的太空应用轻质结构材料，其热稳定性对应用很关键。传统原位透射电子显微镜（TEM）加热存在薄膜效应等问题。本文通过原位TEM加热和原位电子背散射衍射（EBSD）加热直接比较，并辅以差示扫描量热法（DSC）等研究高压扭转制备的UFG AA6061合金。原位EBSD从块状材料中采样约10³个晶粒，确定再结晶起始温度约为198°C。研究表明晶粒细化抑制GP区形成并使析出转移到更低温度，再结晶过程中晶界汇强度下降。建立了原位EBSD加热作为确定先进金属系统微观结构不稳定性的原位方法。
英文摘要
Ultrafine-grained (UFG) aluminium alloys are promising lightweight structural materials for space applications, where a high grain-boundary density can act as sinks for irradiation-induced defects. Their deployment, however, is contingent on thermal stability: aluminium components in low-Earth orbit can reach $\sim$200 $^\circ$C under solar irradiation, close to where severely deformed aluminium alloys recrystallise. Accurate, bulk-representative determination of recrystallisation onset is therefore essential, yet conventional in situ transmission electron microscopy (TEM) heating is compromised by thin-film effects, ambiguous grain-boundary contrast, and small sampling volumes. Here, a UFG AA6061 (Al-Mg-Si) alloy produced by high-pressure torsion was studied by a direct comparison of in situ TEM heating and in situ electron backscatter diffraction (EBSD) heating, complemented by differential scanning calorimetry (DSC), analytical scanning transmission electron microscopy (STEM-EDX) and microhardness. In situ EBSD sampled $\sim 10^{3}$ grains from bulk material and resolved the microstructural evolution into sequential recovery, recrystallisation and grain-growth regimes, placing the onset of instability at $\sim$198 $^\circ$C. Calorimetry, microhardness and nanoscale elemental mapping showed that grain refinement suppresses GP-zones formation and shifts precipitation to lower temperatures, with precipitation neither retarding recrystallisation nor restoring strength once the UFG structure is consumed. Revisiting the Brailsford-Bullough-Hayns sink-strength theory with a KAM-informed, temperature-dependent internal sink strength, we show that the grain-boundary sink strength collapses as recovery and recrystallisation proceed. We establish in situ EBSD heating as an in operando method for bulk-representative determination of microstructural instabilities in advanced metallic systems.
