用透射菊池衍射法研究α + β钛合金中的α变体
Using transmission Kikuchi diffraction to characterise α variants in an α + β titanium alloy
摘要：
两相钛合金是高性能工程部件的重要材料，如航空发动机盘。这些合金的微观结构在热机械加工过程中进行定制，以精确控制相分离、形态和晶体取向。在双峰两相（α + β）Ti-6Al-2Sn-4 Zr-2 Mo（Ti-6242）合金中，通常需要考虑三种显微组织长度尺度：大的（~10 μm）等轴初生α;具有网篮状形貌的>200 nm厚的板状α;以及在被保留的β包围的较大α板之间生长的非常细尺度（>50 nm板厚）的次生α。在这项工作中，我们利用高空间分辨率透射菊池衍射（TKD，也称为基于透射的电子背散射衍射，t-EBSD）和基于扫描电子显微镜（SEM）的前向散射电子成像来解析Ti-6242中的编织物和二次α的结构和取向。我们分析了在一个先前的β晶粒内形成的α变体，并测试现有的相变惯习面理论是否成立。我们的分析对于理解新型双峰两相钛合金的热机械加工策略以及这些合金在复杂负载制度（如驻留疲劳）中的最终性能都很重要。我们的论文支持使用透射技术显着提高空间分辨率，结合使用传统电子反向散射衍射（EBSD）系统和前向散射检测器（FSD）成像进行基于SEM的分析，以研究现实世界工程合金的纳米结构。
英文摘要：
Two phase titanium alloys are important for high performance engineering components, such as aeroengine discs. The microstructures of these alloys are tailored during thermomechanical processing to precisely control phase factions, morphology and crystallographic orientations. In bimodal two phase (α + β) Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloys there are often three microstructural lengthscales to consider: large (~10 μm) equiaxed primary α; >200 nm thick plate α with a basketweave morphology; and very fine scaled (>50 nm plate thickness) secondary α that grows between the larger α plates surrounded by retained β. In this work, we utilise high spatial resolution transmission Kikuchi diffraction (TKD, also known as transmission based electron backscatter diffraction, t-EBSD) and scanning electron microscopy (SEM) based forward scattering electron imaging to resolve the structures and orientations of basketweave and secondary α in Ti-6242. We analyse the α variants formed within one prior β grain, and test whether existing theories of habit planes of the phase transformation are upheld. Our analysis is important in understanding both the thermomechanical processing strategy of new bimodal two-phase titanium alloys, as well the ultimate performance of these alloys in complex loading regimes such as dwell fatigue. Our paper champions the significant increase in spatial resolution afforded using transmission techniques, combined with the ease of SEM based analysis using conventional electron backscatter diffraction (EBSD) systems and forescatter detector (FSD) imaging, to study the nanostructure of real-world engineering alloys.
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