The main objective of the present study was to understand the oxygen ingress in titanium alloys at high temperatures. Investigations reveal that the oxygen diffusion layer (ODL) caused by oxygen ingress significantly affects the mechanical properties of titanium alloys. In the present study, the high-temperature oxygen ingress behavior of TC21 alloy with a lamellar microstructure was investigated. Microstructural characterizations were analyzed through optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Obtained results demonstrate that oxygen-induced phase transformation not only enhances the precipitation of secondary α-phase (αs) and forms more primary α phase (αp), but also promotes the recrystallization of the ODL. It was found that as the temperature of oxygen uptake increases, the thickness of the ODL initially increases and then decreases. The maximum depth of the ODL was obtained for the oxygen uptake temperature of 960 °C. In addition, a gradient microstructure (αp + β + βtrans)/(αp + βtrans)/(αp + β) was observed in the experiment. Meanwhile, it was also found that the hardness and dislocation density in the ODL is higher than that that of the matrix.

中文翻译：

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层状微结构TC21合金中的氧诱导相变

本研究的主要目的是了解高温下钛合金中的氧气进入。研究表明，由氧气进入引起的氧气扩散层（ODL）显着影响钛合金的机械性能。在本研究中，研究了具有层状微结构的TC21合金的高温氧侵入行为。通过光学显微镜（OM），扫描电子显微镜（SEM），电子背散射衍射（EBSD）和透射电子显微镜（TEM）分析了微观结构特征。所得结果表明，氧诱导的相变不仅增强了次级α相（αs）的沉淀并形成了更多的初级α相（αp），而且还促进了ODL的重结晶。已经发现，随着摄氧温度的升高，ODL的厚度首先增大，然后减小。对于960°C的氧气吸收温度，获得了ODL的最大深度。另外，在实验中观察到梯度微观结构（αp+β+βtrans）/（αp+βtrans）/（αp+β）。同时，还发现ODL中的硬度和位错密度高于基体的硬度和位错密度。