Abstract The processing route of the current TNM alloy (Ti-43.4Al–4Nb–1Mo-0.5B [in at %]) involves casting/HIP'ing plus forging and multiple heat treatments to achieve the required properties. This study seeks to design a modified TNM alloy with superior properties by utilising a simpler processing route, namely casting/HIP'ing plus a single-step heat treatment. The modified alloy composition was melted, cast, treated with HIP and given various heat treatments at selected temperatures near TG (gamma solvus). Images of the samples' microstructures were produced with a scanning electron microscope (SEM) and were evaluated with quantitative image analysis. Phase transformations as a function of temperature were determined using differential scanning calorimetry (DSC). These experimental results were assessed and integrated to identify a single-step heat treatment (1260 °C/1 h/30 K/min) that generates a two-phase (γ + α2) nearly fully lamellar (NFL) microstructure in the cast/HIP-treated material. The resulting FL microstructure was characterized by refined colonies consisting of irregularly arranged laths with apparently low anisotropy, which may potentially yield higher temperature mechanical properties in comparison with TNM-NL.

中文翻译：

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单步热处理硼改性铸造TNM合金层状微观结构的演变

摘要 当前 TNM 合金（Ti-43.4Al-4Nb-1Mo-0.5B [in at %]）的加工路线包括铸造/HIP'ing 加锻造和多次热处理以达到所需的性能。本研究旨在通过使用更简单的加工途径，即铸造/HIP'ing 加单步热处理，设计一种具有优异性能的改性 TNM 合金。改性合金组合物被熔化、铸造、用 HIP 处理并在接近 TG（伽马溶解线）的选定温度下进行各种热处理。样品微观结构的图像是用扫描电子显微镜 (SEM) 产生的，并通过定量图像分析进行评估。使用差示扫描量热法 (DSC) 确定作为温度函数的相变。对这些实验结果进行评估和整合，以确定在铸件中产生两相 (γ + α2) 几乎完全层状 (NFL) 微观结构的单步热处理 (1260 °C/1 h/30 K/min)。经过 HIP 处理的材料。由此产生的 FL 微观结构的特征是精细的菌落，由不规则排列的板条组成，各向异性明显较低，与 TNM-NL 相比，这可能会产生更高的温度机械性能。