Effect of Substrate Bed Temperature on Solute Segregation and Mechanical Properties in Ti-6Al-4V Produced by Laser Powder Bed Fusion
Effect of Substrate Bed Temperature on Solute Segregation and Mechanical Properties in Ti-6Al-4V Produced by Laser Powder Bed Fusion
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基体床温对激光粉末床熔融Ti-6Al-4V溶质偏析和力学性能的影响
DOI：
10.1007/s11661-023-07070-4
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
Pedrazzini S
中科院分区：
文献类型：
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作者：
Pedrazzini S
由于钛合金的双相微观结构和对吸氧量的敏感性，钛合金在增材制造过程中对温度特别敏感。在本文中，激光粉末床熔融（LPBF）与100℃、570℃和770℃下的加热基体床结合使用来生产Ti-6Al-4V样品，以研究机械性能的变化和合金元素的偏析。当温度从 100 °C 升高到 570 °C 时，观察到延展性最初增加，随后在 770 °C 生产样品时延展性显着损失。一套多尺度表征技术表明，打印时的微观结构在不同温度范围内存在显着差异。在 100 °C 时，鉴定出 α+α' 相。在 a 相中广泛观察到变形孪晶，Al 和 V 在孪晶界面偏析。在 570 °C（最具延展性的样品）下，观察到 α'、α 和 β 纳米粒子，其中纠缠位错网络显示 V 偏析。在 770 °C 时，没有发现马氏体α'。显微组织为α+β显微组织，纠缠位错体积分数增加，并伴有局部V偏析。基于吉布斯自由形成能的热力学模型表明，位错处增加的 V 浓度不足以局部成核 β 相。然而，晶界处的 b 相成核（而非位错）会导致晶界钉扎，阻碍滑移并导致延展性降低。在升高的温度下打印的样品中氧含量的增加很可能也在高温脆化中发挥了关键作用。因此，构建操作最好在低于相变温度以下进行，以通过溶质分离促进强化相的生长，并且必须严格控制构建气氛以减少样品内的氧气吸收。
Titanium alloys are particularly sensitive to temperature during additive manufacturing processes, due to their dual phase microstructure and sensitivity to oxygen uptake. In this paper, laser powder bed fusion (LPBF) was used in conjunction with a heated substrate bed at 100 °C, 570 °C and 770 °C to produce specimens of Ti–6Al–4V, to investigate the change in mechanical properties and segregation of alloying elements. An initial increase in ductility was observed when increasing the temperature from 100 °C to 570 °C, followed by a significant loss in ductility when samples were produced at 770 °C. A suite of multi-scale characterisation techniques revealed that the as-printed microstructure was drastically different across the range of temperatures. At 100 °C,α+α′ phases were identified. Deformation twinning was extensively observed in the a phase, with Al and V segregating at the twin interfaces. At 570 °C (the most ductile sample),α′,αand nano-particles ofβwere observed, with networks of entangled dislocations showing V segregation. At 770 °C, no martensiticα′ was identified. The microstructure was anα+βmicrostructure and an increased volume fraction of tangled dislocations with localised V segregation. Thermodynamic modelling based on the Gibbs-free energy of formation showed that the increased V concentration at dislocations was insufficient to locally nucleateβphase. However, b-phase nucleation at grain boundaries (not dislocations) caused pinning of grain boundaries, impeding slip and leading to a reduction in ductility. It is likely that the increased O-content within specimens printed at increased temperatures also played a key role in high-temperature embrittlement. Building operations are therefore best performed below sub-transus temperatures, to encourage the growth of strengthening phasesviasolute segregation, and the build atmosphere must be tightly controlled to reduce oxygen uptake within the samples.