Powder Reuse in Electron Beam Melting Additive Manufacturing of Ti6Al4V: Particle Microstructure, Oxygen Content and Mechanical Properties
Powder Reuse in Electron Beam Melting Additive Manufacturing of Ti6Al4V: Particle Microstructure, Oxygen Content and Mechanical Properties
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DOI：
10.1016/j.addma.2020.101216
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发表时间：
2020-10-01
影响因子：
11
通讯作者：
Ramulu, M.
中科院分区：
文献类型：
--
作者：
Montelione, A.;Ghods, S.;Ramulu, M.
随着金属添加剂制造(AM)在航空航天和整形外科行业得到越来越广泛的应用，人们对提高零件质量和降低总体成本的需求越来越大。粉末原料的高成本引起了人们对在建造室内回收未熔化的粉末并在随后的建造中重复使用的兴趣。虽然随着回收和重复使用，粉末性能的下降可能会导致部分性能的下降，但这个话题得到的关注相当有限。在这项研究中，评估了Ti6Al4V金属粉末在电子束熔炼(EBM)AM中的30个构建周期的性能对横截面粉末颗粒的形态、显微结构、机械和化学变化进行了评估，并与分离的对照样品进行了比较，以了解降解机理。结果表明，随着造型室温度的升高，粉末经历了亚贝塔时效热处理和粉末再利用。根据纳米压痕硬度测量，颗粒相对于核心的近表面硬度增加(最高可达2 Gpa)。此外，着色刻蚀显示出与阿尔法涂层形成一致的氧化表面层。颗粒硬化似乎是由于粉末回收过程中氧的扩散造成的，而不是与该过程的机械方面有关的加工硬化。这些结果表明，管理/减轻金属粉末原料的氧化对提高其可重用性和延长其整体寿命具有重要意义。
As metal Additive Manufacturing (AM) becomes more widely adopted in the aerospace and orthopedic industries, there is increasing demand to improve part quality and reduce overall cost. The high cost of powder feedstock has raised interest in recovering unmelted powder in the build chamber and its reuse in subsequent builds. While degradation in powder properties with recovery and reuse can cause degradation in part properties, this topic has received rather limited attention. In this study the properties of Ti6Al4V metal powder are evaluated over 30 build cycles in Electron Beam Melting (EBM) AM. The morphological, microstructural, mechanical, and chemical changes are evaluated in cross-sectioned powder particles and compared to isolated control samples to understand the mechanisms of degradation. Results show that in response to the elevated build chamber temperature, the powder undergoes a sub-beta-transus aging heat treatment with powder reuse. Based on nanoindentation hardness measurements, the particles undergo an increase in near-surface hardness (up to 2 GPa) with respect to the core. Moreover, tint etching revealed an oxidized surface layers consistent with alpha case formation. The particle hardening appears to result from oxygen diffusion during powder recovery and not work hardening related to the mechanical aspects of that process. These results demonstrate the importance of managing/mitigating oxidation of metal powder feedstock to improve its reusability and increasing its overall lifetime.