Zafer Yunus Emre, Goel Sneha, Ganvir Ashish, Jansson Anton, Joshi Shrikant
Department of Engineering Science, University West, 461 86 Trollhättan, Sweden.
Research & Technology, Department of Process Engineering, GKN Aerospace Engine Systems AB, 461 81 Trollhättan, Sweden.
Materials (Basel). 2020 Mar 9;13(5):1226. doi: 10.3390/ma13051226.
Defects in electron beam melting (EBM) manufactured Alloy 718 are inevitable to some extent, and are of concern as they can degrade mechanical properties of the material. Therefore, EBM-manufactured Alloy 718 is typically subjected to post-treatment to improve the properties of the as-built material. Although hot isostatic pressing (HIPing) is usually employed to close the defects, it is widely known that HIPing cannot close open-to-surface defects. Therefore, in this work, a hypothesis is formulated that if the surface of the EBM-manufactured specimen is suitably coated to encapsulate the EBM-manufactured specimen, then HIPing can be effective in healing such surface-connected defects. The EBM-manufactured Alloy 718 specimens were coated by high-velocity air fuel (HVAF) spraying using Alloy 718 powder prior to HIPing to evaluate the above approach. X-ray computed tomography (XCT) analysis of the defects in the same coated sample before and after HIPing showed that some of the defects connected to the EBM specimen surface were effectively encapsulated by the coating, as they were closed after HIPing. However, some of these surface-connected defects were retained. The reason for such remnant defects is attributed to the presence of interconnected pathways between the ambient and the original as-built surface of the EBM specimen, as the specimens were not coated on all sides. These pathways were also exaggerated by the high surface roughness of the EBM material and could have provided an additional path for argon infiltration, apart from the uncoated sides, thereby hindering complete densification of the specimen during HIPing.
电子束熔炼（EBM）制造的718合金在一定程度上不可避免地会存在缺陷，这些缺陷令人担忧，因为它们会降低材料的机械性能。因此，EBM制造的718合金通常要进行后处理，以改善制成材料的性能。尽管热等静压（HIPing）通常用于封闭缺陷，但众所周知，HIPing无法封闭通向表面的缺陷。因此，在本研究中，提出了一个假设：如果对EBM制造的试样表面进行适当涂层以封装该试样，那么HIPing在修复此类与表面相连的缺陷方面可能会有效。在进行HIPing之前，使用718合金粉末通过高速空气燃料（HVAF）喷涂对EBM制造的718合金试样进行涂层，以评估上述方法。对同一涂层试样在HIPing前后的缺陷进行X射线计算机断层扫描（XCT）分析表明，一些与EBM试样表面相连的缺陷被涂层有效封装，因为它们在HIPing后被封闭。然而，这些与表面相连的缺陷中仍有一些保留了下来。此类残余缺陷的原因归因于环境与EBM试样原始制成表面之间存在相互连通的通道，因为试样并非各面都进行了涂层。除了未涂层的面之外，EBM材料的高表面粗糙度也加剧了这些通道，并且可能为氩气渗入提供了额外路径，从而在HIPing过程中阻碍了试样的完全致密化。
