Encapsulation of Electron Beam Melting Produced Alloy 718 to Reduce Surface Connected Defects by Hot Isostatic Pressing

Abstract

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.

Additive Manufacturing of AlSi10Mg and Ti6Al4V Lightweight Alloys via Laser Powder Bed Fusion: A Review of Heat Treatments Effects

“… Lack of Fusion (LOF) pores classifying as pores: ( a ) with un-melted particles, ( b ) poor bonding defects (Adapted from references [ 95 , 96 ]). Schematic representation of the LOF formation during the L-PBF process: ( c ) lack of adequate laser scan tracks overlap; ( d ) presence of defects such as spatter.…”

Additive Manufacturing Processes in Selected Corrosion Resistant Materials: A State of Knowledge Review

“…Although hot isostatic pressing (HIP) is commonly used to close defects, it cannot close open-to-surface ones. Therefore, a possible solution could be that, if the surface of the EBM-manufactured specimen is suitably coated to encapsulate the EBMmanufactured specimen, then HIPing can be effective in healing such surface-connected defects [39]. It is remarkable that the residual properties of EBM-fabricated components are usually as good as or better than conventional cast or wrought products, even after post processing.…”

“…LOF defects are the result of an interaction of spatter particles of the material with the incident laser beam. Kim et al [39] classified two porosity types in AM-produced parts: lack-of-fusion (LOF) porosity, resulting from the interaction of spatter particles of the material with the incident laser beam, and gas porosity, (GP). LOF does not necessarily come from the interaction of spatter particles but can also result from an insufficient energy input which does not completely melt the powder bed.…”

Boriding of Laser-Clad Inconel 718 Coatings for Enhanced Wear Resistance

“…Coating technologies enable an economical alternative to traditional monolithic materials. Laser cladding as a coating process is particularly suitable for such a purpose [4,[9][10][11]. By creating a metallurgical bond between the cladding and the substrate, high adhesive strengths can be achieved.…”