Abstract
Alloy 718 finds application in gas turbine engine components, such as turbine disks, compressor blades and so forth, due to its excellent mechanical and corrosion properties at elevated temperatures. Electron beam melting (EBM) is a recent addition to the list of additive manufacturing processes and has shown the capability to produce components with unique microstructural features. In this work, Alloy 718 specimens were manufactured using the EBM process with a single batch of virgin plasma atomized powder. One set of as-built specimens was subjected to solution treatment and ageing (STA); another set of as-built specimens was subjected to hot isostatic pressing (HIP), followed by STA (and referred to as HIP+STA). Microstructural analysis of as-built specimens, STA specimens and HIP+STA specimens was carried out using optical microscopy and scanning electron microscopy. Typical columnar microstructure, which is a characteristic of the EBM manufactured alloy, was observed. Hardness evaluation of the as-built, STA and HIP+STA specimens showed that the post-treatments led to an increase in hardness in the range of ~50 HV1. Tensile properties of the three material conditions (as-built, STA and HIP+STA) were evaluated. Post-treatments lead to an increase in the yield strength (YS) and the ultimate tensile strength (UTS). HIP+STA led to improved elongation compared to STA due to the closure of defects but YS and UTS were comparable for the two post-treatment conditions. Fractographic analysis of the tensile tested specimens showed that the closure of shrinkage porosity and the partial healing of lack of fusion (LoF) defects were responsible for improved properties. Fatigue properties were evaluated in both STA and HIP+STA conditions. In addition, three surface conditions were also investigated, namely the ‘raw’ as-built surface, the machined surface with the contour region and the machined surface without the contour region. Machining off the contour region completely together with HIP+STA led to significant improvement in fatigue performance.
Highlights
In recent years, additive manufacturing (AM) has attracted attention from the industry and from researchers globally due to its capability to manufacture complex shaped components with relative ease compared to the conventional processing routes
Electron beam melting (EBM) offers some benefits over selective laser melting (SLM), the other powder bed fusion technology, such as the capability to control the build environment using a controlled vacuum and elevated processing temperature in the build chamber which reduces the residual stresses in the built component and so forth [5]
Formation oxides of particulate oxides surface, on the deformation powder surface, powder surfaces and changes in size distribution have been observed after the recycling of powders deformation of the powder surfaces and changes in size distribution have been observed after the used in powder bed additive
Summary
Additive manufacturing (AM) has attracted attention from the industry and from researchers globally due to its capability to manufacture complex shaped components with relative ease compared to the conventional processing routes. EBM offers some benefits over selective laser melting (SLM), the other powder bed fusion technology, such as the capability to control the build environment using a controlled vacuum (minimizing the risk of oxide formation during the processing) and elevated processing temperature (approximately 1000 ◦ C for superalloys) in the build chamber which reduces the residual stresses in the built component and so forth [5]. Ti-based alloys manufactured by SLM and EBM and showed that EBM manufactured alloys exhibited superior mechanical properties (higher ductility and lower brittle phase formation) [6]. EBM is a promising processing route for the manufacturing of high-performance engineering components
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