Title : Microstructure and properties evolution of additively manufactured alloy 718
Abstract:
In this study, the laser powder bed fusion (L-PBF) and heat treatment response of a plasma atomised Alloy 718 powder is investigated using advanced characterisation techniques and mechanical testing. In particular, the study focused on the impact of different heat treatment regimes on the microstructure and mechanical properties. Initially, the investigation focuses on a detailed powder characterisation to have a comprehensive understanding on how physical (apparent and tap density, flowability, particle size distribution and morphology) and chemical properties of the powder can affect the L-PBF built quality. Following L-PBF process, samples were subjected to two different heat treatment regimes. The first heat treatment was based on the AMS5663N standard, while in the second one, an higher solution temperature assisted via the use HIP was employed. The microstructure of as-built and heat treated samples was characterised using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), electron backscatter diffraction (EBSD) to evaluate the presence of secondary phases, grain size and structure, recrystallization mechanisms and grain boundary characteristics. Following a detailed microstructure analysis, samples were subjected to SEM in-situ tensile, room and elevated temperature tensile testing, Charpy impact and fatigue testing. The results reveal that Alloy 718 processed using L-PBF exceed the AMS 5383F aerospace standard minimum specifications for both heat treatment regimes. However, the use of HIP in combination with higher solution treatment was proved beneficial in achieving a fully recrystallized microstructure with a better balance of mechanical properties due to a reduction of detrimental Laves and delta (δ) phases in the microstructure.
Audience Take Away Notes:
- The audience will get an understanding on how to characterize powder, L-PBF microstructure in as-built and heat treated condition
- How heat treatment impacts on the microstructure and mechanical properties of complex alloys such as Alloy 718
- Mechanical properties including Tensile, Charpy and Fatigue of Alloy 718. Failure mechanisms in Alloy 718 through in-situ SEM tensile testing
- The audience can apply the presented characterization techniques to assess the microstructure and properties of L-PBF materials
- Understand the potential of additive manufacturing and propose new solutions for complex-shaped parts
- General link between microstructure and materials’ properties that can be extended to a wide range of materials
- Yes, this research utilize state-of-the-art characterization facilities and technique to understand the microstructural evolution, tensile properties and failure mode, thus it would be highly valuable in research and/or teaching
- Understanding how materials’ properties can be improved through heat treatment can lead to a sharp increase in the industrialization of additive manufacturing, with consequent reduction in material waste
- Manufacturing parts through L-PBF processes would allow to manufacture much more complex geometries which would increase the design flexibility
- Extend the audience knowledge on HIP technique
- Awareness on the importance of powder characterization for L-PBF process
