Abstract
In the last years, powder-based Laser Metal Deposition (LMD) has been attracting attention as a disruptive Additive Manufacturing (AM) technique for both the fabrication and restoration of Inconel 718 components, enabling to overcome current limitations faced by conventional manufacturing processes in terms of manufacturing costs, tool wear, and lead time. Nevertheless, the uncertainty related to the final mechanical performance of the as-built LMD parts limits a wider adoption of such technology at industrial level. This research work focuses on the mechanical characterization of as-built Inconel 718 specimens through split Hopkinson tensile bar tests performed at different strain rate conditions. The influence of laser power on the final mechanical behavior of the as-built tensile samples is discussed and compared with the mechanical response of as-cast ones. The as-built specimens exhibit a high internal density (i.e., 99.92% and 99.90% for 300 W and 400 W, respectively) and a more ductile behavior compared to the as-cast ones for every evaluated strain rate condition. The strain hardening capacity of the as-built samples increases with the laser power involved in the LMD process, reaching an average Yield Strength of 703 MPa for specimens realized at 400 W and tested at 800/s.
Highlights
Inconel 718 is a Ni-based Superalloy designed to endure severe operating conditions that demand significant mechanical resistance to critical dynamic loads applied under harsh working environments [1]
Despite the presence of spattering is limited, uneven single linear track (ST) edges bring to irregular single layers (SLs) formations that are detrimental for both the structural integrity and the geometrical accuracy of the metal build, inducing internal defects and uncontrolled layer formation when neighboring STs are deposited
Inconel 718 exhibits a wide processability window with respect to the range of evaluated Laser Metal Deposition (LMD) process parameters, allowing the formation of proper metal beads with deep melt pool penetration depths to be involved in the refurbishment of worn Inconel 718 components;
Summary
Inconel 718 is a Ni-based Superalloy designed to endure severe operating conditions that demand significant mechanical resistance to critical dynamic loads applied under harsh working environments [1]. The absence of cutting tools and the limited Heat Affected Zone (HAZ) generated during the deposition process allow LMD to be suitable for the manufacturing and repairing of Inconel 718 components, enabling the production of optimized and complex industrially driven geometrical shapes by means of a more efficient management and use of the raw material [5] Despite such great technological advantages, both the high thermal gradients and the rapid cooling rates involved in the LMD process have the potential to deteriorate the final quality of the as-built part, inducing internal defects (e.g., internal cracks and keyholes), undesired geometrical distortions, or detrimental residual stresses affecting both the structural integrity and the mechanical performance of the manufactured part [7]. Their research work has identified an optimized range of heat inputs suitable to realize defect-free Inconel 718 boss components exhibiting an acceptable internal porosity and no structural cracks, demonstrating the feasibility of LMD in realizing bulk Inconel 718 components on pre-existing curved surfaces
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