Papers by Keyword: Inconel 718

Abstract: Laser Powder Bed Fusion (LPBF) of Inconel 718 (IN718) enables near-net-shape fabrication of complex components but is limited by narrow processing windows, crack susceptibility, and defect formation. In this work, the influence of substrate preheating on LPBF processability, densification, microstructure, and hardness of IN718 is investigated. Cuboid samples (10 × 10 × 10 mm³) were fabricated at three preheating temperatures (80 °C, 300 °C, and 500 °C), while laser power was varied between 100 W and 200 W with fixed layer thickness (30 µm) and hatch spacing (80 µm). Density was assessed using helium pycnometry and optical microscopy, while both optical and scanning electron microscopy (SEM) were used to characterize melt pool (MP) geometry, cellular substructure, cracking behavior, and oxide inclusions. Vickers hardness (HV10) measurements were performed to assess as-built mechanical response under high load of 10kg, whereas micro hardness under a load of 0.3kg was used to evaluate the hardening and/or softening phenomena occurring during LPBF processing. The results show that increasing preheating temperature significantly widens the full-density processing window, suppresses cracking, stabilizes MPs, and promotes partial in-situ ageing, leading to enhanced as-built hardness. Nevertheless, to high preheating temperatures appear to promote both the occurrence of large porosities and the formation of oxides inclusions. These findings highlight the need for preheating-aware LPBF process metrics beyond classical volumetric energy density.

Abstract: Electromechanical impedance (EMI) sensing with bonded piezoelectric patches is a compact option for structural health monitoring at high frequencies. This study evaluates the detectability of submillimeter microcracks in an Inconel 718 plate using a surface-bonded lead zirconate titanate (PZT) transducer through a finite element-based harmonic analysis. A two-dimensional coupled-field model represents a 20 × 20 × 5 mm³ plate and a PIC255 patch with an in-plane size of 10 × 10 × 0.5 mm³. The model performs a 10–100 kHz voltage sweep at 0.5 V to compute electrical resistance. Damage is introduced as circular notch-like defects with diameters of 0.25, 0.50, and 0.75 mm at nine locations that vary the sensor-to-defect distance. A mesh convergence study ensures numerical stability. Damage sensitivity is quantified using Root Mean Square Deviation (RMSD) of impedance signatures relative to the healthy baseline. Results show that frequency bands around local resonances provide the strongest separation between healthy and damaged states, with the most discriminative band observed near 54–57 kHz. RMSD increases monotonically with defect diameter and decreases with distance from the sensor, demonstrating an anisotropic positional sensitivity that is stronger along the patch axis.

Abstract: Diffusion bonded joint of Commercially Pure Aluminum (CpAl) with Inconel 718 (IN718) superalloy was investigated for its mechanical and microstructural characteristics. Diffusion Bonding (DB) of CpAl/IN718 was performed at 500 °C for 60 minutes using vacuum tube furnace in the presence Argon (Ar) gas under pressure at a heating rate of 10 °C/minutes followed by furnace cooled. The resultant joint interface was investigated by using Optical and Scanning Electron Microscopy (OM and SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), microhardness and shear strength. The microstructural analysis shows the formation of various Intermetallic Compounds (IMCs) at the bonding interface, such as NiAl_3, FeAl₂, FeAl₃, Fe₂Al₅ along with austenitic matrix, which was confirmed by XRD. Additionally, the hardness of the bonding interface was 15% and 255 higher as compared to BM of IN718 and CpAl respectively. Lastly, an average lap shear strength of 61 MPa was achieved with a joint efficiency of 84%.

Abstract: The use of coolants for cutting process in metal cutting operations is customary. Turning causes high cutting heat in nickel base super alloy Inconel 718. Nonetheless, it should be acknowledged that although flooding techniques are commonly used in the machining of super alloys, these flood cooling methods have extremely poor efficiencies. Another alternative to increase the cooling capabilities of fluids would be an internal-cooling approach that would enable to lower machining temperatures significantly. The heat dissipation ability in the tool is also greatly influenced by the micro-channel diameter of tool which further causes a significant effect on the coolant outlet velocity. A design of an internal-cooling single point cutting tool with micro channel structures for enhanced coolant heat transfer capability and reduced machining temperature is used for turning Inconel 718 under dry, flooded cooling and internal cooling to study the effects of cooling conditions on cutting force, cutting temperature and surface quality. A regression model is built using the Random Forest (RF) and Support Vector Regression (SVR) methods in machine learning framework. These models were then used to forecast input parameters, such as channel diameter and inlet pressure, which made it easier to obtain output data, such as pressure and maximum velocities at different notches. Eighty percent of the data in the dataset is used to train the model and with the remaining twenty percent set aside for evaluating the model's functionality. When comparing internal-cooling technology to traditional flood cooling, there are clear benefits including increased heat transfer efficiency, which leads to lower cutting temperatures, less cutting force, and better surface quality. More specifically, in the internal-cooling configuration, a direct relationship is shown between rising coolant inlet pressure and falling cutting force and temperature over time. Further highlighting the advantages of this cooling strategy is the relationship between increased intake pressure and decreased surface roughness.

Abstract: Manufacturing effectiveness is highly demanded in the aerospace industry; therefore, hybrid manufacturing technologies have gained considerable attention in order to overcome the limitations of a single manufacturing technology. Actually, the hybridisation of different manufacturing processes consists in taking advantage of the strengths of each process and compensating the weaknesses. In this work, the Laser Directed Energy Deposition (L-DED) process is hybridised with forging. The L-DED is an Additive Manufacturing technology which enables to add material on existing parts in order to add geometrical details or repair damaged areas. Thereby, the flexibility of the L-DED can be combined with the high-productivity and lower cost of the forging. A nickel-based superalloy employed in aeronautical applications is selected, the Inconel 718, which is suitable for high-temperature applications, such as the turbine casing of jet engines. Depending on the manufacturing process and final heat treatment, the Inconel 718 presents different properties. Hence, simulation tools are considered as a key element for the material properties characterization, where digital testing is becoming a fundamental pillar. Thermal and mechanical simulations with FEM enable the evaluation of the complete thermal history of the part and the resulting mechanical behaviour in-service conditions. In this work, the feasibility of hybridising forging and L-DED is studied. For this purpose, the resulting properties of the parts manufactured by each individual process are quantified and the interaction between both processes is analysed. Moreover, a test part is manufactured to show the hybridisation capabilities. Afterwards, to determine the behaviour of such demonstrator, a digital testing is performed by means of finite element modelling. Both thermal and structural analysis are carried out and the results obtained for the hybrid component are compared with those of an entirely forged part, focusing on a critical assessment of the performance of each manufacturing approach.

Abstract: As an increasingly mature additive manufacturing technology for metal materials, Selective Laser Melting (SLM) technology has become a hot topic in many application fields. However, due to the fast-moving velocity and small scale of the laser beam in the SLM process, it is very difficult to directly observe the microstructural changes in the SLM additive manufacturing process. In this study, a macro-micro coupled simulation model of Inconel 718 SLM process was established to study the solidification behavior of the molten pool. The macro temperature field is obtained by the finite difference method based on the birth and death grid algorithm. The local temperature intercepted from the macro temperature field is employed as the input condition for phase field microstructure calculation. Dendrite morphology, intercellular spacing, and microsegregation are simulated under the coupled model. The result shows that the solidification structure of IN718 alloy in the micro molten pool formed by SLM grows in the form of a non-flat interface. The primary dendrite spacing predicted by the simulation is in good agreement with Hunt model at the initial stage of solidification. The solute trapping caused by non-equilibrium solidification makes dendrites dissolve more Nb, resulting in microsegregation.

Abstract: The in-situ contour strategy during Laser-Powder Bed Fusion (L-PBF) process remains one of the most promising solutions to improve the poor surface quality of the parts. On the other hand, it is well established that contour step affects the formation of sub-surface defects. The aim of this work is to assess the entity of sub-surface defects during the Laser-Powder Bed Fusion of Inconel 718 samples for which different contour processing conditions are considered. Cubic samples with 10 mm side were produced through L-PBF using a Concept Laser Cusing M2 L-PBF machine. The samples were printed with fixed bulk laser parameters, adopting a layer thickness of 30 μm and a chessboard laser scanning strategy. The in-situ contour conditions were changed in terms of laser scanning speed and hatch zone border. Afterwards, the samples were analyzed in terms of surface roughness (Sa) and sub-surface density through confocal microscopy. The results revealed that the surface roughness was the most affected output as a function of the varied process parameters, including the sample position on the building platform, with values ranging from 13 to 32 μm. On the other hand, the sub-surface density was always higher than 99%.

Abstract: Additive manufactured (AM) 316L and Inconel 718 (IN718) parts using laser powder bedfusion technique and the weldability of the mixed pair by laser welding was investigated in this paper.The effect of prior heat treatment of the materials was also taken in to consideration. The motivationbehind this work was to investigate if hybrid products could be manufactured from these materials formore cost­efficient production of AM products. The results showed good reliability of the welds asthe tensile results were on par with the 316L base material. The hardness of the weld fusion zone was50 HV lower compared to the 316L base material hardness at 225 HV. In general, the results showedlaser welding is a very promising method for joining these printed materials and can be utilized asanother tool when integrating these materials into a design.

Abstract: The paper describes determining the optimal direct laser deposition mode when processing the results of a two-factor experiment by the steep ascent method. The dependence of the ultimate tensile strength on the volumetric energy density and the lateral pitch was chosen as the target function.

Abstract: This paper focuses on the laser weldability of additively manufactured (AM) Inconel 718. The experiments of this research were conducted on different series of AM Inconel 718 alloy, i.e. as­-built, heat­ treated (HT), and HT after welding, and comprehensively characterized using optical microscope and electron back scattering diffraction (EBSD). The weld morphology and microstruc­tural evolution of the fusion zone were recorded. The mechanical properties of the welded AM Inconel 718 were evaluated by tensile tests and hardness measurements. It was found that solidification crack and micropore defects are induced in the as­built AM Inconel 718. However, defect­free weld was promoted in the HT alloy. The changes in hardness profiles and tensile strength under the experimen­tal parameters were further reported. Homogenous hardness of 500 HV across the weld was obtained when HT was applied after the LW.