Processing of inconel 718 super alloy with vacuum induction gas atomization (VIGA) and laser powder bed fusion

The present work concerns the investigation of production processes/microstructure/mechanical behavior properties of Inconel 718 superalloy samples produced by a combination of vacuum induction gas atomization (VIGA), selective laser melting (SLM) and heat treatment. In this study, scanning electron microscopy (SEM), Helium pycnometer, particle size distribution analyzer, carbon-sulfur (C-S) and oxygen-nitrogen-hydrogen (O-N-H) analysis, inductively coupled plasma optical emission spectrometry (ICP-OES) characterization, Archimedes' density measurement, optical microscope, Vickers hardness measurement and tensile test methods were used. By using Inconel 718 series super alloy raw material, laser powder bed melting (LPBF) powder with 20-45 µm particle size distribution in accordance with the SLM technology of additive manufacturing was produced with VIGA, and then physical and chemical characterization tests were carried out. With this powder group, samples for mechanical characterization were produced with the local ENAVISION-250 metal additive manufacturing SLM machine. The samples were classified as the as-built samples, solutionized and aged heat treated and recrystallization heat treated samples. At the same time, mechanical tests were applied together with microstructural examinations to observe the effects of heat treatment. In this context, it is aimed to create a material data sheet for Inconel 718 with the Enavision-250 SLM machine by determining the optimum process parameter set for each sample group of the variable laser power parameters used in sample production with SLM. Chemical characterization analyzes with C-S, O-N-H and ICP-OES to detect whether there is a change in the chemical content of Inconel 718 ingots despite any potential reaction or contamination risks during and/or after atomization. No change was found in the results with the analyzes. Besides, the morphology of the powder, which is another important factor in the processability of Inconel 718 powder with SLM, was investigated; it has been understood that the powder is completely close to spherical, and a relatively satelliteless powder is produced. The density of the powder was measured at the level of 99.6%, and the Hausner ratio, was calculated as 1.08 and it was determined that the powder showed an excellent flow/layability ability, and it was determined by SEM, Helium pycnometer, tapped density/apparent densities measurement, respectively. Microstructural and mechanical evaluations are made on the samples, which have been subjected to as-built, solutionizing-aging and recrystallization heat treatments, Inconel 718 powders atomized with VIGA. Single-line scanning, tensile test samples and cube-shaped samples were produced with SLM. Herein, when the melt pool continuities were evaluated with optical microscope images and single-line scanning, it was observed that the laser powers that exhibited the most smooth and uninterrupted scanning performance were 350W and 430W. According to tensile tests, the highest yield stress was reached with 370W in the sample group as-built, with 370W in the sample group with solutionizing-aging heat treatment, and with 350W in the recrystallized samples. The highest tensile stress was reached with 390W in the sample group as-built, with 390W in the sample group with solutionizing-aging heat treatment, and with 430W in the sample group that underwent recrystallized samples. Within the scope of the study, it was determined that the elongation values of the samples with solution-aging heat treatment at elongation% values were below the expectations with the related optical microscopy examinations, especially at the grain boundaries, and the δ phase showed notch effect at high temperatures due to its sharp-edged morphology, crack growth The highest elongation% values were reached with 350W in the sample group as-built, with 390W in the sample group with solution-aging heat treatment, and with 430W in the sample group with recrystallization heat treatment. According to Vickers hardness measurement, the highest hardness value was reached with 350W in the sample group as-built, with 350W in the sample group with solutionizing-aging heat treatment, and with 370W in the heat treatment. With Archimedes' density measurements, the maximum density level was reached with 350W in the sample group as-built, with 390W in the sample group with solution-aging heat treatment, and with 370W in the recrystallization heat treatment samples. With these results, it has been determined that the optimum laser power is 350W for the as-built samples produced with variable laser powers in the material data sheet, which is aimed to be created by determining the optimum process parameters for the LPBF Inconel 718 with the local Enavision-250 metal additive manufacturing SLM machine, with solution taking-aging heat treatment. It has been concluded that the parameter set can be preferred according to the mechanical properties requested according to the application area of 350W for the samples and LPBF Inconel 718 for the recrystallization heat treated sample group.