The Influence of the Powder Stream on High-Deposition-Rate Laser Metal Deposition with Inconel 718

For the purpose of improving the productivity of laser metal deposition (LMD), the focus of current research is set on increasing the deposition rate, in order to develop high-deposition-rate LMD (HDR-LMD). The presented work studies the effects of the powder stream on HDR-LMD with Inconel 718. Experiments have been designed and conducted by using different powder feeding nozzles—a three-jet and a coaxial powder feeding nozzle—since the powder stream is mainly determined by the geometry of the powder feeding nozzle. After the deposition trials, metallographic analysis of the samples has been performed. The laser intensity distribution (LID) and the powder stream intensity distribution (PID) have been characterized, based on which the processes have been simulated. Finally, for verifying and correcting the used models for the simulation, the simulated results have been compared with the experimental results. Through the conducted work, suitable boundary conditions for simulating the process with different powder streams has been determined, and the effects of the powder stream on the process have also been determined. For a LMD process with a three-jet nozzle a substantial part of the powder particles that hit the melt pool surface are rebounded; for a LMD process with a coaxial nozzle almost all the particles are caught in the melt pool. This is due to the different particle velocities achieved with the two different nozzles. Moreover, the powder stream affects the heat exchange between the heated particles and the melt pool: a surface boundary condition applies for a powder stream with lower particle velocities, in the experiment provided by a three-jet nozzle, and a volumetric boundary condition applies for a powder stream with higher particle velocities, provided by a coaxial nozzle

Experimental study of porosity reduction in high deposition-rate Laser Material Deposition

For several years, the interest in Additive Manufacturing (AM) is continuously expanding, owing to the paradigm shift that new production processes, such as Laser Material Deposition (LMD), provide over conventional manufacturing technologies. With LMD, three-dimensional, complex components out of a wide range of materials can be manufactured consecutively layer-by-layer. Despite the technological advantages of the LMD process, currently achieved deposition-rates of approx. 0.5 kg/h for Inconel 718 (IN 718) remain a major concern in regards to processing times and economic feasibility. Moreover, processing conditions need to be chosen carefully or else material defects can be systematically formed either at the interface separating two adjacent clad layers, at the bonding zone or within the bulk of the layer. In this respect, the effects of powder humidity, laser power, nominal powder particle size, powder morphology and shielding gas flow rate on the porosity in laser deposited single tracks at an increased deposition-rate of approx. 2 kg/h was investigated through experiments. Based on experimental results, several approaches of reducing porosity in high deposition-rate LMD are proposed in this paper

Experimental study of effects of main process parameters on porosity, track geometry, deposition rate, and powder efficiency for high deposition rate laser metal deposition

Laser metal deposition (LMD) is an additive manufacturing process. Although much research regarding effects of process parameters on deposition quality has been conducted in recent decades, the studies in this field are still lacking for high deposition rates (>0.3 kg/h) LMD. Most of the previous investigations were based on traditional LMD process, characterized by a low deposition rate (<0.3 kg/h). This paper presents a pilot study to find the answer on the effects of main process parameters on track dimensions and process characteristics in high deposition-rate LMD. Inconel 718 (IN718) powder was used as additive material. Chemical composition, porosity, shape, and morphology of the used powder were analyzed to ensure that the necessary specifications are met. Based on a high deposition-rate LMD process, which has a deposition rate of approximately 2 kg/h, experiments were designed and carried out on a dedicated high deposition-rate LMD experimental setup. Furthermore, effects of main process parameters (laser power, scanning speed, and powder mass flow) on porosity, track geometry, deposition rate, and powder efficiency were investigated. It is found that track porosity decreases with an increase of laser powder or a decrease of powder mass flow; the consistency of cross-sectional porosity is relative poor if laser powder is insufficient or powder mass flow is excessive. The transition between substrate surface and track surface becomes smoother with increasing laser power, increasing scanning speed or decreasing powder mass flow. Deposition rate and powder efficiency keep relatively constant after a significant increase with increased laser power until a certain threshold, but they are not correlated with scanning speed. Deposition rate increases whereas powder efficiency decreases with an increase of powder mass flow

Improvement of material performance of Inconel 718 formed by high deposition-rate laser metal deposition

As precipitation hardening nickel-based super-alloy, the mechanical properties of Inconel 718 (IN718) formed by high deposition-rate LMD (HDR-LMD) are far lower than the relevant specifications, making it unable to be used in practical industry applications. With the purpose of improving its material performance, the current study has been carried out. The microstructure characteristics of the as-deposited IN718 have been analysed, and the mechanical properties of it have been tested. Based on which, reasons that result in its poor mechanical properties have been identified. Furthermore, aiming to solve these problems the methods in order to improve material performance have been studies. It is found: the poor mechanical properties of the as-deposited IN718 could be significantly improved by HIPing (Hot Isostatic Pressing) and proper heat treatments. In addition, the mechanical properties of the heat-treated material are superior to AMS specifications for IN718 fabricated by conventional manufacturing processes. It concluded: HIP can dramatically reduce the porosity of the as-deposited material; the columnar grains can be transformed to equiaxed grains by homogenization, eliminating material anisotropy; Laves phase could be dissolved by solution treatment, transforming to needle-like δ phase; strengthening phases will be precipitated by double aging, therefore strengthening/hardening the material

The Influence of the Powder Stream on High-Deposition-Rate Laser Metal Deposition with Inconel 718

For the purpose of improving the productivity of laser metal deposition (LMD), the focus of current research is set on increasing the deposition rate, in order to develop high-deposition-rate LMD (HDR-LMD). The presented work studies the effects of the powder stream on HDR-LMD with Inconel 718. Experiments have been designed and conducted by using different powder feeding nozzles—a three-jet and a coaxial powder feeding nozzle—since the powder stream is mainly determined by the geometry of the powder feeding nozzle. After the deposition trials, metallographic analysis of the samples has been performed. The laser intensity distribution (LID) and the powder stream intensity distribution (PID) have been characterized, based on which the processes have been simulated. Finally, for verifying and correcting the used models for the simulation, the simulated results have been compared with the experimental results. Through the conducted work, suitable boundary conditions for simulating the process with different powder streams has been determined, and the effects of the powder stream on the process have also been determined. For a LMD process with a three-jet nozzle a substantial part of the powder particles that hit the melt pool surface are rebounded; for a LMD process with a coaxial nozzle almost all the particles are caught in the melt pool. This is due to the different particle velocities achieved with the two different nozzles. Moreover, the powder stream affects the heat exchange between the heated particles and the melt pool: a surface boundary condition applies for a powder stream with lower particle velocities, in the experiment provided by a three-jet nozzle, and a volumetric boundary condition applies for a powder stream with higher particle velocities, provided by a coaxial nozzle

Influence of solution heat treatment on microstructure and tensile properties of Inconel 718 formed by high-deposition-rate laser metal deposition

The influence of solution heat treatment on microstructure and tensile property of Inconel 718 formed by high-deposition-rate laser metal deposition has been investigated in this paper. Two different heat treatment regimes were employed: 1100 °C × 0.5 h/WQ+720 °C × 8 h/FC to 620 °C × 8 h/AC (this type of samples is called type-S) and 1100 °C × 1 h/WQ+720 °C × 8 h/FC to 620 °C × 8 h/AC (this type of samples is called type-L). The results showed that niobium segregation and Laves phases were eliminated both in type-S and type-L samples. This means that heat treatment at 1100 °C for no more than 0.5 h is enough, if initial epitaxial columnar grains are needed and niobium segregation and Laves phases are tend to be removed. Twins only existed in type-L sample, which was the main reason why the elongation of type-L was superior to that of type-S. The fracture mechanism of these two samples was microvoids coalescence ductile rupture. The separation of the granular sub-micron particles and the γ matrix was the main nucleus of the micro-voids

Case study on AM of an IN718 aircraft component using the LMD process

11th CIRP Conference on Photonic Technologies, LANE, , 7 Sep 2020 - 10 Sep 2020; Procedia CIRP 94, 324-329 (2020). doi:10.1016/j.procir.2020.09.061 special issue: "11th CIRP Conference on Photonic Technologies [LANE 2020] / Edited by M. Schmidt, F. Vollertsen, E. Govekar