Directed energy deposition of 18NiM300 steel: effect of process and post processing conditions on microstructure and properties

This current study investigates the effect of Direct Energy Deposition (DED) process conditions on the properties and microstructure of M300 maraging steel samples. The investigation centers on two key factors: laser power and deposition environment. The microstructure of this tool steel is analyzed by computing the Primary Cellular Arm Spacing. The findings revealed a significant influence of both inert atmosphere and laser power on cooling conditions. These different cooling rates influence the phase content as demonstrated by X-Ray Diffraction and Electron Backscatter Diffraction measurements. It was demonstrated the presence of different content of residual austenite at cell boundaries. These distinct microstructural features caused variations in the hardness values of the printed samples. Furthermore, a direct aging heat treatment was implemented, that was chosen from Differential Scanning Calorimetry measurements results. This heat treatment proves effective in achieving consistent hardness increases and eliminated the differences among samples built in different process conditions. This outcome suggests the possibility of selecting the most economically viable DED parameters for optimal results

On the use of Areal Roughness Parameters to Assess Surface Quality in Laser Cutting of Stainless Steel with CO2 and Fiber Sources

AbstractLaser cutting provides various advantages such as high flexibility in terms of process parameters and cut material type, as well as the possibility to obtain complex geometry in different dimensions with high precision. From industrial point of view, the two more competitive laser cutting technologies are based on the use of CO2 and active fiber sources, which produce samples visually different, with non-uniform surface and different depth of the striations. The quality assessment between the two laser systems within the industry is commonly based on standard ISO 9013; that covers several aspects of quality, the most used are the surface roughness and edge perpendicularity; however 2D profilometers adopted for measures are not able to analyze the complex 3D surface topography of the cutting edge. As a result, despite the fact that the differences are visually appreciated, measured 2D roughness values of different CO2 and fiber laser cutting conditions are very similar. Recently, a greater diffusion of 3D surface profilometry devices is present. These devices allow areal surface roughness parameters to be defined, which are potentially suitable to better quantify the laser cut quality. This work points out the use of a focus-variation microscopy to acquire 3D surfaces and evaluate analytically the surface quality of laser cut edges using areal surface roughness parameters. In particular, the purpose is to define a simple and repeatable method to identify the type of cutting process analyzed through the reconstruction of surface characteristics and quality of the cut-edge. As a case study, two stainless steel samples with the same geometry obtained with different laser sources, CO2 and active, fiber is presented. For comparison purposes the cutting conditions were fixed to represent the state of the art of respective laser cutting technologies, which actually show distinct cutting edge characteristics

Accelerated Process Parameter Optimization for Directed Energy Deposition of 316L Stainless Steel

Among additive manufacturing technologies, Directed Energy Deposition (DED) processes enable the part production by melting and depositing material where needed according to a CAD design. In DED processes, a laser is focused into a narrow spot to heat a substrate, melt a portion of that and simultaneously melt powder that is being deposited into the melt pool. Traditionally, the process parameters optimization has been done by simple shape specimens fabrication followed by metallography observations. However, this process is time-consuming and expensive. In this study, a quick approach is developed to optimize the process parameters in a short period of time without wasting material. Moreover, it is shown that in the fabrication of 316L stainless steel components by DED process, apart from the process parameters, other factors such as the type of powder, powder preheating and carrier gas flow rate play important roles in the final oxide content

Directed Energy Deposition of 316L Steel: Effect of Type of Powders and Gas Related Parameters

Directed Energy Deposition is an additive manufacturing technique for manufacturing or repairing of metallic parts. A number of studies have recently demonstrated that the part quality depends on various process parameters. However, the roles of gas related parameters and type of powder are still not well understood. In the present study, the influence of carrier gas flow rate, shielding gas and type of powder on the porosity and oxide contents of the as-deposited 316L steel, produced with the optimum process parameters, is investigated. The results show that, in order to obtain a rather fully dense component, optimum carrier gas flow rate and proper shielding gas together with as-received powder should be used. Furthermore, the research outcomes indicate that the presence of shielding gas and the type of used powder are an important key point to be considered in minimizing oxides in as-deposited parts

Performance and efficiency of an industrial direct diode source with an extremely low BPP in laser cutting of Fe-based and reflective alloys

The performance and efficiency of a 2kW industrial direct diode laser source with an extremely low BPP are investigated when carbon and stainless steels as well as aluminium and brass sheetsare laser cut. The results confirm the industrial feasibility and robustness of the direct diode laser source as tool for laser processes. In particular in the oxidation laser cutting of iron-based alloys the low BPP together with relative larger transport fiber diameter allows quality and cutting speed equivalentto the active fiber and disk laser sources in a very large range of thickness (up to 15 mm). When higher power densities are required, because inert laser fusion cutting of structural steel is carried out or because high reflective alloys need to be cut, the low BPP and the shorter wavelength are favorable figures and produce comparable performances with the mentioned laser sources

Laser Cutting of Copper and Brass Alloys by High Brilliance Diode Source with an Extremely Low BPP

Copper and copper-based alloys are difficult materials to laser cut due to their high thermal conductivity, high reflectivity and tendency to lose zinc on the zone adjacent to the cut. The study explores the potential of laser cutting process of copper and brass sheets with a TeraDiode TeraBlade direct diode source whose high brilliance is given by the very low BPP and by the small fiber diameter (100 micron). Results show that it is possible to obtain good quality cuts operating with nitrogen and oxygen assist gas in the case of brass and copper alloys respectively. Moreover larger process stability, higher productivity and easier-to-cut conditions are obtained cutting brass alloys than pure copper

Single scan track analyses on aluminium based powders

Powder bed additive manufacturing technologies gained much attention in past years not only thanks to design freedom but also because of the peculiar microstructures and mechanical properties that can be obtained thanks to the extremely high cooling rate. However the phenomena that arise during the laser scanning are not yet deeply understood. In this work the effect of the main building parameters and of powder properties on the shape, the microstructure and the properties of Al-based LPBF single scan tracks was evaluated. The experiments were carried out with three different powders in order to understand of the effect of the material thermo-physical properties on the consolidation phenomena