Effects of the powder, laser parameters and surface conditions on the molten pool formation in the selective laser melting of IN718

International audienceA series of single-track selective laser melting (SLM) experiments was carried out on IN718 plates with and without a powder layer and with different laser processing parameters (power and scan velocity) and surface conditions (original surface and sand blasted surface). The impacts of the powder, laser parameters, and surface conditions on the molten pool (MP) formation in SLM were systematically investigated through characterizations of the geometry of the resolidified MP, including width, depth, and area. Clear-cut correlations between the dimensions of the MP and the parameters were deduced from the measured data, such as between width/depth of the MP and the power of the laser beam, or between the area of the MP and the laser energy density. We also show that without a powder layer, an increased roughness of the surface consistently increases the MP cross-section area, whereas it has no impact for the cases with powder layer. Finally, the occurrence of defects, such as insufficient melting, unstable MP, and porosities/keyhole effect, is investigated and linked to the SLM parameters. We propose a processing map that defines the range of laser velocity and power for a defect-free solidification of the MP and the occurrence of the different types of defects

Solidification microstructure during selective laser melting of Ni based superalloy: experiment and mesoscopic modelling

International audienceA set of single track laser melting experiments was performed in a selective laser melting (SLM). The tracks were done on an Inconel 718 plate with various laser scan velocities at a constant laser power of 150 W. The geometries of the molten pool (MP), as well as the solidified dendrite structures, i.e., primary and secondary dendrite arm spacing (PDAS and SDAS), in the cross sections of the molten path were characterized to evaluate the effect of the laser scan velocity during SLM. Moreover, the local solidification thermal conditions (cooling rate R*, tip growth velocity V* and temperature gradient G*) at the MP bottom were deduced from the SDAS and the geometries of the molten pool. Finally, the mesoscopic envelope model was used to simulate the PDAS selection of the columnar dendrite growth in the molten pool. The simulated results were compared with the experimental data, and a good agreement was achieved under different laser scan velocities

Mechanical properties and microstructural study of homogeneous and heterogeneous laser welds in α, β,and α + β titanium alloys

International audienceHeterogeneous welding has been investigated for three different couples of titanium alloys: α/α + β, α/β,andα + β/β. Plates of 100 × 60 mm and 1.6 or 1.8 mm thick were welded with a Yb:YAG laser. Tensile tests show that the resistance of the heterogeneous welded specimens was generally controlled by those of the weakest material except for the α + β/β where the ultimate tensile strength was approximately equal to the average value of both materials. In every case, the elongation of the welded sample was found to be smaller than that of the base metals. The rupture generally took place outside the weld metal and was found to be most of the time located in the alloy having the lowest mechanical properties. Nevertheless, a few large-size porosities detected by tomography in the α + β/β couple could explain why rupture for these samples occurred in the weld bead. For each couple, the porosities were situated at the board between the heat-affected zone and the molten zone. EBSD maps and EDX enabled the observation of different microstructures, which could be correlated to the heterogeneous composition and diffusion into the melted bath. When the stable microstructure of one of the couple alloys is the β phase, the molten zone of the bead consists of an alternative disposition of thin layers made of large equiaxed β grains and nano-martensite α′. That is explained by the weak diffusion of the alloying elements

Novel RP-HPLC based assay for selective and sensitive endotoxin quantification

The paper presents a novel instrumental analytical endotoxin quantification assay. It uses common analytical laboratory equipment (HPLC-FLD) and allows quantifying endotoxins (ETs) in different matrices from about 109 EU / mL down to about 40 EU / mL (RSE based). Test results are obtained in concentration units (e.g. ng ET / mL), which can then be converted to commonly used endotoxin units (EU / mL) in case of known pyrogenic activity. During endotoxin hydrolysis, the endotoxin specific rare sugar acid KDO is obtained quantitatively. After that, KDO is stoichiometrically reacted with DMB, which results in a highly fluorescent derivative. The mixture is separated using RP-HPLC followed by KDO-DMB quantification with a fluorescence detector. Based on the KDO content, the endotoxin content in the sample is calculated. The developed assay is economic and has a small error. Its applicability was demonstrated in applied research. ETs were quantified in purified bacterial biopolymers, which were produced by Gram-negative bacteria. Results were compared to LAL results obtained for the same samples. A high correlation was found between the results of both methods. Further, the new assay was utilized with high success during the development of novel endotoxin specific depth filters, which allow efficient, economic and sustainable ET removal during DSP. Those examples demonstrate that the new assay has the potential to complement the animal-based biological LAL pyrogenic quantification tests, which are accepted today by the major health authorities worldwide for the release of commercial pharmaceutical products

Analytical platforms at swiss universities of applied sciences

Numerous projects and industrial and academic collaborations benefit from state-of-the-art facilities and expertise in analytical chemistry available at the Swiss Universities of Applied Sciences. This review summarizes areas of expertise in analytical sciences at the University of Applied Sciences and Arts Northwestern Switzerland (FHNW), the University of Applied Sciences and Arts Western Switzerland (HES-SO), and the Zurich University of Applied Sciences (ZHAW). We briefly discuss selected projects in different fields of analytical science

Analytical platforms at Swiss universities of applied sciences

Numerous projects and industrial and academic collaborations benefit from state-of-the-art facilities and expertise in analytical chemistry available at the Swiss Universities of Applied Sciences. This review summarizes areas of expertise in analytical sciences at the University of Applied Sciences and Arts Northwestern Switzerland (FHNW), the University of Applied Sciences and Arts Western Switzerland (HES-SO), and the Zurich University of Applied Sciences (ZHAW). We briefly discuss selected projects in different fields of analytical sciences