Effect of Molten Pool Spatial Arrangement on Texture Evolution in Pulsed Laser Additive Manufacturing of Inconel 718.

The epitaxial growth of dendrites, which often results in a strong texture, is the most common phenomenon during the laser additive manufacturing process. In this study, the epitaxial growth of dendrites and texture evolution in three directions were studied by changing the z-increment, pulse period, and track offset, respectively. The influence of the molten pool interface on the growth and competition of dendrites is analyzed. Both green grains (<110> // BD) with rotated cube texture in the molten pool overlapping zones and red grains (<100> // BD) with fiber texture in the molten pool center zones coexist for different z-increment samples, forming the typical sandwich texture feature. In a short pulse period, the dendrites can grow directly epitaxially and form the strong fiber texture due to gentle interface and short distance. With the decrease of the track offset, the molten pool morphology changes from flat to narrow and deep. When θ is close to 90°, dendrites grow along the secondary dendrite arms at the overlapping zone, forming V-shape grains. This work also provides a promising method for texture customization for laser additive manufacturing.

Six Unusual Meroterpenoids from the Leaves of Psidium guajava L. and Their PTP1B Inhibitory Activities.

Six unusual meroterpenoids, psidiguajadiol A-J (1-6), and three known meroterpenoids (7-9) were isolated from the leaves of Psidium guajava L. Compounds 2-6 represent the first examples of 6/8-formyl-5,7-dihydroxy-4-phenylchromane-coupled sesquiterpenoids. The structures of the undescribed compounds, including their absolute configurations, were elucidated by spectroscopic analyses, X-ray diffraction, and computational calculations. Compounds 3, 4, and 6 exhibited inhibitory activities against PTP1B with IC50 values of 9.83, 18.52, and 16.87 µM, respectively. In light of these findings, we performed molecular docking studies to predict their inhibition mechanisms at the atomic level.

Online Stress Measurement During Laser-aided Metallic Additive Manufacturing.

In situ measurement of residual stress is a challenge, and it is a source of many defects during additive manufacturing (AM). Usually, postmortem measurement is too late to save the product once a defect appears. Most of the existing technologies are predictive simulations and postmortem analysis. However, these technologies cannot directly reflect the stress evolution during the fabrication process. This paper introduces a computer vision-based stress monitoring system combined with finite element method (FEM) technology to estimate the stress development inside of the deposition layer. The system uses a CCD camera and a line laser beam to measure the height of the melt pool and solidified layer, forms a real-time FEM model, and uses the surface displacement between the two states to calculate the stress development during the solidification process. The results show that there is no obvious shape change after solidification. The shape of the melt pool and its solid state is similar. The stress distribution obtained through online monitoring is similar to that from the traditional thermal-stress simulation.