Microstructure and morphology of Si crystals grown in pure Si and Al-Si melts

Microstructure of Al-40 wt%Si samples solidified in electromagnetic levitation furnace is studied at high melt undercooling. Primary Si with feathery and dendritic structures is observed. As this takes place, single Si crystals either contain secondary dendrite arms or represent faceted structures. Our experiments show that at a certain undercooling, there exists the microstructural transition zone of aceted to non-faceted growth. Also, we analyze the shape of dendritic crystals solidifying from liquid Si as well as from hypereutectic Al-Si melts at high growth undercoolings. The shapes of dendrite tips grown at undercoolings >100 K along the surface of levitated Al-40 wt%Si droplets are compared with pure Si dendrite tips from the literature. The dendrite tips are digitized and superimposed with theoretical shape function recently derived by stitching the Ivantsov and Brener solutions. We show that experimental and theoretical dendrite tips are in good agreement for Si and Al-Si samples.

Microstructure and Mechanical Properties of the ((CoCrFeNi)95Nb5)100−xMox High-Entropy Alloy Coating Fabricated under Different Laser Power

In this paper, the ((CoCrFeNi)95Nb5)100−xMox (x = 1, 1.5 and 2) high-entropy alloy (HEA) coatings were fabricated on the substrate of 45# steel by laser cladding process under different laser beam power. The influence of laser beam power and molybdenum element content on the microstructure and microhardness of the HEA coatings was investigated. Results show that the HEA coatings were composed of face-centered cubic (FCC) phase and Laves phase, had low porosity, and bonded well to the substrate. The Mo1 coating is composed of cellular dendritic structures and columnar dendritic structures. With the increase of molybdenum element content, the columnar dendritic structures disappeared, the grains are refined, and the arrangement of grains is more compact. The volume fraction of the interdendritic phase under the laser beam power of 800 W was small and irregular. After the laser beam power was increased to 1000 W, the volume fraction of the interdendritic phase was increased. Under the laser beam power of 1200 W, the volume fraction of the interdendritic phase was small again. Therefore, the coatings fabricated under the laser beam power of 1000 W had a larger volume fraction of the interdendritic phase and higher microhardness. With the increase in molybdenum content, the grain changed from columnar dendrite to cellular dendrite, and the microhardness of the coating increased. The characteristics of the laser cladding process, the formation of Laves phase, and the fine grain strengthening lead to high microhardness of the coatings.

Stereolithographic Additive Manufacturing of Zirconia Electrodes with Dendritic Patterns for Aluminum Smelting

Zirconia electrodes with dendritic patterns were fabricated by stereolithographic additive manufacturing (STL-AM). A solid electrolyte of yttria-stabilized zirconia (YSZ) was selected for oxygen separation in the molten salt electrolysis of aluminum smelting without carbon dioxide excretion. Thereafter, 4, 6, 8 and 12-coordinated dendritic structures composed of cylindrical lattices were designed as computer graphics. The specific surface area of each structure was maximized by changing the aspect ratio. The spatial profile and surface pressure of the hot liquid propagation in the dendrite patterns were systematically visualized by computational fluid dynamics (CFD). During the fabrication process, a photosensitive resin containing zirconia particles was spread on a substrate, and an ultraviolet (UV) laser beam was scanned to create a two-dimensional (2D) cross-section. Through layer laminations, three-dimensional (3D) objects with dendritic structures were successfully fabricated. The ceramics were obtained through dewaxing and sintering.

Hybrid Phosphorus-viologen-dendrimers as new soft nanoparticles. Design and properties.

Various dendritic structures were prepared during the last decades and their properties emphasized in a number of reviews. Among these macromolecular structures, those incorporating phosphorus units – phosphorus dendrimers –...