Dendritic Zone Research Articles

Evaluation of Physical Microphysical Property Retrieval Algorithms During the 2020 IMPACTS Field Campaign

Abstract The NASA Investigation of Microphysics and Precipitation for Atlantic Coast Threatening Snowstorms (IMPACTS) field campaign provides high-quality, high-altitude aircraft lidar (532 nm), radar (W-band) and in-cloud microphysical aircraft data taken during wintertime storm events impacting the United States. This study evaluates two mass-dimensional relationships (Brown and Francis (1995, BF95); Heymsfield (2014, H14) and two lidar-radar microphysical retrieval algorithms (Cloudsat and CALIPSO Ice Cloud Property Product (2C-ICE); VarPy (a variational method derived from the satellite lidar-radar data community)) to estimate aircraft-retrieved volume extinction coefficient (σ), ice water content (IWC), and effective radius (re) during the 2020 IMPACTS deployment. BF95 and H14 have a close 1:1 correlation (R2 = 0.98) with in-situ observations of σ. However, only BF95 displays a linear, consistent, and almost temperature-independent low bias for IWC and re, which likely arises from the environmental conditions used to determine each. Unlike the field-campaign-derived BF95 and H14 relationships, VarPy and 2C-ICE directly ingest the aircraft-based lidar and radar data to simulate σ, IWC, and re. For all three microphysical parameters, VarPy and 2C-ICE retrieval errors became notably more pronounced around the dendritic growth zone (−15°C to −10°C) and near freezing (≥−5°C), which suggests that both algorithms experience difficulty addressing riming and aggregation processes and with larger particles (dendrites and plates) due in part to their simplified ice particle assumptions. However, the mean-melt diameter ice-particle assumption did yield more accurate IWC estimates, which led to slightly better overall results for VarPy.

Hydrogen-induced failure analysis of bimetallic clad pipes

This study investigated the mechanical properties and fracture characteristics of an alloy 825/L360 bimetallic clad pipe after it was subjected to hydrogen charging. The results indicated that the elongation loss of the pipe increased from 12.3% to 50.0% with increasing hydrogen charging time. In addition, results obtained from hydrogen microprinting and scanning Kelvin probe force microscopy indicated that the hydrogen distribution characteristics of the aforementioned material influenced the hydrogen fracture failure mechanism of the clad pipe. Specifically, carbides and TiN initiated hydrogen cracking, and crack extension occurred through brittle cracking at grain boundaries, which was caused by the interaction of hydrogen with dislocation slip bands within the dendritic zone.

Research on the effect of remelting on the epitaxial growth process of single crystal superalloy

In this paper, the remelting process is applied to Laser Directed Energy Deposition (L-DED) to repair single crystal superalloys. The main formation modes of stray grains in single crystal epitaxial growth were analyzed, and the inhibitory effect of remelting process on stray grains in single crystal epitaxial growth using L-DED was studied. Comparative experiments between remelting and non-remelting processes have been conducted. Three process parameters in the remelting process: power, z-axis lift and cladding-remelting interval time were studied. The impact of different remelting process parameters on single crystal epitaxial growth and the formation of stray grains has been studied. Remelting has been shown to effectively prevent the formation of stray grains during the solidification of the melt pool, which are otherwise caused by the presence of unmelted powder during the powder feeding phase of the L-DED process. A cladding layer without stray grains on both sides is obtained. After remelting, the epitaxial growth structure can achieve larger cellular and columnar dendritic zones and smaller primary dendrite arms. A favorable epitaxial growth structure was obtained in this paper, under the optimized remelting process window.

Heat transfer analysis in a horizontal anisotropic porous channel with Bi-viscous Bingham nanofluid and temperature-dependent Brownian diffusion

PurposeThe purpose of this article is to present a mathematical model for the fully developed flow of Bi-viscous Bingham nanofluid through a uniform-width anisotropic porous channel. The model incorporates a generalized Brinkman-Darcy formulation for the porous layers while considering the motion of nanoparticles influenced by both Brownian diffusion and thermophoresis effects.Design/methodology/approachThe similarity transformations derived through Lie group analysis are used to reduce the system from nonlinear partial differential equations to nonlinear ordinary differential equations. The finite difference method-based numerical routine bvp4c is employed to collect and graphically present the outcomes for velocity, temperature, and nanoparticle concentration profiles. The flow pattern is analyzed through streamlined plots. Furthermore, skin friction, heat, and mass transmission rates are investigated and presented via line plots.FindingsIt is observed that in anisotropic porous media, the temperature profile is stronger than in isotropic porous media. The thermal anisotropic parameter enhances the concentration profile while reducing the temperature.Practical implicationsAnisotropy arises in various industrial and natural systems due to factors such as preferred orientation or asymmetric geometry of fibers or grains. Hence, this study has applications in oil extraction processes, certain fibrous and biological materials, geological formations, and dendritic zones formed during the solidification of binary alloys.Originality/value1. The permeability and thermal conductivity are not constant; instead, they have different values in the x and y directions. 2. This study considers the dependency of thermophoresis on nanoparticle volume fraction and Brownian diffusion on the temperature in both the fluid flow equations and boundary conditions. 3. A novel similarity transformation is derived using Lie group analysis instead of using an existing transformation already available in the literature.

Influence of Alumina, Ferric Oxide, and Mn as Composites on the Properties of Recycled Aluminium Alloy

Recycling of aluminium alloys is gaining significant attention due to its economic and environmental benefits. However, close loop recycled aluminium alloys can be adversely affected by impurities and alloying elements present in the recycled feedstock. In this study, the influence of three composites, namely alumina (Al2O3), ferric oxide (Fe2O3), and manganese (Mn), on the properties of recycled aluminium taldon scraps was investigated to enhance the tensile behaviour of the alloys. The effects of these composites on the mechanical properties, microstructure, and corrosion behaviour of the recycled aluminium alloys were evaluated through experimental characterization techniques. The results showed that the addition of these composites had a significant influence on the properties of recycled aluminium alloys, providing insights into the potential for improving the performance of recycled aluminium alloys through composite additions. The addition of Al2O3 enhanced the tensile strength by 44.18 % and the variation can be attributed to the strengthening of the dendritic zones by the formation of α-Al.

Multi-scale and multi-physics simulation of central segregation in an equiaxed dendritic mushy zone during continuous casting of steel

Centreline segregation during continuous casting of steel is highly detrimental to the end-product mechanical properties. In this study, a 3D multi-scale and multi-physics model is developed and validated that directly predicts alloy segregation occurring in peritectic steel grades having centreline equiaxed grain morphology. The model consists of four models: (1) a 1D macroscale heat transfer and solidification model, (2) a 3D mesoscale dendritic solidification model, (3) a 3D mesoscale dendritic fluid flow model, and (4) a 3D mesoscale solute transport and redistribution model. The use of a mesoscale domain where the solid and liquid phases are separately discretized allows for consideration of physical phenomena affecting segregation that are classically hidden by the averaging procedures of fully continuum approaches. Thus the new model is able to account for the multiple phenomena occurring during continuous casting while also directly considering the stochastic effects resulting from grains having randomly-placed nuclei as well as interactions between the liquid and solid phases. The results demonstrate that solute partitioning combined with intra-dendritic fluid flow leads eventually to liquid channels enriched with solute that result in centreline segregation. The predicted composition in these discrete liquid channels shows excellent agreement with a Mn centreline segregation profile experimentally-measured via microscopic X-ray fluorescence of a commercially-cast steel slab. Finally, the effects of alloy composition, and soft reduction on the degree of centreline segregation are examined.

Differences in hardness and microstructure of laser cladding M2 coatings

The M2 coatings on medium carbon steel were prepared using a laser cladding process, and the microstructure and microhardness of the coatings were studied. The results show that the microhardness of the coating shows an increasing trend from the coating top to the bonding interface. The microhardness is 694 HV1 at the surface of the coating, which reaches 836 HV1 in the bottom regions of the coating. The wear rate of the coating is 0.32 mm3/N·m, which shows lower wear rate and better wear resistance. The coating microstructure is also different, and the coating consists of overlapping and non overlapping regions. The microstructure of overlapping region is a dendritic solidified crystalline structure encapsulated on α - Fe phase primary crystals with a dispersed carbide. The microstructure of non overlapping zone is composed of columnar crystal zone, basket crystal zone, and dendritic zone from the bottom of the coating to the surface, respectively, with the carbides distributed along the grain boundaries in the form of a network. Near the coating interface, needle-like high-carbon martensite forms in the coating. The carbides in the coating are relatively coarse.

Elucidating the promoting mechanism of nitrogen in the columnar-to-equiaxed transition of steel ingot

Based on the behavior of heat and mass transfer ahead of the advancing columnar front, combined with the nucleation and growth of dendrites, as well as the blocking mechanism of columnar-to-equiaxed transition (CET), the promoting mechanism of nitrogen in the CET of steel ingot was elucidated. It was found that the CET moves from the center to the edge of the ingot as the nitrogen content increases, resulting in a decrease in the columnar dendrite zone and an increase in the equiaxed dendrite zone. The occurrence of this phenomenon can be attributed to two factors. On the one hand, an increase in nitrogen content leads to an increase in critical nucleation supercooling and incubation time of dendrites, causing a decrease in the number of dendrites nucleation. Additionally, the higher nitrogen content reduces the restriction effect of solute on the growth of columnar dendrites, leading to an increase in dendrite size. On the other hand, within the constitutional supercooling (CS) zone ahead of the advancing columnar front, both the CS and temperature gradient decrease with increasing nitrogen content, while the CS increases and the temperature gradient decreases with the distance from the advancing columnar front. Consequently, the nitrogen solute primarily influences the nucleation and growth of columnar and equiaxed dendrites, as well as the length, temperature gradient, and growth restriction factor Qc of the CS zone, resulting in changes in the heat and mass transfer behavior ahead of the advancing columnar front, thereby promoting CET.

Materials characterization of Ti6Al4V to NbZr1 bimetallic structure fabricated by wire arc additive manufacturing

This study investigated the microstructures and mechanical properties of a bimetallic structure (BS) of a titanium alloy (Ti6Al4V) and a niobium alloy (NbZr1) manufactured by wire arc additive manufacturing (WAAM). Three BS thin-walls were deposited with different heat input conditions: low (180 amperes (A)), medium (200 A), and high (220 A). Microstructural characterization at the interface showed that the Niobium (Nb) diffusion on the Ti6Al4V side increased as the heat input was increased. The interfacial microstructure comprised an island area and a dendritic zone with solid solutions of (β Ti and Nb) and (α + β Ti and Nb), respectively. The hardness ranged from 99 to 367 Vickers Hardness (HV), with a considerable decrease at the interface due to the migration of Nb. Maximum ultimate tensile strength of 567 MPa was achieved for the low heat input sample, and the failure occurred at the NbZr1 side. The fractography revealed intergranular and transgranular fracture morphologies, indicating a brittle failure. The results showed that the proposed BS has a good bonding strength, and neither defects (e.g., pores and cracks) nor intermetallic compounds were observed at the interface.

Effect of Mo on high entropy Ti-Nb-Zr-Ta alloy: Phase equilibria, microstructure and mechanical properties

Thermal and mechanical properties of Ti-Nb-Ta-Zr high entropy alloys are often influenced by element content and manufacturing routes, producing significant differences between mechanical properties and microstructure. This work presents a Ti-Nb-Ta-Zr alloy in which Mo is added by adjusting the composition with phase equilibria simulation, improving the mechanical properties based on a mixture of two chemically different solid solutions (BCC1 and BCC2). The materials were produced by arc-melting suction casting. Characterization of the dendritic and interdendritic zones was carried out by means of X-ray spectroscopy, indicating the segregation of Ta and Nb in BCC1 and Zr and Ti in BCC2 phases. The dislocation density increased preferentially in the interdendritic Zr-Ti rich zones. The mechanical properties results were related to the chemical differences between the BCC1 and BCC2 lattice parameters induced by the Mo addition. With Mo segregating between both BCC cells, the resulting microstructure increased the yield strength, being confirmed with the kernel average maps, which showed that, after compression tests, the interdendritic zone accumulated a high density of dislocations, resulting in the segregation of Ti and Zr, affecting the mechanical response of Mo containing alloy.

Design of Fe36.29Cr28.9Ni26.15Cu4.17Ti1.67V2.48C0.46 HEA using a new criterion based on VEC: Microstructural study and multiscale mechanical response

The present work updated empirical parameter ranges with a high adjustment to the experimental results as obtained by the means of the exploratory data analysis (EDA) method. A new high entropy alloy with FCC structure reinforced by precipitation of intermetallic phases fabricated by vacuum-argon induction melting was designed and modeled. The main results showed that the valence electron concentration (VEC) is the predominant empirical phase prediction parameter in high entropy alloys and that the lattice packing factor is necessary to determine the presence of intermetallic phases effectively. Phase stability ranges based on VEC associated with the base crystal structures and the presence of intermetallics corroborated computationally by CALPHAD and experimentally were reported. The interdendritic zone proved to be a preferential precipitation zone with precipitates of σ, TiC, and γ' phases. The γ' phase showed a size difference between the dendritic and interdendritic zone associated with diffusive Ti mechanisms. The nanoscale mechanical response determined that dislocation creep and reinforcement in the interdendritic zone are predominant creep mechanisms that obtained an effective entanglement of the dislocations increasing the strain hardening coefficient. The mechanical response of the alloy obtained is superior to the average of the alloys with FCC structure. It maintains a high ductility that allows reaching an energy absorption and damage tolerance of 43.56 GPa% showing severe plastic slip lines being in the range of use for aerospace applications and hydrogen tanks.

Формирование биметаллического материала Ti–Al методом проволочного электронно-лучевого аддитивного производства

Currently, there is a request from aerospace and aircraft for the construction materials with sufficiently high mechanical strength, thermal creep, corrosion and oxidation resistance. The conventional alloys used for these purposes are too heavy. At the same time, alternative light materials such as Ti–Al-based alloys have many flaws, when they are produced by conventional methods. This work considers the possibility to produce the Ti–Al-based alloys by the method of a wire-feed electron-beam additive manufacturing (EBAM). We study the chemical and phase compositions, microstructure and microhardness of a bimetallic Ti–Al alloy, obtained by this method. It is found the formation of five characteristic regions between titanium and aluminum parts of the bimetallic billet. The mixing zone consists of TiAl and TiAl3 intermetallics, that is confirmed by the investigation of microstructure, chemical and phase compositions. According to XRD (X-ray diffraction) and EDS (energy-dispersive X-ray spectroscopy) analyses, it can be assumed that TiAl intermetallic prevails over TiAl3 one. The average microhardness of the mixing zone equals to 450 HV (≈4.4 GPa). This zone has developed dendritic microstructure, and even distribution of the phases without link to dendritic and inter-dendritic zones. The cracks appearing in this area are filled with the material of the upper layers, so the whole material is poreless and defect-free. Thus, the results of this work have shown a fundamental possibility to produce the intermetallic Ti–Al alloys with the use of the EBAM.

Powder-pack boronizing of CoCrFeNiAl0.5Nb0.5 HEA: Modeling of kinetics, microstructural, mechanical, and tribological characterizations

This study is dedicated to the detailed investigation of boronization kinetic, microstructural, mechanical, and wear properties of high entropy alloys (HEAs) considering their sluggish diffusion effect properties. A CoCrFeNiAl0.5Nb0.5 HEA was powder-pack boronized in the interval of 850–1050 °C for 2, 4, and 6 h in the boronizing medium containing 90 wt% of boron carbide and 10 wt% of sodium tetrafluoroborate. Boronizing of CoCrFeNiAl0.5Nb0.5 HEA was successfully produced. The obtained multi-phase boronized layers were characterized by compactness and flatness showing up inside its typical dendritic zones. The X-Ray Diffraction (XRD) studies showed the presence of ternary phases inside the boronized layers having a thickness of 4.38–92.16 µm. The nano and microhardness values were also determined and the adhesion force was analyzed through the Rockwell indentation tests. In addition, the Vickers fracture toughness values (0.46–1.83 MPa m−1/2) of the treated samples were found to be very dependent on the boronizing temperature. The wear losses have decreased due to the increase in hardness and an improvement of up to 99% has been achieved. The average diffusion coefficient model was implemented to deduce the boron activation energy in the CoCrFeNiAl0.5Nb0.5 HEAs. Finally, the predicted layers’ thicknesses were coincident with the experimental data.

Microstructure and mechanical properties during dissimilar welding of AA2060-T8 and AA6061-T6 by circular laser beam oscillations

Circular laser beam oscillations have been applied at 0.5 mm and 1 mm amplitude with four different frequencies of 30, 60, 100 and 200 Hz during dissimilar laser beam welding of 2-mm-thick heat-treated AA2060-T8 with AA6061-T6. The results have been compared with a rectilinear welding case. The width of solidified weld beads produced by laser beam oscillations is wider than that of rectilinear welding due to an increase in the area of the processed zone. Welding defects inside the fusion zone were evaluated by subjecting the joints to 100% of X-ray examination, and it was found that there was absolutely no crack and negligible level of porosity in the fusion zone. Laser beam oscillations have been applied the first time to investigate the evolution of the dendritic equiaxed zone in the central region as well as the nondendritic equiaxed zone besides the fusion line in case of 2060-T8. Optical microscopy was employed to observe the microstructure. It was found that laser beam oscillations have a significant positive impact on the microstructure both in the central region and in the vicinity of the fusion line. The inhibited ability of the formation of equiaxed dendrites due to lesser solute content has been compensated by altering the thermal conditions inside the fusion zone, and a wider equiaxed dendritic region has been achieved. In addition, the nondendritic equiaxed zone, which is undesirable during welding of aluminum–lithium alloys, has been significantly reduced in width by employing laser beam oscillations. In case of rectilinear welding, the average width of the nondendritic equiaxed zone was found to be 43 [Formula: see text]m, while the oscillatory welding reported an average width of the nondendritic equiaxed zone as low as 6 [Formula: see text]m. Enhanced fluid flow inside the melt pool and repeated interaction of the beam with the molten pool are the most probable causes of the observed results. This investigation suggests that laser beam oscillations can be successfully used to alter the microstructure and produce high-quality welds using AA 2060-T8/6061-T6 and can be replaced with conventional rectilinear laser welding for industrial applications.

A local interplay between diffusion and intraflagellar transport distributes TRPV-channel OCR-2 along C. elegans chemosensory cilia

To survive, Caenorhabditis elegans depends on sensing soluble chemicals with transmembrane proteins (TPs) in the cilia of its chemosensory neurons. Cilia rely on intraflagellar transport (IFT) to facilitate the distribution of cargo, such as TPs, along the ciliary axoneme. Here, we use fluorescence imaging of living worms and perform single-molecule tracking experiments to elucidate the dynamics underlying the ciliary distribution of the sensory TP OCR-2. Quantitative analysis reveals that the ciliary distribution of OCR-2 depends on an intricate interplay between transport modes that depends on the specific location in the cilium: in dendrite and transition zone, directed transport is predominant. Along the cilium motion is mostly due to normal diffusion together with a small fraction of directed transport, while at the ciliary tip subdiffusion dominates. These insights in the role of IFT and diffusion in ciliary dynamics contribute to a deeper understanding of ciliary signal transduction and chemosensing.

Study on shear buckling failure of laser-welded dissimilar aluminum alloy (Al-Li-2099/Al-Li-S4) stiffened panel

Laser welding of L-shaped aluminum alloy joints is of great significance in lightweight and efficient manufacturing of thin-wall reinforced aerospace structures. Shear performance is an important reference index for the structural design of aluminum alloy-reinforced panels. In this study, in-plane shear experiments of a continuous double-sided laser welded dissimilar Al-Li alloy (Al-Li-2099/Al-Li-S4) stiffened thin-walled panels were carried out. The deformation and buckling mode evolution of the stiffened panel were measured by the combination of fringe projection profilometry and strain gauge measurement. The results show that in the macroaspect, the stiffened panel first exhibits local skin buckling and then develops into overall buckling along the diagonal tensile direction. Finally, the stiffened panel shows weld desoldering failure. Metallographic examination and scanning electron microscopy were performed on the L-shaped joints at different positions of the stiffened panel. The microstructure observation shows that the weld was composed of a nondendritic equiaxed zone, a columnar dendritic zone, and an equiaxed dendritic zone. The failure mode of the weld is mainly brittle fracture with a small amount of shear dimples, indicating that the welded seam of the stiffened panel under the shear load is tensile shear coupling. After the force reaches material strength, the crack nucleates in the weld and extends along the weld until it penetrates the whole weld. This shows that the mechanical properties of the weld microstructure are closely related to the macroshear properties of the stiffened panel.

Influence of laser power on microstructure and mechanical properties of laser welded TWIP steel butted joint

The twinning-induced plasticity (TWIP) steel is a newly developed which possesses fantastic mechanical properties and high potential for anti-crash weight-optimized structural applications. In this study, the weldability of 2 mm thick TWIP steel plate by laser welding method was investigated. The welded joint exhibited fully austenitic structure, and the weld seam consisted three types of solidification structures: columnar dendrite, cellular crystal and equiaxed dendrite. The microsegregation of C and Mn elements occurred in the interdendritic regions during the solidification of the weld seam. The toughness of the heat-affected zone (HAZ) was higher than that of the weld seam. The microhardness diagram of cross-section of welded joints presented V-shaped under different laser power. The microhardness of equiaxed dendrite zone was higher than that of the weld seam and coarse grain heat affected zone (CGHAZ). The average strain and tensile strength increased first and then decreased with the rising of laser power. Further study demonstrated that the fracture of the laser welding TWIP steel joints during tensile test presented ductile mode characteristics. The results show that the appearance and performance of the welded joint are optimal with laser power of 1800 W in present study, and the tensile strength and total elongation are 915 MPa and 48%, respectively.

A Case Study of Cloud-Top Kelvin–Helmholtz Instability Waves near the Dendritic Growth Zone

Abstract Kelvin–Helmholtz instability (KH) waves have been broadly shown to affect the growth of hydrometeors within a region of falling precipitation, but formation and growth from KH waves at cloud top needs further attention. Here, we present detailed observations of cloud-top KH waves that produced a snow plume that extended to the surface. Airborne transects of cloud radar aligned with range height indicator scans from ground-based precipitation radar track the progression and intensity of the KH wave kinetics and precipitation. In situ cloud probes and surface disdrometer measurements are used to quantify the impact of the snow plume on the composition of an underlying supercooled liquid water (SLW) cloud and the snowfall observed at the surface. KH wavelengths of 1.5 km consisted of ∼750-m-wide up- and downdrafts. A distinct fluctus region appeared as a wave-breaking cloud top where the fastest updraft was observed to exceed 5 m s−1. Relatively weaker updrafts of 0.5–1.5 m s−1 beneath the fluctus and partially overlapping the dendritic growth zone were associated with steep gradients in reflectivity of −5 to 20 dBZe in as little as 500-m depths due to rapid growth of pristine planar ice crystals. The falling snow removed ∼80% of the SLW content from the underlying cloud and led to a twofold increase in surface liquid equivalent snowfall rate from 0.6 to 1.3 mm h−1. This paper presents the first known study of cloud-top KH waves producing snowfall with observations of increased snowfall rates at the surface.

Primary microstructure characterization of Co-20Ni-9Al-7W-3Re-2ti superalloy

The characterization of the primary microstructure of the new Co-based superalloy of Co-20Ni-9Al-7W-3Re-2Ti type was shown in this article. The investigated alloy was manufactured by induction melting process from pure feedstock materials. The fundamental technological problem related to Co-Al-W-X multicomponent alloys casting process is a strong susceptibility to interdendritic segregation of alloying elements, especially tungsten and rhenium. The performed analysis revealed that the observed effect of alloying elements segregation was detectable and much stronger than for Co-9Al-9W and Co-20Ni-7Al-7W alloys, related to titanium, nickel, and aluminium migration to inter-dendritic spaces. Consequently, the tungsten concentration gradient between dendritic and interdendritic zones was higher than for Co-9Al-9W and Co- 20Ni-7Al-7W alloys. The same situation was in the case of rhenium and cobalt, but Co concentration in the interdendritic zone was only slightly lower.

Macrosegregation and thermosolutal convection-related freckle formation in directionally solidified Sn–Ni peritectic alloy in crucibles with different diameters

Different from other alloys, the observation in this work on the dendritic mushy zone shows that the freckles are formed in two different regions before and after peritectic reaction in directional solidification of Sn–Ni peritectic alloys. In addition, the experimental results demonstrate that the dendritic morphology is influenced by the temperature gradient zone melting and Gibbs–Thomson effects. A new Rayleigh number (RaP) is proposed in consideration of both effects and peritectic reaction. The prediction of RaP confirms the freckle formation in two regions during peritectic solidification. Besides, heavier thermosolutal convection in samples with larger diameter is also demonstrated.