Dendritic Orientation Research Articles

The effect of secondary dendrite orientation on thickness debit effect of nickel-based single-crystal superalloy with tubular samples

Secondary dendrite orientation and wall thickness considerably affect the stress rupture life of thin-walled samples. However, the effect of the secondary dendrite orientation on the thickness debit effect of nickel-based single-crystal superalloys has not been thoroughly investigated until now. Owing to geometrical constraints, typical sheet samples cannot reveal the mechanism responsible for the thickness debit effect in turbine blades. This study examined the effect of secondary dendrite orientation on the thickness debit effect of nickel-based single-crystal superalloys at 1100 °C/137 MPa in tubular samples. As the wall thickness decreased from 1.5 mm to 0.3 mm, the stress rupture life decreased from approximately 170 h to 64 h, demonstrating a noticeable thickness debit effect. Among the different secondary dendrite orientation areas, the variation in plastic deformation difference increased from 7 % (1.5 mm) to 45 % (0.5 mm) and subsequently decreased to 4 % (0.3 mm). In thinner samples, the thickness contraction and microstructure evolution were more pronounced in the [100] areas than that in the [110] and [210] areas. The theoretical calculation quantitatively indicated that for the effective stress increased, the contribution of plastic deformation (45 %) was slightly lower than that of oxidation (55 %) in 0.3 mm samples; nevertheless, plastic deformation played a prominent role in 0.5, 0.8, 1, and 1.5 mm samples and increased from 61 % (0.5 mm samples) to 85 % (1.5 mm samples). In thinner samples, the larger plastic deformation in the secondary dendrite orientation of the [100] areas and oxidation increased the effective stress, resulting in a shorter rupture life. These findings are conducive to the structural optimization and performance improvement of turbine blades.

The Microstructure characteristic and Its influence on the stray grains of Nickel-based single crystal superalloys prepared by Laser directed energy deposition

The microstructure adjustment and the stray grains inhibition are important for the preparation of Nickel-based single crystal (SX) superalloys by laser directed energy deposition (L-DED). In this work, the single channel monolayer and single channel five-layers DD6 SX superalloys have been prepared by L-DED. The macroscopic simulations in the deposition processing and multiscale characterizations of deposition structure were used to analyze the formation and evolution mechanisms of unique precipitations and stray grains. Results shows that the larger laser power and higher powder feed rate have a positive impact on the epitaxial growth of columnar dendrite and the elimination of stray grains. The residual stress caused by the complex thermal cycles is not the direct reason that induce the formation of SGs, but the rapid movement of dislocations result in the formation of sub-grain boundary. According to the columnar transition to equiaxed theory (CET), temperature field simulation and analysis of element segregation behaviors, the element segregation results in the unique microstructure, include petal-shaped γ/γ′ eutectic and demarcation band with a thickness of a single γ/γ′ eutectic. Besides, the geometric size of γ/γ′ eutectic decrease with respect to the deposition height. With the change of height at deposition region, dendritic orientation deviations affect the uniformity of element segregation, resulting in variations in γ′ phase and γ/γ′ eutectic dimensions between dendritic core and the inter-dendrite zone at the microscopic level and manifesting as grain boundaries at the mesoscale. At the same time, the formation mechanisms of carbide and adjacent γ/γ′ eutectic leads to the misorientations between the dendrite core and the inter-dendrite zone, which also appears as stray grains at the mesoscopic scale.

A petavoxel fragment of human cerebral cortex reconstructed at nanoscale resolution.

To fully understand how the human brain works, knowledge of its structure at high resolution is needed. Presented here is a computationally intensive reconstruction of the ultrastructure of a cubic millimeter of human temporal cortex that was surgically removed to gain access to an underlying epileptic focus. It contains about 57,000 cells, about 230 millimeters of blood vessels, and about 150 million synapses and comprises 1.4 petabytes. Our analysis showed that glia outnumber neurons 2:1, oligodendrocytes were the most common cell, deep layer excitatory neurons could be classified on the basis of dendritic orientation, and among thousands of weak connections to each neuron, there exist rare powerful axonal inputs of up to 50 synapses. Further studies using this resource may bring valuable insights into the mysteries of the human brain.

New insights on dislocation forming mechanism of nickel-based superalloy fabricated by laser powder bed fusion

In this work, the forming mechanism of dislocation in laser powder bed fusion (LPBF) built IN738LC alloy was elucidated by studying the intrinsic relationships between the density and distribution of dislocation and the orientation and size of dendrite. The substructures with different dislocation densities and cell spacings were customized by controlling solidification conditions, and analyzed by multi-scale characterizing methods. The results show that an increase in geometrically necessary dislocation (GND) density from 1.48 × 1014 to 1.82 × 1014m−2 is accompanied by a decrease in cell spacing from 1046 nm to 640 nm as the solidification rate increases. However, the relationship between GND density and cell spacing doesn't follow Ashby's model. This indicates that GNDs are not entirely generated by thermal strain itself. On the other hand, the characterization results of cell structures show that a number of misfit dislocations are formed by the thermal strain induced deflection growth of the dendrites. These prove that the dislocations are comprehensively generated by thermal strain itself and dendritic deflection growth.

Microstructure and tribological properties of laser-cladded TiCx/TiAl composite coatings on TC4 alloy

In this study, TiC/TiAl composite coatings are prepared on TC4 substrate via laser cladding. The effect of TiC content (5, 10, 15, and 20 vol%) on the microstructure, microhardness, and wear characteristics of the coatings are investigated. The results show that the physical phases in all four coatings are mainly TiAl, Ti3Al, TiC, and Ti2AlC. The amount of rod-shaped Ti2AlC increases and the TiC dendrite orientation is weakened and significantly refined with decreasing TiC content. The hardness of the four coatings is 1.8–2.4 times that of the substrate, with the 15 vol% coating being the hardest (799 HV1.0). The wear rate of the 5 vol% coating is the lowest, 1.6 times lower than that of the substrate. This is mainly attributed to the heterogeneous structure of the coating composed of Ti-Al substrate, hard TiC particles, and self-lubricating Ti2AlC phase. The surface energy of the 5 vol% coating is the lowest, resulting in a very slight material migration from the wear surface, and the wear mechanism is micro-cutting.

Phase-field simulation for anisotropic dendrite growth in Mg-3wt.%Zn alloy

The anisotropy interfacial energy changes the growth tendency of dendrites in different directions during solidification, when the growth tendency in a specific direction appears or disappears, the transition of dendrite orientation will happen. In this study, three-dimensional simulations of anisotropic α‐Mg dendrite were conducted by changing the anisotropic interface energy in the phase field model. The variation in the preferred growth direction of equiaxed dendrite in α‐Mg was analyzed by controlling the anisotropic function of the interfaces. The changes in the growth direction of dendrites on different dendrite planes and the distribution of solute were investigated. The dendrites of α‐Mg equiaxed crystals mainly grow in ⟨112‾0⟩ and ⟨112‾3⟩ directions, and the transition of dendrite orientation depends on ⟨112‾0⟩ direction. When ⟨112‾0⟩ direction branching disappears, α‐Mg dendrite is transformed from 18 branches to 12 branches. The solute distribution at the front of the dendrite boundary changes significantly with the growth trend. Differences in the degree of solute distribution affect the solid-liquid interface and change the microstructure of the material.

Putative Cellular Identity of Dystrophic Neurites in FTLD‐TDP Type C

AbstractBackgroundApproximately 90% of individuals diagnosed with the clinical syndrome of semantic variant of primary progressive aphasia (PPA‐S) will present at autopsy with the TDP‐43 type C pathologic form of frontotemporal lobar degeneration (FTLD‐TDP‐C). FTLD‐TDP‐C is primarily characterized by the presence of TDP‐43‐immunoreactive long, thick dystrophic neurites (DNs), which tend to be found in superficial cortical layers, perpendicular to the cortical surface. The cellular identity of long DNs is not yet known. This study aims to understand the neuronal origin of DNs via colocalization of pathologic TDP with axonal and dendritic markers.MethodTwo right‐handed cases with FTLD‐TDP‐C as the sole pathologic diagnosis and a clinical diagnosis of PPA‐S were identified from the Northwestern University Alzheimer’s Disease Research Center (NU‐ADRC) brain bank. Participants were co‐enrolled in the NU PPA program, a longitudinal study of individuals with this dementia syndrome. Paraffin‐embedded sections of right inferior frontal gyrus (IFG) were fluorescently double‐stained immunohistochemically with an antibody to TDP‐43 phosphorylated at Ser 409 / 410 (pTDP) and antibodies to either phosphorylated neurofilament (pNFH) or non‐phosphorylated neurofilament (npNFH) to visualize axons or proximal dendrites, respectively. A digital image of each slide was obtained at 20X magnification using the Olympus VS200 Slide Scanner and analyzed using QuPath software (v.0.4.3).ResultIn both cases, staining revealed that a small amount (∼2%) of total DNs per section colocalize with npNFH (see Figure 1). Both long and short DNs, the latter of which are commonly apparent in other pathologic TDP subtypes (e.g., type A), demonstrated colocalization. By observation, half of colocalized DNs were oriented vertically. No DNs were found to colocalize with pNFH.ConclusionPreliminary findings suggest that DNs in FTLD‐TDP‐C may be remnants of dystrophic dendrites. The vertical orientation of colocalized DNs could reflect the orientation of apical dendrites in superficial layers of cortex. It is possible that DNs that did not colocalize with dendritic or axonal protein may be of distal dendritic origin or may reflect loss of dendritic protein in affected neurons. While it is difficult to determine the pathogenic history of DNs, these observations are promising and warrant future in‐depth investigation.

Atomistic insight into dendrite growth orientation transition in Al-Cu alloy

In this study, we investigate the impact of solid-melt interfacial energy anisotropy on the microstructure of components. Our focus is on the Al-Cu system's Al-rich side, where we compute the solid-melt interfacial free energy and its anisotropy using Molecular Dynamics (MD) simulations. Our findings reveal that, as the Cu concentration in the melt increases, the preferred dendrite growth orientation shifts from <100> to <110>. Furthermore, atomic density profile analysis shows an improvement in ordering in the (110) plane at higher Cu concentrations. Our results suggest that the transition in dendrite growth orientation is a consequence of the weakened anisotropy between (100) and (110) interfacial energies at higher Cu concentrations and undercooling temperatures. We also observe displaced atomic density profiles between Al and Cu atoms in proximity to the interface. We propose that a displaced atomic density profile between solute and solvent atoms could be a characteristic feature of systems undergoing a dendrite orientation transition.

Effect of geometry of crystalline dendrite on the uniaxial tension behavior of metallic glass matrix composites based on molecular dynamics simulations

Introducing crystalline dendrites can effectively enhance the plasticity of metallic glass matrix composites. The geometry (e.g., shape and orientation) of the crystalline dendrites can significantly influence the mechanical properties of the material. In this study, we create numerical Cu-Zr glassy samples containing crystalline dendrites of realistic geometries and study their mechanical behaviors under uniaxial tension loading through large-scale molecular dynamics simulations. The results indicate that shear band formation is sensitive to the shape and orientation of the dendrites. The geometry of the dendrites significantly affects the behavior of shear bands in the materials and ultimately leads to different tensile plasticity. This work is aimed at providing guidelines for the design of metallic glass matrix composites with complex second phase dendritic structures.

Experimental determination of solid-liquid interfacial free energy anisotropy in Al-Zn via equilibrium droplet method

The increasing Zn content causes dendrite orientation transition during solidification of Al-Zn alloys, which is supposed to be related to the change of solid-liquid interfacial energy anisotropy. In this paper, experimental measurements of the interfacial energy anisotropy were performed in Al-17, 30 and 75wt.%Zn alloys with equilibrium droplet method. Droplets shape in relation to crystal orientation and droplets morphology are obtained by Electron Back-Scatter Diffraction and X-ray Computed Tomography, respectively. The result indicates that anisotropic parameters ε1 and ε2 both decreases with increasing Zn concentration and the directions of maximum interfacial energy transform from 〈100〉 directions in Al-17wt.%Zn and Al-30wt.%Zn to 〈110〉 directions in Al-75wt.%Zn. In addition, the Wulff plot and normalized interfacial stiffness are quantified and compared with the corresponding Al-Zn dendrites orientation selection.

Dendrite Deformation in the Rejoined Platforms of Ni‐Based Single‐Crystal Superalloys

Dendrite deformation often occurs during the preparation of single‐crystal superalloy blades by directional solidification and can cause solidification defects, such as low‐angle boundaries (LABs), slivers, and orientation deviations. Continuous dendritic deformation is uncommon and its mechanisms and influencing factors are poorly understood. However, this can lead to significant orientation deviation and performance degradation. Herein, a model with rejoined platforms is designed to study the dendrite growth and orientation evolution in a rejoined platform of Ni‐based single‐crystal superalloys. It is indicated in the results that, under certain conditions, the developed secondary dendrites deform continuously near the mold wall of the rejoined platforms and the resulting disorientation has a cumulative effect. Finally, LABs and dendritic fragments appear on the rejoined platforms. Thus, the integrity of the single crystal is destroyed. This can be the result of the local shrinkage stress on the long secondary dendrites within a sufficient growth space.

A coupled domain–boundary type meshless method for phase-field modelling of dendritic solidification with the fluid flow

PurposeThis study aims to simulate the dendritic growth in Stokes flow by iteratively coupling a domain and boundary type meshless method.Design/methodology/approachA preconditioned phase-field model for dendritic solidification of a pure supercooled melt is solved by the strong-form space-time adaptive approach based on dynamic quadtree domain decomposition. The domain-type space discretisation relies on monomial augmented polyharmonic splines interpolation. The forward Euler scheme is used for time evolution. The boundary-type meshless method solves the Stokes flow around the dendrite based on the collocation of the moving and fixed flow boundaries with the regularised Stokes flow fundamental solution. Both approaches are iteratively coupled at the moving solid–liquid interface. The solution procedure ensures computationally efficient and accurate calculations. The novel approach is numerically implemented for a 2D case.FindingsThe solution procedure reflects the advantages of both meshless methods. Domain one is not sensitive to the dendrite orientation and boundary one reduces the dimensionality of the flow field solution. The procedure results agree well with the reference results obtained by the classical numerical methods. Directions for selecting the appropriate free parameters which yield the highest accuracy and computational efficiency are presented.Originality/valueA combination of boundary- and domain-type meshless methods is used to simulate dendritic solidification with the influence of fluid flow efficiently.

Microstructure characterisation of directionally solidified MnNi damping alloy under strong magnetic field

In order to reveal the effect of the magnetic field on the microstructure and the martensitic transformation of directional solidified MnNi alloy, four specimens were prepared by applying different magnetic fields during the directional solidification. The results show that the external magnetic field induces the formation of α-Mn phase, changes the orientations of dendrites as well as increases the dislocation density. The external magnetic field eliminates the fco→fct2 phase transformation and retains the fct→fcc transformation, meanwhile has little effect on the antiferromagnetic transition. The internal friction from twin boundary and phase transformation of directionally solidified MnNi alloy is 3–4 times that of as-rolled MnNi alloy, showing excellent high damping capacity in a wide temperature range.

An assistive characterized method for growth morphology and orientation of dendrites based on 3D reconstruction technique

An assistive characterized method for growth morphology and orientation of dendrites based on 3D reconstruction technique

Influence of the grain orientation and δ-ferrite on the cyclic deformation behavior of an austenitic CrNi steel manufactured by wire and arc additive manufacturing

In contrast to most additive manufacturing processes, Wire and Arc Additive Manufacturing enables the production of big metallic components, as it offers sufficient building rates and dimension limits. As the larger dimensions and higher building rates lead to other thermal conditions compared to other, more frequently used additive manufacturing processes, a sound analysis of the resulting microstructure and the corresponding mechanical properties is required. As shown in the presented work for the austenitic stainless steel X1CrNi19-9 (AISI 308L; DIN EN-ISO: 1.4316), the process-induced microstructure features textured austenite grains with intragranular δ-ferrite dendrites, both arranged in dependency with the building direction. Thus, the monotonic and cyclic deformation behavior was analyzed for three different orientations of the loading direction to the building direction, i.e., parallel (vertical), 45° and perpendicular (horizontal). The presented results reveal a strong anisotropy in elastic and plastic deformation behavior. Due to the preferential orientation of the austenite grains, the 45° orientation led to a higher stiffness, a more pronounced plastic deformability and a higher cyclic hardening potential, when compared to the other orientations. Because of this, at lower stress amplitudes the 45° orientation shows a higher fatigue life than the vertical and horizontal orientation. However, besides the texture also the grain elongation and the orientation of the δ-ferrite dendrites towards the loading direction influence the plastic deformation processes. This results in higher monotonic strength for the horizontal orientation in relation to the vertically oriented specimens.

Growth of Si particles and Al dendrites during solidification of a hypereutectic Al-Si-Cu alloy

Hypereutectic Al-Si alloys containing up to 16-20 wt% Si and often several wt% Cu are widely applied in automobile and aerospace industry, because of their high wear resistance and high-temperature resistance. The mechanical and physical properties of these alloys are strongly influenced by the size and morphology of the primary silicon particles. Here, rod-like bulk samples of hypereutectic Al-18wt%Si-10wt%Cu alloys were solidified in a Bridgman-Stockbarger furnace with different solidification parameters. Microstructure analysis of longitudinal and radial cross-sections demonstrated nearly equiaxed growth of Silicon particles in the 3D samples. At low cooling rate a few but larger Si particles exist compared to many and smaller Si particles for solidification with higher cooling rate. Also the structure of the Al dendrites is much finer at higher cooling rates. Additionally, sheet-like samples were solidified under isothermal cooling conditions. A real-time observation method using X-ray radiography allowed for the in-situ observation. During cooling down below the liquidus temperature, facetted Si particles are the first to nucleate. Reaching the nucleation temperature of Al, growth of non-facetted Al dendrites was observed simultaneously in the whole melt, generally not starting from the surface of existing Si particles. Some Al dendrites growing in the plane of the sheet-like samples develop rather rapidly in one direction, whereas other Al dendrites grow more equiaxed, which is attributed to different grain orientations of the Al-rich dendrites in quasi-2D solidification.

Sucrose Consumption during Late Adolescence Impairs Adult Neurogenesis of the Ventral Dentate Gyrus without Inducing an Anxiety-like Behavior.

Sucrose consumption impairs behavioral and cognitive functions that correlate with decreased neurogenesis in animal models. When consumed during early adolescence, this disaccharide promotes anxious and depressive behaviors, along with a reduction in the generation of new neurons in the dentate gyrus of the hippocampus. Data concerning sucrose consumption during late adolescence are lacking, and the effect of sucrose intake on the ventral dentate gyrus of the hippocampus (which modulates anxiety and depression) remains elusive. Here, we tested whether sucrose intake during late adolescence causes anxiety or impaired neurogenesis in the ventral dentate gyrus. Rats did not display anxiety-like behaviors neither at the light-dark box test nor at the open field exploration. However, there was a significant increase in proliferative cells in the subgranular zone of the ventral dentate gyrus in rats exposed to sucrose (p &lt; 0.05). This increased proliferation corresponded to neural stem cells (Radial Type 1 cells) in the group exposed to sucrose until adulthood but was not present in rats exposed to sucrose only during late adolescence. Remarkably, the phosphorylation of ERK1/2 kinases was increased in the hippocampi of rats exposed to sucrose only during late adolescence, suggesting that the increased proliferation in this group could be mediated by the MAPK pathway. On the other hand, although no differences were found in the number of immature granular neurons, we observed more immature granular neurons with impaired dendritic orientation in both groups exposed to sucrose. Finally, GAD65/67 and BCL2 levels did not change between groups, suggesting an unaltered hippocampal GABAergic system and similar apoptosis, respectively. This information provides the first piece of evidence of how sucrose intake, starting in late adolescence, impacts ventral dentate gyrus neurogenesis and contributes to a better understanding of the effects of this carbohydrate on the brain at postnatal stages.

Drosophila GSK3β promotes microtubule disassembly and dendrite pruning in sensory neurons.

The evolutionarily conserved Glycogen Synthase Kinase 3β (GSK3β), a negative regulator of microtubules, is crucial for neuronal polarization, growth and migration during animal development. However, it remains unknown whether GSK3β regulates neuronal pruning, which is a regressive process. Here, we report that the Drosophila GSK3β homologue Shaggy (Sgg) is cell-autonomously required for dendrite pruning of ddaC sensory neurons during metamorphosis. Sgg is necessary and sufficient to promote microtubule depolymerization, turnover and disassembly in the dendrites. Although Sgg is not required for the minus-end-out microtubule orientation in dendrites, hyperactivated Sgg can disturb the dendritic microtubule orientation. Moreover, our pharmacological and genetic data suggest that Sgg is required to promote dendrite pruning at least partly via microtubule disassembly. We show that Sgg and Par-1 kinases act synergistically to promote microtubule disassembly and dendrite pruning. Thus, Sgg and Par-1 might converge on and phosphorylate a common downstream microtubule-associated protein(s) to disassemble microtubules and thereby facilitate dendrite pruning.

Repetitively burst-spiking neurons in reeler mice show conserved but also highly variable morphological features of layer Vb-fated "thick-tufted" pyramidal cells.

Reelin is a large extracellular glycoprotein that is secreted by Cajal-Retzius cells during embryonic development to regulate neuronal migration and cell proliferation but it also seems to regulate ion channel distribution and synaptic vesicle release properties of excitatory neurons well into adulthood. Mouse mutants with a compromised reelin signaling cascade show a highly disorganized neocortex but the basic connectional features of the displaced excitatory principal cells seem to be relatively intact. Very little is known, however, about the intrinsic electrophysiological and morphological properties of individual cells in the reeler cortex. Repetitive burst-spiking (RB) is a unique property of large, thick-tufted pyramidal cells of wild-type layer Vb exclusively, which project to several subcortical targets. In addition, they are known to possess sparse but far-reaching intracortical recurrent collaterals. Here, we compared the electrophysiological properties and morphological features of neurons in the reeler primary somatosensory cortex with those of wild-type controls. Whereas in wild-type mice, RB pyramidal cells were only detected in layer Vb, and the vast majority of reeler RB pyramidal cells were found in the superficial third of the cortical depth. There were no obvious differences in the intrinsic electrophysiological properties and basic morphological features (such as soma size or the number of dendrites) were also well preserved. However, the spatial orientation of the entire dendritic tree was highly variable in the reeler neocortex, whereas it was completely stereotyped in wild-type mice. It seems that basic quantitative features of layer Vb-fated RB pyramidal cells are well conserved in the highly disorganized mutant neocortex, whereas qualitative morphological features vary, possibly to properly orient toward the appropriate input pathways, which are known to show an atypical oblique path through the reeler cortex. The oblique dendritic orientation thus presumably reflects a re-orientation of dendritic input domains toward spatially highly disorganized afferent projections.

Dendrite evolution and quantitative characterization of γ′ precipitates in a powder metallurgy Ni-based superalloy by different cooling rates

The effect of cooling rate after super-solvus heat treatment on the morphological evolution of γ′ precipitates in an advanced powder metallurgy Ni-based superalloy, FGH4113A, was systematically investigated. The quantitative relationship between the cooling rate and γ′ precipitates was elucidated in detail. The results showed that at cooling rates of 200 °C/min and 600 °C/min, the primary branch of dendritic γ′ grew along the< 111 > direction, whereas the secondary branch grew along the< 100 > and {111} directions. In addition to the interfacial and elastic strain energies, the width of the γ′ channel significantly impacted the evolution of the secondary dendritic orientation of γ′. As the cooling rate decreased, the size and volume fraction of the γ′ precipitates increased, whereas the nucleation density of the γ′ precipitates decreased. A strong power-law relationship between the characterization of the γ′ precipitates (such as volume fraction, nucleation density, particle size) and the cooling rate was revealed analytically. Meanwhile, the γ′ morphologies evolved from spheres to cuboids, concave cuboids, octets, and dendrites as the cooling rate decreased. The evolution mechanism and stability of γ′ precipitates were proposed to control their morphology and optimize the properties of superalloys. • The width of γ channel affected the dendrite evolution direction of γ′ secondary branches were demonstrated. • The growth mechanisms of different secondary branches of dendrite γ′ were illustrated. • The different morphology evolution paths of γ′ during cooling rates were revealed. • The power exponential relationship between d s γ ′ , d t γ ′ , f , ρ d grain boundary width and cooling rates were revealed.