Columnar Pattern Research Articles

Comparison of Electroplated Ni and PVD Ni Coating Layers after Soft Soldering Process

This work is part of a publicly funded project called ReffiMaL (resource efficient material solutions for power electronics), which aims to substitute electroplated Nickel (Ni) as contact material in power electronic modules. The baseplates of these power electronic modules are based on the metal matrix composite material AlSiC, which needs to be coated to become solderable. Today, it is state-of-the-art technology to coat the baseplate with electroplated Ni to form an adhesive layer to the system solder. In this paper we present a performance comparison of physical vapor deposited (PVD) Ni and electroplated Ni. The main advantage of PVD Ni is a significant reduction of layer thickness compared to the electroplating process. Second advantage of PVD Ni is the limitation of the deposition to areas that get soldered, in contrast to a non-selective electroplated coating. When deposited by PVD at room temperature, Ni exhibits columnar growth patterns, whereas electroplated Ni tends to form a laminar layer. The columnar growth leads to an increase in interface area affecting phase formation behavior. To compare both adhesion layers, we investigate the phase formation after soldering with a Sn based soft solder-copper composite material. The baseplates are reflow-soldered at different temperatures and process times. Temperature varied between 270°C and 400°C. The corresponding process time ranged from 10 to 40 minutes. We inspect the samples optically to determine the phase formation. Intermetallic phase (IMP) composition is evaluated using energy dispersive X-ray analysis (EDX). ReffiMaL is funded by the German Federal Ministry of Education and Research (BMBF).

Falling film flow of [EMIm]Ac ionic liquid aqueous solution on horizontal tubes considering the Marangoni effect

Experiments on falling film flow with a 60 wt% [EMIm]Ac (1-ethyl-3-methylimidazolium acetate) aqueous solution on cooled/heated horizontal tubes were conducted using an infrared thermal imaging camera to investigate the effect of Marangoni flow on the flow pattern and film width. The thermal stability of the [EMIm]Ac ionic liquid and the dependence of viscosity and surface tension on the temperature were presented. The physics of film flows with the Marangoni effect on horizontal tubes was analyzed. It is evidenced that the Marangoni effect exists on horizontal tubes and has significant influence on the falling film flow pattern and film width. When the film was heated, the film contracted and exhibited a sheet flow pattern, whereas a columnar pattern was observed under isothermal conditions. When the film was cooled, the film expanded and the columnar flow pattern was retained but with an increase in number of columns. Compared to the pure water, the average spreading film width with the 60 wt% [EMIm]Ac aqueous solution was narrower by approximately 20.1% and 9.8% at a liquid flow rate of 0.2473 kg m−1 s−1 as the film was cooled and heated, respectively.

Optical intrinsic signal imaging with optogenetics reveals functional cortico-cortical connectivity at the columnar level in living macaques

Despite extensive research on primate cognitive function, understanding how anatomical connectivity at a neural circuit level relates to information transformation across different cortical areas remains primitive. New technology is needed to visualize inter-areal anatomical connectivity in living monkeys and to tie this directly to neurophysiological function. Here, we developed a novel method to investigate this structure-function relationship, by combining optical intrinsic signal imaging (OISI) with optogenetic stimulation in living monkeys (opto-OISI). The method involves expressing channelrhodophsin-2 in one area (source) followed by optical imaging of optogenetic activations in the other area (target). We successfully demonstrated the potential of the method with interhemispheric columnar projection patterns between V1/V2 border regions. Unlike the combination of optogenetics and functional magnetic resonance imaging (opto-fMRI), opto-OISI has the advantage of enabling us to detect responses of small clusters of neurons, even if the clusters are sparsely distributed. We suggest that opto-OISI can be a powerful approach to understanding cognitive function at the neural circuit level, directly linking inter-areal circuitry to fine-scale structure and function.

Effect of Ni Content on Double-Target Co-sputtered CrNiN Coatings

Double-target co-sputtered CrNiN coatings were deposited by DC-pulsed magnetron reactive sputtering. The nickel content increases from 0.7 to 5.0 at.% with the increased Ni target current from 0.10 to 0.40 A. The influence of Ni content on preferred orientation and properties of CrNiN coatings was investigated. The results show that the doped Ni enters CrN to form (Cr,Ni)N solid solution. CrNiN coatings are mainly composed of CrN phase and demonstrate CrN(111) preferred orientation. All the coatings present columnar growth pattern. And the less obvious the preferred orientation, the more intense competitive growth, the less sufficient the columnar growth, the finer the columnar crystal and the denser the microstructure. In spite of the most dense structure with finest grains, the hardness of CrNiN coating containing 0.7 at.% Ni is the lowest. The hardness is affected by multiple effects of preferred orientation, grain size, solid solution strengthening, morphology and stress, especially the intensity degree of preferred orientation.

Numerical Modelling and Effects of Reinforcement Addition on the Microstructural Evolution of Additive Manufactured Ti-6Al-4V Alloy

Abstract Ti-6Al-4V alloy possesses extensive usage and unique properties, but its poor hardness and susceptibility to fail by galling under conditions of sliding contact or fretting and poor tribological behaviour in terms of large and unstable friction coefficient have limited its industrial applications. The microstructure of these alloys is highly influenced by processes involving plastic deformation and thermal treatments which, in effect, determines the mechanical properties adhering to desired properties. Direct laser metal deposition (DLMD) technique can be used to address the limitations associated with titanium alloy. This is mostly achieved by integration of reinforcement materials into the main matrix to form coating. Thereby inducing microstructural changes to the material.The morphology and also the hardness property of the various composite coatings were examined. Strong metallurgical bond without pores and cracks were observed between the coating and the substrate. Grain refinement was observed within the microstructure as the grains grew in a columnar and dendritic pattern in a counter direction to heat flow. Nevertheless, further results revealed that addition of titanium and copper brought transformation to the microstructure of Al-Cu-Ti coatings from a dendritic structure to a flower-like microstructure. Therefore, the coating exhibited a defect free, refined microstructure with significantly improved micro-hardness due to formation of various intermetallics. COMSOL Multiphysics was used to model the temperature distribution within the melt pool.

Influence Of Rapid Solidification And Optimized Laser Parameters Relationship On The Geometrical And Hardness Properties Of Ti-Al-Cu Coatings

Abstract The development of laser based advanced coatings are continually implemented in order to meet the desired demands and performances of materials in industries. This research paper focuses on the effect of hybrid coating of Ti-Al-Cu on a grade five titanium alloy (Ti-6Al-4V) using laser metal deposition (LMD) process at different laser process parameters. The evolution of the microstructure during the cyclic cooling and heating of the titanium alloy was ascertained by taking the thermal transient measurements which had occurred during the deposits of the layer built.The rates of cooling for the deposited Ti-6Al-4V/Ti-Al-Cu coating was studied to ascertain the influence that the processing parameters had on the morphology during the solidification process. an analysis was conducted that included the ascertaining of the solid-state transmutation which had occurred with the titanium alloy and the microstructural transformation of the Ti-Al-Cu which had occurred during the solidification process. The microstructure and elemental and phase composition of coatings were studied. Ti-6Al-4V/Ti-Al-Cu composites were analyzed using optical microscopy, scanning electron microscopy (SEM) with energy dispersive microscopy (EDS), and x-ray diffraction (XRD). Moreover, the relationships were observed of the factors that governed the microstructural evolution resulting from the processing rates of solidification with the process build parameters from the direct energy deposition laser-based process of Ti-6Al-4V/Ti-Al-Cu composite. The results obtained for the titanium alloy based on microscopy observation revealed that in all subsequent deposits, the microstructure was martensitic and needle-like in structure. Grain refinement was observed within the microstructure as the grains grew in a columnar and dendritic pattern in a counter direction to heat flow. Existence of amorphous phase revealed via XRD was also observed in the coatings. Finally, it was observed that the fast cooling rate (at 1.2 m/min) resulted in fine dendritic microstructure. When the scanning speed was increased, it resulted in longer but finer grains due to decreased energy density to the previously deposited layer, therefore the thickness of the layers was decreased. The Geometry of the coatings was influenced by the interplay of laser power, scanning speed, powder feed rate and melt pool size.

Influence of rotational speed on structure, mechanical and electrical properties of TiC/GLC composite films

In this work, magnetron sputtering deposition facility was performed to fabricate TiC/graphite-like carbon (denoted as GLC) composite films. The microstructure and element composition of the as-fabricated TiC/GLC composite films were analyzed by field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Moreover, the influence of rotational speeds of specimen holder on microstructure, mechanical, and electrical properties of the as-prepared TiC/GLC composite films were systemically investigated. Results indicate that the microstructures of TiC/GLC composite films experience the transition from layered growth pattern to columnar growth pattern with increasing rotational speed. The transmission electron microscope characterizations show that multilayered microstructure was self-organized in the TiC/GLC composite film deposited at rotational speed of 5°/s. The TiC crystallite embedded in carbon networks composite structure dominates the films with other rotational speeds. The TiC/GLC film with multilayered structure has lower internal stress and higher adhesion to the substrate compared to composite structure. The mechanical and electrical measurement results demonstrate that the nano-hardness and conductivity are enhanced owing to formation of high content of hard and conductive TiC phase embed in the carbon networks nanostructure in TiC/GLC composite films. Meanwhile, the growth mechanisms of TiC/GLC composite films at different rotational speeds are also proposed. The excellently electrical and mechanical properties indicate that the GLC/TiC composite film possesses widespread potential as transducers for biosensors in biology and carbonaceous electrode materials.

Static and dynamic comprehensive response of additively manufactured discrete patterns of Ti6Al4V

Additively manufactured (AM) discrete patterns made of Ti6Al4V offer potential energy absorption for engineering applications, including blast and impact protection systems, aircraft structure, automotive, and medical applications. In this study, we compared three different cylindrical printed patterns fabricated by selective laser melting (SLM), patterns sharing similar cross section and mass, in order to identify the "optimal" design of such structures for energy absorption purposes. The specimens consist of one columnar and two tubular patterns. The columnar pattern (8-Column) was constructed out of uniformly distributed columns. The first tubular pattern (Tube I) was constructed with the same outer diameter and tapered inner profile. The second tubular pattern (Tube II) had adjusted internal and external diameters. Quasi-static and impact (dynamic) load tests were performed to investigate the strain rate dependency, compressive response and failure mode of each pattern, including a comparison with a printed solid reference cylinder. Numerical simulations were carried out to complement the experimental work and to develop a generic numerical tool for future structural optimization applications. The results show that the geometry has a strong influence on its overall compressive performance, including energy absorption. The most effective of the patterns investigated was Tube I for both quasi-static and dynamic regimes.

Microstructure, precipitates and hardness of selectively laser melted AlSi10Mg alloy before and after heat treatment

The microstructure and precipitates within selectively laser melted (SLM) AlSi10Mg alloys in the as-built state and after T6 heat treatment were examined and correlated to the hardness evolution. The as-built alloy exhibited columnar patterns perpendicular to the build-direction and fish-scale pattern along the build-direction originating from the melt pool. The microstructure consisted of fine Al cells and eutectic structure with up to 4 μm in size. Tiny needle-like Si particles with highly faulted structure were identified within the Al cells and formed semi-coherent interface with the matrix. Nanoscale Si particles and π-Al8Si6Mg3Fe phase were observed to segregate along the cell and grain boundary. Solution heat treatment (SHT) at 520 °C resulted in the dissolution of Al cellular microstructure. Precipitation and coarsening of the Si particles occurred, while the aspect ratio of Si particles remained nearly constant. The π-Al8Si6Mg3Fe phase decomposed into plate-shaped β-Al5SiFe. The artificial aging (AA) at 160 °C did not alter the microstructure but led to the formation of metastable Mg2Si precipitates. The GP zones and β″ were identified through transmission electron microscopy after AA of 6 h, and β″ existed up to AA of 24 h. The hardness decreased after SHT due to the coarsening of the microstructure and reduced solid solution hardening. Hardness reached maximum magnitude after AA of 6–10 h due to the precipitation hardening, and remained relatively unchanged up to AA of 24 h. Microstructure and/or hardness of gas atomized powders and bulk cast AlSi10Mg alloys were also examined as references.

A Theory of How Columns in the Neocortex Enable Learning the Structure of the World.

Neocortical regions are organized into columns and layers. Connections between layers run mostly perpendicular to the surface suggesting a columnar functional organization. Some layers have long-range excitatory lateral connections suggesting interactions between columns. Similar patterns of connectivity exist in all regions but their exact role remain a mystery. In this paper, we propose a network model composed of columns and layers that performs robust object learning and recognition. Each column integrates its changing input over time to learn complete predictive models of observed objects. Excitatory lateral connections across columns allow the network to more rapidly infer objects based on the partial knowledge of adjacent columns. Because columns integrate input over time and space, the network learns models of complex objects that extend well beyond the receptive field of individual cells. Our network model introduces a new feature to cortical columns. We propose that a representation of location relative to the object being sensed is calculated within the sub-granular layers of each column. The location signal is provided as an input to the network, where it is combined with sensory data. Our model contains two layers and one or more columns. Simulations show that using Hebbian-like learning rules small single-column networks can learn to recognize hundreds of objects, with each object containing tens of features. Multi-column networks recognize objects with significantly fewer movements of the sensory receptors. Given the ubiquity of columnar and laminar connectivity patterns throughout the neocortex, we propose that columns and regions have more powerful recognition and modeling capabilities than previously assumed.

The Effect of Base Pressure on Crystal Structure and Microstructure of CrN Thin Film Deposited by Reactive Magnetron Sputtering

The CrN thin films were deposited using reactive magnetron sputtering by varying base pressure to investigate the crystal structure, microstructure and composition of thin film. In this work, the films properties were characterized by XRD, FE-SEM and EDX techniques. The crystal structures were obtained the cubic of CrN with the crystal size between 23.23 – 28.25 nm and lattice parameters a = b = c = 4.142 - 4.160 Å. The XRD results indicated that the growth of preferred orientation was changed from (200) to (111) plane with increased the base pressure. The surface morphology of CrN thin films did not affected from base pressure. The thickness of CrN thin films which obtained from cross section analysis was decreased from 1788 to 1745 nm by varying the base pressure. The columnar pattern acccompany with the dense structure were investigated from the cross-section analysis. The Cr composition was substantly decreased whereas theN2 composition were increased which observed from EDX technique.

Influence of Al2O3 content on crystallization behaviors of blast furnace slags in directional solidification process

Focusing on the heat recovery of BF slag by dry granulation technology, an improved directional solidification method combines with X-ray diffraction (XRD) is promoted to explore the influence of Al2O3 content on crystallization behaviors of BF slags in a phase-change cooling process. In the current research, the crystallization process is on real-time reflected by the temperature distribution inside the slag. Moreover, the type and content evolutions of crystal phase were obtained by analyzing the XRD patterns. Furthermore, Scanning Electron Microscope (SEM) was adopted to investigate the morphology evolution of the crystal phase. The results indicated that with an increase in Al2O3 content, the primary crystal structure transformed from Akermanite to Gehlenite. Moreover, the transformation of the crystal structure led to a decrease of critical cooling rate and an increase in critical supercooling degree. Furthermore, the crystal phase precipitated in a varying temperature interval, which was governed by the average cooling rate and primary crystal structure. In addition, the growth mode of the crystal phase transformed from columnar pattern to equiaxed pattern with a decrease in average cooling rate. Furthermore, the transformational cooling rate of growth mode decreased with increasing the Al2O3 content.

Optimization of functional MRI for detection, decoding and high-resolution imaging of the response patterns of cortical columns

The capacity of functional MRI (fMRI) to resolve cortical columns depends on several factors. These include the spatial scale of the columnar pattern, the point-spread of the fMRI response, the voxel size, and the signal-to-noise ratio (SNR) considering thermal and physiological noise. However, it remains unknown how these factors combine, and what is the voxel size that optimizes fMRI of cortical columns.Here we combine current knowledge into a quantitative model of fMRI of realistic patterns of cortical columns with different spatial scales and degrees of irregularity. We compare different approaches for identifying patterns of cortical columns, including univariate and multivariate based detection, multi-voxel pattern analysis (MVPA) based decoding, and high-resolution imaging and reconstruction of the pattern of cortical columns. We present the dependence of the performance of each approach on the parameters of the imaged pattern as well as those of the data acquisition. In addition, we predict voxel sizes that optimize fMRI of cortical columns under various scenarios.We found that all measures associated with multivariate detection and decoding could be approximately calculated from a measure we termed “multivariate contrast-to-noise ratio” (mv-CNR), which is a function of the contrast-to-noise ratio (CNR) and number of voxels. Furthermore, mv-CNR implied that the optimal voxel width for detection and decoding is independent of changes in response amplitude, SNR and imaged volume that are not caused by changes in voxel size.For regular patterns, optimal voxel widths for detection, decoding and imaging/reconstructing the pattern of cortical columns were approximately half the main cycle length of the organization. Optimal voxel widths for irregular patterns were less dependent on the main cycle length, and differed between univariate detection, multivariate detection and decoding, and reconstruction. We compared the effects of different factors of Gradient Echo fMRI at 3 Tesla (T), Gradient Echo fMRI at 7T, and Spin-Echo fMRI at 7T on the detection, decoding, and reconstruction measures considered and found that in all cases the width of the fMRI point-spread had the most significant effect. In contrast, different response amplitudes and noise characteristics played a relatively minor role. We recommend specific voxel widths for optimal univariate detection, for multivariate detection and decoding, and for high-resolution imaging of cortical columns under these three data-acquisition scenarios. Our study supports the planning, optimization, and interpretation of high-resolution fMRI of cortical columns and the decoding of information conveyed by these columns.

Triangular-shaped sapphire patterning for HVPE grown AlGaN layers

AlGaN growth by hydride vapor phase epitaxy on patterned sapphire substrates has been investigated. Growth on honeycomb-shaped holes is disturbed by parasitic growth of c-plane oriented AlGaN crystallites on n-plane sapphire facets. Triangular hole-like structures allow for complete suppression of parasitic c-plane oriented AlGaN crystallites and coalescence of c-plane AlGaN at very low layer thickness. Additionally, triangular columnar sapphire patterns allow for biaxial strain relaxation and higher crystalline perfection. A total pressure of 400 hPa is favored for lateral overgrowth of ternary AlGaN by hydride vapor phase epitaxy. Lower pressures lead to strong composition inhomogeneity and higher pressure to lower crystal perfection. Additionally, very low V/III ratios of less than 10 yield best results. Lower ammonia supply support the growth of beneficial {11–22}-AlGaN crystallites on sapphire m-sidewalls which supresses undesired AlGaN growth on sapphire n-facets.

The life of the cortical column: opening the domain of functional architecture of the cortex (1955-1981).

The concept of the cortical column refers to vertical cell bands with similar response properties, which were initially observed by Vernon Mountcastle’s mapping of single cell recordings in the cat somatic cortex. It has subsequently guided over 50 years of neuroscientific research, in which fundamental questions about the modularity of the cortex and basic principles of sensory information processing were empirically investigated. Nevertheless, the status of the column remains controversial today, as skeptical commentators proclaim that the vertical cell bands are a functionally insignificant by-product of ontogenetic development. This paper inquires how the column came to be viewed as an elementary unit of the cortex from Mountcastle’s discovery in 1955 until David Hubel and Torsten Wiesel’s reception of the Nobel Prize in 1981. I first argue that Mountcastle’s vertical electrode recordings served as criteria for applying the column concept to electrophysiological data. In contrast to previous authors, I claim that this move from electrophysiological data to the phenomenon of columnar responses was concept-laden, but not theory-laden. In the second part of the paper, I argue that Mountcastle’s criteria provided Hubel Wiesel with a conceptual outlook, i.e. it allowed them to anticipate columnar patterns in the cat and macaque visual cortex. I argue that in the late 1970s, this outlook only briefly took a form that one could call a ‘theory’ of the cerebral cortex, before new experimental techniques started to diversify column research. I end by showing how this account of early column research fits into a larger project that follows the conceptual development of the column into the present.

Two symmetry-breaking mechanisms for the development of orientation selectivity in a neural system

Orientation selectivity is a remarkable feature of the neurons located in the primary visual cortex. Provided that the visual neurons acquire orientation selectivity through activity-dependent Hebbian learning, the development process could be understood as a kind of symmetry breaking phenomenon in the view of physics. The key mechanisms of the development process are examined here in a neural system. Found is that there are at least two different mechanisms which lead to the development of orientation selectivity through breaking the radial symmetry in receptive fields. The first, a simultaneous symmetry breaking mechanism, bases on the competition between neighboring neurons, and the second, a spontaneous one, bases on the nonlinearity in interactions. It turns out that only the second mechanism leads to the formation of a columnar pattern which characteristics accord with those observed in an animal experiment.

Electric field controlled columnar and planar patterning of cholesteric colloids.

We study how dispersions of colloidal particles in a cholesteric liquid crystal behave under a time-dependent electric field. By controlling the amplitude and shape of the applied field wave, we show that the system can be reproducibly driven out of equilibrium through different kinetic pathways and navigated through a glassylike free energy landscape encompassing many competing metastable equilibria. Such states range from simple Saturn rings to complex structures featuring amorphous defect networks, or stacks of disclination loops. A nonequilibrium electric field can also trigger the alignment of particles into columnar arrays, through defect-mediated force impulses, or their repositioning within a plane. Our results are promising in terms of providing new avenues towards controlled patterning and self-assembly of soft colloid-liquid crystal composite materials.

Columnar organization of stack-assembled trimesic acid on graphene

The stack-assembly of trimesic acid molecules into a highly organized columnar structure and their adsorption on graphene has been investigated by a DFT-based ab initio calculation method. Trimesic acid (TMA, benzene-1,3,5-tricarboxylic acid) constitutes an interesting building block for intermolecular hydrogen-bonding architecture by creating a strong net dipole moment which favors a symmetric π-stacking of molecular wire. Both the single orientation (syn) and alternating orientation (anti) of two- and three-unit TMA configurations are optimized, and determine that anti or AB pattern TMA wire is energetically more favorable than the syn case. Meanwhile, a decreasing band gap during the formation of the molecular wire proves the presence of delocalized π-electrons over the entire stack-assembly. The adsorption energy for a columnar TMA stack on graphene was found to be roughly less than of a single TMA adsorbed on graphene. The relative contribution of hydrogen bonding to column packing energy showed to be comparative and reasonable, with the energy of a conventional hydrogen bond. The magnitude of the band gap opening appears strongly correlated with the breaking of the symmetry of π-states of graphene by the TMA columnar patterning on the surface. Our results suggest that a stack-assembled molecular could be used to tune and control the electronic properties of graphene.

Numerical simulation of horizontal tube bundle falling film flow pattern transformation

It is important to study the falling-film pattern of a horizontal tube bundle in order to set up a heat and mass transfer model accurately. The falling-film pattern of a horizontal tube bundle is simulated in this paper. The technique is based on computational flow dynamics (CFD) for the two-phase flow of gas and water. The experimental results were used to validate the mathematical model. It indicates that the simulation results accord with experimental data well. The simulated results show that the flow pattern varies with different flow rates. Under the different flow rates, it observes the droplet, droplet-columnar, columnar, columnar-sheet and sheet flow patterns. The critical value is 0.0125 kg/s between droplet and columnar, and the critical value is 0.02 kg/s between columnar and sheet.

Phase separation during thin film deposition

A model for phase separation of two immiscible components during a thin film deposition is presented. The model includes the processes of adsorption and phase separation. The process of phases separation is described using Cahn and Hilliard (1958) equation. Diffusion is allowed to occur in a layer of an arbitrary thickness near the surface. The formations of various columnar or granular-like patterns are shown by numerical simulations of the presented model. The influence of the model parameters on obtained results is discussed. The modeling results showed that thin film structure depends on the ratio of diffusion coefficient near the surface over the growth rate.