Columnar Structure Research Articles

Superior tensile creep behavior of a novel oxide dispersion strengthened CrCoNi multi-principal element alloy

The creep behavior of an additively manufactured (AM) yttrium oxide dispersion strengthened (ODS) CrCoNi multi-principal element alloy (MPEA) is investigated in this study. Tests were conducted over a constant tensile stress range of 40–200 MPa and a temperature range of 973–1173 K. A stress exponent of 6.5 ± 0.1 and activation energies in the range of 335–367 kJ/mol were measured. Compared to its non-ODS counterpart and its parent alloy (CrMnFeCoNi), AM ODS CrCoNi has superior creep resistance at all tested stresses and temperatures. The mechanism contributing to the excellent creep resistance of AM ODS CrCoNi is attributed to the interaction of mixed character dislocations with oxide particles. The creep ductility of AM ODS CrCoNi is higher than its non-ODS counterpart due to a large percentage of low angle grain boundaries associated with its columnar grain structure. It was also found that creep ductility is significantly greater at the highest applied stress of 200 MPa compared to lower stresses. The steady state dislocation structure of AM ODS CrCoNi consists of long arrays of dislocations, which is different from that observed in non-ODS CrCoNi which consists of individual curved dislocations.

Studies on the Effect of Substrate Preheating, Interlayer Dwell, and Heat Treatment on Microstructure, Residual Stress, and Mechanical Properties of IN625 Superalloy Built by Direct Metal Deposition

Abstract In this investigation, IN625 alloy samples were processed by the directed energy deposition (DED) approach under various metal deposition strategies such as substrate preheating, interlayer dwell and with combined substrate preheating, interlayer dwell, as well as postheat treatment. The processed sample’s microstructural characteristics, residual stress, microhardness, and tensile properties are assessed in comparison to the manufacturing strategies. Rapid heat dissipation caused finer microstructure near the substrate. There is a growth of columnar grain structure epitaxially in the build direction. The progressive microstructure change seen in the build direction across the cross section was due to the gradual rise of heat accumulation between subsequent layers. The interdendritic zones contained Laves phases. Laves phases have a high Nb, Mo, as well as Si content, according to the energy-dispersive spectroscope (EDS) spectrum. The field emission scanning microscopy (FESEM) microstructural morphology of the deposited samples after their postheat treatment has shown a new microstructure with the combination of equiaxed (recrystallized) and columnar dendritic structure with the reconstruction of columnar dendritic solidification microstructure into equiaxed grains. Heat treatment caused the Laves phases to dissolve in the matrix of IN625 alloy, which led to the precipitation of nanometric γ″ phases. The deposition strategies with substrate preheating significantly decreased the residual stress with moderately improved mechanical properties. The combination of substrate preheating, interlayer dwell, and postheat treatment has shown an outstanding reduction of residual stress along with a remarkable improvement in tensile strength with the retainment of an equivalent ductility compared with other strategies.

Effect of tilted closed-field magnetron design on the microstructure and mechanical properties of TiZrNbTaN coatings

A common design of sputtering systems is to integrate many magnetron sources in a tilted closed-field configuration, which can drastically affect the magnetic field in the chamber and thus plasma characteristics. To study this effect explicitly, multicomponent TiZrNbTaN coatings were deposited at room temperature using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) with different substrate biases. The coatings were characterized by x-ray diffraction, scanning electron microscopy, nano-indentation, and energy dispersive x-ray spectroscopy. Magnetic field simulations revealed ten times higher magnetic field strengths at the substrate in single-magnetron configuration when compared to the closed-field. As a result, the substrate ion current increased ∼3 and 1.8 times for DCMS and HiPIMS, respectively. The film microstructure changed with the discharge type, in that DCMS coatings showed large sized columnar structures and HiPIMS coatings show globular nanosized structures with (111) orientation with a closed-field design. Coatings deposited from a single source showed dense columnar structures irrespective of the discharge type and developed (200) orientation only with HiPIMS. Coatings deposited with closed-field design by DCMS had low stress (0.8 to −1 GPa) and hardness in the range from 13 to 18 GPa. Use of HiPIMS resulted in higher stress (−3.6 to −4.3 GPa) and hardness (26–29 GPa). For coatings deposited with single source by DCMS, the stress (−0.15 to −3.7 GPa) and hardness were higher (18–26 GPa) than for coatings grown in the closed-field design. With HiPIMS and single source, the stress was in the range of −2.3 to −4.2 GPa with a ∼6% drop in the hardness (24–27 GPa).

Thermal stability of hierarchical microstructural features in additively manufactured stainless steel

Additive manufacturing of austenitic stainless steel results in an unconventional hierarchical microstructure. This hierarchical microstructure was investigated in detail in the as-built condition. The hierarchical microstructure consists of elongated austenite grains and melt pool fusion boundaries with a spherical cap morphology at the largest length scale. At a smaller length scale elongated columnar cell structures exist with elemental segregation at the cell walls. The cells were found not to be a misorientation structure in themselves as often noted, but rather groups of cells with a specific orientation, which are collected in 3–5 μm domains. At even smaller length scales, amorphous spherical silicates are found along with a high dislocation density along cell walls. The thermal stability of the unconventional features as melt pool boundaries, elongated austenite grains, cell domains, cell structure, amorphous precipitates was investigated systematically in the temperature range 400–1100 °C. The dislocation network forming the cell boundaries dissolves gradually and remains thermally stable up to about 800 °C. The melt pool boundaries are more thermally stable and dissolve above 900 °C. The elongated austenite grains and crystallographic texture are fully stable within the investigated temperature range. The cell domains appear to be pinned by precipitation as the cellular structure is dissolved and gradually straighten and resemble regular low angle grain boundaries. The amorphous silicates act as heterogeneous nucleation sites for the formation of σ-phase in the temperature range 700–800 °C, while at higher treatment temperatures these silicates are replaced by large, oblong Si–Mn oxides and small, round Mn–Cr oxides.

Dynamics of upstream ESCRT organization at the HIV-1 budding site

In the late stages of the HIV-1 life cycle, membrane localization and self-assembly of Gag polyproteins induce membrane deformation and budding. Release of the virion requires direct interaction between immature Gag lattice and upstream ESCRT machinery at the viral budding site, followed by assembly of downstream ESCRT-III factors, culminating in membrane scission. However, molecular details of upstream ESCRT assembly dynamics at the viral budding site remain unclear. In this work, using coarse-grained (CG) molecular dynamics (MD) simulations, we investigated the interactions between Gag, ESCRT-I, ESCRT-II, and membrane to delineate the dynamical mechanisms by which upstream ESCRTs assemble templated by late-stage immature Gag lattice. We first systematically derived “bottom-up” CG molecular models and interactions of upstream ESCRT proteins from experimental structural data and extensive all-atom MD simulations. Using these molecular models, we performed CG MD simulations of ESCRT-I oligomerization and ESCRT-I/II supercomplex formation at the neck of the budding virion. Our simulations demonstrate that ESCRT-I can effectively oligomerize to higher-order complexes templated by the immature Gag lattice both in the absence of ESCRT-II and when multiple copies of ESCRT-II are localized at the bud neck. The ESCRT-I/II supercomplexes formed in our simulations exhibit predominantly columnar structures, which has important implications for the nucleation pathway of downstream ESCRT-III polymers. Importantly, ESCRT-I/II supercomplexes bound to Gag initiate membrane neck constriction by pulling the inner edge of the bud neck closer to the ESCRT-I headpiece ring. Our findings serve to elucidate a network of interactions between upstream ESCRT machinery, immature Gag lattice, and membrane neck that regulate protein assembly dynamics at the HIV-1 budding site.

Microstructure and mechanical properties of nano dual-phase TiCuNi metallic glass films achieved by modulating magnetron sputtering temperature

Nano-dual phase TiCuNi metallic glass film having amorphous matrix with some ∼8.5 nm CuTi nanograins dispersed were achieved by magnetron sputtering at deposition temperature of 200 °C. The temperatures below or above that resulted in the totally amorphous or columnar crystalline structures of as-deposited TiCuNi films, respectively. The nano dual-phase TiCuNi metallic glass film exhibited the greatest hardness of 7.5 GPa, which was greatly higher than those of the uncoated Ti6Al4V substrate, amorphous and crystalline TiCuNi films by ∼114.3%, 11.9% and 23.0%, respectively. It also performed the highest wear resistance with the lowest wear rate of 1.32 × 10−5 mm3/Nm, slower than those of the uncoated substrate, amorphous and crystalline TiCuNi by 14.3%, 5.0%, and 7.0%, respectively. This work reveals an effective method to realize nano-dual phase structure of TiCuNi metallic glass films with mechanical properties improved, which is significant for the further development of titanium-based metallic glass films.

Stability maps for columnar structures

ABSTRACT We have previously explored the hysteresis and reversibility of transitions between ordered packings of soft spheres of diameter d in cylindrical channels of diameter D [A. Mughal, J. Winkelmann, D. Weaire, S. Hutzler, Phys. Rev. E 98, 043303 (2018)]. Here we extend these initial results to include transitions between all columnar structures without inner spheres (i.e. packings in which all of the spheres are in contact with the cylindrical boundary). These results can be represented by a directed network showing permissible transitions between structures. From the hard sphere limit we deduce that there are two different types of transitions, reversible and irreversible. We explore the nature of these transitions for soft spheres as a function of pressure and due to changes in the ratio D/d. These results are illustrated by the use of schematic diagrams, indicating the topological features of each transition. Specific cases are tabulated and can be understood by reference to the appropriate schematic diagram.

Silica botryoids from chemically oscillating reactions and as Precambrian environmental proxies

Abstract In this petrographic and geochemical study, we differentiated diverse quartz botryoids, including circular-concentric, twinned, columnar, wavy, and stromatolite-like structures versus synchronous biotic patterns of similar geometry and size dimensions (filamentous traits and stromatolites) in Precambrian cherts of Barberton, South Africa, and Gunflint, Canada. The botryoidal habits explored retained self-similar patterns of radially aligned acicular quartz with concentric laminae, which are not documented in biologically built stromatolites. These ancient fractals and their composition imitate those in chemically oscillating reactions, implying that the precipitation of botryoids was fueled by abiotic diagenetic degradation of organic matter and subsequently metamorphosed into chert.

Investigating the effects of double-pass TIG welding on the mechanical and microstructural properties of AISI 1008 steel

ABSTRACT Most premature failures of double-pass weldments are associated with limited knowledge of the mechanical and microstructural evolution following the welding process. Thus, this study aims to investigate the effect of double-pass tungsten inert gas welding on the mechanical and microstructural properties of type AISI 1008 mild steel joints. Double-pass TIG welding in butt joint configuration was adopted to weld the plates maintaining a 2.5 mm root gap in between plates. The double-pass tungsten inert gas welded AISI 1008 joints showed improved ultimate tensile strengths in contrast to the unwelded counterpart, with the least joint efficiency of 82.67 % (weld W3). An increase in the heat input led to a corresponding increase in the weld metal hardness, whereas the hardness of the heat-affected zones increased first and then decreased. The internal geometry of the welds reveals an increase in the bead width, height of reinforcement, width of the heat-affected zone, and weld metal area as the heat input increases. Lastly, the microstructural evolutions of the weld metal zones were primarily dominated by widmanstatten ferrite, acicular ferrite, and pearlite structures, accounting for the enhanced tensile strength and hardness of the joints. Meanwhile, the heat-affected zones were characterised by coarse columnar dendrite structures resulting in lower hardness values. This study gives an insight into the mechanical and microstructural properties of the industry’s most frequently used steel grade, which has not been given much attention in past studies. The research finding enriches the welding theory of A1SI 1008 steel for industrial and academic benefits.

Self-assembly of three-component bolaform giant surfactants with branched architectures

Branched architecture profoundly influences the physical properties of polymers, making it an important topic in the field of polymer science. Herein, we report a facile synthetic strategy to introduce one site-specific side chain at the junction point to fabricate a series of bolaform giant surfactants with branched architecture. By tuning the volume fraction and the ratio between the linking chain and side chain, various phases have been identified, including three-phase-four-layer lamellae, graphene-like honeycombs, tetragonally packed cylinders, and two-phase lamellae. Notably, the lattice dimension of obtained columnar structures is ∼12 nm, corresponding to sub-10 nm cylinder diameters. As revealed by temperature-dependent small-angle X-ray scattering profiles, a branched architecture significantly decreases the order-disorder transition temperature by ∼90 °C. We also use semi-quantitative calculations to analyze the thermodynamic properties of the observed phases and build rational connections between phase behaviors and the corresponding branching ratios. This study shed light on fine-tuning the macromolecular assembly via molecular topology engineering.

DRX mechanisms of a Ni-Co-W type superalloy with typical columnar grains during hot compression

Columnar evolution and DRX mechanisms of a Ni-Co-W type superalloy with typical columnar grains during hot deformation were investigated processed at the γ′ sub/super-solvus temperatures. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) was employed to characterize the nucleation at columnar boundary. The results show that columnar grains gradually replaced by new dynamic recrystallization (DRX) grains and nucleation was prioritized at original columnar boundary or/and folding position. Meanwhile, DRX mechanisms of the columnar structure associated with γ′ phase were identified deeply. Discontinuous dynamic recrystallization (DDRX) was the main mechanism when deformation processed at γ′ sub/super-solvus temperatures. Bulging columnar grain boundaries are first as the nucleation sites of the new DDRX grains under various conditions. High angle grain boundaries (HAGBs: θ > 15°) bends to the side with γ′ phase, and then the DRX grains formed at the bulging grain boundary. In addition, high dislocation density zone occurred around the large size γ′ phases (more than 1 µm), leading to the misorientation generated rapidly and then the HAGBs formed. The formation of DRX grains by this way is also called particle stimulated nucleation (PSN) mechanism. Continuous dynamic recrystallization (CDRX) occurs when hot deformation processed at γ′ sub-solvus temperature with high strain level, which is accompanied by dislocation accumulation and an obviously increase in the fraction of grain boundaries with 10–15° misorientation angle. The findings help to understand different DRX mechanisms of Ni-based superalloy with columnar structure during microstructure evolution under hot forming, and are also beneficial for optimizing the microstructure to control the required properties of the Ni-based superalloys for manufacturing turbine disc.

Verification of Automotive Monopost Seat Strength through Dynamic and Quasi-Static Simulations

A monopost seat is a novel, lightweight seat developed to utilize most of the interior space of vehicles. The space under the seat can be utilized by inserting a monopost columnar structure between a monopost seat rail and the floorboard. This design increases the perceived spaciousness of the vehicle and imparts passengers with a higher degree of freedom, because the seats can be adjusted more easily than standard seats. Meeting these requirements will require the seats to be sufficiently strong and sturdy in order to maintain passenger safety. Compared to traditional seats, it is more likely that a monopost seat will shift under the mass of the passenger, and these seats are more vulnerable to external vehicle collisions. Passenger safety is further compromised if an operational function is added. Therefore, further research on monopost seats is required. This study performed quasi-static and dynamic simulations to determine if the attachment of monopost seats to a vehicle meets international safety requirements in collision events. With a focus on clarifying the dynamic simulation process, the outcomes of quasi-static simulations were compared with the results obtained from dynamic simulations.

Effect of deposition temperature on columnar structure of α-C nano-coatings of PEMFC metal bipolar plates

Amorphous carbon (α-C) nano-coatings are the most commonly used coating materials for the metal bipolar plates in fuel cells due to their low cost, excellent electrical conductivity, and good corrosion resistance. However, α-C usually forms a columnar structure during the deposition process, which seriously affects its performance and service life. This study proposes that the columnar structure of α-C nano-coatings can be controlled by modifying the deposition temperature during magnetron sputtering. Further, the effects of deposition temperature on the composition, microstructure, electrochemical corrosion behavior, interfacial conductivity and hydrophilicity of α-C nano-coatings were systematically studied. The results show that the columnar structure of α-C nano-coatings is inhibited by increasing the deposition temperature. When the deposition temperature is above 300 °C, the microstructure of the α-C nano-coatings changes from columnar to denser microcrystalline. At the same time, a higher deposition temperature leads to a higher proportion of sp2 carbon in the α-C nano-coatings; resulting in significant improvement in the corrosion resistance, interfacial conductivity and hydrophobicity of the coatings.

Microwave joining of SS-316 plates: A multi-physics simulation study

Microwave hybrid heating has emerged as a new technique for joining metallic materials. The presence of a multi-material system (bulk and powder) and the selection of suitable interface powder in microwave joining offer challenges. The present work addresses these issues for microwave joining of SS-316L plates using different interface powders nickel-based (EWAC 1004 EN) and SS-316L interface powders. A multi-physics model of the microwave joining setup was developed to theoretically study the joining characteristics of SS-316L joints using both powders at 2.45 GHz and 900 W. The SS-316L joints were developed experimentally in 720 s and 680 s while using interface powders EWAC and SS-316L, respectively. The model was validated with experimental results and simulation was performed to analyse the electric field distribution, resistive losses, temperature distribution, thermal stress distributions, and energy utilization. The simulation results showed that the electric field intensity was 4.96 % higher in EWAC-based joint as compared to SS-316L-based joint; consequently, the EWAC-based joint attained a temperature of 1450 °C at the central plane. The resistive loss was found maximum between the susceptor and joint interlayer in both joints. Thermal stress was 62 % higher in EWAC-based joint than SS-316L-based joint. Microstructural investigation of the joints revealed that EWAC-based joints contained columnar and dendritic grain structures; while equiaxed grains were present in SS-316L-based joints. Porosity and grain size were higher by 34 % and 53 %, respectively in EWAC-based joint than SS-316L-based joint.

Impact of Silver on the Structural and Wettability Properties of ZnO Films Grown by Oblique Angle Magnetron Sputtering

Un-doped (uZO) and silver-doped zinc oxide (SZO) films were prepared by oblique incidence sputtering deposition under different process parameters. The crystalline structure, chemical composition, and surface morphology were correlated with the optical properties, as well as with the wettability of the films. In the case of uZO films, the orientation, inclination, and morphology of the columnar structure determined the wettability of the layer, moving from a hydrophilic- to hydrophobic-like character. In the case of SZO films, although almost all of them displayed hydrophobic behavior, the hydrophobic character increased with the Ag content. The most hydrophobic surface was obtained when the Ag content in the layers was greater than 7 at.% and, in these cases, the structural results indicate that the layers were formed by a disordered mixture of Zn and Ag oxides.

Efficient Anti-Fog and Anti-Reflection Functions of the Bio-Inspired, Hierarchically-Architectured Surfaces of Multiscale Columnar Structures.

Today, in the fields of optical precision instruments, medical devices, and automotive engineering, the demand for anti-reflection and anti-fog surfaces is growing rapidly. However, the anti-fog function often compromises the efficiency of the anti-reflection function. Therefore, optical precision instruments are always restricted by the inability to combine high anti-reflection efficiency and excellent anti-fog performance into one material. In addition, the synergistic mechanism of harmonizing anti-fogging and anti-reflection is currently unclear, which has a negative impact on the development and optimization of multifunctional surfaces. Herein, bio-inspired anti-fogging and anti-reflection surfaces (BFRSs) possessing multiscale hierarchical columnar structures (MHCS) were obtained using a brief and effective preparation technique, combining the biotemplating method and sol-gel method. Specifically, condensed fog droplets distributed on the BFRS can be absolutely removed within 6 s. In addition, the BFRSs endow the glass substrate with a relatively higher reflectance (17%) than flat glass surfaces (41%). Furthermore, we demonstrated the synergistic mechanism of the anti-fogging and anti-reflection functions of BFRSs. On the one hand, the high transparency benefits from the multiple refraction and scattering of light in the MHCS array. On the other hand, the excellent anti-fogging performance is attributed to the imbalance of the capillary force of the MHCS acting on the liquid film. The explanation for these two mechanisms provides more possibilities for the subsequent preparation of multifunctional surfaces. At the same time, the bionic research concept provides new solutions for the researcher to conquer the combination of high transmission and anti-fog properties for precision optical surfaces.

Relationship between Internal Stress Distribution and Microstructure in a Suspension-Sprayed Thermal Barrier Coating with a Columnar Structure

The suspension plasma spray (SPS) method is expected to become a novel coating method because it can achieve various microstructures using a suspension with submicron spray particles. Thermal barrier coatings (TBCs) with a columnar structure, which might achieve high strain tolerance, can be obtained using the SPS technique. This study evaluated the internal stress distribution of the suspension-plasma-sprayed thermal barrier coating (SPS-TBC) with different columnar structures using hybrid measurement using high-energy synchrotron X-ray diffraction analysis and laboratory low-energy X-rays. The relationship between the microstructure and the internal stress distribution of the SPS-TBC was discussed on the basis of the experimental results. In addition, the in-plane internal stress was decreased by decreasing the column diameter. The thin columnar microstructure of the SPS-TBC has superior strain tolerance. The internal stresses in the SPS-TBC are periodic decrements caused by stress relaxation in porous layers in its column.

Microstructural characterization, mechanical properties and erosion behavior of Y2O3–MgO nanocomposite films by magnetron sputtering

The effect of Y2O3: MgO ratio on the microstructures, mechanical properties, and plasma erosion behaviors of Y2O3–MgO (YM) nanocomposite films were investigated. The columnar growth structure of the YM nanocomposite film is disrupted as the MgO content increases, resulting in the refinement of the Y2O3 grains. When the Y2O3: MgO ratio is 40 : 60, the columnar crystal structure of the YM nanocomposite film can be refinement effectively due to thermodynamic incompatibility of Y2O3 and MgO. As a result, YM nanocomposite film is strengthened significantly with the maximum hardness and elastic modulus of 16.78 ± 0.8 GPa and 149.24 ± 4.7 GPa, respectively. X-ray photoelectron spectroscopy revealed few changes in the elemental and chemical compositions of the surface layer after fluorination in the YM nanocomposite film, confirming the chemical stability of the YM nanocomposite samples. The etching depth is ∼48% lower on the YM nanocomposite film (with a MgO content of 60%) than on the commercial Y2O3 film. The findings show that the strengthened YM nanocomposite film is more erosion resistant than the commercial Y2O3 coating.

Microstructure and adsorption characteristics of Zr–Co–RE getter films deposited using krypton as sputtering gas

The vacuum level in micro-electro-mechanical system devices needs to be achieved and maintained using non-evaporable getter film technology. Zr–Co–RE getter films are deposited by direct current (DC) magnetron sputtering using krypton (Kr) as the sputtering gas. The influence of sputtering gas pressure and DC sputtering power on the microstructure and adsorption characteristics of films is investigated. Zr–Co–RE films deposited at different gas pressures all grow in a columnar shape. Films grown at low Kr pressures are relatively dense and have a structure with fewer cracks, whereas high Kr pressures result in a uniform cluster and columnar structure with more gaps and micro-cracks. In addition, it is revealed that DC sputtering power has great influence on the film structure and adsorption performance. The films deposited at low sputtering power contain more micro-cracks, which are distributed uniformly. At high sputtering power, the cluster structure is not obvious. Consequently, high Kr pressures and low sputtering power are beneficial to improve the adsorption performance. Hydrogen adsorption tests are carried out using a special vacuum system, keeping the pressure constant. The highest initial adsorption speed is 89 (ml/s)/cm2, obtained at 4.0 Pa Kr pressure and 300 W sputtering power. Meanwhile, the Zr–Co–RE films deposited under these conditions have excellent adsorption stability.

Effect of the microstructure parameters on the corrosion characteristics of Mg-Zn-Ca alloy with columnar structure

Magnesium alloys with homogeneous degradation and controlled degradation rate are desirable for biodegradable materials. In the present work, Mg-3 wt.%Zn-0.2 wt.%Ca alloys with different columnar structures were fabricated and the degradation in 0.9 wt.% NaCl were investigated. With the increase of the growth rate for the directional solidification, the microstructure of the directionally solidified (DSed) alloy evolved from cellular to dendritic coupled with the change of the spacing of the primary trunks (λ1) and the volume fraction (fv) of Ca2Mg6Zn3 phase. The results of the corrosion test suggested that the alloy with cellular structure experienced homogeneous corrosion and exhibited the lowest corrosion rate. The good corrosion resistance of the alloy with cellular structure was attributed to the protective corrosion products film (CPF), which was closely related to the fv of Ca2Mg6Zn3 phase and λ1. To evaluate the corrosion rates (CR) of the DSed Mg-Zn-Ca alloys with different microstructures, a parameter α was proposed in this work, which was calculated by λ1 and the fv of Ca2Mg6Zn3 phase. The fitting result showed that there was a linear relationship between CR and α, which was CR = 4.1899 + 0.00432α. This means that the CR of the DSed Mg-Zn-Ca alloy can be evaluated if the microstructure had been characterized.