Columnar Zone Research Articles

Consideration of medial anatomical structures at risk when placing quadricortical syndesmotic fixation: A cadaveric study

BackgroundSurgical fixation of syndesmotic instability using quadricortical fixation, whether screws or suture-button devices, places structures on the medial side of the tibia at iatrogenic risk. This study aims to radiographically map the anatomic course of structures on the medial aspect of the distal tibia to be able to at-risk zones (ARZs) for syndesmotic fixation. MethodsEighteen fresh-frozen cadaveric ankle specimens were dissected. The saphenous neurovascular bundle (SNVB) and the posterior tibial tendon (PTT) were identified and marked with copper wiring. Standardized and calibrated lateral radiographs of the distal tibia and fibula were analyzed using a grid system consisting of 3 columnar zones from anterior to posterior and five 1-cm rows to chart the anatomic course of the SNVB and the PTT. ResultsThe SNVB was located in the more anterior zones (1, 2, or anterior to Zone 1) in 97.3% of specimens. The SNVB traversed from posterior to anterior as it descended proximal to distal. The PTT was found in Zone 3 (most posterior zone) for all specimens. The PTT was noted to pass behind (radiographically overlap) the tibia in 83.3% (15 of 18) of specimens between 1 and 3 cm above the tibiotalar joint. ConclusionsPlacement of quadricortical syndesmotic fixation places structures on the medial ankle at risk. The SNVB is at considerable risk along the anterior course of the distal tibial while the PTT is only at risk in zone 3 at the distal extent of the tibia.

Fabrication of Fe3Al cladding layers by cold metal transfer arc deposited technique

Fe3Al cladding layers were fabricated on the steel plate using cold metal transfer arc deposited technique. The effect of current intensity on the morphologies, microstructures, and mechanical properties of the cladding layers was investigated. Under low-current conditions, the Fe3Al cladding layer exhibited excellent formability, favourable wettability, and low dilution rate without defects such as gas holes and cracks. The cladding layer was composed of Fe3Al phase and FeAl phase. The microstructure of the cladding layer was divided into a fine grain zone, a columnar grain zone, and an equiaxed grain zone. A transition layer appeared at Fe3Al/steel interface, and the bonding strength between the cladding layer and steel plate was high. With increasing current, cracks were generated at Fe3Al/steel interface and the bonding strength was reduced.

Microstructure and mechanical properties in three-dimensional laser-arc hybrid welding of AA2219 aluminum alloy

The weld microstructure and property of the three-dimensional laser-arc hybrid welding of AA2219 aluminum alloy were studied in this paper. It is indicated that they were mainly influenced by the gravity-laser angle (β). The results showed that the width of the columnar grains zone gradually reduced with increased β, and it disappeared when β increased to 60°. When β was constant, an optimized arc current value existed with which the best tensile property was obtained. The tensile property increased first then decreased with increased β. When β reached 60°, the maximum tensile strength and elongation 320 Mpa and 5%, respectively, were acquired. It was concluded that the enhancement of weld property depended on porosity decreasing and microstructure refinement.

Effect of Ultrasonic Flexural Vibration on Solidification Structure and Mechanical Properties of Large-Size 35CrMoV Cast Ingot

In order to improve the performances of large-size 35CrMoV cast ingot, ultrasonic flexural vibration was guided into 35CrMoV steel melt through L-shaped ultrasonic waveguide rod during the solidification, and the effects of ultrasonic flexural vibration on macrostructure, microstructure, and mechanical properties of large-size 35CrMoV cast ingot were investigated. It is found that the columnar crystal zone has disappeared and the ingot is composed of the equiaxed crystals present in the ultrasonic ingot. The size of grains treated by ultrasonic are significantly smaller than conventional ingot. The distribution of ferrite in matrix structure is also more uniform than conventional ingot. The tensile strength is increased by 3.14%∼17.12%, and the elongation is increased by 39.13%∼287.50% compared with the conventional ingot at different positions.

Research on Grain Refinement in Hypoeutectic Al-Si Alloy during Solidification under an Alternating Electric Current Pulse

Experiments on transient directional solidification were carried out to study the columnar to equiaxed transition (CET) in Al-7Si alloy without and with an alternating electric current pulse (AECP). Without AECP, the macrostructure consists of typical columnar and equiaxed zones, separated by a near horizontal plane. As the AECP is applied during solidification, an additional fine equiaxed zone (FEZ) occurs in the as-cast macrostructure. From measured temperature profiles, cooling rate and temperature gradient are determined. It is found that CET occurs for a critical value of the cooling rate, which is observed to be about 0.14 K·s−1 in the present investigation. Furthermore, the macrostructural observation with mold for embedding the mesh plate demonstrates that the major factor responsible for the formation of fine equiaxed grains is the detachment of crystal nuclei from the upper contact surface and the lateral wall. The detachment is in turn ascribed to electric current-associated free energy change (ΔGe)-induced the driving force F.

Solidification Structure and Segregation of High Magnetic Induction Grain-Oriented Silicon Steel

The solidification structure and centerline segregation of high magnetic induction grain-oriented silicon steel slabs were studied to describe the characteristics of solidification and compare the degree of centerline segregation of continuously cast slabs. Industrial experiments were conducted to investigate the solidification behavior of slabs by secondary cooling segment electromagnetic stirring. Three typical slabs were produced by S-EMS with current intensities of 0, 200, and 350 A. Molten steel cast at a low stirring intensity (0 A) resulted in a coarse structure relative to those cast at higher stirring intensities (200 and 350 A). The centerline segregation of carbon and silicon markedly increased with increases in S-EMS current intensity. Composition distribution by electron probe microanalysis identified segregation spots as the sources of centerline segregation. Experimental results indicate that to optimize the centerline segregation of grain-oriented silicon steel slabs, the columnar crystal zone should be enlarged and the equiaxed crystal zone be reduced.

Influence of minor additions on Icosahedral Short-Range Order (ISRO) and its consequences on nucleation and solidification growth kinetics in fcc alloys

The present contribution reviews the recent progress related to the influence of Icosahedral Short-Range Order (ISRO) and icosahedral Quasicrystals (i-QC) formation on the solidification of fcc alloys through minor solute element additions. From intensive crystallographic analysis of multi-twinned regions in as-cast Al-based and Au-based fcc alloys, Kurtuldu et al. have shown recently that a so-called “iQC-mediated” nucleation mechanism occurs when a few hundred ppm of Cr and Ir, respectively, are added to the melt [1] [2]. Similarly, it appears that the growth directions of dendrites in Al-Zn:Cr is also influenced by ISRO in the liquid, thus showing an attachment kinetics effect [3]. In a recent contribution, we have shown that iQC-mediated nucleation also occurs in pink gold alloys with Ir-additions, but two additional phenomena at high solidification speed [4]: (i) a spinodal-type decomposition of the liquid, leading to the formation of twinned Cu precipitates in addition to multi-twinned Au-rich grains; (ii) a change of the microstructure of the Au-rich grains, from 〈100〉 dendrites to 〈111〉 textured cells in the columnar zone.

Prediction of solidification structures in a 9.8 t steel ingot

The control of the carbon macrosegregation level in steel ingots is important for the structural integrity of the final component. During solidification, the fragmentation of the columnar dendrites is an important source of equiaxed grains, and has a large influence on the macrosegregation and the grain structure. The goal of this study is to show that a numerical model that takes into account fragmentation can describe the formation of the structures and the macrosegregation during solidification of a large steel ingot. The present article describes the multiphase numerical model used in the simulations. The simulation results are compared to experimental data from a 9.8 t ingot cast in A5/6 steel by ArcelorMittal Industeel. The model can then be used to explain the formation of the observed structures. For example, we show that the structural transitions, first from columnar to equiaxed globular and then to equiaxed dendritic at the bottom of the ingot are a consequence of the concurrent transport and growth of the dendrite fragments from the columnar zone. Furthermore, we show that most of the structures are formed very early on during solidification, whereas macrosegregation develops much more gradually.

Analysis of columnar-to-equiaxed transition experiment in lab scale steel casting by a multiphase model

Correct prediction of composition heterogeneities and grain structure across a steel ingot is critical in optimizing the industrial processing parameters for enhanced performance. The columnar to equiaxed transtion (CET) is a microstructural transition which is strictly controlled as it affects the mechanical properties of the final product along with the macrosegregation patterns. Larger equiaxed regions are preferred for most industrial applications. CET is significantly affected by the number density of equiaxed grains and by the nucleation undercooling. 8 kg 42CrMo4 alloy steel ingots (240 mm x 60 mm x 60 mm) were cast. The cast structure was characterized by ASCOMETAL. The experiments were simulated with a process-scale model of solidification that incorporates a multiscale description of the microstructure formation. The goal of the present study is to show the capabilities of such a process-scale solidification model to explain the observed structure distributions (extent of the columnar and equiaxed zones, equiaxed-to-columnar transition).

The Corrosion Behavior of 50-Kg As-Cast Fecrnicomnx Alloys

FeCrNiCoMn, one familiar type of high entropy alloys, has drawn much attention due to its interesting mechanical properties at cryogenic temperatures. In this research, the microstructure and corrosion behavior of 50-kg as-cast FeCrNiCoMnx alloys were studied. The X-Ray Diffractometer (XRD) results show that both alloys are single fcc structures. The influence of manganese content on the corrosion behavior of FeCrNiCoMnx was investigated using electrochemical methods in H2SO4 and NaCl solutions. Dendritic structures were observed in each alloy and the interdendritic regions are enriched with manganese and nickel by Energy Dispersive X-ray Spectroscopy (EDS). The corrosion resistance of FeCrNiCoMnx is improved with decreasing manganese contents in both H2SO4 and NaCl solutions. It was also found that the passive film of central zone acts more active than that of columnar zone in H2SO4 due to the segregation level. Moreover, the onset of pitting in NaCl is related to the manganese content of the FeCrNiCoMnx.

Effect of different parameters on solidification structure of multi-crystalline silicon produced by continuous casting

Continuous casting is a promising technology for massive production of multi-crystalline silicon. Solidification structure has an important influence on the conversion efficiency of solar cells. However, there is no relevant research on the effect of different parameters on the solidification structure during continuous casting, using the continuous casting apparatus of multi-crystalline silicon firstly designed in our research. In order to improve this situation, numerical and experimental works were carried out. The results indicate that the area of columnar grain zone perpendicular to the billet bottom is mainly affected by the casting speed, the pouring temperature and the bottom block cooling intensity. Moreover, the grain size is mainly affected by the density of nuclei and the nucleation undercooling.

Influence of cerium on the microstructure and mechanical properties of an as-cast and Q&T steel

ABSTRACTIn the present work the influence of Cerium on the microstructure and the mechanical properties of a cast, quenched and tempered GS33NiCrMo744 steel is analysed. The study shows that the addition of cerium to the steel melt results in an increase of the number of CeS dispersoids with a size between 0.5 and 3.0 µm. The CeS dispersoids change the solidification morphology and the as-cast microstructure because as a nucleating agent for ferrite. Furthermore, a part of the cerium remains dissolved in the steel. The width of the columnar zone in 25 mm thick castings diametrically correlates with the amount of cerium. Furthermore, the secondary dendritic arm spacing (SDAS) has a tendency to decrease. The tensile strength of these cerium treated and then quenched and tempered (Q&T) steels increases with the number of cerium-containing dispersoids. However, samples with a wall thickness of 75 mm do not show this behaviour.

Analysis of droplet transfer, weld formation and microstructure in Al-Cu alloy bead welding joint with pulsed ultrasonic-GMAW method

The ultrasonic intensity was changed in different ultrasonic radiator heights (URH). Compared with conventional GMAW, the pulsed ultrasonic assisted gas metal arc welding (PU-GMAW) was an effective and newly-developed aluminum alloy welding method, because of its rapid droplet transfer and deep weld penetration. In PU-GMAW, the penetration and width of weld was increased due to the increase of the arc energy. When the URH was 20 mm and 22 mm, the droplet transfer mode of projected transfer changed to the mixed transition, which included projected transfer and short-circuiting transfer. The hardness of welded joint increased with the effect of pulsed ultrasonic, and the columnar crystal zone width of weld seam decreased. Ultrasonic radiation force was a determinant factor in arc compression and droplet transfer acceleration. The microstructure improvement in the PU-GMAW was caused by ultrasonic vibration and ultrasonic cavitation.

Characterization of ferroniobium topologically close-packed phase inclusion in nickel-based 152 cladding of dissimilar metal welds

Ferroniobium topologically close-packed (TCP) phase inclusions were found in the nickel-based152 nickel-based cladding of dissimilar metal weld joint in pressurized water nuclear reactor. A systematical investigation on the morphologies, microstructures and mechanical properties was conducted by using multi-scale techniques. The formation causes of the TCP-phase inclusion and its possible influences on crack initiation and propagation during long-term operation are also discussed. The ferroniobium TCP-phase inclusions originate from large-size ferroniobium supplement particles in 152 welding electrode flux during welding. The inclusion with core has a homogeneous kernel and a continuous transition zone between the core and eutectic zone, and the transition zone consists of columnar grain zone and isometric grain zone. The inclusion core is confirmed as single-phase rhombohedral Fe7Nb6 (μ phase), and columnar grain zone in the transition zone is also mainly Fe7Nb6, while the isometric grain zone and the Nb-rich phase in the eutectic zone are both mainly hexagonal Fe2Nb (Laves phase), the other phase in the eutectic zone is austenite. The Fe2Nb is formed by eutectic metallurgical reaction between inclusion core and 152 cladding. The average hardness of inclusion core (17.89 GPa) is over 4.5 times as high as cladding matrix (3.91 GPa). The TCP-phase inclusion is of higher cracking susceptibility than 152 cladding, and acts as the initiation of brittle cracks during in-situ tensile test. The ferroniobium TCP-phase inclusions are of higher cracking susceptibility than 152 cladding.

Formation of Lamellar Carbides in Alloy 617-HAZ and Their Role in the Impact Toughness of Alloy 617/9%Cr Dissimilar Welded Joint

The relationship between the microstructure and impact toughness, especially the formation of the lamellar carbides and its effect on the impact toughness of the heat-affected zone of Alloy 617 (Alloy 617-HAZ), was systematically investigated. Impact test was performed on Alloy 617/9%Cr dissimilar welded joints aged for different time at 620 °C. The results showed that the characteristic zones of the whole welded joint revealed decreased impact toughness with increasing the aging time. The impact energies in weld metal showed high stability despite the aging process, while the Alloy 617-HAZ for all testing specimens presented the lowest impact toughness with various aging time. Meanwhile, the mixed grains were found in the base metal (BM) and heat-affected zone of Alloy 617, together with the twins with different widths located in the interior of the large grains. The columnar and equiaxed grain zones appear alternately due to the multilayer and multi-pass welding technique. In particular, compared with Alloy 617-BM, coarsened and even lamellar carbides were observed in Alloy 617-HAZ. These special carbides can separate the grains and therefore result in the formation of intergranular fracture morphology in Alloy 617-HAZ. Besides, the microhardness distribution was tested with a proper load, and the results exhibited that the weld possessed the highest hardness for all specimens with various aging time. The higher microhardness in Alloy 617-HAZ compared with that in Alloy 617-BM was attributed to the high density of the dislocations, which could be detected by transmission electron microscope. As a result, the coarsened carbides aggregated in the grain boundaries to form the lamellar layer are deemed as the main factor to reduce the impact toughness in Alloy 617-HAZ.

Endochondral ossification in hindlimbs during bufo gargarizans metamorphosis: A model of studying skeletal development in vertebrates

Background Endochondral ossification, the process by which most of the skeleton is formed, is accurately regulated by many specific groups of molecules and extracellular matrix components. The molecular mechanisms of endochondral ossification have been extensively investigated in mammals. However, there are few studies about it in amphibians. Results Ossification of femur and tibiofibula was observed at Gs 40, and tarsals and metatarsals were ossified at Gs 42. Most of the skeletons in hindlimbs were completely ossified except for articular cartilages at Gs 46. Thirty-two genes related to endochondral ossification were found in the differentially expressed genes (DEGs) library of hindlimbs, and nine of these genes were validated by qRT-PCR during metamorphosis. Sox9 was expressed in the columnar, prehypertrophic, and upper hypertrophic zones, and the expression of Ihh was observed in prehypertrophic chondrocyte zone in hindlimbs of B. gargarizans. Conclusions The ossification of hindlimbs increased gradually, and the ossification sequence was from proximal to distal in B. gargarizans during metamorphosis. Thirty-two genes found in the DEGs library were related to the regulation of endochondral ossification of hindlimbs in amphibians. The present study will provide a valuable genomic resource for the future study of endochondral ossification in amphibian. Developmental Dynamics 247:1121-1134, 2018. © 2018 Wiley Periodicals, Inc.

Microstructure and mechanical properties of TiC-Fe surface gradient coating on a pure titanium substrate prepared in situ

A TiC-Fe surface gradient coating was prepared on the surface of pure titanium by a simple two-step heat-treatment process (1150 °C × 5 min + 1000 °C × 10 h). The phase composition, microstructure, nanoindentation hardness, elastic modulus, fracture toughness, and adhesion strength of the TiC-Fe surface gradient coating were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), nanoindentation testing, and scratch testing. The results reveal that the TiC-Fe surface gradient coating was composed of dense TiC grains and a small amount of α-Fe. The TiC-Fe surface gradient coating was divided into three zones according to the variation in the volume fractions of TiC particulate and α-Fe phase. These zones were labeled as follows: a columnar TiC zone (I zone), a large particle TiC zone (II zone) and a large bulk TiC zone (III zone). The formation process and mechanism of the TiC-Fe surface gradient coating include the nucleation growth of TiC grains, followed by diffusion and in situ reactions between titanium and carbon. The nanoindentation hardness and elastic modulus for cross section of the TiC-Fe surface gradient coating ranged from 19.1 to 31.7 GPa and from 368.1 to 464.3 GPa, respectively. The fracture toughness values of I zone, II zone and III zone are 3.5, 1.6 and 3.1 MPa m1/2, respectively, and these values largely depend on composition and microstructure. Investigations of crack surface morphologies indicate that radial cracks at the corners of the indentation originate from the crossing of slip bands and that the toughening mechanism was mainly crack deflection and bridging. In addition, the scratch testing indicated that the coating exhibited excellent coating/substrate adhesion strength.

Pulse MIG Welding of 6061-T6/A356-T6 Aluminum Alloy Dissimilar T-joint

Dissimilar T-joints between 4-mm-thick wrought 6061-T6 and cast A356-T6 aluminum alloy plates are made with pulse metal inert gas welding (P-MIG) process, and the weld geometry, microstructure and mechanical properties of the joints are investigated. The average tensile load of the joints is 9488 N at travel speed 12 mm/s and welding current 165 A with 6061 aluminum alloy as web plate and A356 aluminum alloy as flange plate. The weld zone (WZ) is composed of dendrite zone and columnar zone, which is wide at bottom of weld making it become a weak zone. Besides, grain boundary (GB) liquation, consisting of GB eutectic and solute-depleted α-Al, occurs in the partially melted zone on 6061 aluminum alloy side. The T-joint with highest tensile load fails at the root of WZ and the flange plate near the weld with different fracture modes.

Consideration of Medial Anatomical Structures at Risk when Placing Quadricortical Syndesmotic Fixation

Category: Trauma Introduction/Purpose: Surgical fixation of ankle fractures with syndesmotic instability using quadricortical fixation through the fibula and tibia is commonly performed to maintain mortise congruency. Quadricortical fixation can be achieved by screws or suture buttons however both involve unprotected drilling and placement of hardware through the medial distal tibia which places anatomic structures at iatrogenic risk. These structures may include the anterior tibialis tendon, the saphenous neurovascular bundle (SNVB) and posteriorly, the posterior tibialis tendon (PTT). This study aims to radiographically map the anatomic course of these structures at risk on a lateral radiograph as would be used intraoperatively during syndesmotic fixation. Methods: Eighteen fresh-frozen cadaveric feet were dissected with preservation of all soft tissue and neurovascular structures over the medial distal tibia. While preserving fascial and tendinous sheath attachments, the SNVB and the PTT were identified and marked with metal wiring. Standardized and calibrated lateral radiographs were obtained to determine the anatomic course of these structures. Lateral radiographs of the distal tibia and fibula were analyzed by a grid system comprised of 1 cm row-increments moving cranially from the ankle joint up to 5 cm and by 3 evenly distributed parallel columnar zones from anterior to posterior (see Figure). The anterior boundary of the columnar zone was placed at the anterior tibial shaft and the posterior boundary was placed at the posterior malleolus of the tibia. The position of respective metal wires placed within the SNVB and the anterior portion of the PTT were charted according to this grid system and results compiled. Results: The SNVB was located in zone 1 or 2 (or anterior to zone 1) in 97.3% of specimens (107/110). The SNVB traversed from proximal-posterior to distal-anterior. For the 16 specimens that crossed a columnar zone, the most common crossover was from zone 2 to zone 1 at 3-4 cm above the ankle joint which occurred in 43.8% (7 of 16) specimens. The PPT was found in zone 3 in all specimens (n=18) with only one specimen demonstrating crossover of a columnar zone into zone 2 at its most distal extent (0-1 cm). The PTT was noted to pass behind (radiographically overlap) with the tibia in 83.3% (15 of 18) of specimens between 1 and 3 cm above the ankle joint. Conclusion: Inappropriate placement of quadricortical syndesmotic fixation may place structures on the medial ankle at risk given blind drilling and hardware placement. The SNVB is at considerable risk along the anterior course of the distal tibial while the PTT is only at risk in zone 3 at the distal extent of the tibia when a true lateral radiograph is obtained. This grid system allows a simple intra-operative check to guide safer placement of quadricortical syndesmotic fixation.

High-resolution 3D seismic study of pockmarks and shallow fluid flow systems at the Snøhvit hydrocarbon field in the SW Barents Sea

The Barents Sea is an epicontinental shelf sea with a fragmented structure consisting of long fault complexes, basins and basement highs. Fluid leakage from deep-seated hydrocarbon accumulations is a widespread phenomenon and mostly related to its denudation history during the glacial/interglacial cycles. In this study, we aimed to better understand shallow fluid flow processes that have led to the formation of numerous pockmarks observed at the seabed, in this area. To achieve this goal, we acquired and interpreted high-resolution 3D seismic and multibeam swath bathymetry data from the Snøhvit area in the Hammerfest Basin, SW Barents Sea. The high-resolution 3D seismic data were obtained using the P-Cable system, which consists of 14 streamers and allows for a vertical resolution of ~1.5 m and a bin size of 6.25 × 6.25 m to be obtained. The frequency bandwidth of this type of acquisition configuration is approximately 50–300 Hz. Seismic surfaces and volume attributes, such as variance and amplitude, have been used to identify potential fluid accumulations and fluid flow pathways. Several small fluid accumulations occur at the Upper Regional Unconformity separating the glacial and pre-glacial sedimentary formations. Together, these subsurface structures and fluid accumulations control the presence of pockmarks in the Snøhvit study area. Two different types of pockmarks occur at the seabed: a few pockmarks with elliptical shape, up to a few hundred meters wide and with depths up to 12 m, and numerous circular, small, “unit pockmarks” that are only up to 20 m wide and up to 1 m deep. Both types of pockmarks are found within glacial ploughmarks, suggesting that they likely formed during deglaciation or afterwards. Some of the larger normal pockmarks show columnar leakage zones beneath them. Pressure and temperature conditions were favourable for the formation of gas hydrates. During deglaciation, gases may have been released from dissociating gas hydrates prolonging the period over which active seepage occurred. At present, there is no evidence from the 3D seismic data of active gas seepage in the Snøhvit area. Low sedimentation rates or the influence of strong deep ocean currents may explain why these pockmarks can still be identified on the contemporary seabed.