Columnar Structure Research Articles

Effect of the Diffusion of Copper Atoms in Polycrystalline CdTe Films Doped with Pb Atoms

The process of diffusion of labeled copper atoms in p-CdTe<Pb> coarse-block films with a columnar grain structure has been studied. The CdTe<Pb> film is a p-type semiconductor, where an increase in the Pb concentration in the composition of the CdTe films increases the resistivity ρ of the structure. When the Pb concentration in CdTe changes from 1018 to 5·1019 cm-3, the hole concentration decreases by more than 3 orders of magnitude at a constant operating level depth of EV + (0.4 ± 0.02) eV. This may indicate that the concentration of acceptor defects, which are formed in the films due to self-compensation upon doping with a PbCd donor, exceeds the number of the latter. Electrical measurements by the Hall method were carried out at a direct current and a temperature of 300 K. As a result, an increase in the temperature of films on a Mo-p-CdTe<Pb> substrate during annealing affects the electrical parameter of charge carrier mobility µ, it decreases significantly. X-ray diffraction analysis showed that on the diffraction patterns of samples of p-CdTe<Pb> films, all available reflections correspond to the CdTe phase and up to х = 0.08 do not contain reflections of impurity phases and have a cubic modification. Based on the results of the calculation, it was established that the low values of the diffusion coefficient of Cu atoms are due to the formation of associates of the A type , which are directly dependent on the concentration of atoms. Diffusion length Ln and lifetime τn of minority current carriers in large-block p-type cadmium telluride films, which can also be controlled by introducing lead atoms into cadmium telluride.

Performance evaluation of interfacial characteristics between cold metal transfer-wire arc additive manufactured SS308LSi and wrought SS304L with controlled and uncontrolled interlayer temperature

The present work investigates the mechanical behavior and microstructure evolution of the interface between the cold metal transfer (CMT)-wire arc additive manufactured (WAAM) SS308LSi and wrought SS304L via controlled interlayer temperature (CIT) of 100–120°C and uncontrolled interlayer temperature (UIT). The thermal cycles on the substrate were recorded using K-type thermocouples and correlated with the mechanical and microstructure properties of deposited walls. Microstructure analysis of the interface cross-section revealed a defect-free interfacial bond with a columnar solidification structure with slightly coarser grains under UIT deposition compared to CIT deposition. The microhardness of wrought SS304L is in the range of 196 ± 9 HV, while that of UIT and CIT deposited 308LSi is 178.4 ± 7.02 HV and 183.4 ± 6 HV, respectively, with no aberrant hardness values at the interface. Tensile tests were performed on the wrought SS304L and WAAM SS308LSi transverse to their interface. The results revealed that interface strength is higher than that of WAAM deposits and failed with average ultimate tensile strengths of 589.1 and 580.9 MPa under CIT and UIT depositions, respectively. This work reveals that CMT-WAAM can produce high-quality interfacial bonding between WAAM SS308LSi and wrought SS304L.

Selective laser melting of AlCoCrFeMnNi high entropy alloy: Effect of heat treatment

The dilemma concerning the trade-off between the strength and ductility of alloys has persistently been a significant problem in engineering applications. Conventional techniques such as grain refinement, severe plastic deformation, and precipitation strengthening usually increase strength at the expense of ductility. High entropy alloys with dual-phase structures, on the other hand, generally display excellent strength-ductility synergy. In this study, we attempted to mix pre-alloyed powders of two distinct phases (body-centered cubic - bcc and face-centered cubic - fcc) to fabricate AlCoCrFeMnNi HEAs with a dual-phase structure by selective laser melting. Furthermore, we investigate the impact of varying heat treatment temperatures (900 °C, 1000 °C, and 1100 °C) on its phase composition, microstructure, and mechanical properties. The results show that with an increase in the heat treatment temperature, the volume of the fcc phase increases gradually and the volume of the bcc phase decreases. The columnar structure in the fcc phase transforms into a cellular structure, and a spinodal decomposition is observed with the bcc phase. As the heat treatment temperature increases, the yield strength decreases while the elongation substantially increases, with the samples heat-treated at 1100 °C showing the best comprehensive properties (yield strength ∼700 MPa, tensile strength ∼950 MPa, and ∼15% ductility).

High-temperature oxidation resistance of CrAlN thin films prepared by DC reactive magnetron sputtering

CrAlN thin films were prepared by using the reactive DC unbalanced magnetron sputtering method from the single alloy target on a silicon substrate. The effect of annealing temperature in the air which ranges from 500℃ to 900℃ for 1 h on phase structure, film composition, surface morphology, microstructure, and hardness was investigated by XRD, EDS, FE-SEM, and Nanoindentation techniques, respectively. The high-temperature (up to 900℃) oxidation resistance of the thin film was also evaluated. The result shows that solid solutions of (Cr,Al)N with (111), (200), and (220) planes for the as-deposited film and no oxide phase were found after annealing with different temperatures. The O content slightly increases with an increase in the annealing temperature with various Cr, Al, and N contents found by the EDS. From the FE-SEM result, as increased annealing temperature, the evolution of cross-sectional morphology from dense to compact columnar structure was exhibited but the oxides layer was not detected. These results concluded that the as-deposited thin film showed good oxidation resistance when annealed in air at an elevated temperature reaching 900℃. Moreover, the film’s hardness decreased from 61.19 GPa to 50.11 GPa with increasing the annealing temperature observed by the Nanoindentation technique.

Creep property and microstructural evolution of laser powder bed fused binary Al–10Ce alloy

Aluminum–Cerium (Al–Ce) based alloys have shown promise as cost-efficient high temperature creep-resistant aluminum alloy. These alloys are also highly printable with laser powder bed fusion (LPBF) additive manufacturing. This study investigates the creep property of a near eutectic binary Al–10Ce (wt. %) alloy manufactured by LPBF and its microstructural evolution during creep. The as-built alloy exhibited columnar grain structure with a weak cube texture and its microstructure consisted of fine eutectic Al + Al11Ce3. Compressive creep tests with incremental stresses were performed perpendicular to the build direction at temperatures ranging from 275 to 400 °C. The stress exponent was approximately 1 in the low stress regime and 5–7 in the high stress regime, corresponding to diffusion and dislocation creep, respectively. The average activation energy was approximately 229 kJ/mol·K in the temperature between 275 and 375 °C. After creep deformation, the melt pool boundary faded and the eutectic Al11Ce3 intermetallics slightly coarsened. The grain structure remained relatively stable and the grain boundary became more pronounced. By comparing the minimum creep strain rate to other alloys, it was found that LPBF Al–10Ce is more creep resistant than similar cast binary Al–Ce counterpart, some ternary Al–Ce alloys and LPBF AlSi10Mg alloy. This benchmark results on the creep property of LPBF binary eutectic Al–Ce alloy provide insights to future development of creep-resistant Al–Ce alloys.

(Invited) 5,15-Diazatetrabenzoporphyrins: Evaluation as Organic Semiconductors

Tetrabenzo-5,15-diazaporphyrin (TBDAP) is a structural hybrid molecule of tetrabenzoporphyrin (TBP) and phthalocyanine (Pc). As compared with TBP, TBDAP has energetically lower HOMO and LUMO because of the higher electronegativity of nitrogen atom at meso-position. Moreover, its optoelectronic properties, solubility and molecular arrangement in the solid state can be controlled by introducing various substituents at another meso-carbons. These electronic and structural tunabilities of TBDAP are advantageous to the organic electronic application such as organic field-effect transistors (OFETs) and organic photovoltaics (OPVs), but selective and efficient synthetic methods for TBDAP are limited. Triisopropylsilyl (TIPS)-ethynyl group is one of the most popular substituents for organic semiconducting molecules. We synthesized 5,15- bis(triisopropylsilylethynyl)tetrabenzoporphine (TIPS-TBP) and its metal complexes. TIPS-TBP has reasonable solubility for solution-processed OFETs and exhibits excellent hole mobilities of 1.1 cm2 V− 1 s− 1 and 2.16 cm2 V− 1 s− 1 in dip-coating FET and single-crystal FET, respectively [1, 2]. These values are higher than that of pristine free-base TBP (0.07 cm2 V−1 s−1), indicating that TIPS-ethynyl group is also useful for porphyrin analogues. Herein, we report the synthesis of 10,20-bis(triisopropylsilylethynyl)tetrabenzo-5,15-diazaporphine (TIPS-TBDAP) by metal-template aza-annulation reaction [3,4]. TIPS-TBDAP exhibited efficient far-red fluorescence in solution and formed one-dimensional (1D) columnar structure in crystal packing. Its charge transporting property evaluated by preparing dip-coating FET and single-crystal FET will be also reported.

Petrology and Geochemistry of Microgabbro in Watugajah Area, Gedangsari, Southern Mountains

An intrusive igneous rock with a columnar joint structure having a height of approximately 55 m cropped out in the Watugajah area, Gedangsari, Gunung Kidul Regency, Yogyakarta Special Province. This region geologically is in the western part of the Southern Mountains, part of the Baturagung Subzone, which belongs to the Kebo Formation. This study aims to characterize the igneous rock in the Watugajah area of the Southern Mountains. It suggests the petrogenetic information of this igneous rock and gives a new consideration of the geological history in the Kebo Formation.Geological field mapping was managed in the research area to identify the correlation with other rock units. Rock samples were collected to characterize their composition by petrographical and geochemical analyses. The results suggest the igneous rocks intruded sedimentary rocks of the Kebo Formation, which consists of intercalations coarse sandstone and tuff, fine sandstone and siltstone, and tuff and fine sandstone units. The igneous rocks are classified as microgabbro and basalt in the form of the sill and dyke intrusions. The microgabbro and basalt consist of plagioclase, clinopyroxene, and magnetite, formed by the cooling of magma in the shallow depths. Based on geochemical studies, the igneous rocks of the Watugajah area were formed by subduction zone tectonic setting with the tholeiitic affinity. Keywords: Gedangsari, microgabbro, Southern Mountains, subduction, Watugajah.

The Fine-scale Structure of Polar Coronal Holes

Coronal holes are thought to be composed of relatively broad columnar structures known as plumes. Here, we demonstrate that the plumes (and interplumes) in polar coronal holes are composed of fine-scale filamentary structure, with average scales of 2″–10″. The fine structure is the off-limb analog of the previously found “plumelets” of Uritsky et al. The off-limb observations enable an examination of the fine structure without the influence of the underlying atmosphere along the line of sight. Hence, we show that the fine-scale structure is present at least until the edge of the field of view of the Solar Dynamics Observatory. The fine structure is found to have spatial distribution that follows a k −1 power law perpendicular to the inferred magnetic field direction. For a small sample of the fine structure, the cross-sectional profiles are measured as a function of height. In some cases, the measurements indicate that the fine structure expands super-radially, consistent with existing models of polar field expansion and the expansion of the plumes. We discuss the implications of the presence of the fine structure with respect to understanding wave propagation in the coronal holes and their contribution to powering the solar wind.

Comparison of Solidification Microstructure Evolution of Al-10Si and Recycled Aluminium Beverage Can Strips Made in a Strip Caster

A strip caster was used to cast two types of aluminium alloys: an almost eutectic Al-Si alloy (Al 10 Si) with contaminants of 0.6 Fe, 0.2 Pb, and 1.4 Sn, which exhibits a polyphase microstructure upon solidification, and recycled aluminium beverage cans made from Al 0.8 Mn alloy containing 0.4 Si, 0.5 Fe, and 0.1 Mg, which has a monophase microstructure upon solidification. The molten materials were poured at 650 oC (Al 10 Si) and 670 oC (Al 0.8 Mn, 0.4 Si, 0.5 Fe, 0.1 Mg) on a cooling slope specially designed to obtain a semisolid material. This semisolid material was then dragged between rolls at a rate of 0.2 m/s to obtain high-quality metal strips. There was less eutectic modification with larger Al-α grains in the middle region of the sheet between the fine eutectic layers, indicating a lower cooling rate. However, during the recycling of aluminium beverage cans, large grains were formed with a columnar structure at the interface of the rolls, and semisolid melts with cracks were formed between the columnar grain boundaries owing to the compression of the rolls. The middle of these grains contained smaller equiaxial grains that were subjected to dragging. The as-cast specimens were submitted to homogenisation heat treatment at 560 oC for a period of 10 h and cooled to room temperature before being cold rolled (Temper H18) and recrystallised (Temper O) to examine the effect of these treatments on the tensile mechanical properties. During cold rolling (Temper H-18), grain alignment occurred with a yield stress, maximum stress, and elongation of 209.5 MPa, 210.1 MPa, and 2.8%, respectively. The strength decreased (yield stress of 58 MPa and maximum stress of 120.2 MPa) under recrystallisation conditions (Temper O), but the ductility increased (8.9%). This is in contrast to the Al-Si (Al 10Si) strip, which exhibited a yield stress, maximum stress, and elongation of 103.3 MPa, 128.7 MPa, and 1.9%, respectively. The A1 10Si strips also fractured during cold rolling, indicating high material fragility.

α-parvin controls chondrocyte column formation and regulates long bone development

Endochondral ossification requires proper control of chondrocyte proliferation, differentiation, survival, and organization. Here we show that knockout of α-parvin, an integrin-associated focal adhesion protein, from murine limbs causes defects in endochondral ossification and dwarfism. The mutant long bones were shorter but wider, and the growth plates became disorganized, especially in the proliferative zone. With two-photon time-lapse imaging of bone explant culture, we provide direct evidence showing that α-parvin regulates chondrocyte rotation, a process essential for chondrocytes to form columnar structure. Furthermore, loss of α-parvin increased binucleation, elevated cell death, and caused dilation of the resting zones of mature growth plates. Single-cell RNA-seq analyses revealed alterations of transcriptome in all three zones (i.e., resting, proliferative, and hypertrophic zones) of the growth plates. Our results demonstrate a crucial role of α-parvin in long bone development and shed light on the cellular mechanism through which α-parvin regulates the longitudinal growth of long bones.

Magnetic and geochemical scanning reveals growth history of marine ferromanganese crust on Detroit Seamount, northwest Pacific since the early Miocene

The Hawaiian Chain-Emperor Seamounts is known to be one of the most active regions influenced by mantle hotspot. However, previous studies have provided limited information on the growth process and metal enrichment of marine ferromanganese crusts as indicators of post-eruption history. In this study, we conducted a geochronological and major elemental study of a hydrogenetic ferromanganese crust, from the Detroit Seamount using high-resolution magnetic and geochemical scanning. Our findings are as follows: (1) A total of 39 magnetozones are recognized in the studied section of the crust, which can be preliminarily correlated to the geomagnetic polarity timescale from chrons C1n to C5Dn. This correlation yields growth rates of 1.48–2.18 mm/Myr over the past ∼18 Myr. (2) Columnar and lamellar growth structures are identified with distinct metal enrichment patterns. A significant transition from lamellar to columnar growth occurred at ∼11.6 Ma. (3) The quantified elements can be clustered into three groups, (Mn, Cu–Co–Ni, and Al–Si), (Fe and Ti), and Ca. A strong correlation between metal enrichment in the crust and the global benthic foraminifera δ13C record is then observed. Based on these results, we suggest a predominant role of deep-sea redox conditions in the growth history of ferromanganese deposits on the Detroit Seamount since the Early Miocene.

Effect of laser energy density on surface morphology, microstructure and mechanical behaviour of direct metal laser melted 17-4 PH stainless steel

Abstract The surface and microstructural characteristics of 3D printed parts play a significant role under mechanical loading. The authors have explored the effect of laser energy densities on the surface morphology, microstructure and mechanical behaviour of 17-4 precipitation hardened stainless steel fabricated under the direct metal laser melting technique. The considered processing parameters were laser energy density and its technical parameters: laser power, layer thickness, hatch spacing and scanning speed. The mechanical and metallurgical properties of the as-printed samples appeared better than the wrought counterpart due to the higher densification level (99.74 %) induced by the rotating scanning strategy. X‐ray diffraction revealed the presence of both the martensitic α phase and austenitic γ phase in the as-printed sample. There is no significant anisotropy in the mechanical behaviour as the build direction has a random texture with a fine columnar grain structure. The high laser energy density with low layer thickness results in an excellent surface finish. The tensile strength (1180 MPa) and the elongation for the as-printed sample (45.0 %) were considerably more significant than that for the wrought sample (1160 MPa and 26.0 %), which is attributed to the combination of low and high-angle boundaries, as confirmed by the electron backscatter diffraction results.

Understanding the effects of cortical gyrification in tACS: insights from experiments and computational models.

The alpha rhythm is often associated with relaxed wakefulness or idling and is altered by various factors. Abnormalities in the alpha rhythm have been linked to several neurological and psychiatric disorders, including Alzheimer's disease. Transcranial alternating current stimulation (tACS) has been proposed as a potential tool to restore a disrupted alpha rhythm in the brain by stimulating at the individual alpha frequency (IAF), although some research has produced contradictory results. In this study, we applied an IAF-tACS protocol over parieto-occipital areas to a sample of healthy subjects and measured its effects over the power spectra. Additionally, we used computational models to get a deeper understanding of the results observed in the experiment. Both experimental and numerical results showed an increase in alpha power of 8.02% with respect to the sham condition in a widespread set of regions in the cortex, excluding some expected parietal regions. This result could be partially explained by taking into account the orientation of the electric field with respect to the columnar structures of the cortex, showing that the gyrification in parietal regions could generate effects in opposite directions (hyper-/depolarization) at the same time in specific brain regions. Additionally, we used a network model of spiking neuronal populations to explore the effects that these opposite polarities could have on neural activity, and we found that the best predictor of alpha power was the average of the normal components of the electric field. To sum up, our study sheds light on the mechanisms underlying tACS brain activity modulation, using both empirical and computational approaches. Non-invasive brain stimulation techniques hold promise for treating brain disorders, but further research is needed to fully understand and control their effects on brain dynamics and cognition. Our findings contribute to this growing body of research and provide a foundation for future studies aimed at optimizing the use of non-invasive brain stimulation in clinical settings.

Pirh2-dependent DNA damage in neurons induced by the G-quadruplex ligand pyridostatin

Noncanonical base pairing between four guanines (G) within single-stranded G-rich sequences leads to formation of а G-quartet. Self-stacking of G-quartets results in a columnar four-stranded DNA structure known as the G-quadruplex (G4 or G4-DNA). In cancer cells, G4-DNA regulates multiple DNA-dependent processes, including transcription, replication, and telomere function. How G4s function in neurons is poorly understood. Here, we performed a genome-wide gene expression analysis (RNA-Seq) to identify genes modulated by a G4-DNA ligand, pyridostatin (PDS), in primary cultured neurons. PDS promotes stabilization of G4 structures, thus allowing us to define genes directly or indirectly responsive to G4 regulation. We found that 901 genes were differentially expressed in neurons treated with PDS out of a total of 18,745 genes with measured expression. Of these, 505 genes were downregulated and 396 genes were upregulated and included gene networks regulating p53 signaling, the immune response, learning and memory, and cellular senescence. Within the p53 network, the E3 ubiquitin ligase Pirh2 (Rchy1), a modulator of DNA damage responses, was upregulated by PDS. Ectopically overexpressing Pirh2 promoted the formation of DNA double-strand breaks, suggesting a new DNA damage mechanism in neurons that is regulated by G4 stabilization. Pirh2 downregulated DDX21, an RNA helicase that unfolds G4-RNA and R-loops. Finally, we demonstrated that Pirh2 increased G4-DNA levels in the neuronal nucleolus. Our data reveal the genes that are responsive to PDS treatment and suggest similar transcriptional regulation by endogenous G4-DNA ligands. They also connect G4-dependent regulation of transcription and DNA damage mechanisms in neuronal cells.

Polymer Containing Multiple Secondary Structures—A Competition between Helical Induction and C‐T Complexation

AbstractThough “foldamers” have greatly developed, molecules that fold beyond 2° structures are less common. The design and synthesis of triblock copolymers of the “A‐B‐A” type containing two types of helix formation blocks are presented. Two blocks (A and B) are chosen, with one comprised of L‐polyproline as block “A” and the other block (B) comprised with three naphthalene diimide‐derivatives separated by two proline residues. Block (B) is carefully designed to serve as a bifunctional initiator for the ring‐opening polymerization of proline‐N‐carboxy anhydride as well as to encapsulate an electron‐rich aromatic species by charge transfer complexation (C‐T). As a result of (C‐T) complexation with dialkoxy pyrene, the native helical structure of the middle block is transformed into a 1D columnar structure without affecting the 2° structure of the polyproline block. In this way, the initial helix1‐b‐helix2‐b‐helix1 structure of the block copolymers is transformed into a helix1‐b‐columnar‐b‐helix1 structure. The C‐T complexation and related structural changes of the block copolymers are characterized using UV‐vis, fluorescence, and circular dichroism spectroscopy.

An in-situ oxide-dispersion-strengthened AlCoCrFeNiY high-entropy alloy composite coating prepared by AC-HVAF with superior oxidation and spallation resistance

We report an in-situ oxide-dispersion-strengthened AlCoCrFeNiY high-entropy alloy composite coating (ODS-HEA composite coating) with exceptional oxidation and spallation resistance at 1100 °C and 1150 °C. The coating is manufactured by activated combustion-high velocity air fuel (AC-HVAF) and has an ultrafine-grained microstructure that comprises γ, β and nanoscale oxide particles (Al2O3, Cr2O3 and Y2O3) formed in-situ in coating processing. The thermally grown oxides (TGOs) on the coating at 1100 °C and 1150 °C are exclusively α-Al2O3 with a columnar grain structure. The parabolic rate constant of the coating is about half of that of the conventional NiCoCrAlY coating (CNA coating) at both 1100 °C and 1150 °C, respectively. The lower TGO growth rate is primarily attributed to its coarser TGO grains that reduce the efficient oxygen diffusivity. Compared to the CNA coating, a higher TGO/coating interfacial toughness is achieved via inhibiting the formation of interfacial pores for ODS-HEA composite coating. The low TGO growth rate decreases the driving force for TGO spallation and the high interfacial toughness increases the TGO adhesion, thus contributing to the strong spallation resistance for the ODS-HEA composite coating. The superior oxidation and spallation resistance of the ODS-HEA composite coating at 1100 °C and 1150 °C make it a candidate bond coat for advanced thermal barrier coatings.

Deposition Temperature Induced Texture and Strengthening of Ti/Ni Multilayer Thin Films

Abstract Strong thermal effect on microstructure and mechanical properties of Ti/Ni multilayer thin films was observed from in situ heating during deposition and subsequent annealing. Films deposited at low-temperature show preferred crystallographic texture for both Ti and Ni layers, with columnar structure extending through the layers. The columnar structure becomes more distinct and complete with the increase of temperature up to 300 °C, and meanwhile, more atomic diffusion and intermixing occur along the Ti/Ni interfaces, promoting the formation of Ti-Ni intermetallic precipitates. High-temperature deposition causes disintegration of the layered structure. Columnar Ti-Ni alloys and further recrystallized alloys were detected with the preferred crystallographic texture. For material strength, an increased hardness trend was observed with increasing deposition temperature even with much larger grain size compared to room temperature case. Furthermore, for multilayer systems deposited under low temperature, post-annealing resulted in higher hardness with minimal microstructure modification, with more strengthening observed in lower deposition temperature case.

Effects of RF magnetron sputtering power on the structure and nanohardness of high-entropy alloys (TiVCrNbSiTaBY)N hard coatings

High-entropy alloys (TiVCrNbSiTaBY)N hard coatings were deposited on silicon wafers and stainless steel plates using radio-frequency (RF) magnetron sputtering. The effects of RF power on the elemental composition, morphology, structure and nanohardness of coatings are evaluated. The coatings exhibit smooth surface with low roughness less than 1 nm. Higher RF power introduces more silicon into coatings and densifies the columnar structure. The coatings present nanocomposite structure of face-centered cubic phase and amorphous Si3N4. With increasing RF power, the content of amorphous phase rises and crystal grains are refined. The changes in structure lead to a tendency for nanohardness and elastic modulus of coatings to first increase and then decrease. The coating grown at 800 W has the highest nanohardness and highest elastic modulus of ∼38.1 GPa and ∼451.2 GPa, respectively. The strengthening mechanism is explained by the nanocrystal-TiN/amorphous-Si3N4 model. The annealing treatment in air demonstrates that the coating exhibits excellent oxidation resistance at 800 °C.

Study on the Effect of Remelt Scanning and Heat Treatment Processes on the Structure and Properties of Laser Powder Bed Fusion Formed Al-Mg-Sc-Zr Alloys

Laser Powder Bed Fusion (LPBF) technology was used to form Al-Mg-Sc-Zr alloys to investigate the effects of remelting scanning and heat treatment processes on their tissue evolution and mechanical properties. The results show that the surface roughness (Sa) of the upper surface of the unmelted and once-remelted scans are similar. In contrast, the surface roughness (Sa) of the upper surface of the twice-remelted scans is significantly higher. The surface roughness (Sa) of the specimen sides gradually increases with the number of scans. The Al-Mg-Sc-Zr alloy has a unique mixed crystal structure, with many Al3(Sc, Zr)-L12 precipitates precipitating at the melt pool boundary to promote the formation of fine equiaxed crystals.In contrast, the interior of the melt pool is a coarse columnar crystal structure due to the low precipitation of Al3 (Sc, Zr)-L12 precipitates. After heat treatment, more Al3 (Sc, Zr)-L12 precipitates will precipitate inside the melt pool. After the aging heat treatment, the specimens’ yield and tensile strength increased significantly while the elongation at break decreased.

Grain size manipulation by wire laser direct energy deposition of 316L with ultrasonic assistance

The epitaxial growth of coarse and columnar grain structures along the build direction of additive manufactured metals is a usual phenomenon. As a result, as-built components often exhibit pronounced anisotropic mechanical properties, reduced ductility, and, hence, a high cracking susceptibility. To enhance the mechanical properties and processability of additive manufactured parts, the formation of equiaxed and fine grained structures is thought to be most beneficial. In this study, the potential of grain refinement by ultrasonic excitation of the melt pool during laser wire additive manufacturing has been investigated. An ultrasound system was developed and integrated in a laser wire deposition machine. AISI 316L steel was used as a substrate and feedstock material. A conversion of coarse, columnar grains (dm = 284.5 μm) into fine, equiaxed grains (dm = 130.4 μm) and a weakening of typical <100>-fiber texture with increasing amplitude were verified by means of light microscopy, scanning electron microscopy, and electron backscatter diffraction analysis. It was demonstrated that the degree of grain refinement could be controlled by the regulation of ultrasound amplitude. No significant changes in the dendritic structure have been observed. The combination of sonotrode/melt pool direct coupling and the laser wire deposition process represents a pioneering approach and promising strategy to investigate the influence of ultrasound on grain refinement and microstructural tailoring.