Direct Deposition Research Articles

Contribution of Streptococcus pseudopneumoniae and Streptococcus salivarius to vocal fold mucosal integrity and function.

Structural changes to the vocal fold (VF) epithelium, namely, loosened intercellular junctions, have been reported in VF benign lesions. The potential mechanisms responsible for the disruption of cell junctions do not address the contribution of resident microbial communities to this pathological phenomenon. In this study, we focused on determining the relationship between Streptococcus pseudopneumoniae (SP), a dominant bacterial species associated with benign lesions, and Streptococcus salivarius (SS), a commensal bacterium, with human VF epithelial cells in our three-dimensional model of the human VF mucosa. This experimental system enabled direct deposition of bacteria onto constructs at the air/liquid interface, allowing for the assessment of bacterium-host interactions at the cellular, molecular and ultrastructural levels. Our findings demonstrate that SP disrupts VF epithelial integrity and initiates inflammation via the exported products HtrA1 and pneumolysin. In contrast, SS attaches to the VF epithelium, reduces inflammation and induces Mmp2-mediated apical desquamation of infected cells to mitigate the impact of pathogens. In conclusion, this study highlights the complexity of microbial involvement in VF pathology and potential VF mucosal restoration in the presence of laryngeal commensals.

Hierarchically heterogeneous microstructure and mechanical properties in laser-directed energy deposition of γ-TiAl alloy through intrinsic cyclic heat treatment

The complex thermal effects of laser direct energy deposition (L-DED) provide significant advantages for production of high-performance γ-TiAl alloy, whereas challenges still exist in microstructure tailoring and mechanical properties. This work focuses on the influence of intrinsic cyclic heat treatment (ICHT) on the evolution of microstructures and mechanical properties in different building height regions of an L-DED TiAl alloy thin-wall sample. The results indicate that ICHT induces discontinuous coarsening (DC) effects by consuming the lamellar interface energy of the initial lamellae, resulting in grain refinement. With the increase in building height, the thermal accumulation leads to an increase in the initial lamellar spacing, which weakens the DC effect. At the top, insufficient thermal cycles prevent fine grain growth and erode coarse grains, hindering overall grain refinement. Ultimately, the hierarchically heterogeneous microstructure forms in the L-DED TiAl alloy, including refinement of hierarchical lamellar colony structure decorated with fine (α2+γ) lamellar structure and (α2+6H-LPS) lamellar structure (6H-LPS refers to 6H long-period structure phase). Specifically, the bottom region exhibits the best combination of ultimate tensile strength (706 ± 33 MPa) and strain (0.68 ± 0.05 %). The high tensile strength can be attributed to the hindrance of dislocation movement by the fine lamellae and the 6H-LPS phase ,caused by the high cooling rate of L-DED, while the elongation is attributed to the reduction in crack propagation energy due to the presence of fine grains.

Wire Arc Additive Manufacturing of Aluminum Foams Using TiH2-Laced Welding Wires.

Composite materials made from aluminum foam are increasingly used in aerospace and automotive industries due to their low density, high energy absorption capacity, and corrosion resistance. Additive manufacturing processes offer several advantages over conventional manufacturing methods, such as the ability to produce significantly more geometrically complex components without the need for expensive tooling. Direct Energy Deposition processes like Wire Arc Additive Manufacturing (WAAM) enable the additive production of near-net-shape components at high build rates. This paper presents a technology for producing aluminum foam structures using WAAM. This paper's focus is on the development of welding wires that are mixed with a foaming agent (TiH2) and produce a foamed weld metal as well as their processing using MIG welding technology.

Assessment of structural defects and mechanical characteristics of IN718/St6 functionally graded material produced by direct laser deposition

Functionally graded materials (FGM) do not show special processing in the composite structure due to the combination of mechanical, thermal, magnetic and stress gradient properties. The aim of this study is to produce IN718/St6 FGM samples by direct laser deposition method. The product of this model should enable the development of mechanical products. Best of all, this can be done without significant reduction in texture and case to residual stress that are a consequence of rapid changes in mechanical and thermal properties in non-FGM samples. To fabricate part, direct laser deposition system equipped with a 1 kW continuous fiber laser is used, SEM/EDS analysis and microhardness testing to measure porosity, chemical composition, and quantify gradient mechanical properties is used. In this study, the cladding composition is selected from 100% IN718 to 100% St6 with a 25% change in St6 composition. To prevent the formation of defects, both single-parameter modes and individual layering are examined, considering the diverse nature of the combination. The result shows that using an individual layering structure, reduces 100% Lack of fusion defects in the IN718/St6 structure. EDS analysis confirmed that the St6 content gradually increased from the first to the fifth layer. The substrate hardness gradually increases from 200 Vickers hardness to 550 Vickers hardness, showing an almost linear trend. Moreover, by using individual layering, the coaxial structure is reduced by 55% and the relative orientation of the vertical line is reduced by 18° compared to using the St6 directly (non-FGM).

Effect of the Cooling Liquid on the Milled Interface in the Combined Process of Milling and Direct Metal Deposition.

The combination of Direct Metal Deposition (DMD) with milling offers numerous advantages for the manufacturing of complex geometry parts demanding high dimensional accuracy and surface quality. To reach this, a process strategy alternation between both processes is often required, leaving the milled surface with a layer of cooling fluid before adding material by DMD. This paper investigates the effect of cooling liquid on the milled interface in the combined process of milling and DMD. Five different interface conditions were examined, employing four distinct cleaning techniques to assess their impact on the quality of the interface. Key metrics analysed included hydrogen content, carbon content, and porosity levels at the interface. Cleaning techniques were evaluated to determine their necessity in enhancing the interface quality in the combined DMD and milling production process. Results from this study provide essential insights into the optimal cleaning requirements for improving the interface integrity in hybrid manufacturing processes, which could lead to more reliable and efficient production methods in industrial applications.

Dynamics of pore formation and evolution during multi-layer directed energy deposition additive manufacturing via in-situ synchrotron X-ray imaging: A case study on high-entropy Cantor alloy

Blown-powder directed energy deposition (DED) additive manufacturing is impeded for novel alloys processing by perceivable and detrimental porosity. During multi-layer depositions, however, mechanisms of pore formation and evolution remain elusive for developing pore mitigation strategies. Here, conduction-mode multi-layer DED process of an exemplary high-entropy Cantor alloy have been investigated in-situ by high-energy high-speed synchrotron X-ray imaging. Three new pore formation mechanisms are unveiled when depositing first layer and successive layers: gas pore induced by high-velocity powder injection into melt pool, pore generated from swirl shear of turbulent melt flow, and pore trapped by surface wave. Three pore formation mechanisms are reconfirmed: pore inheritance from feedstock powder, pore generation when laser remelting defect-sensitive locations of existing pore from previous layer or unmelted powder attached on the melt pool surface, and pore formation as cooling of melt pool. A unique mechanism for pore elimination is proposed: a counter-Marangoni melt flow is experimentally found in the stable melt pool and contributes to the prolonged pore lifetime at tens of milliseconds scale; pores are prone to coalesce into larger sizes in laser interaction zone and the adjacent location with circulation zone; coalesced larger pores driven by combined effect of Marangoni and buoyant forces easily get eliminated from melt pool. The results of pore formation and evolution dynamics revealed in Cantor alloy provide quantified experimental data for high-fidelity computational modeling and in-depth insights of porosity control for high-entropy alloy printing down to melt pool scale.

Effect of molten-pool inertia in variable-width arc-based direct energy deposition by regulating parameters

Varied-thickness deposition faces the challenge of simultaneously achieving the expected width and maintaining a flat layer. Herein, the current and wire feed speed (WFS) were synchronously regulated for variable-width deposition. In forward regulation, the parameter values were changed from large to small, corresponding to the changes in the formation from wide to narrow. The opposite was true for the reverse regulation. During consecutive alternating deposition, the width for forward regulation was greater than that for reverse regulation at the same position, corresponding to the phenomenon of lag formation.To explain this phenomenon, the concept of molten-pool inertia and its corresponding mechanism were established. It was found that the inertia was directly proportional to the quality of the molten pool and was consistently directed toward a smaller parameter. The forward inertia of the molten pool in forward regulation promoted its stabilization, while the reverse inertia of the pool in reverse regulation hindered its stabilization. As a result, staggered arrangements were produced, and multilayer deposition caused varying degrees of lag formation. A more significant inertial effect was observed for higher molten-pool quality.Finally, an optimization method was proposed to weaken the molten-pool inertia and reduce bidirectional lag formation. Using this method, the sidewall surface roughness, Sa, of the variable-width region was reduced by 17.3 % compared with that before optimization.

Microstructure and mechanical properties of Al-Zn-Mg-Cu alloy fabricated by multi-wire arc-based directed energy deposition

ER5356, ER2319 and Zn wires were synchronously fed using a multi-wire gas metal arc directed energy deposition (DED) system. This allowed the successfully fabrication of Al-6.0Zn-2.5Mg-1.5Cu alloy. The microstructure and mechanical properties of the fabricated parts were studied. It is shown that the main precipitated phases are η and nanoscale η'. The upper and lower parts of the deposited parts are composed by coarse equiaxed grains and columnar dendrite structures, respectively. The average microhardness of the fabricated alloy was 118.5 HV. The ultimate tensile strength and elongations in the perpendicular to the building direction (BD) and parallel to the BD were 267 MPa and 2.7 %, 238 MPa and 2.3 %, respectively. The average tensile strength is higher than that of 7075-O alloy. The fracture mode of the samples composed brittle and ductile features, although the former dominated. This multi-wire arc DED approach provides a new choice for the in-situ synthesis of Al-Zn-Mg-Cu alloys.

Martensitic transformation induced strength-ductility synergy in additively manufactured maraging 250 steel by thermal history engineering

Maraging steels are known for their exceptional strength but suffer from limited work hardening and ductility. Here, we report an intermittent printing strategy to tailor the microstructure and mechanical properties of maraging 250 steel via tuning the thermal history during wire-arc directed energy deposition. By introducing a dwell time between adjacent layers, the maraging 250 steel is cooled below the martensite start temperature, triggering thermally-driven martensitic transformation during the printing process. Thermal cycling during subsequent layer deposition results in the formation of reverted austenite which shows a refined microstructure and induces elemental segregation between martensite and reverted austenite. The Ni enrichment in the austenite promotes stabilization of the reverted austenite upon cooling to room temperature. The reverted austenite is metastable during deformation, leading to strain-induced martensitic transformation under loading. Specifically, a 3 min interlayer dwell time produces a maraging 250 steel with approximately 8% reverted austenite, resulting in improved work hardening via martensitic transformation induced plasticity during deformation. Meanwhile, the higher cooling rate and refined prior austenite grains lead to substantially refined martensitic grains (by approximately fivefold) together with an increased dislocation density. With 3 min interlayer dwell time, the yield strength of the printed maraging 250 steel increases from 836 MPa to 990 MPa, and the uniform elongation is doubled from 3.2% to 6.5%. This intermittent deposition strategy demonstrates the potential to tune the microstructure of maraging steels for achieving strength-ductility synergy by engineering the thermal history during additive manufacturing.

Microstructural evolution and phase analysis of SS410–Al2O3–SiC multilayered functionally graded composite fabricated through laser cladding

In the present study, a functionally graded metal-ceramic composite structure comprising SS410, Al2O3, and SiC particles with varying composition, structure and properties in a single deposit was successfully fabricated using direct energy deposition (DED). The composition varied from 90 % SS410 with 10 % (xAl2O3 + ySiC) to 10 % SS410 with 90 % (xAl2O3 + ySiC), where x = 70 % and y = 30 % in a five-layered FGM design. The microstructure, phase evolution and mechanical properties of the components with different composition gradients were characterized by microscopy, energy dispersive spectroscopy, wavelength dispersive spectroscopy, X-ray diffraction and micro hardness. The investigation revealed that complex phases such as C0.12Fe0.79Si0.09, M7C3, Fe3C, and Fe3Si formed as a result of the interaction between SiC and SS410 during the cladding process. Microstructural analysis showed a transition from columnar dendrites at the bottom zone of the cladding to a typical cellular structure and carbide particle agglomerates in the middle zone, with finer grains at the top zone. This gradation in microstructure correlated with an increase in microhardness ranging from 299 HV at the bottom to 966 HV at the top. This enhancement in hardness is primarily attributed to solid solution strengthening from C and Si originating from the decomposition of SiC and the precipitation of intermetallic phases.

Toward developing remanufactured Ti6Al4V alloys with high fatigue crack growth resistance by in-situ cooling during laser remanufacturing

The fatigue performance of remanufactured titanium alloy blade components has garnered significant attention in recent years. The repaired titanium alloy components using the direct energy deposition (DED) method exhibit structural differences, leading to an inhomogeneous microstructure that directly impacts the service life of the remanufactured component. The work presented here aimed to investigate novel approaches for enhancing the resistance to crack propagation and to gain a deeper insight into the fatigue crack propagation characteristics of the Ti6Al4V remanufactured interface with an inhomogeneous microstructure. The research focused on analyzing the microstructure evolution and fracture properties of remanufactured components using in-situ cooling. The results indicate that in-situ cooling has the potential to decrease the anisotropy of the repaired zone (RZ) and enhance the resistance to crack propagation in the heat-affected zone (HAZ) and base metal (BM). The high cooling rate associated with the in-situ cooling can elevate the presence of high-angle grain boundaries (HAGBs) in the RZ, diminish the phase transformation between the HAZ and BM, and decrease the size of the secondary α phase. The research contributes to a deeper comprehension of fatigue crack propagation in remanufactured components and provides a pathway for the improvement of fatigue performance of remanufactured titanium alloy.

Enhanced mechanical properties and corrosion resistance of electro-deposited NiCoP composite coatings with ZrB2 particle addition

This work was initiated with the purpose of expanding the utilization of nickel-based composite coatings, especially in wear and corrosion-related industrial applications. NiCoP coatings have long attracted scientific and engineering interest due to their enhanced mechanical properties reinforced by incorporation with a reinforcement phase. In the present study, NiCoP composite coatings reinforced with ZrB2 ceramic particles were synthesized by direct current deposition using a modified Watt’s type bath. The microstructures of composite coatings were studied by x-ray diffraction analysis, energy dispersive x-ray spectroscopy, and scanning electron microscopy, respectively. The hardness and tribological properties of the composite coatings were evaluated and compared. The corrosion behaviors of the deposits were investigated using electrochemical spectroscopy and potentiodynamic polarization techniques in simulated seawater. The effect of ZrB2 content on the microstructures and mechanical properties of the composite coatings was explored and discussed. The present study indicates that there is a progressive enhancement in the hardness, corrosion resistance, and wear resistance of the composite coatings with the increase in ZrB2 loading. The NiCoP-12 g/l-ZrB2 coating possesses the highest microhardness and superior wear performance, while the NiCoP-6 g/l-ZrB2 coating exhibits the best anti-corrosion properties. The present study shows a cost-effective and feasible solution for the preparation of NiCoP protective coatings with enhanced properties, which holds great potential for industrial applications requiring wear and anti-corrosion protection.

Thickness-dependent structure and properties in zirconium carbide ceramic via orientated deposition

The fine-tuning of controlled structure and property evolution of zirconium carbide (ZrC) ceramic is essential for its functional applications, especially with insufficient understanding of the size effect mechanisms. In this investigation, the physically vapor-deposited ZrC (PVD-ZrC) ceramic was fabricated through magnetron sputtering, with a specific focus on its thickness-dependent growth and evolution of composition, microstructure, growth texture and mechanical properties. As prepared PVD-ZrC presents a hybrid structure characterized by amorphous carbon and nanocrystalline ZrC, with diversity in crystallinity, crystallite size, and growth pattern determined by target power, gas-flow pressure and substrate temperature. Moreover, the PVD-ZrC ceramic deposited by directional deposition, exhibits a structure transition from equiaxed crystals to dense columnar fiber crystals and an isotropy-toward texture. As the thickness increases, the stress gradually shifts towards tensile stress with a weaker fracture toughness. Through the First-principle calculation, it is illustrated that the mechanical properties of bulk polycrystalline ZrC are evidently different from low-dimensional polycrystalline ZrC film. This mechanism of thickness-dependent structure and properties is dominant by the surface effect, size effect, grain boundary effect, and stress effects.

Tailoring microstructure and mechanical properties of U75V steel manufactured by laser direct energy deposition combining cobalt addition with preheating treatment

Laser direct energy deposition (LDED) exhibits great potential for application in rail repairing due to its low cost and high process automation. However, the martensite transformation accompanied by rapid solidification leads to the decrease in the mechanical properties and threatens the service safety. In this study, the reinforcement strategy of combining cobalt (Co) addition with preheating treatment was investigated systematically by combining thermodynamic calculations with experimental characterization to optimize the microstructure and mechanical properties of U75V steel by LDED. The results indicate that cobalt addition can promote the pearlite percentage by facilitating the leftward shift of the continuous cooling transformation (CCT) curve, and refining the interlamellar spacing. But the martensite start (Ms) temperature will also increase from 206.4 °C to 324.1 °C after 7 wt% Co addition. 350 °C preheating treatment on the substrate can also promote the pearlite transformation by elevating the valley temperature of thermal cycling over Ms, as well as the subsequent decrease in cooling rate, but it is not sufficient to prevent martensite formation. A synergistic reinforcement strategy of 7 wt% Co addition and 350 °C preheating was established, which can effectively suppress the occurrence of martensite in the bottom area of deposition layers and expand the pearlite range in the top area. The bonding strength between the substrate and deposition layers has been elevated by ∼20%, accompanied by the increase in elongation and wear resistance. A mixed mode of adhesive and abrasive wear has transformed into a mode dominated by adhesive wear after optimization.

Regulating strength and ductility of additively manufactured Inconel 718 alloy via adding nano-TiC and deep cryogenic treatment

The morphology and size of Laves phases play a crucial role in influencing mechanical properties of the additively manufactured Inconel 718 alloy. The current study explores the effects of deep cryogenic treatment (DCT) and the addition of nano-TiC on the microstructure and tensile properties of Inconel 718 alloy manufactured through direct energy deposition (DED). It is found that the addition of 1.5 wt% nano-TiC is conducive to transforming long-striped Laves phases into granular shapes, and the reduced porosity and finer grains are obtained. Compared to the Inconel 718 alloy, the 1.5 wt% nano-TiC/Inconel 718 composite exhibits an enhancement in ultimate tensile strength by approximately 46.81 MPa. Through the thermodynamic simulations, the microstructural evolution induced by the addition of nano-TiC is discussed, which includes the suppression of Laves phases and precipitation of MC particles. Moreover, finer Laves phases and uniform distribution of dislocations are observed in the Inconel 718 alloy after DCT. Dynamic recrystallization occurs within the Inconel 718 alloy during the DCT process, and the grain refinement mechanism is facilitated by a high dislocation density. Consequently, the elongation increases by about 24.8 %, while the strength remains virtually unchanged. Furthermore, the synergistic effect of the addition of nano-TiC and the DCT on Inconel 718 is investigated, and the elongation of nano-TiC/Inconel 718 composite is increased by about 32.7 % with more uniform fracture dimples. This study provides guidance for DED-fabricated Ni-based alloys with excellent strength and ductility.

Multispecies-coadsorption-induced rapid preparation of graphene glass fiber fabric and applications in flexible pressure sensor

Direct chemical vapor deposition (CVD) growth of graphene on dielectric/insulating materials is a promising strategy for subsequent transfer-free applications of graphene. However, graphene growth on noncatalytic substrates is faced with thorny issues, especially the limited growth rate, which severely hinders mass production and practical applications. Herein, graphene glass fiber fabric (GGFF) is developed by graphene CVD growth on glass fiber fabric. Dichloromethane is applied as a carbon precursor to accelerate graphene growth, which has a low decomposition energy barrier, and more importantly, the produced high-electronegativity Cl radical can enhance adsorption of active carbon species by Cl–CH2 coadsorption and facilitate H detachment from graphene edges. Consequently, the growth rate is increased by ~3 orders of magnitude and carbon utilization by ~960-fold, compared with conventional methane precursor. The advantageous hierarchical conductive configuration of lightweight, flexible GGFF makes it an ultrasensitive pressure sensor for human motion and physiological monitoring, such as pulse and vocal signals.

Analysis of structure and strength properties of heat‑resistant iron‑chromium‑nickel (Inconel 718) alloy obtained using secondary metal powder composition in direct laser deposition

This work presents investigations on the structure, chemical analysis, and strength properties of deposited metal using two types of metal powder compositions, namely the primary powder and the residuals (secondary) of the heat‑resistant ironchromium‑nickel alloy Inconel 718.Based on the obtained results, the causes of the formation of a fine‑cellular‑dendritic directional structure with needle and dendritic morphology were determined, as well as the decrease in heat resistance of the deposited material from the secondary powder of the heat‑resistant iron‑chromium‑nickel alloy Inconel 718 at elevated temperatures.

Self-regulating shielding layer induces (002) plane directional deposition of zinc metal anode

Rechargeable aqueous zinc batteries (AZIBs) are ideal for grid-scale energy storage due to their safety and economic characteristics. However, uncontrollable side reactions and dendrite growth severely affect the reversibility of zinc anodes. In the interfacial reaction, inducing smooth deposition of dominant planes is crucial for stabilizing the zinc anodes. Herein, we report a highly concentrated 1‑butyl‑3-methylimidazolium ion (BMIM+) modified electrolyte to improve the diffusion and deposition behavior of Zn2+. Thanks to the strong adsorption effect of BMIM+ at the zinc anode interface, the self-regulating shielding layer inhibits water-induced parasitic reactions. Under the action of BMIM+, Zn2+ has the lowest diffusion energy barrier towards the (002) plane, thus transforming the electrodeposition from a randomly stacked sheet to a dense deposited layer in the Zn(002) plane. The results showed that the symmetric cell composed of the modified electrolyte had a cycle life of 3200 h at 1 mA cm−2, and the average coulombic efficiency (CE) of the asymmetric cell was as high as 99.8 %. The full cell assembled with ZnxV2O5·nH2O still provided 86 % capacity retention at 2 A g−1 after 500 cycles. This electrolyte modification strategy provides a promising option for modulating the anode/electrolyte interface chemistry to achieve high-performance AZIBs.

Mesoscopic characteristics, microstructure evolution, friction mechanisms, and corrosion behavior of Ni60-SiCp coatings fabricated by laser-based directed energy deposition

The influence of varying SiCp on the mesoscopic characteristics, microstructural evolution, microhardness, frictional mechanisms, and corrosion resistance behavior of laser-based directed energy deposition Ni60-SiCp composite coatings was investigated. Coatings reinforced with varying SiCp, the innovative concept of the ''Temperature-SiCp joint effect'' mechanism was proposed. The microstructure was progressively refined due to the SiCp, while microhardness was affected by the solid solution strengthening and diffusion strengthening effects of high SiCp. Furthermore, based on wear scar morphologies, wear scar EDS analysis, and wear mechanism modeling, the frictional mechanisms were elucidated. Simultaneously, a clear understanding of the relationship between SiCp and corrosion behavior were established. It is evident that the analysis of SiCp reinforcement content in composite holds significant guiding significance.

Thermal, Microstructural, and Mechanical Analysis of Complex Lattice Structures Produced by Direct Energy Deposition.

Lattice structures have gained attention in engineering due to their lightweight properties. However, the complex geometry of lattice structures and the high melting temperature of metals present significant manufacturing challenges for the large-scale fabrication of these structures. Direct Energy Deposition (DED) methods, such as the Wire Arc Additive Manufacturing (WAAM) technique, appear to be an interesting solution for overcoming these limitations. This study provides a detailed analysis of the manufacturing process of carbon steel lattice structures with auxetic geometry. The study includes thermal analysis using infrared thermography, microstructural characterization through metallography, and mechanical evaluation via hardness and mechanical testing. The findings reveal the significant impact of heat input, thermal cycles, and deposition sequence on the morphology and mechanical properties of the lattice structures. Fast thermal cycles are related to areas with higher hardness values, smaller strut diameters, and porous formations, which shows that controlling heat input and heat dissipation is crucial for optimizing the properties of lattice structures produced using WAAM.