Metal Transfer Research Articles

Microstructure evolution and mechanical properties of large-size AZ31 magnesium alloy block fabricated by wire arc additive manufacturing

With the urgent demand for lightweight and integrated structural parts in the aerospace field, the use of cold metal transfer wire arc additive manufacturing (CMT-WAAM) to form large-size magnesium alloy structural parts has become a research hotspot. In this paper, a large AZ31 magnesium alloy multilayer block with a lower porosity was successfully prepared by CMT-WAAM. The AZ31 block exhibits a fully equiaxed grain morphology, the average grain diameters of the top, middle, and bottom are 16.1 µm, 12.4 µm, and 10.4 µm, respectively. The submicron spherical particles measuring 0.09 to 0.4 µm are Mg17Al12 phases, irregular particles are Al8Mn5 + Mg17Al12 composite phases and large particles measuring 5 to 10 µm are Al8Mn5 in AZ31 block. The UTS of CMT-WAAM AZ31 block from the bottom of 239.9 ± 5.0 MPa to the top of 237.3 ± 3.1 MPa, and the EL from the bottom of 22.7 ± 0.6 % to the top of 30.0 ± 1.1 %, exceeding the casting standards. In the CMT-WAAM processed AZ31 alloy, the pre-existing coarse second phase particles in the AZ31 filaments acted as nucleating agents, and the electromagnetic stirring effect in the WAAM process broke up the dendrites and increased the number density of nucleation sites to improve the rate of nucleation, and the complex thermal conditions in the WAAM process restricted the growth of the grains and the precipitated phases. The mechanical properties of AZ31 alloy were improved by effectively refining its grain size and precipitated phase size.

Microstructure and properties of Al–Zn–Mg–Cu alloy fabricated by cold metal transfer additive manufacturing

Al–Zn–Mg–Cu alloy additive manufacturing components were fabricated by cold metal transfer advance (CMT-A) and metal inert-gas welding (MIG). The results indicate that the CMT-A as-deposited sample has fine grains with small-sized η'-strengthened precipitates and supersaturated solid solution, and the hardness is increased by 16.1% compared to the MIG as-deposited sample, and its peak aging hardness increased by 36.8% compared to the MIG. It indicates that CMT-A can directly produce Al–Zn–Mg–Cu products that have the potential to achieve high strength without the need for re-solutionizing.

Mechanical behavior of dissimilar AL6XN-IN718 welded joint obtained by cold metal transfer

Cold metal transfer (CMT) welding process was used to join the AL6XN super-austenitic stainless steel to a nickel-based super alloy IN718. Microhardness, tensile and low cycle fatigue tests were carried out to determine the mechanical properties of the welded joint. The heat used to perform the weld decreases the microhardness in the heat affected zone (HAZ) of the IN718 material. A decrement of about 50% with respect to the base material (∼410 HV0.2) was observed, which is attributed to the microstructural transformation produced by the weld thermal cycles, inducing the partial dissolution of the γ'′ phase in the nickel matrix. In contrast, the HAZ on the AL6XN side, the microhardness tends to be similar with respect to the base material (∼203 HV0.2). In terms of the fracture energy, determined from the stress-strain plot, the welded joint decreases about 60–65% with respect to the base materials. This tendency was also observed in the case of the Charpy impact test behavior. From the low cycle fatigue test, it was observed that AL6XN material and AL6XN-IN718, performed better than the IN718 alloy, i.e. more tolerance to the strain cyclic, increasing the number of cycles to failure. A 3-D transient thermal conduction finite element model was developed to correlate the thermal history with the microstructural transformation on the HAZ and mechanical properties. The weld thermal cycles are in good agreement with the experimental measurements obtained by K-type thermocouples.

Influence of cold metal transfer welding parameters on the welding hot crack of Mar-M247 nickel-based superalloy

Mar-M247 is widely used in several fields as a material with excellent overall performance at high temperatures. However, its complex fabrication process and extremely poor weldability make it very difficult to repair and fabricate. In this study, a novel flux-cored wire with microstructures and composition similar to that of Mar-M247 nickel-based superalloy had been successfully developed, and the superalloy had been effectively repaired by cold metal transfer welding technique. Under the strict control of welding parameters, good metallurgical bonding between the weld and the base metal can be realized, and the hot cracking problem of the joint was successfully suppressed. In the weld, there were closely arranged γ′ phase precipitates with nanoscale and γ/γ′ eutectic structure, granular carbides dispersed at grain boundaries. The hardness of the weld was about 410–430 HV. It had been found that solidification cracks in welds were caused by intergranular liquid films, and grain orientation was found to be an important factor affecting solidification cracking. Optimized welding parameters of cold metal transfer could control the grain orientation of weld and reduce the size of intergranular liquid film, which could effectively suppress the size of weld solidification cracks. Additionally, liquefaction cracks were caused by eutectic reaction liquefaction in the heat-affected zone. The cold metal transfer welding process with optimized parameters can effectively reduce welding heat input, weaken eutectic reactions, and successfully obtain joints without crack in heat-affected zone.

Effect of depositional strategy on surface roughness of Al-5%Mg wall fabricated via Cold Metal Transfer based Wire Arc Additive Manufacturing

Cold Metal Transfer (CMT) based Wire Arc Additive Manufacturing (WAAM) is the future-driven novel technology for fabricating complex metal components, having advantages like high deposition rates, increased material efficiency, lesser lead time, low heat input, and low cost. Despite of above advantages, the CMT-WAAM process possesses few limitations in terms of producing metal components with high geometrical accuracy. Al-Mg alloys are particularly appealing for their lightweight and exceptional mechanical properties, making them attractive for various industrial applications such as marine, automobile, aerospace, etc. In this study, an Al-5%Mg alloy single wall has been built through CMT-WAAM using Current at 110A, Travel Speed (TS) of 7 mm/sec, and Gas Flow Rate (GFR) of 15L /min. The effect of unidirectional and bidirectional deposition direction on the surface quality of the fabricated sample has been investigated. Surface roughness (Ra) tests were conducted at three different zones (upper, middle, and bottom) of the specimen wall before the machining operation using a taylor hobson surtronic tester. It is concluded from the results that the S2 wall (unidirectional) has more Ra value than the S1 wall (bidirectional) in all zones due to the presence of a humping defect which results in more waviness over the S2 wall’s surface. In the bidirectional strategy, the roughness value reduces by 8.567 % (upper zone), 9.95 % (middle zone), and 13.019 % (bottom zone) than the unidirectional strategy. Thereby establishing that the deposition direction tends to build WAAM wall with a better surface finish.

The effect of soil types, pH, and geographical locations on carcinogenic metal buildup in Oryza sativa cultivated in Ghana.

This study investigated the impact of soil type, pH, and geographical locations on the accumulation of arsenic (As), lead (Pb), and cadmium (Cd) in rice grains cultivated in Ghana. One hundred rice farms for the sampling of rice grains and soil were selected from two regions in Ghana-Volta and Oti. The concentrations of As, Pb, and Cd were analyzed using ICP-OES. Speciation modeling and multivariate statistics were employed to ascertain the relations among measured parameters. The results showed significant variations in soil-As, Pb, and Cd levels across different soil types and pH ranges, with the highest soil-As and Cd found in alkaline vertisols. For soil-As and Cd, the vertisols with a pH more than 7.0 exhibited the highest mean concentration of As (2.51 ± 0.932 mgkg-1) and Cd (1.00 ± 0.244 mgkg-1) whereas for soil-Pb, the luvisols of soil types with a pH less than 6.0 exhibited the highest mean concentration of Pb (4.91 ± 1.540 mgkg-1). Grain As, Pb, and Cd also varied across soil types and pH levels. In regards to grain-As, the vertisols soil type, with a pH less than 6.0, shows the highest mean concentration of grain As, at 0.238 ± 0.107 mgkg-1. Furthermore, vertisols soil types with a pH level less than 6.0 showed the highest mean concentration of grain Cd, averaging at 0.231 ± 0.068 mgkg-1 while luvisols, with a pH less than 6.0, exhibited the highest mean concentration of grain Pb at 0.713 ± 0.099 mgkg-1. Speciation modeling indicated increased bioavailability of grains Cd2+ and Pb2+ ions in acidic conditions. A significant interaction was found between soil-Cd and pH, affecting grain-As uptake. The average concentrations of soil As, Pb, and Cd aligned with international standards. Generally, the carcinogenic metals detected in grain samples collected from the Volta region are higher than that of the Oti region but the differences are insignificant, and this may be attributed to geographical differences and anthropogenic activities. About 51% of the study area showed a hazard risk associated with grain metal levels, although, no carcinogenic risks were recognized. This study highlights the complex soil-plant interactions governing metal bioaccumulation and emphasizes the need for tailored strategies to minimize metal transfer into grains.

Polydimethylsiloxane (PDMS)-assisted non-destructive transient thermoreflectance characterizations.

The conventional pump-probe thermoreflectance (pump-probe TR) techniques are routinely performed on a thin (typically <100nm) metal transducer deposited on samples, ensuring the most fundamental principle of thermoreflectance: the reflectance change (∆R/R) of the sample surface is directly and linearly related to the temperature change (∆T) within a finite temperature range. However, general metal coating methods may damage the sample by forming a mixed layer with the sample. In this article, we present a non-destructive pump-probe transient thermoreflectance (TTR) characterization using the polydimethylsiloxane (PDMS)-assisted metal transfer technique. Our method utilizes PDMS dry transfer to transfer common transducer metals (Au and Al) to the target substrate. This method effectively avoids impurities and damage to the sample. In particular, we have utilized Au as a transition layer to study the application of Al transfer in TTR measurements. The substrate thermal conductivity measurement results show that they can all be used for TTR measurement, and the thermal boundary conductance results show that the transferred metals have low bonding to the substrate. In addition, Al/Au can be transferred over a large area at room temperature compared to Au. After measurement, the samples can be restored to their original state by a simple cleaning method. This method provides a simple and reliable way to characterize samples without metal coating for TTR.

Experimental investigation of electrochemical and mechanical properties of stainless steel 309L at different built orientation by cold metal transfer assisted wire arc additive manufacturing

In this article, a multi layered wall of stainless steel 309 L (ER309L) material was WAAM printed over a substrate, at optimized parameters using gas metal arc welding as heat input source assisted by cold metal transfer machine, aiming to evaluate mechanical and electrochemical properties at different built orientations i.e., 0°, 30°, 45°, 60°, and 90°. Wall samples were cut-out by wire cut electric discharge machine to compare their properties. Microstructural properties and phases were confirmed by Scanning Electron Microscopy, Energy-Dispersive Spectrometry (EDS) and X-ray diffractometry (XRD), as they change on melting and solidification along the building direction. Columnar dendrite and vertical ferritic grains were observed through an optical microscope. SEM images suggests the presence of Widmanstatten austenite laths forming δ/γ duplex phase. Element distribution by EDS was further verified by Schaeffler’s diagram. XRD pattern confirms various elements and their phase compositions. The tensile strength and yield strength of samples decreased with increase in orientation angle, which is attributed to decrease in the inter-layer length which restricts the slipping of grains and reestablishment of the residual forces., tableau software was used to theoretically predict values for 45° sample as it broke outside the gauge length. electrochemical properties and corrosion behaviour were studied by electrochemical impedance spectroscopy (EIS) and Potentiodynamic polarization (PDP) where in highest Rct=170 Ω and lowest corrosion rate, 0.56 mils per year (MPY) was observed for 45° is attributed to diffusion of chromium to the metal-solution interface forming a passive film. The corrosion rate range 0.48–2.7 MPY, advocates SS309L have a uniform passive film. The properties studied certifies that WAAM printed stainless steel component can be exploited for critical applications.

Industrial hemp (Cannabis sativa L.) can utilize and remediate soil strongly contaminated with Cu, As, Cd, and Pb by phytoattenuation

Industrial hemp (Cannabis sativa L.) has great application potential in heavy metal-polluted soils owing to its safe non-food utilization. However, the fate of heavy metals in different varieties of hemp planted in strongly contaminated natural soils remains unknown. Here, we investigated the growth, heavy metal uptake, distribution, and transfer of nine hemp varieties in soils strongly contaminated with Cu, As, Cd, and Pb. Hemp variety and metal type were the main factors affecting the growth and heavy metal uptake in hemp. The nine hemp varieties grew well in the contaminated soils; however, differences existed among the varieties. The biomass of Z3 reached 5669.1 kg hm−1, whereas that of Yunma No. 1 was only 51.8 % of Z3. The plant height, stalk diameter, and stalk bark thickness of Z3 were greater than those of the other varieties, reaching 168 cm, 9.2 mm, and 0.56 mm, respectively. Permanova's analysis revealed that the total effects of Cu, As, Cd, and Pb on the growth of the nine hemp varieties reached 60 %, with leaf As having the greatest effect, reaching 16 %. , Even in strongly contaminated soils, the nine varieties showed poor Cu, As, Cd, and Pb uptake. Most of the Cu, As, Cd, and Pb were retained in the root, reaching 57.7–72.4, 47.6–64.7, 76.0–92.9, and 70.0–87.8 %, respectively. Overall, the Cu, As, Cd, and Pb uptake of Wanma No.1 was the highest among the nine varieties, whereas that of Guangxi Bama was the lowest. These results indicate that hemp is a viable alternative for phytoattenuation in soils contaminated with heavy metals because of its ability to tolerate and accumulate Cu, As, Cd, and Pb in its roots, and Guangxi Bama is superior to the other varieties considering the safe utilization of hemp products.

Sulfide mineralization in orogenic eclogites of the North Muya block (northeastern Transbaikalia): genesis and the first data on the isotopic composition of sulfur

Subduction processes are accompanied by the sites of hydrothermal activity including large deposits of gold and transitional metals of island-arc or back-arc origin, whereas volcanic arcs host most part of the worldwide resources of metallic minerals. However, the role of suprasubduction metal transfer and the associated role of redox processes in their formation are still ambiguous and require direct studies of sulfide mineralization in high-pressure rocks, as well as their formation stages and sulfide preservation during progressive and peak metamorphism. In order to describe the behavior of chalcophile elements in the paleozones of continental subduction we performed preliminary mineralogical (SEM-EDX) and isotope (S) studies of sulfides in the North Muya block eclogites (northeastern Transbaikalia). Sulfide mineralization of pyrite-chalcopyrite-pyrrhotite composition has a metasomatic origin associated with the retrograde fluid transformation of initially “dry” eclogite assemblages during exhumation to lower- or mid-crust levels after or synchronously to the decompression and formation of plagioclase-diopside±amphibole symplectites (below 10-12 kbar). Extremely heterogeneous isotopic composition of pyrite sulfur (δ34SVCDT) was caused by various sources of fluids of presumably metasedimentary origin (from -8.2 to -6 %) in the paragneiss segments of the North Muya block. But they also could be predominantly buffered by hydrothermally altered metabasites (from +0.7 to +7.1 %). An alternative mechanism could be the participation of a single predominantly oxidized (sulfate-containing) fluid with the significant isotopic fractionation (up to ~15–20 %).

Responses of plankton community to threshold metal concentrations of cadmium and lead in a mesocosm experiment at Bay of Bengal

Metals are essential at trace levels to aquatic organisms for the function of many physiological and biological processes. But their elevated levels are toxic to the ecosystem and even brings about shifts in the plankton population. Threshold limits such as Predicted No Effect Concentration (PNEC - 0.6 μg/l of Cd; 2.7 μg/l of Pb), Criterion Continuous Concentration (CCC - 3.0 μg/l of Cd; 4.5 μg/l of Pb) and Criterion Maximum Concentration (CMC - 23 μg/l of Cd; 130 μg/l of Pb) prescribed for Indian coastal waters were used for the study. Short-term mesocosm experiments (96 h) were conducted in coastal waters of Visakhapatnam to evaluate responses of the planktonic community on exposure to threshold concentrations of cadmium and lead for the first time. Four individual experimental bags of 2500 L capacity (Control, PNEC, CCC & CMC) were used for the deployment and ambient water samples were analysed simultaneously to evaluate the impacts of the threshold levels in the natural waters. Chaetoceros sp. were dominant group in the control system whereas, Prorocentrum sp. Ceratium sp. Tintinopsis sp. Chaetoceros sp. and Skeletonema sp. were major groups in the test bags. Throughout the experiment the phytoplankton community did not show any significant differences with increased nutrients and plankton biomass (Chl-a <8.64 mg/m3). Positive response of plankton community was observed in the experimental bags. High abundance of diatoms were observed in PNEC, CCC & CMC bags at 48 h and the abundance decreased with shift in the species at 72–96 h. The catalase activity in phytoplankton (5.99 nmol/min/ml) and the zooplankton (4.77 nmol/min/ml) showed induction after exposure to PNEC. The present mesocosm study is confirmed that short-term exposure to threshold metal concentration did not affects the phytoplankton community structure in PNEC, but CCC and CMC affects the community structure beyond 24 h. The insights from this study will serve as a baseline information and help develop environmental management tools. We believe that long-term mesocosm experiments would unravel metal detoxification mechanisms at the cellular level and metal transfer rate at higher trophic levels in real-world environment.

Assessing the Health Risk and Trophic Transfer of Lead and Cadmium in Dairy Farming Systems in the Mantaro Catchment, Central Andes of Peru.

This study investigated lead (Pb) and cadmium (Cd) transfer in three dairy farming areas in the Mantaro river headwaters in the central Peruvian Andes and at varying distances from the mining complex at La Oroya. At each of these sites, the transfer of trace metals from the soil to raw milk was estimated, and a hazard assessment for lead and cadmium was carried out in scenarios of minimum, average, and maximum milk consumption in a Peruvian population aged 2-85. Pb and Cd were quantified by flame atomic absorption spectrometry. Significantly, the concentrations of lead and cadmium were found to exceed the maximum limits recommended by the World Health Organization, with a positive geospatial trend correlated with the distance from mining activity. Both Pb and Cd were found to be transferred through the soil-pasture-milk pathway, with the primary source of Cd being phosphate-based fertilizers used in pasture improvement. Pb was found to be the most significant contributor to the Hazard Index (HI) with those under 19 years of age and over 60 recording an HI of >1, with infants being the most vulnerable group due to their greater milk consumption in relation to their body weight. A marginal increase in contamination was observed in the dry season, indicating the need for studies to be expanded over several annual cycles.

Corrosion behavior of δ-ferrite in AISI 316 austenitic stainless steel exposed to oxygen-saturated lead‑bismuth eutectic at 550 °C

δ-ferrite is usually found in the 300 series austenitic stainless steels (ASS), but the role of δ-ferrite on corrosion behaviors exposed to oxygen-controlled lead–bismuth eutectic (LBE) has not yet been elucidated. The corrosion behaviors of AISI 316 ASS containing δ-ferrite in the oxygen-saturated static LBE at 550 °C were studied in terms of their solution-treated and accelerated-aging treated conditions. The δ-ferrite and decomposed δ-ferrite exhibit the superior resistance to oxidation attack compared to the austenite, and the δ-ferrite possesses a better corrosion resistance than the decomposed δ-ferrite. Compared with the austenite, the higher diffusivities of Cr and Si in δ-ferrite cause a reduction in the critical concentration required for the formation of chromium oxide and Si-rich oxide. A mixture of Cr2O3 oxide and Fe-Cr-Si spinel oxide developed on the surface of δ-ferrite can effectively impede the metal transfer, leading to the superior resistance to oxidation attack. The retained δ-ferrite and M23C6 carbides in the decomposed δ-ferrite oxidizes independently into FeCr2O4 and Cr2O3 oxides, respectively. The presence of Cr2O3 scale around the retained δ-ferrite decreases its oxidation rate, resulting in the non-uniform oxide phenomenon.

ELECTRODE WIRE FEEDER FOR MIG/MAG AND TIG WELDING PROCESSES

The electrode wire feeding mechanisms of welding machines are designed to transport the electrode wire from the spool to the welding zone at a constant, predetermined speed or at a speed that varies according to a given law. One of the most promising areas for improving arc welding and surfacing equipment is to control the transfer of electrode metal by pulsing the electrode wire. Therefore, the feeding mechanisms of welding machines must ensure compliance with the conditions of continuous feeding at a constant speed or pulsed feeding with an intermittent movement. The problem of forming pulses with the required parameters can be solved by feeding mechanisms with a vibration drive. The main advantage of such a technical solution is the ability to produce pulsed motion with controllable frequency and amplitude parameters. Due to the high resolution of movement and high dynamic properties in transient motion modes, vibration-driven feeding mechanisms are able to provide high accuracy of bar material feeding into the working area of technological equipment. The principle of operation of such a mechanism is based on the transformation of spatial vibrations into linear displacements. The analytical dependencies obtained in this work allow us to determine the parameters of electrode wire movement by the vibratory feeding mechanism. The proposed technical solution makes it possible to provide different movements of the wire along its axis, and changing the pulsation mode is made possible by adjusting the oscillation frequency of the drive.

Microstructure and tribological properties of solid lubricant-doped CMT-WAAMed Stellite deposits

AbstractA large share of the world’s total energy consumption is used to overcome friction. Therefore, low friction wear-resistant materials are needed. Solid lubricants are solid-phase materials that can reduce friction at different temperatures between two surfaces sliding against each other without the need for a grease or liquid oil medium. In this study, Cold Metal Transfer Wire Arc Additive Manufacturing (CMT-WAAM) was used to deposit solid lubricant (WS2, MoS2, CaF2) doped hypoeutectic Stellite alloy. Fabricated deposits possessed crack- and pore-free microstructures consisting of γ-Co and M7C3 carbide eutectics embedded with chromium sulfides and microhardness values of ~ 530 HV1. They were also tested in self-mated unidirectional sliding wear tests in dry conditions at room temperature (RT) and at 300 °C in an air atmosphere. The results showed that the dynamic coefficient of friction (COF) decreased ~ 27% at RT and ~ 21% at 300 °C without losing the wear properties. During sliding wear tests severe strain hardening occurred and γ-Co was found to transform to ε-Co. The developed deposits can be used as hard facings or 3D printed components in applications that require good sliding wear properties at different temperatures such as metal forming tools, power transmission components, valves, and internal parts of combustion engines.

Trophodynamics and health risk assessment of heavy metals in seafood from a tropical estuary in the gulf of Guinea

Seafood is an essential protein source for coastal communities. However, they can accumulate heavy metals from human activities which could pose a potential health risk to consumers. In this study, we investigated the distribution, bioaccumulation, trophic transfer and potential human health risk of heavy metals in sediments, shell and fin fish collected from the Escravos Estuary in southern Nigeria. Heavy metals (Ni, Cd, V, Pb and Cu) in sediments, periwinkles and tongue soles from the two study sites were lower than the permissible limits for fishery products. The metal distribution in fish tissues was in the decreasing order of liver > gills > muscles > gonads > rest of the fish. Moderate to high BSAF (>1) was reported for Cd, Pb and Cu. All the studied metals, except Pb, showed evidence of biomagnification from periwinkle to tongue sole. The estimated daily intake (EDI) and hazard ratio (HR) for metals in periwinkles from both study sites were lower or within the USEPA reference doses (RfD) for the respective daily intake and HR value < 1, except for Cd, V and Pb for children. In contrast, EDI values in the muscle of tongue soles were higher than the RfD values for heavy metals except for Ni and Pb, whereas HR values > 1 except for Ni, Cd and V. In the whole fish, EDI and HR values were disproportionately high in both study sites with higher values reported for children. This study provides the first insights on the trophic transfer and risk assessment of heavy metals from petroleum and gas operations impacting the Escravos Estuary and the implications to public health.

Study on Microstructure and Properties of Cold Metal Transfer and Pulse Hybrid Welded Super Duplex Stainless Steel

The investigation focuses on the microstructure, impact toughness, and pitting corrosion resistance of cold metal transfer and pulse hybrid welded joints of unified numbering system (UNS) S32750 duplex stainless steel. The results show that the filler pass exhibits the highest austenite ratio (47.9%), whereas the heat‐affected zone (HAZ) shows the lowest (32.3%). Notably, secondary austenite (γ2) is present in both the backing pass and HAZ, but conspicuously absent in the filler pass, indicating that reheating from subsequent weld pass is a prerequisite for the precipitation of γ2. Additionally, chromium nitride (Cr2N) also precipitates in the HAZ and backing pass. Comparative analysis with the weld metal (WM) and base metal (BM) indicates that the HAZ displays lower impact toughness, primarily attributing to imbalanced phase ratio, coarse ferrite grains and the brittle Cr2N. Owing to the lower austenite content and Cr2N precipitation in the backing pass, its toughness (122.6 J cm−2) is found to be inferior to that of the filler pass (130.1 J cm−2). Furthermore, the HAZ with a lower critical pitting temperature compared to the WM (79.1 °C) and BM (87 °C), and exhibits the worst pitting corrosion resistance due to the abundant precipitation of secondary phases and excessive ferrite with low pitting resistance equivalent number.

Hybrid Fabrication of Cold Metal Transfer Additive Manufacturing and Laser Metal Deposition for Ti6Al4V: The Microstructure and Dynamic/Static Mechanical Properties.

The titanium alloy components utilized in the aviation field are typically large in size and possess complex structures. By utilizing multiple additive manufacturing processes, the precision and efficiency requirements of production can be met. We investigated the hybrid additive manufacturing of Ti-6Al-4V using a combination of cold metal transfer additive manufacturing (CMTAM) and laser metal deposition (LMD), as well as the feasibility of using the CMT-LMD hybrid additive manufacturing process for fabricating Ti-6Al-4V components. Microstructural examinations, tensile testing coupled with digital image correlation and dynamic compressive experiments (by the split Hopkinson pressure bar (SHPB) system) were employed to assess the parts. The results indicate that the interface of the LMD and CMTAM zone formed a compact metallurgical bonding. In the CMTAM and LMD zone, the prior-β grains exhibit epitaxial growth, forming columnar prior-β grains. Due to laser remelting, the CMT-LMD hybrid additive zone experiences grain refinement, resulting in equiaxed prior-β grains at the interface with an average grain size smaller than that of the CMTAM and LMD regions. The microstructures reveal significant differences in grain orientation and morphology among the zones, with distinct textures forming in each zone. In the CMT-LMD hybrid zone, due to interfacial strengthening, strain concentration occurs in the arc additive zone during tensile testing, leading to fracture on the CMTAM zone. Under high-strain-rate dynamic impact conditions, the LMD region exhibits ductile fracture, while the CMTAM zone demonstrates brittle fracture. The hybrid zone combines ductile and brittle fracture modes, and the CMT-LMD hybrid material exhibits superior dynamic impact performance compared to the single deposition zone.

Development of a gas metal arc based prototype for direct energy deposition with micrometric wire

In recent years, efforts have been focused on the development of metal additive manufacturing (AM) processes to address the growing trend of miniaturization in industries such as aerospace and electronics. Thus, new technologies have been developed based on a downscaled approach using direct energy deposition (DED) processes, now referred to as μ-DED. In this context, the development of a downscaled DED prototype based on gas metal arc (GMA) working with micrometric wires (μ-GMA) has the potential to unify the positive characteristics of GMA-based DED, increasing the complexity of the design and resolution of the produced parts. Therefore, this work focuses on developing a μ-GMA prototype and assessing its technical feasibility. This paper describes the development of the μ-GMA prototype, characterizes the metallic transfer mode, and statistically analyzes the effect of deposition parameters on bead width and height. Additionally, microstructural analysis, Vickers microhardness, and reduced Young's modulus tests were performed. The μ-GMA prototype demonstrated the capability to deposit beads with an approximate width of 1 mm, nearly 5 times thinner than standard GMA-based DED deposition, with a build rate of 30 cm3/h, which is lower than GMA-based DED but higher than other μ-DED processes. Furthermore, the mechanical properties of the μ-GMA depositions are comparable to regular GMA-based DED parts.

Gram-negative bacteria recognition and photodynamic elimination by Zn-DPA based sensitizers

The abuse and overuse of antibiotics let drug-resistant bacteria emerges. Antibacterial photodynamic therapy (APDT) has shown outstanding merits to eliminate the drug-resistant bacteria via cytotoxic reactive oxygen species produced by irradiating photosensitizer. However, most of photosensitizers are not effective for Gram-negative bacteria elimination. Herein conjugates of NBS, a photosensitizer, linked with one (NBS-DPA-Zn) or two (NBS-2DPA-Zn) equivalents of zinc-dipicolylamine (Zn-DPA) have been designed to achieve the functional recognition of different bacteria. Due to the cationic character of NBS and metal transfer channel effect of Zn-DPA, NBS-DPA-Zn exhibited the first regent to distinguish P. aeruginosa from other Gram-negative bacteria. Whereas NBS-2DPA-Zn showed broad-spectrum antibacterial effect because the two arm of double Zn-DPA enhanced interactions with anionic membranes of bacteria, led the bacteria aggregation and thus provided the efficacy of APDT to bacteria and corresponding biofilm. In combination with a hydrogel of Pluronic, NBS-2DPA-Zn@gel shows promising clinical application in mixed bacterial diabetic mouse model infection. This might propose a new method that can realize functional identification and elimination of bacteria through intelligent regulation of Zn-DPA, and shows excellent potential for antibacterial application.