Increasing Laser Energy Density Research Articles

Evaluation of antibacterial effect of a cationic porphyrin derivative on Pseudomonas aeruginosa in photodynamic therapy

BackgroundPseudomonas aeruginosa is a gram-negative bacterium without spores, and it is one of the pathogens that easily cause secondary infectious diseases when human immune function is low. The purpose of this study is to explore the inhibitory effect of photodynamic antibacterial chemotherapy-induced by cationic porphyrin derivative on clinical P. aeruginosa and its mechanism. MethodsThe uptake of photosensitizer by P. aeruginosa and L929 cells was measured by an ultraviolet spectrophotometer. Effect of laser energy density on the bacterial activity of P. aeruginosa and post antibiotic effect were measured by bacterial suspension and tenfold dilution method. Flow cytometry and scanning electron microscopy were used to observe the activity and morphological changes of P. aeruginosa after PACT treatment. ResultsThe uptake of Tetra-ATPP-Lys-by P. aeruginosa and L929 was shown as concentration-dependent and time-dependent. However the uptake of L929 cell had a clear difference with P. aeruginosa at the same time and concentration intervals(P < 0.05).The increasing laser energy density had a high inactivation effect of on P. aeruginosa at the same Tetra-ATPP-Lys-concentration(P < 0.05). Post-antibiotic effect of Tetra-ATPP-Lys -PACT was dose-dependent(P < 0.05). Bacterial viability which evaluated by the flow cytometry method demonstrated that the proportion of viable bacteria is decreased with the photosensitizer dose-dependent. The morphology and microstructure of P. aeruginosa after Tetra-ATPP-Lys -PACT was demonstrated by a scanning electron microscope(SEM). After PACT, the morphology of P. aeruginosa was rod-shaped, the outer membrane surface was rough, and the bacteria were dry flat, sunken, shrunk and deformed. ConclusionsCationic porphyrin photosensitizer had a great damage effect on P. aeruginosa under the PACT, which can effectively destroy the microstructure of bacteria and lead to bacterial inactivation and death.

Effect of laser cleaning on adhesive properties of carbon fiber composite materials

A pulsed fiber laser was used to conduct laser cleaning experiments on the composite paint layer on the surface of carbon fiber composite materials (carbon fiber-reinforced plastic (CFRP)). The influence of laser energy density and laser travel speed on the cleaning effect was studied. The surface morphology, surface roughness and phase composition of the cleaned sample were analyzed. After bonding, tensile testing was conducted on the bonding part to verify the impact of laser cleaning on the bonding performance. The research results indicate that the cleaning effect gradually improves with the increase of laser energy density or the decrease of travel speed. In this experiment, when the laser energy density is 4.00[Formula: see text]J/cm2 and the travel speed is 6.5[Formula: see text]mm/s, the phase composition of the cleaned substrate surface is only C, without TiO2 and BaSO4. This indicates that the paint layer has been completely removed under this process parameter. By selecting reasonable process parameters, the surface paint layer of CFRP can be effectively removed, and a good surface morphology can be obtained without damage to the carbon fiber. Meanwhile, the mechanical properties after bonding can be improved.

Effects of low-level laser on the expression of interleukin-6, tumor necrosis factor‑α, osteoprotegerin, and receptor activator of nuclear factor-κB ligand in human periodontal ligament cells.

This study aims to determine the effects of low-level laser (LLL) on the expression of interleukin-6 (IL-6), tumor necrosis factor (TNF)-α, osteoprotegerin (OPG), and receptor activator of nuclear factor-κB ligand (RANKL) in human periodontal ligament cells (HPDLCs) stimulated by high glucose; and identify the molecular mechanism of LLL therapy in the regulation of periodontal inflammation and bone remodeling during orthodontic treatment in diabetic patients. HPDLCs were cultured in vitro to simulate orthodontic after loading and irradiated with LLL therapy. The cultured cells were randomly divided into four groups: low glucose Dulbecco's modification of Eagle's medium (DMEM)+stress stimulation (group A), high glucose DMEM+stress stimulation (group B), hypoglycemic DMEM+LLL therapy+stress stimulation (group C), and hyperglycemic DMEM+LLL therapy+stress stimulation (group D). Groups C and D were further divided into C1 and D1 (energy density: 3.75 J/cm2) and C2 and D2 (energy density: 5.625 J/cm2). Cells in groups A, B, C, and D were irradiated by LLL before irradiation. At 0, 12, 24, 48, and 72 h, the supernatants of the cell cultures were extracted at regular intervals, and the protein expression levels of IL-6, TNF-α, OPG, and RANKL were detected by enzyme-linked immunosorbent assay. 1) The levels of IL-6 and TNF-α secreted by HPDLCs increased gradually with time under static pressure stimulation. After 12 h, the levels of IL-6 and TNF-α secreted by HPDLCs in group A were significantly higher than those in groups B, C1, and C2 (P<0.05), which in group B were significantly higher than those in groups D1, and D2 (P<0.01). 2) The OPG protein concentration showed an upward trend before 24 h and a downward trend thereafter. The RANKL protein concentration increased, whereas the OPG/RANKL ratio decreased with time. Significant differen-ces in OPG, RANKL, and OPG/RANKL ratio were found among group A and groups B, C1, C2 as well as group B and groups D1, D2 (P<0.05). 1) In the high glucose+stress stimulation environment, the concentrations of IL-6 and TNF-α secreted by HPDLCs increased with time, the expression of OPG decreased, the expression of RANKL increased, and the ratio of OPG/RANKL decreased. As such, high glucose environment can promote bone resorption. After LLL therapy, the levels of IL-6 and TNF-α decreased, indicating that LLL therapy could antagonize the increase in the levels of inflammatory factors induced by high glucose environment and upregulate the expression of OPG in human HPDLCs, downregulation of RANKL expression in HPDLCs resulted in the upregulation of the ratio of OPG/RANKL and reversed the imbalance of bone metabolism induced by high glucose levels. 2) The decrease in inflammatory factors and the regulation of bone metabolism in HPDLCs were enhanced with increasing laser energy density within 3.75-5.625 J/cm2. Hence, the ability of LLL therapy to modulate bone remodeling increases with increasing dose.

Effect of laser energy density on microstructure and properties Cu–Fe–P immiscible alloys fabricated by laser selective melting: heterogeneous and high strength and magnetic

Through the incorporation of phosphorus (P) as a third component, an in-situ formation of a magnetic phase with a nanotwin structure was achieved. The utilization of selective laser melting (SLM) enabled the synthesis of a Cu–Fe–P immiscible alloy that exhibits an integrated structure and function. The microstructure predominantly consists of a magnetic heterogeneous Fe–P-rich phase, comprising a mixture of Fe2P and a small quantity of Fe3P, which is distributed within the ε-Cu Cu-rich matrix in alternating “fiber-layer” and “particle-shape” forms. Additionally, the fibrous Fe2P phase exhibited precipitation of α-Fe, while the Fe–P-rich phase experienced the precipitation of high-density nanotwinned Cu (nt-Cu) particles. The microstructure density and structural characteristics of Cu–Fe–P immiscible alloys were enhanced through the adjustment of laser energy density, leading to improvements in their mechanical and magnetic properties. It was observed that the microstructure density initially increased and then decreased with increasing laser energy density. The highest relative density of the Cu–Fe–P immiscible alloy microstructure (98%) was achieved at a laser energy density of 53 J/mm3. Furthermore, the influence of laser energy density on the mechanical and soft magnetic properties of Cu–Fe–P immiscible alloys was examined. The findings indicate that the mechanical and soft magnetic properties of these alloys are affected by the laser energy density. The findings indicate that the compact Cu–Fe–P immiscible alloys exhibit favorable compression mechanical properties and soft magnetic properties. Specifically, the ultimate compressive stress can reach 890.5 ± 20 MPa, while the failure strain can reach 20.5 ± 2%. Additionally, the coercivity is observed to be as low as 20.0 Oe, the magnetic saturation strength as high as 93.5 emu/g, and the residual magnetization at 1.1 emu/g.

Effect of laser remelting on the organization and properties of WC/Ni-based coatings generated in situ by laser cladding

In order to study the effect of laser remelting on the properties of H13 steel, WC/Ni-based coating was prepared on its surface by laser cladding. The macroscopic morphology, microstructure, element distribution and mechanical properties of the coatings before and after remelting were compared by means of scanning electron microscopy, energy spectrometer, XRD, hardness tester and friction and wear tester. The results show that the in-situ prepared cladding layer has no obvious defects such as cracks and pores. With the increase of laser energy density, the microstructure distribution in the remelted coating becomes more and more uniform, and the surface roughness of the coating becomes lower and lower. However, the microhardness and wear resistance of the coating have no obvious difference. When the laser energy density reaches 1500 J/mm, the ceramic particles inside the remelting coating basically disappear, the coating uniformity and surface smoothness are the best, the hardness reaches 768 HV0.5, and the wear resistance is 3.75 times that of the substrate.

Laser powder bed fusion of bimetallic stainless steel/Nickel-based superalloy: Interface and mechanical properties

Potential applications of steel/nickel bimetals in corrosive environments are of increasing interest. In this study, bimetallic 316L/Hastelloy X was processed via laser powder bed fusion (L-PBF) using different parameters. Results indicated that the rapid cooling of L-PBF reduced the element segregation and carbide formation, thus leading to an interface free of cracks. However, also due to rapid solidification, the constituent elements of dissimilar materials at the interface were not mixed properly. With the increasing laser energy density, the interfacial width increased from dozens to hundreds of microns. The epitaxial grain growth from 316L to Hastelloy X was observed under the optimal processing parameters. The microhardness first declined at the front of the 316L side and then continuously increased in the interfacial region with the addition of Hastelloy X. During the tensile tests, the optimally built samples failed at the 316L side, implying the formation of solid bonding between the two metals.

Hydrogen production by oxidation of aluminum nanopowder in water under the action of laser pulses

The possibility of hydrogen production by the action of laser pulses (1064 nm, 14 ns, 10 Hz, 0.5–6 J/cm2) on a suspension containing 0.03 wt % aluminum (100 nm) in water is shown. It was found that aluminum nanoparticles absorb the laser energy and heat up. As a result of heating, the continuity of the oxide film is disrupted, and metallic aluminum reacts with water. It is shown that there is a complete transformation of aluminum into products (gibbsite, boehmite, bayerite). The maximum hydrogen yield Vm = 8.4 mL does not depend on the energy density of the laser radiation. The time to reach Vm decreases according to the hyperbolic law with increasing laser energy density, reaching 3.5 min at an energy density of 6 J/cm2.

Amorphous alloy reinforced Cu-based immiscible coatings by laser melting deposition: Separation mechanism and corrosion behavior

In order to clarify the effect of Fe-based amorphous alloy on the separation mechanism and corrosion behavior of Cu-based immiscible coatings, 10 wt% Fe-based amorphous powder was designed into 90 wt% pure Cu powder to produce the amorphous alloy reinforced Cu-based immiscible coatings by laser melting deposition. The self-organized microstructure and corrosion behavior of immiscible coatings with different laser energy densities were investigated. When the different laser energy densities are adopted, many carbides (M23C6 and M12C) are dispersed in the lower α-Fe layer and large amounts of α-Fe particles containing carbides are embedded in the upper ε-Cu layer due to liquid phase separation. With increasing laser energy density (LED), the α-Fe dendrites are coarser and the area of carbides decrease. The interface of coating and substrate experiences a transition from “poor bonding (gaps) to “good bonding” and “crack debonding”. Moreover, the corrosion characteristics of immiscible coatings also experience a transformation from “crevice corrosion” to “enhanced protection of passive films” and “reduced protection of passive films”. As a result, the corrosion resistance increases first then decreases and the immiscible coating deposited by the LED of 31.25 J/mm2 exhibits the highest corrosion resistance.

Laser‐Induced Polymerization of Photosensitive Resin for Silk Fabric Joining

Herein, a new joining method for silk fabrics based on polymerization of polyurethane acrylate (PUA) photosensitive resin induced by a nanosecond 355 nm ultraviolet laser is proposed. After the resin is applied and cured, not only the space between the fiber bundles, but also the gaps within the bundles are filled up with the resin, forming strong interlocking bonds. The infrared spectra of the joint area indicate that there is no textile burning or chemical change on silk fibers. The increase of laser energy density can improve the polymerization degree of the resin and increase the joint strength. However, when the energy density exceeds 1.68 J cm−2, ablation of the photosensitive resin occurs. The amount of filled resin affects the thickness of the joint and its strength. When the resin filling rate is 0.76 mL min−1, the joint has a high filling density and high bearing capacity. The tensile force of the joint reaches 297.10 N, which is higher than the breaking force of the base silk fabric. The tensile force of the joint also increases with the increasing of the joint width. This study provides an alternative process for conventional sawing and stitching in garments fabrication.

Investigation of the Effect of Laser Fluence on Microstructure and Martensitic Transformation for Realizing Functionally Graded NiTi Shape Memory Alloy via Laser Powder Bed Fusion

Nowadays, additive manufacturing (AM) of NiTi shape memory alloy is a challenging topic for the realization of 3D functional parts. Particularly, Laser Powder Bed Fusion (LPBF) of NiTi powder is one of the most challenging processes belonging to AM, thanks to its best performances in terms of productivity and precision of geometrical complexity. The control of the functional performances in NiTi components requires a strong interaction between technological and metallurgical approaches. In fact, a strong correlation among the process conditions, the microstructure, and the final functional performances, beyond the defects associated with the process are needed to be understood and analyzed. In the present work, the correlation between the feasibility map of processability and the obtained microstructure, which can be tailored according to the use of different energy density values, of Ni-rich NiTi powder processed with LPBF is investigated. In detail, discrete energy density values, in the range 60–300 J/mm3, were correlated to microstructure, Ni:Ti ratio, and transformation temperatures of the martensitic transformation, analyzed with SEM, EBSD, EDX, and DSC characterizations, respectively. An increase in laser energy density was found to promote Ni evaporation, which induced a change of the microstructure from austenite to martensite at room temperature. A consequent shift of the transformation temperatures to higher values and a change in microstructural texture was achieved. These achievements can support the identification of the feasibility range for manufacturing functionally graded NiTi SMA, requiring tailored functional properties located in selected positions in the 3D parts.

Enhancing the machinability of Cf/SiC composite with the assistance of laser-induced oxidation during milling

Carbon fiber-reinforced silicon carbide matrix (Cf/SiC) composites have been widely used in aerospace for its superior properties. However, due to high hardness, heterogeneity, and anisotropy, many problems such as machining damage, low process efficiency, and rapid tool wear are encountered in machining Cf/SiC composite. In this study, laser-induced oxidation-assisted milling (LOAM), as novel hybrid machining process, was proposed to enhance machinability of Cf/SiC composites. Pulsed laser was used to induce reaction between Cf/SiC composites and oxygen. Easily removable loose and porous oxides were produced, which were simultaneously removed with milling tool, leading to improved material removal rate and tool life. Oxidation mechanisms and influences of laser parameters on oxidation behavior of Cf/SiC composite were studied. Conventional milling (CONV) without the assistance of laser was also performed on Cf/SiC composite for comparative analysis. Milling force, tool wear, and surface quality were studied in detail. Under laser irradiation, Cf/SiC composite was modified into metamorphic-layer that consisted of oxide layer and transition layer. Material irradiated with laser got melted, vaporized, and then reacted with oxygen, producing oxide. Oxide layer was formed due to the accumulation of oxide. Increasing laser energy density boosted oxidation reaction and increased the thickness of oxide layer. In contrast, increase in laser scanning speed decreased thickness of oxide layer. Results show that cutting force was extremely low and no tool wear occurred during milling oxide layer, indicating significant enhancement in machinability. Abrasive wear mainly occurred on flank face when milling transition layer. Surface damages, for instance fiber fracture and matrix fragmentation, were significantly contained by LOAM. Surface roughness Sa obtained via LOAM was 9.5 μm, which was lower than that obtained by CONV (35 μm). This study indicates that LOAM can achieve high-efficiency processing, low-defect surface, and prolonged tool life when machining Cf/SiC composite.

Improving the crystal quality of AlN films by nanosecond laser annealing

Aluminum nitride (AlN) thin film of thickness 300 nm grown on sapphire substrate was annealed by a nanosecond laser at a wavelength of 532 nm. The laser energy values were 2 J, 3 J, 4 J, and 4.5 J, respectively. In order to increase the absorption of laser energy by the sample, 50 nm thick tungsten films were deposited on the left half of the sample. Surface morphology and Raman spectrum of AlN films were characterized before and after annealing using scanning electron microscope (SEM) and Raman spectrometer, respectively. The SEM micrographs have shown that the surface of AlN film had a large number of voids before annealing. After annealing, the size of the voids becomes smaller and their number decreases with the increase of laser energy density. The full width at half maximum (FWHM) of AlN film was roughly 6-10 cm−1 before annealing and 4-8 cm−1 after annealing. The results showed that the surface morphology and FWHM of the AlN films were improved after laser annealing compared with those before annealing. Finally, COMSOL Multiphysics simulated the temperature field change of AlN film after laser irradiation and the evolution of its surface.

A multiscale composite silicon carbide wick with excellent capillary performance

Wick is the key component of the heat pipe. Composite wick with multiscale porous structure has gained increasing interest for the high permeability and large capillary pressure. In this study, a grooved silicon carbide wick (GSCW) with a multiscale porous structure was fabricated via sintering and laser ablation. The resultant wick is composed of main grooves, the surrounding porous space formed by the stacking silicon carbide (SiC) particles, the microscale netted pores, and nanoscale pores on the groove walls. The effects of laser energy density on the surface morphology, wettability, capillary rise velocity, and overall capillary performance parameter of the GSCW are investigated. The presented wick is hydrophilic. The capillary rise velocity in the initial stage of GSCW was 7 times that of sintered SiC wick. The capillary performance parameter increased with the increasing laser energy density. The laser-ablated grooves improve the capillary performance parameter over 50 times. The rising performances of water, acetone, methanol, and ethanol were tested. The wick thickness has a significant effect on the capillary performance. The comparison of GSCW with other composite wicks in the literature reveals that it has very good capillary performance, making it an excellent wicking structure for heat pipe.

Microstructure Evolution and Performance of Laser-Remelted Ti-6Al-4V Alloy

Herein, Ti-6Al-4V alloy was remelting by high-energy laser, the influence of laser energy density of mobile laser source on the evolution of solidification structure of Ti-6Al-4V alloy was studied, and the changes of relevant service performance of Ti-6Al-4V alloy after laser-remelting were explored. The results showed that there were four distinct regions: overheated zone, melting zone, heat-affected zone and substrate zone in Ti-6Al-4V alloy after laser remelting. The overheated zone and melting zone were dominated by primary α phase and secondary α phase, and a heat-affected zone was dominated by β phase. With the increase of laser energy density, the depth of molten pool and the range of melting zone in Ti-6Al-4V alloy increased, and the crystal phase distribution and grain size changed significantly. Laser-remelting Ti-6Al-4V alloy could still maintain a good passive state in the potentiodynamic polarization curve test, and the optimal laser power during remelting was 1200 W. This study proved that the crystal phase composition and grain size during the solidification process after laser-remelting were a key factor affecting the service performance of Ti-6Al-4V alloy.

Effects of Process Parameters on Density of GH5188 High-temperature Alloy after Selective Laser Melting

GH5188 high-temperature alloy specimens were fabricated by selective laser melting (SLM) and influencing laws of laser power, laser velocity and laser energy density on density of specimens were researched. The results shows that along with the laser energy density increases from 73.02 J/mm3 to 88.18 J/mm3, porosity in specimens decrease and relative density increases from 98.86% to 99.75%. However, as the laser energy density increase further, the density begins to decrease continuously. The main causes that effects relatively density including: the powder is not fused at low energy density, as well as the powder splash and gasification at higher energy density. Neither inadequate nor excessive laser energy density is conducive to improvement of density of specimens. As the increase of laser velocity and laser power, density of specimens increases firstly and then decreases. The variation trend of relative density is similar with that of laser energy density and there are reasonable ranges of laser velocity and laser power. However, influencing laws of laser velocity and laser power on density of specimens are different.

Study on the response and wear property of die steels with varying compositions to laser remelting bionic treatment

In order to research the wear property of die steel, based on the bionic theory, bionic units were manufactured by laser remelting treatment on the surface of five kinds of die steels with varying chemical compositions alloying element contents (1.77%, 5.73%, 8.66%, 9.38% and 14.39%). The differences and regularities in the characteristics (depth, width, area and depth to width ratio), microstructure and hardness of samples with varying laser energy density and compositions of the matrix were analyzed. Then, the wear property of die steel was experimentally evaluated. The results displayed that the cross-sectional area of the bionic unit increased with the increase of laser energy density for the same material. Meanwhile, when the energy density was constant, the cross-sectional area of the bionic unit increased with an increase in alloying element content, but the average hardness of the bionic unit first increased and then decreased. Compared with the untreated sample, the bionic sample is beneficial to enhance the wear property. Moreover, the wear property of die steels with chemical compositions alloying element content of 8.66% reinforced with bionic unit was more effective than other samples. The wear enhancement mechanism of the bionic sample was discussed.

A crack-free and high-strength Al-Cu-Mg-Mn-Zr alloy fabricated by laser powder bed fusion

Laser Powder Bed Fusion (LPBF) is considered as one of the most current additive manufacturing technologies that could prepare customized and complex parts. There have been challenges for LPBF-fabricating 2xxx (Al–Cu) alloy because that own alloy elements cause large solidification ranges and hot cracking is susceptible to generate during solidification. In this study, a crack-free and high-strength Al–Cu–Mg–Mn–Zr alloy was designed and manufactured by LPBF. The results showed that the laser energy density has an important effect on microstructure and density, and it was sufficient to melt the alloy powder and deliver high-quality builds at 333 J/mm3. The microhardness, tensile strength, and yield strength of the LPBF-fabricated Al–Cu–Mg–Mn–Zr alloy increased with increasing laser energy density. In addition, the tensile fracture surfaces exhibited mixed brittle and ductile fracture features at low energy density values (231–358J/mm3). The ductile fracture was observed at higher energy density values (>463J/mm3). When the laser density was set at 500 J/mm3, the LPBF-fabricated alloy exhibited high relative density (99.88%) and the most optimal mechanical properties, with microhardness of 141.5 Hv, tensile strength of 343.9 MPa, yield strength of 311.0 MPa, and elongation of 6.1%. After solution treatment at 560 °C for 2 h and water quenching, the Al–Cu–Mg–Mn–Zr alloy exhibits the excellent mechanical properties with ultimate tensile strength of 483.6 MPa, yield strength of 365.5 MPa, and elongation of 13.4%.

Toward tunable microstructure and mechanical properties in additively manufactured CoCrFeMnNi high entropy alloy

Tailoring microstructure and mechanical properties of structural materials to meet application requirements is a long-standing challenge in materials science. Here we have studied the effects of laser energy density (LED) on the microstructure and mechanical properties of single-track CoCrFeMnNi high entropy alloy (HEA) samples fabricated by laser directed energy deposition (LDED). The results indicate that the molten pool size of the single-track HEA samples gradually increases with increasing LED. All of the samples possess a single face-centered cubic (FCC) solid solution structure. The microstructures of the single-track HEA samples are mainly composed of columnar and equiaxed grains, and as the LED increases, their grain size increases while the micro-hardness decreases. Additionally, the relationship among the processing parameters, cooling rate and grain size was investigated via combining the numerical simulation and experimental observations. This work provides mechanistic insights into establishing the processing-structure-property relationships in the additively manufactured HEAs and contributes to achieve LDED of tunable HEA parts with desired microstructure and mechanical performance.

Densification and microstructure formation mechanisms of 80 W-14Ni-6Fe fabricated by laser powder bed fusion

Tungsten heavy alloys (WHAs) are typically refractory alloy, and machining tungsten alloy components at room temperature is a challenge. Currently, Laser additive manufacturing (LAM) provides a feasible route for machining complex tungsten alloy parts. In this study, the high relative density and almost defect-free 80 W-14Ni-6Fe specimens were successfully obtained via using laser powder bed fusion (LPBF). The densification, microstructure formation mechanisms and tensile properties of LPBFed tungsten alloy were systematically investigated. The results revealed that the relative density of tungsten alloy increases and then decreases with the laser energy density increases. Nearly full densification 80 W-Ni-Fe alloys were obtained when the volumetric energy density (VED) was 80–100 J/mm3. The typical microstructure contained irregular tungsten grain consolidation, W dendrites, spherical tungsten particles and Ni-Fe bonding phase, which was due to melting of partial tungsten particles during LPBF. Interestingly, many ultra-fine crystals occurred in the Ni-Fe matrix, which was closely related to the rapid heat and cooling during LPBF. Besides, there were two strengthening mechanisms in LPBFed 80 W alloy, respectively solid solution strengthening and dispersion strengthening. Hence, the 80 W-Ni-Fe alloy with optimum process parameters exhibited high tensile strength, and the ultimate tensile strength (UTS) reached 1064MP. This work will aid in the additive manufacturing of refractory metal alloys with excellent properties and expand the application prospects of tungsten alloys.

Laser powder bed fusion of cemented carbides by developing a new type of Co coated WC composite powder

The study addresses the issue of the absence of high-quality WC-Co composite powder for laser powder bed fusion and assessing the printability of the new powder in terms of densification, microstructure and mechanical properties. The fluidized bed chemical vapor deposition (FBCVD) combined with electroless plating process was adopted to make core-shell structured WC-Co composite powder. The excellent uniformity of Co and good powder flowability were achieved by tuning the size and distribution of Co catalyst during FBCVD and regulating their relationship to the subsequent electroless plating behavior. The newly developed composite powder exhibited excellent printability. The densification mechanism was largely dependent on the laser energy density. The liquid formed by the melting of Co was responsible for the densification at low laser energy density, while the Co-W-C ternary liquid resulted from the dissolution of WC into Co melt dominated the densification at high laser energy density. Microstructurally, the morphology and size of WC grains were insignificantly changed because of its non-participation with liquid formation at low laser energy density. The rectangular/triangular WC grain morphology similar to the traditional sintered was formed at high laser energy density because of the precipitation of WC from the Co-W-C ternary liquid. Affected by the different liquid formation processes, increasing laser energy density increased the relative density, promoted the W 2 C phase formation and decreased WC grain size, which remarkably improved the hardness and tribological properties of the printed cemented carbide.