To overcome the unworkability of hot work molds in conventional manufacturing, laser additive manufacturing (AM) is widely adopted to print molds/dies with complex internal structures. However, in ...the AM process, some hot work steels easily crack (e.g., H11 and H13 tool steel) or exhibit dissatisfactory wear resistance (e.g., MS1 maraging steel). To tackle this issue, toughened functionally graded metal matrix/ceramic composite materials can be fabricated on existing molds by laser directed energy deposition (L-DED). Contrary to previous studies that clad Co on WC to avoid the decomposition of ceramic, in this work, we innovatively utilized a type of WC-12Co powder with a substructure to accelerate its decomposition and improve the toughness of composites. It was found that the unmelted tens-micrometer-magnitude WC-12Co powder and in situ synthesized nano WC coexist in the laser-deposited H13 steel/WC-12Co composites to act as the reinforcement phase. Particularly, all the brittle phases (WC and FexWxC) are wrapped by soft γ phases, alleviating the coefficient of thermal expansion (CET) mismatch between materials and the residual stress generated by laser AM. Consequently, defect-free deposits with varied WC contents are manufactured by L-DED and exhibit high hardness and superior wear resistance at both room and elevated temperatures due to the second phase and grain refinement strengthening mechanisms. These findings provide a disparate metal matrix composite design route for laser additive manufacturing to improve the toughness of metal matrix/ceramic composite materials and obtain exceptional performance.
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•The micro/nano strengthening mechanism of WC is studied in Fe-based WC composite.•The Co-coated WC powder with a large specific surface area promotes the in situ synthesis of nano WC precipitates.•All the brittle strengthening phases are wrapped by the ductile austenite to avoid crack.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Incorporating boride nanocrystals could significantly impact the mechanical properties of aluminum alloys. Molten salts synthesis offers opportunities to fabricate superhard boride nanoparticles, ...which can sustain the harsh conditions during the liquid‐phase design of metallic nanocomposites. Here hafnium diboride‐aluminum nanocomposites are unveiled from molten salt‐derived HfB2 nanoparticles sequentially dispersed in aluminum by ultrasound treatment. The structure and size of the nanocrystals are retained in the final nanocomposites, supporting their high chemical stability. Semicoherent interfaces between the nanoparticles and the matrix are then evidenced by TEM, suggesting that the nanocrystals could promote heterogeneous nucleation of Al and then limit the Al grain size to ≈20 µm. Nanoindentation measurements reveal significant grain boundary strengthening and grain refinement effects. It is finally shown that HfB2 nanoparticles also enable a decrease in matrix grain size and an increase in the hardness of the AlSi7Cu0.5Mg0.3 alloy. These proof‐of‐concept materials are paving the way to light‐weight Al matrix nanocomposites doped by molten‐salt synthesized nanoparticles.
Molten salts synthesis is coupled with molten metal processing to deliver metal matrix nanocomposites embedding metal boride nanocrystals, which provide a way to enhance the mechanical properties of light metals.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The physics of dynamic friction on water molecule contaminated surfaces is still poorly understood. In line with the growing interest in hydrophobic contact for industrial applications, this paper ...focuses on friction mechanisms in such interfaces. As a commonly used material, contact with graphite is considered in a twin-fold approach based on experimental investigations using the circular mode atomic force microscopy technique combined with molecular dynamic simulations. We demonstrate that an intuitive paradigm, which asserts that water molecules are squeezed out of a hydrophobic contact, should be refined. As a consequence, we introduce a mechanism considering a droplet produced within the sliding nanocontact by the accumulation of water adsorbed on the substrate. Then we show that a full slip regime of the droplet sliding on the hydrophobic substrate explains the experimental tribological behavior.
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IJS, KILJ, NUK, PNG, UL, UM
A performing photoinitiating system based on paprika spice was developed (i) to efficiently initiate, according to a green photoinduced process, the cationic polymerization of a biosourced and ...renewable monomer, e.g., gallic acid, and (ii) to synthesize environmentally friendly antibacterial coatings in a reduced time. A decrease of 100% of the adhered bacteria was demonstrated upon visible light illumination without any remaining live bacteria.
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IJS, KILJ, NUK, PNG, UL, UM
The tribological behavior of dual-phase steels have been studied at the macroscopic scale taking the macrohardness as the main material property to control friction and wear. However, the ...contribution to the macroscopic behavior of the varying properties of the phase at the microscopic scale are yet to be fully understood. In this study, dual-phase microstructures with various grain sizes and martensite volume fraction are generated. Microhardness of ferrite and martensite are measured by nanoindentation tests while their friction and wear behavior are studied by conducting scratch tests with various conical tips. Results show that for martensite, friction coefficient and wear resistance are proportional to its carbon content, whatever the martensite grain size. Whereas changing the ferrite grain size has two effects on the tribological behavior of the microstructure. First, the friction and wear resistance of ferrite are related to its grain size through a Hall–Petch relationship. Second, at a given martensite volume fraction, the mean wear resistance changes from the Equal Wear mode to the Equal Pressure mode as the ratio of the contact size to the ferrite grain size increases, while the mean friction coefficient always correlates to the Equal Pressure mode.
Laser-assisted metal processing has received great attention for repair, manufacturing, and surface modification in various industries. However, the mesoscopic segregation and oxidation phenomena ...during these processes require further investigations. In present work, the H13 tool steel is remelted by a laser beam. The generation of oxide layer, the profile and the mesoscopic segregation of the molten pool, Marangoni convection, the and hardening effect are studied by an experimentation combined with a multiphysics coupled simulation. An oxide layer was formed on the remelted surface with a thickness of ∼ 60 µm in the middle and ∼10 µm in the edges. The lightweight elements (Si, V, Cr, and Mn) float upon the molten pool driven by both buoyancy and Marangoni convection. In addition, due to their higher redox activity, they tend to have a higher proportion in the oxide layer with respect to the base metal. As a consequence, elemental mesoscopic segregation appeared in the remelted zone. The oxide layer shows an average hardness of 11.8 GPa, which is similar to that of the remelted zone (11.7 GPa). However, the brittleness of the oxide layer leads to cracks, hence deteriorating its mechanical properties. Together, these results bring a further fundamental understanding of the mesoscopic segregation that is attributed to the Marangoni convection and oxidation phenomenon during the laser processing of alloys, which might be a critical factor to optimize the mechanical properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The influence of sliding velocity on the adhesion force in a nanometer-sized contact was investigated with a novel atomic force microscope experimental setup that allows measuring adhesion forces ...while the probe is sliding at continuous and constant velocities. For hydrophobic surfaces, the adhesion forces (mainly van der Waals forces) remain constant, whereas for hydrophilic surfaces, adhesion forces (mainly capillary forces) decrease linearly with a logarithmic increase of the sliding velocity. The experimental data are well explained by a model based on a thermally activated growth process of a capillary meniscus.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
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