Search Results (118)

A (NiCoCr)_99.25C_0.75 medium entropy alloy (MEA) was developed via laser powder bed fusion (LPBF) using pre-alloyed powder feedstock containing 0.75 at%C, followed by a precipitation heat treatment. The as-built alloy exhibited high density (>99.9%), columnar grains, fine substructures, and strong <111> texture. Heat treatment at 700 °C for 1 h promoted the precipitation of Cr-rich carbides (Cr₂₃C₆) along grain and substructure boundaries, which stabilized the microstructure through Zener pinning and the consumption of carbon from the matrix. The heat-treated alloy achieved excellent cryogenic tensile properties at 77 K, with a yield strength of 1230 MPa and an ultimate tensile strength of 1.6 GPa. Compared to previously reported LPBF-built NiCoCr-based MEAs, this alloy exhibited superior strength at both room and cryogenic temperatures, indicating its potential for structural applications in extreme environments. Deformation mechanisms at cryogenic temperature revealed abundant deformation twinning, stacking faults, and strong dislocation–precipitate interactions. These features contributed to dislocation locking, resulting in a work hardening rate higher than that observed at room temperature. This study demonstrates that carbon addition and heat treatment can effectively tune the stacking fault energy and stabilize substructures, leading to enhanced cryogenic mechanical performance of LPBF-built NiCoCr MEAs. Full article

This study systematically explores the synergistic effects of direct aging treatment (480 °C for 6 h) combined with cryogenic treatment (−196 °C for 8 h) on the mechanical properties and microstructural evolution of 18Ni300 maraging steel fabricated via selective laser melting (SLM). Three conditions were investigated: as-built, direct aging (AT6), and direct aging plus cryogenic treatment (AT6C8). Microstructural characterization was performed using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), while the mechanical properties were evaluated via microhardness and tensile testing. The results show that the AT6C8 sample achieved the highest microhardness (635 HV_0.5) and tensile strength (2180 MPa), significantly exceeding the as-built (311 HV_0.5, 1182 MPa) and AT6 (580 HV_0.5, 2012 MPa) samples. Cryogenic treatment induced a notable phase transformation from retained austenite (γ phase) to martensite (α phase), with the peak relative intensity ratio ranging from 1.42 (AT6) to 1.58 (AT6C8) in the XRD results. TEM observations revealed that cryogenic treatment refined lath martensite from 0.75 μm (AT6) to 0.24 μm (AT6C8) and transformed reversed austenite into thin linear structures at the martensite boundaries. The combination of direct aging and cryogenic treatment effectively enhances the mechanical properties of SLM-fabricated 18Ni300 maraging steel through martensite transformation, microstructural refinement, and increased dislocation density. This approach addresses the challenge of balancing strength improvement and residual stress relaxation. Full article

The Polish Free-Electron Laser (PolFEL), which is currently under construction in the National Centre for Nuclear Research in Świerk near Warsaw, will comprise an electron gun and from four to six cryomodules, each accommodating two nine-cell TESLA RF superconducting resonant cavities. To cool the superconducting resonant cavities, the cryomodules will be supplied with superfluid helium at a temperature of 2 K. Other requirements regarding the cooling power of PolFEL result from the need to cool the power couplers for the accelerating cryomodules (5 K) and thermal shields, which limit the heat inleaks due to radiation (40–80 K). The machine will utilize several thermodynamic states of helium, including two-phase superfluid helium, supercritical helium, and low-pressure helium vapours. Supercritical helium will be supplied from a cryoplant by a cryogenic distribution system (CDS)—transfer line and valve boxes—where it will be thermodynamically transformed into a superfluid state. This article presents the architecture of the CDS, discusses several design solutions that could have been decided on with the use of second law analysis, and presents the design methodology of the chosen CDS elements. Full article

This study aims to comprehensively assess the suitability of post-processing annealing (at 900–1200 °C) for enhancing the key properties of 316L steel fabricated via laser powder bed fusion (LPBF). It adopts a holistic approach to investigate the annealing-driven evolution of microstructure–property relationships, focusing on tensile properties, nanoindentation hardness and modulus, impact toughness at ambient and cryogenic temperatures (−196 °C), and the corrosion resistance of LPBF 316L. Annealing at 900–1050 °C reduced tensile strength and hardness, followed by a moderate increase at 1200 °C. Conversely, ductility and impact toughness peaked at 900 °C but declined with the increasing annealing temperature. Regardless of the annealing temperature and testing conditions, LPBF 316L steel fractured through a mixed transgranular/intergranular mechanism involving dimple formation. The corrosion resistance of annealed steel was significantly lower than that in the as-built state, with the least detrimental effect being observed at 1050 °C. These changes resulted from the complex interplay of annealing-induced structural transformations, including elimination of the cellular structure and Cr/Mo segregations, reduced dislocation density, the formation of recrystallized grains, and the precipitation of nano-sized (MnCrSiAl)O₃ inclusions. At 1200 °C, an abundant oxide formation strengthened the steel; however, particle coarsening, combined with the transition of (MnCrSiAl)O₃ into Mo-rich oxide, further degraded the passive film, leading to a sharp decrease in corrosion resistance. Overall, post-processing annealing at 900–1200 °C did not comprehensively improve the combination of LPBF 316L steel properties, suggesting that the as-built microstructure offers a favorable balance of properties. High-temperature annealing can enhance a particular property while potentially compromising other performance characteristics. Full article

Icing on power lines and wings can cause serious economic damage and safety hazards. While superhydrophobic materials show promise for anti-icing applications, their passive anti-icing mechanisms require external energy activation, highlighting the need for the development of active de-icing materials with energy-to-heat conversion capabilities. Here, we developed three photothermal superhydrophobic shape-memory polymers with anti-icing performance (PSSPs), with 3%, 5%, and 7% CNT doping ratios, through a two-step process: resin preparation and laser-processing modification. The results showed that all samples presented good superhydrophobic properties. In addition, the tested materials demonstrated good shape-memory performance (recovery rates were close to 100%). They also showed excellent de-icing performance. Owing to the simplicity of the fabrication process, the material is suitable for mass production. The synergistic interplay between superhydrophobicity and photothermal activation endows the material with dual-functional icephobic performance, demonstrating practical applicability in industrial cryogenic environments. Full article

Interest in hydrogen is rapidly growing due to rising greenhouse gas emissions and the depletion of fossil fuel reserves. Additive manufacturing (AM) is extensively employed to produce high-quality components, with a strong focus on enhancing mechanical properties. The efficiency and cost-effectiveness of AM have further increased interest in its application to manufacturing components capable of withstanding demanding conditions, such as those encountered in hydrogen technology. In this study, 316L stainless steel specimens were fabricated using AM via the selective laser melting (SLM) technique. The specimens then underwent various post-processing heat treatments (PPHT). A subset of these specimens, measuring 50 × 50 × 3 mm³, was tested as electrodes in a water electrolysis cell for oxyhydrogen (HHO) gas production. The HHO gas flow rate and electrolyzer efficiency were evaluated at 60 °C under varying currents. The remaining AM specimens were evaluated for their susceptibility to hydrogen embrittlement under various hydrogen storage conditions, including testing at both room and cryogenic temperatures. Tensile and Charpy impact specimens were fabricated and tested before and after hydrogen charging. The fracture surfaces were analyzed using scanning electron microscopy (SEM) to assess the influence of hydrogen on fracture characteristics. Additionally, as-rolled stainless-steel specimens were examined for comparison with AM and PPHT 316L stainless steel. The primary objective of this study is to determine the most efficient alloy processing condition for optimal performance in each application. Results indicate that PPHT 316L stainless steel exhibits superior performance both as electrodes for HHO gas production and as a material for hydrogen storage vessels, demonstrating high resistance to hydrogen embrittlement. Full article

The Cryo-PoF project is an R&D project funded by the Italian Insitute for Nuclear Research (INFN) in Milano-Bicocca (Italy). The technology at the basis of the project is Power over Fiber (PoF). By sending laser light through an optical fiber, this technology delivers electrical power to a photovoltaic power converter, in order to power sensors or electrical devices. Among the several advantages this solution can provide, we can underline the spark-free operation when electric fields are present, the removal of noise induced by power lines, the absence of interference with electromagnetic fields, and robustness in hostile environments. R&D for the application of PoF in cryogenic environments started at Fermilab in 2020; for the DUNE Vertical Drift detector, it was needed to operate the Photon Detector System on a high-voltage cathode surface. Cryo-PoF, starting from this project, developed a single-laser input line system to power, at cryogenic temperatures, both an electronic amplifier and Photon Detection devices, tuning their bias by means of the input laser power, without adding ancillary fibers. The results obtained in Milano-Bicocca will be discussed, presenting the tests performed using power photosensors at liquid nitrogen temperature. Full article

Ti-6Al-4V (Ti64) alloy is widely utilized in the aerospace industry due to its high strength, fatigue resistance, corrosion resistance, and cryogenic properties. However, its high raw material costs and machining difficulties necessitate the development of efficient manufacturing processes. This study evaluates the mechanical reliability and microstructure of Ti64 components fabricated using wire laser additive manufacturing (WLAM) and subsequently joined via tungsten inert gas (TIG) welding. The WLAM process produces refined microstructures with superior mechanical properties by minimizing defects; however, insufficient process optimization may result in a lack of fusion (LOF) and porosity. Microstructural analysis revealed that the WLAM deposits exhibited a fine basket-weave α structure with an average α-lath width of 1.27 ± 0.69 μm, while the TIG-welded region exhibited a coarsened α-lath, reaching 3.02 ± 2.06 μm, which led to a reduction in ductility. Tensile testing demonstrated that the WLAM deposits exhibited superior mechanical properties, with a yield strength of 910 MPa, ultimate tensile strength of 1015 MPa, and elongation of 12.8%, outperforming conventional wrought Ti64 alloys. Conversely, the TIG-welded joints exhibited reduced mechanical properties, with a yield strength of 812 MPa, ultimate tensile strength of 917 MPa, and elongation of 7.5%, primarily attributed to microstructural coarsening in the weld region. The findings of this study confirm that WLAM enhances the mechanical properties of Ti64, whereas TIG welding may introduce structural weaknesses. This research provides insight into the microstructural evolution and mechanical behavior of WLAM-fabricated Ti64 components, with valuable implications for their application in aerospace structures. Full article

The direct vapor equilibration-laser spectroscopy (DVE-LS) method can be used to measure the stable isotopes of soil water (δ²H and δ¹⁸O), a technique that is easier to operate and quicker for sampling compared to the traditional cryogenic vacuum distillation (CVD) method. However, the soil water isotope values thus obtained often deviate from the true value, which is affected by the equilibrium temperature during the measurement process. Therefore, this study conducted an indoor experiment on five soil samples of varying textures. The dry soil was wetted by reference water samples to four different soil water content (SWC) values and then equilibrated at five different temperatures. The soil water isotope deviation value (SWIDV) of the DVE-LS method was determined by building a correction equation between SWIDV and the influencing factors (equilibrium temperature, soil clay content (SCC), and SWC, after which the correction equation values were compared to those calculated by the CVD method for the field-collected soil samples to check the accuracy. The results shows that the Δδ²H value increased with increasing equilibrium temperature and soil clay content, but decreased with increasing SWC. The multi-factor variance analysis shows that equilibrium temperature, SCC, and SWC significantly affected the Δδ²H values and deviation values with the DVE-LS method, but insignificantly affected the Δδ¹⁸O values and deviation values. The correction equations (3) was built at different equilibrium temperatures, and the RMSE decreased from 4.07‰ to 1.24‰ and from 8.99‰ to 4.14‰, respectively, as calibrated by the isotope values of soil samples collected in Changwu and Suide counties. The correction equations under various equilibrium temperatures increased the accuracy of the DVE-LS method in obtaining soil water isotope values and promoted the application of the DVE-LS method in soil water isotope analysis. Full article

The temperature dependence of the mechanical properties of the CoCrFeNi medium-entropy alloy (MEA) manufactured by laser-directed energy deposition (L-DED) and additionally annealed at 1200 °C for 24 h was studied. The microstructure of the as-deposited alloy was represented by a single-phase face-centered cubic structure with coarse columnar grains and a high density of dislocation. Annealing resulted in the development of recrystallization and a reduction in dislocation density. The CoCrFeNi alloy produced by L-DED demonstrated mechanical properties comparable with those of the fine-grained equiatomic CoCrFeMnNi alloy, produced by casting followed by thermomechanical processing. Namely, as-deposited CoCrFeNi had a yield strength (YS) and ultimate tensile strength (UTS) of YS = 370 MPa and UTS = 610 MPa at room temperature, and YS = 565 MPa and UTS = 965 MPa at cryogenic temperature, along with a ductility of ~60%. Annealing resulted in a decrease in strength to YS = 180/350 MPa at 293/77 K. A quantitative analysis of various strengthening mechanisms showed that some strength increment of the as-deposited alloy was ensured by the high dislocation density formed during L-DED. Full article

The Torsion-Bar Antenna (TOBA) is a torsion pendulum-based gravitational detector developed to observe gravitational waves in frequencies between 1 mHz and 10 Hz. The low resonant frequency of the torsion pendulum enables observation in this frequency band on the ground. The final target of TOBA is to observe gravitational waves with a 10 m detector and expand the observation band of gravitational waves. In this paper, an overview of TOBA, including the previous prototype experiments and the current ongoing development, is presented. Full article

In order to improve the tribological properties of the 7075-T6 aluminum alloy used on the rotor surface, a combined method of cryogenic treatment and laser surface texture treatment was applied. Various tests, including metallographic microscopy, scanning electron microscopy, elemental analysis, microhardness measurements, were conducted to examine the wear morphology and modification mechanism of the treated 7075-T6 aluminum alloy surface. A numerical simulation model of surface texture was established using computational fluid dynamics to analyze the lubrication characteristics of V-shaped texture. The research finding that the 7075-T6 aluminum alloy experienced grain refinement during the cryogenic treatment process, enhancing the wear resistance of the V-shaped textures. This improvement delayed the progression of fatigue wear, abrasive wear, and oxidative wear, thereby reducing friction losses. The designed V-shaped texture contributes to reducing contact area, facilitating the capture and retention of abrasives, and enhancing oil film load-bearing capacity, thereby improving tribological performance. The synergistic effect of cryogenic treatment reduced the friction coefficient by 24.8% and the wear loss by 66.4%. Thus, the combination of surface texture and cryogenic treatment significantly improved the tribological properties of the 7075-T6 aluminum alloy. Full article

This work reports on the possibility of sustaining a stable operation of polarization-doped InGaN light emitters over a particularly broad temperature range. We obtained efficient emission from InGaN light-emitting diodes between 20 K and 295 K and from laser diodes between 77 K and 295 K under continuous wave operation. The main part of the p-type layers was fabricated from composition-graded AlGaN. To optimize injection efficiency and improve contact resistance, we introduced thin Mg-doped layers of GaN (subcontact) and AlGaN (electron blocking layer in the case of laser diodes). In the case of LEDs, the optical emission efficiency at low temperatures seems to be limited by electron overshooting through the quantum wells. For laser diodes, a limiting factor is the freeze-out of the magnesium-doped electron blocking layer for temperatures below 160 K. The GaN:Mg subcontact layer works satisfyingly even at the lowest operating temperature (20 K). Full article

The application of terahertz (THz) science in industrial technology and scientific research requires efficient THz detectors. Such detectors should be able to operate under various external conditions and conform to existing geometric constraints in the required application. Pyroelectric THz detectors are among the best candidates. This is due to their versatility, outstanding performance, ease of fabrication, and robustness. In this paper, we propose a compact pyroelectric detector based on a bioriented poled polyvinylidene difluoride film coated with sputtered metal electrodes for in situ absorption measurement at cryogenic temperature. The detector design was optimized for the registration system of the electron paramagnetic resonance (EPR) endstation of the Novosibirsk Free Electron Laser facility. Measurements of the detector response to pulsed THz radiation at different temperatures and electrode materials showed that the response varies with both the temperature and the type of electrode material used. The maximum signal level corresponds to the temperature range of 10–40 K, in which the pyroelectric coefficient of the PVDF film also has a maximum value. Among the three coatings studied, namely indium tin oxide (ITO), Au, and Cu/Ni, the latter has the highest increase in sensitivity at low temperature. The possibility of using the detectors for in situ absorption measurement was exemplified using two typical molecular spin systems, which exhibited a transparency of 20–30% at 76.9 cm⁻¹ and 5 K. Such measurements, carried out directly in the cryostat with the main recording system and sample fully configured, allow precise control of the THz radiation parameters at the EPR endstation. Full article

The welded joints of high/medium entropy alloys (H/MEAs) have shown sound mechanical properties, indicating high promise for the industrial application of this new type of metal alloy. However, these joints possess either relatively low strength or low ductility. In this paper, we used ultrasonic-assisted laser welding to weld CrCoNi MEA with the nitrogen as shielding gas. The results showed that the tensile strength of the joint at room and cryogenic temperature is 686 MPa and 1071 MPa, respectively. The elongation at room and cryogenic temperature is 26.8% and 27.7%, respectively. The combination of the strength and ductility in our joints exceeds that of other welded H/MEA joints. We attributed this excellent combination to the refined dendrite, the solution of nitrogen into the matrix, and the low stacking fault energy of the CrCoNi MEA. The findings in this paper not only provide a novel way to weld H/MEAs with high strength and ductility, also are useful for additively manufacturing the high-performance component of H/MEAs. Full article