Search Results (118)

NASICON-type Li_1+XFe_XTi_2-X(PO₄)₃ (x = 0.1, 0.3, 0.4) solid electrolytes for all-solid-state Li-ion batteries were synthesized using a sol–gel method. This study investigated the impact of substituting Fe³⁺ (0.645 Å), a trivalent cation, for Ti⁴⁺ (0.605 Å) on ionic conductivity. Li_1+XFe_XTi_2-X(PO₄)₃ samples, subjected to various sintering temperatures, were characterized using TG-DTA, XRD with Rietveld refinement, XPS, FE-SEM, and AC impedance to evaluate composition, crystal structure, fracture-surface morphology, densification, and ionic conductivity. XRD analysis confirmed the formation of single-crystalline NASICON-type Li_1+XFe_XTi_2-X(PO₄)₃ at all sintering temperatures. However, impurities in the secondary phase emerged owing to the high sintering temperature above 1000 °C and increased Fe content. Sintered density increased with the densification of Li_1+XFe_XTi_2-X(PO₄)₃, as evidenced by FE-SEM observations of sharper edges of larger quasi-cubic grains at elevated sintering temperatures. At 1000 °C, with Fe content exceeding 0.4, grain coarsening resulted in additional grain boundaries and internal cracks, thereby reducing the sintered density. Li_1.3Fe_0.3Ti_1.7(PO₄)₃ sintered at 900 °C exhibited the highest density among the other conditions and achieved the maximum total ionic conductivity of 1.51 × 10⁻⁴ S/cm at room temperature, with the lowest activation energy for Li-ion transport at 0.37 eV. In contrast, Li_1.4Fe_0.4Ti_1.6(PO₄)₃ sintered at 1000 °C demonstrated reduced ionic conductivity owing to increased complex impedance associated with secondary phases and grain crack formation. Full article

Cold Spray Additive Manufacturing (CSAM) is a solid-state process that is being increasingly used for structural repairs in aerospace and energy sectors. It enables the deposition of dense material at low temperatures by accelerating metal particles to supersonic velocities, thereby reducing thermal distortion. However, the structural integrity of CSAM repairs—particularly at the interface between the deposited layer and the substrate—remains a critical concern. Various post-treatments and characterization methods have been explored to optimize performance. While X-ray Computed Tomography (XCT) is effective for sub-surface inspection, it cannot be applied in situ during mechanical testing. Digital Image Correlation (DIC), a surface-based method, also lacks sub-surface sensitivity. To address this, Infrared Thermography (IRT) was employed alongside DIC during the tensile and fatigue testing of aluminum CSAM-repaired specimens. A cooled IRT camera operating at 200 FPS captured thermal data, with lock-in processing subsequently applied in post-processing. IRT successfully detected early interfacial damage and enabled the tracking of crack propagation, which was later confirmed through fracture surface analysis. This extended abstract presents findings from fatigue tests using IRT. Full article

Friction stir welding (FSW) has emerged as a solid-state joining technique offering notable advantages over traditional welding methods. Gas metal arc welding (GMAW), a fusion-based process, remains widely used due to its high efficiency, productivity, weld quality, and ease of automation. To combine the benefits of both techniques, a hybrid welding approach integrating GMAW and FSW has been developed. This study investigates the impact of this hybrid technique on the joint quality and properties of AA5083-H111 and AA6082-T6 aluminum alloys. Butt joints were produced on 6 mm thick plates, with variations in friction process parameters. Characterization included macro- and microstructural analyses, mechanical testing (hardness and tensile strength), and corrosion resistance evaluation through stress corrosion cracking tests. Results showed that FSW significantly refined and homogenized the microstructure in both alloys. AA5083-H111 welds achieved a joint efficiency of 99%, while AA6082-T6 reached 66.7%, differences attributed to their distinct strengthening mechanisms and the thermal–mechanical effects of FSW. To assess hydrogen-related behavior, slow strain rate tensile (SSRT) tests were conducted in both inert and hydrogen-rich environments. Hydrogen content was measured in arc, friction, and overlap zones, revealing variations depending on the alloy and microstructure. Despite these differences, both alloys exhibited negligible hydrogen embrittlement. In conclusion, the GMAW–FSW hybrid process successfully produced sound joints with good mechanical and corrosion resistance performance in both aluminum alloys. The findings demonstrate the potential of hybrid welding as a viable method for enhancing weld quality and performance in applications involving dissimilar aluminum alloys. Full article

Additive manufacturing of metal components is predominantly based on fusion-welding processes involving melting and solidification. However, processing high-strength aluminium alloys presents challenges, including reduced mechanical properties and increased susceptibility to hot cracking. To address these issues, alternative solid-state processing methods for aluminium are being explored worldwide. One such method is wire-based friction-stir additive manufacturing, which builds on the principles of friction-stir welding. This study focused on assessing a range of pin tool designs to promote improved mixing between the filler material and substrate. The best results were achieved using a two-stirring-probe configuration, which was then employed to fabricate a multilayer wall made of EN AW-6063 aluminium alloy. The resulting structure showed significant grain refinement, with the deposited layers having an average grain size approximately four times smaller than that of the substrate, indicating dynamic recrystallisation. Tensile testing of the intermediate layer revealed a strength of 147 MPa and 10% elongation, corresponding to 77% of the filler wire strength. These findings highlight the potential of the W-FSAM process for producing near-net-shape, high-quality lightweight metal components with refined microstructures and reliable mechanical performance. Full article

To investigate the effect of laser cleaning on the chromium plating of steel tyre moulds, a solid-state laser with an average power of 500 W was used as the cleaning light source. By varying the energy density and the number of pulses applied to the exact location, the changes in the macro- and micro-morphology of the mould surface, surface element content, and chromium plating thickness before and after laser cleaning were studied. The results show that as the laser energy density increases, the cleaning effect improves significantly. However, when the energy density exceeds $1.02\times {10}^4$ mJ/cm², cracks appear in the chrome-plated layer. By changing the number of pulses applied to a specific location, it was found that cracks also appear in the chrome-plated layer when the number of pulses exceeds three. These results provide a reference for the practical application of laser cleaning in the cleaning of chrome-plated steel tyre moulds. Full article

Thermal stimulation represents an effective method for enhancing reservoir permeability, thereby improving geothermal energy recovery in Enhanced Geothermal Systems (EGS). The phase-field method (PFM) has been widely adopted for its proven capability in modeling the fracture behavior of brittle solids. Consequently, a coupled thermo-mechanical phase-field model (TM-PFM) was developed in COMSOL 6.2 Multiphysics to probe thermal fracturing mechanisms in reservoir rocks. The TM-PFM was validated against the analytical solutions for the temperature and stress fields under steady-state heat conduction in a thin-walled cylinder, three-point bending tests, and thermal shock tests. Subsequently, two distinct thermal fracturing modes in reservoir rock under high-temperature conditions were investigated: (i) fracture initiation driven by sharp temperature gradients during instantaneous thermal shocks, and (ii) crack propagation resulting from heterogeneous thermal expansion of constituent minerals. The proposed TM-PFM has been validated through systematic comparison between the simulation results and the corresponding experimental data, thereby demonstrating its capability to accurately simulate thermal fracturing. These findings provide mechanistic insights for optimizing geothermal energy extraction in EGS. Full article

Nickel is used in aerospace, military, energy, and chemical sectors. Commercially pure (CP) Ni, and its alloys, including solid-solution strengthened (SSS), precipitation strengthened (PS), and specialty alloys (SA), are widely utilized, typically at elevated temperatures, in corrosive settings and in cryogenic milieu. Ni or Ni-based alloys frequently require welding realized, inter alia, via methods using electric arc and beam power. Tungsten inert gas (TIG) and Electron-beam welding (EBW) have been utilized most often. Friction stir welding (FSW) is the most promising solid-state welding technique for connecting Ni and its alloys. The primary weldability issues related to Ni and its alloys are porosity, as well as hot and warm cracking. CP Ni exhibits superior weldability. It is vulnerable to porosity and cracking during the solidification of the weld metal. Typically, SSS alloys demonstrate superior weldability when compared to PS Ni alloys; however, both types may experience weld metal solidification cracking, liquation cracking in the partially melted and heat-affected zones, as well as ductility-dip cracking (DDC). Furthermore, PS alloys are prone to strain-age cracking (SAC). The weldability of specialty Ni alloys is limited, and brazing might provide a solution. Employing appropriate filler metal, welding settings, and minimal restraint can reduce or avert cracking. Full article

Non-uniform friction and lubrication are the key factors affecting the surface quality of the casting billet. Based on the three-layer structure of the casting powder in the mold, the frictional stress in the mold was calculated and analyzed by using the relationship between the frictional stress and the thickness and viscosity of the liquid slag film, and the lubrication state between the cast billet and the mold was evaluated. Based on the actual production data of 40Mn2 steel and combined with the numerical simulation results of the solidification and shrinkage process of the molten steel in the mold by ANSYS 2022 R1 software, the frictional stress on the cast billet in the mold was calculated. It was found that within the range of 44~300 mm from the meniscus, the friction between the cast billet and the mold was mainly liquid friction, and the friction stress value increased from 0 to 145 KPa. Within 300–720 mm from the meniscus, the billet shell is in direct contact with the mold. The friction between the cast billet and the mold is mainly solid-state friction, and the friction stress value increases from 10.6 KPa to 26.6 KPa. It indicates that the excessive frictional stress inside the mold causes poor lubrication of the cast billet. By reducing the taper of the mold and optimizing the physical and chemical properties of the protective powder, within the range of 44~550 mm from the meniscus, the friction between the cast billet and the mold is mainly liquid friction, and the friction stress value varies within the range of 0–200 Pa. It reduces the frictional stress inside the mold, improves the lubrication between the billet shell and the mold, and completely solves the problem of mesh cracks on the surface of 40Mn2 steel cast billets. Full article

Tungsten–diamond metal matrix composites (MMCs) fabricated via L-PBF show potential for applications in nuclear facility shielding, heat sinks, precision cutting/grinding tools, and aerospace hot-end components. In this paper, tungsten (W), diamond (D), and diamond with Ni coating (D-Ni) powders are used to fabricate W+D and W+(D-Ni) composites by L-PBF technology. The results show that at the interface of the W+D sample, the W powder melts while the D powder remains in a solid state during L-PBF processing, and W and C elements gradually diffuse into each other. Due to the high cooling rate of L-PBF processing, the C phase forms a diamond-like carbon (DLC) phase with an amorphous structure, and the W phase becomes a supersaturated solid solution of the C element. At the interface of the W+(D-Ni) sample, the diffusion capacity of Ni and W elements in the solid state is weaker than in the molten state. C and W elements diffuse into the Ni melt, forming a rich Ni area of the DLC phase, while Ni and W elements diffuse into the solid D powder, forming a lean Ni area of the DLC phase. In the rich Ni area of the DLC phase, Ni segregation leads to the precipitation of nanocrystals (several hundred nanometers), whereas in the lean Ni area of the DLC phase, the diffusion capacity of Ni and W elements in the solid D powder is limited, resulting in nanocrystalline sizes of only about tens of nanometers. During W dendrite growth, the addition of the Ni coating and the expelling of the C phenomenon leads to W grain refinement at the interface, which reduces the number and length of cracks in the W+(D-Ni) sample. This paper contributes to the theoretical development and engineering applications of tungsten–diamond MMCs fabricated by L-PBF. Full article

Non-isothermal differential scanning calorimetry (DSC) and Raman microscopy were used to study the crystallization behavior of the 20–50 μm amorphous nifedipine (NIF) powder. In particular, the study was focused on the diffusionless glass-crystal (GC) growth mode occurring below the glass transition temperature (T_g). The exothermic signal associated with the GC growth was indeed directly and reproducibly recorded at heating rates q⁺ ≤ 0.5 °C·min⁻¹. During the GC growth, the α_p polymorphic phase was exclusively formed, as confirmed via Raman microscopy. In addition to the freshly prepared NIF samples, the crystallization of the powders annealed for 7 h at 20 °C was also monitored—approx. 50–60% crystallinity was achieved. For the annealed NIF powders, the confocal Raman microscopy verified a proportional absence of the crystalline phase on the sample surface (indicating its dominant formation along the internal micro-cracks, which is characteristic of the GC growth). All DSC data were modeled in terms of the solid-state kinetic equation paired with the autocatalytic model; the kinetic complexity was described via reaction mechanism based on the overlap of 3–4 independent processes. The kinetic trends associated with decreasing q⁺ were identified, confirming the temperature-dependent kinetic behavior, and used to calculate a theoretical kinetic prediction conformable to the experimentally performed 7 h annealing at 20 °C. The theoretical model slightly underestimated the true extent of the GC growth, predicting the crystallinity to be 35–40% after 7 h (such accuracy is still extremely good in comparison with the standard kinetic approaches nowadays). Further research in the field of kinetic analysis should thus focus on the methodological ways of increasing the accuracy of considerably extrapolated kinetic predictions. Full article

The aim of this work is to study the effect of high-temperature compaction (HTC) upon the polymorphism and the mechanical behavior of an additively manufactured (AM) carbon fiber-reinforced polyamide (PA6). Different pressure and temperature levels during HTC were tested to determine the overall effect on the mechanical behavior and material crystalline composition. Treated, carbon fiber-reinforced PA6 samples were analyzed using differential scanning calorimetry, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and three-point bending testing. When considered with respect to as-printed samples, an HTC temperature of 190 °C combined with 80 psi pressure resulted in an increased flexural modulus and strength of 47% and 58%, respectively. This increase was attributed to the decrease in AM-induced cracking, voids (both inside and between the beads), and crystalline solid-state transition in the PA6. The effect of pressure and temperature on the crystalline structure was discussed in terms of an increased degree of crystallinity and the amount of α-phase. Therefore, HTC can help overcome some limitations of traditional annealing, which can result in recrystallization-induced cracking which can lead to material embrittlement. The proposed HTC method demonstrates the potential in improving the mechanical behavior of AM thermoplastic composites. Full article

The microwave chemical looping synergistic gasification characteristics of municipal solid waste polypropylene plastic and the organic solid waste water hyacinth are experimentally investigated in this study. In addition, the characterizations of oxygen carriers before and after the reaction are combined to analyze the evolution of the microscopic morphology of oxygen carriers and the changes in the relative contents of each valence state of Fe and O elements. The results show that an increase in the water hyacinth mixing ratio presents positive effects on tar cracking and a slight negative effect on syngas yield. At the water hyacinth mixing ratio of 75%, the cold gas efficiency and carbon conversion can reach maximum values of 77.64% and 69.9%, respectively. The H₂ yield and H₂/CO ratio in syngas can be also improved to 0.34 Nm³/kg and 1.62, respectively. In addition, a minimum tar yield of 0.133 g/g (fuel) can be obtained at this mixing ratio. Moreover, the addition of water hyacinth has a continuous increase effect on monocyclic aromatic hydrocarbon (MAH) products of tar, and a continuous decrease effect on naphthalene and bicyclic aromatic hydrocarbons (NAH) products. This work explores the synergistic properties of organic waste plastics and agroforestry wastes during microwave chemical looping gasification, which is a useful exploration for solving the environmental problems caused by waste materials and agroforestry wastes as well as realizing the resourceful utilization of solid wastes. Full article

Thin films of gadolinium-doped ceria (GDC) nanoparticles were fabricated as electrolytes for low-temperature solid oxide fuel cells (SOFCs) by combining electrophoretic deposition (EPD) and the successive ionic layer adsorption and reaction-air spray plus (SILAR-A+) method. The Ce_1−xGd_xO_2−x/2 solid solution was synthesized using hydrothermal (HY) and solid-state (SS) procedures to produce high-quality GDC nanoparticles suitable for EPD fabrication. The crystalline structure, cell parameters, and phases of the GDC products were analyzed using X-ray diffraction. Variations in oxygen vacancy concentrations in the GDC samples were achieved through the two synthetic methods. The ionic conductivities of pressed pellets from the HY, SS, and commercial G_0.2DC samples, measured at 150 °C, were 0.6 × 10⁻⁶, 2.6 × 10⁻⁶, and 2.9 × 10⁻⁶ S/cm, respectively. These values were determined using electrochemical impedance spectroscopy (EIS) with a simplified equivalent circuit method. The morphologies of G_0.2DC thin films prepared via EPD and SILAR-A+ processes were characterized, with particular attention to surface cracking. Crack-free GDC thin films, approximately 730–1200 nm thick, were successfully fabricated on conductive substrates through the hybridization of EPD and SILAR-A+, followed by hydrothermal annealing. EIS and ionic conductivity (1.39 × 10⁻⁹ S/cm) measurements of the G_0.2DC thin films with thicknesses of 733 nm were performed at 300 °C. Full article

Friction stir spot welding (FSSW) technology relies on the generation of frictional heat during the rotation of the welding tool in contact with the workpiece as well as the stirring effect of the tool pin to produce solid-state spot joints, especially for lightweight materials. Although FSSW offers significant advantages over traditional fusion welding, the oxidation of the interfacial bond line remains one of the most challenging issues, affecting the quality and strength of the joint under both static and cyclic loading conditions. In this experimental study, inert argon gas was employed to surround the joint, aiming to prevent or minimize the formation of the interfacial oxides. Two welding processes were conducted with identical welding process parameters and welding tool geometry: the conventional process and another that employs an inert gas cover. Micrographs of as-welded specimens were analyzed using a computerized optical microscope to characterize the interfacial bond lines and an energy-dispersive spectroscope (EDS) was used to quantify the interfacial oxides. Specimens from both welding conditions were tested under static and cyclic loads to investigate the static and fatigue behaviors, respectively. The fatigue tested specimens were examined under different load levels to investigate the fatigue crack behavior and the modes of failure at low-cycle and high-cycle fatigue conditions. The optical micrographs showed significant improvement in bond line morphologies (33% enlarged fully bonded area) and both static and fatigue strengths (35% reduced partially bonded area) when the inert gas cover was used. The EDS analysis revealed a maximum reduction of the interfacial oxide of 41% in the bond line achieved in the argon-surrounded joints compared to specimens of the conventional welding process. Accordingly, an improvement of 14% in the static strength was reached, along with 60% and 26% in the fatigue strengths at low- and high-cycle fatigue conditions, respectively. Full article

Reclaimed asphalt pavement (RAP) reduces energy consumption and enhances economic benefits by recycling road materials, making it an effective approach for the sustainable use of solid waste resources. The performance of reclaimed asphalt pavement is significantly affected not only by the degradation of asphalt binders due to aging but also by the dosage of the rejuvenator used. The master curve of the complex shear modulus is widely recognized as a valuable tool for characterizing the rheological properties of asphalt binders. First, a virgin asphalt binder with a grade of SK70 was subjected to varying degrees of aging, followed by the rejuvenation of the aged asphalt using different dosages of the rejuvenator. Second, frequency sweeps were conducted on the aged and rejuvenated asphalt binders at various temperatures. Complex modulus master curves were constructed, and the CAM model was applied to fit these curves. The viscoelastic properties of asphalt at different aging levels and rejuvenator dosages were then analyzed based on the CAM parameters. Next, by applying a curve-shifting technique based on the least squares method to a reference state, both the time–temperature–aging (TTA) and time–temperature–regenerator (TTR) master curves of the complex modulus were constructed. The relationships between aging shift factors and aging times, as well as between regenerator shift factors and dosages, were established to predict the complex moduli of both aged and rejuvenated asphalt. Finally, the shear stress–strain relationships and material integrity of aged and rejuvenated asphalt were evaluated to assess their fatigue performance. The results indicated that aging significantly increases the complex modulus of asphalt, with TFOT (Thin Film Oven Test) aging having a more pronounced impact than PAV (Pressurized Aging Vessel) aging, resulting in reduced viscous deformation and an increased risk of cracking. Rejuvenator dosage reduces the complex modulus, with a 6% dosage effectively restoring mechanical properties and enhancing low-temperature performance. The TTA master curve demonstrates a strong linear correlation between aging shift factors and time, allowing for accurate predictions of the complex modulus of aged asphalt. Similarly, the TTR master curve reveals a linear relationship between regenerator dosage and shift factor, offering high predictive accuracy for optimizing regenerator dosages in engineering applications. The study further explores how varying levels of aging and rejuvenator dosage affect fatigue life under different strain conditions, uncovering complex behaviors influenced by these aging and regeneration processes. Full article