生长条件对锗酸锶纳米线形成的影响

系统分析了水热温度、保温时间对锗酸锶纳米线形成的影响。扫描电子显微镜和X-射线衍射分析结果表明水热温度和保温时间对锗酸锶纳米线的形成与生长起到了重要作用。随着水热温度的增加,锗酸锶棒状结构的长度不断增加,由无定形结构转变为了斜方SrGeO3晶相。随着保温时间的增加,锗酸锶纳米线的长度由10微米增加至了数十微米。通过晶体核化与生长机制可以解释锗酸锶纳米线的形成。     

Tailoring microwave-millimeter-wave dielectric and mechanical properties in CaO–SiO2 glass-ceramics by P2O5 nucleating agent

Glass-ceramics have demonstrated excellent dielectric properties in low-temperature co-fired ceramic (LTCC) technology used in 5G/6G wireless devices. This work studies the mechanical strengths and dielectric properties from microwave to millimeter-wave frequencies in the CaO–SiO₂ glass-ceramics modified via the P₂O₅ as a nucleating agent. The β-wollastonite phase was identified as the primary structure with the preferred ($20\bar{2}$) orientation and parallel plate-like structure in the matrix as P₂O₅ content increases up to 3.5∼5.5 wt%. The P₂O₅ nucleating agent increases degree of long-range crystallization. Elevated mechanical flexural strength of approximately 170 MPa, hardness of ∼720 MPa, and outstanding high-frequency dielectric properties were obtained in the 3.5–5.5 wt% P₂O₅-added CaO–SiO₂ glass-ceramics, due to the enhanced interatomic Si–O bonding in the network. The improved mechanical and dielectric characteristics of the P₂O₅–added CaO–SiO₂ glass-ceramics make the crystallized wollastonite materials for the 5G/6G devices possible.     

Microstructure and bioactivity in SBF of the hydroxyapatite coatings plasma sprayed with a magnetic field

A 100 mT magnetic field was introduced during the plasma spraying of hydroxyapatite (HA) coating on Ti6Al4V substrate. The influence of the magnetic field on the microstructure, bonding strength, and bioactivity of the coating was investigated. Compared with as-sprayed coating, the coating sprayed under a magnetic field showed fewer porosity and microcracks and a significantly decreased absolute value of the residual stress. The bonding strength of the coating sprayed under a magnetic field was approximately 173.6 % greater than as-sprayed coating. With increasing time in simulated body fluid, the width of microcracks on the surface of both coatings first increased and then decreased. The widths of microcracks on the coating sprayed under a magnetic field were much smaller than as-sprayed coating. During spraying process, the magnetic field would enhance the wetting and flowing ability of the HA molten droplets, prolonging their cooling, which affects the microstructure and bioactivity of the coating.     

Erosion mechanism of the postmortem Al2O3-Ti2O3-Al sliding gate containing novel Al2O3-Ti2O3 raw materials

Al₂O₃-Ti₂O₃-Al sliding gates were prepared from Al₂O₃-Ti₂O₃ raw materials, sintered corundum and aluminum, and used in trials at steel works. The sliding gate with 30 wt% Al₂O₃-Ti₂O₃ added was used on an 80 t ladle for 4 cycles without macrocracks. The postmortem sliding gate can be divided into the permeation layer (0–0.1 mm), transition I layer (0.1–10 mm), transition II layer (10–20 mm) and unchanged layer from the hole working face outward. XRD, SEM and industrial CT were used to analyze the postmortem sliding gate. The results show that, in the Al₂O₃-Ti₂O₃-Al sliding gate, both Al and Ti₂O₃ are involved in reactions, Ti₂O₃ transforms into Ti₂O and TiO in the transition I layer, and part of the Ti₂O₃ in the transition II layer transforms into Ti₈O₁₅. Titanium compounds with different densities are dispersed in the matrix and form microcracks to improve the thermal shock resistance of the sliding gate, which improved the performance.     

Microstructure and mechanical properties of Cf/SiC composite joints joined using AlCoCrFeNi2.1 eutectic high-entropy alloy filler via spark plasma sintering

C_f/SiC composites were joined by spark plasma sintering technology using AlCoCrFeNi_2.1 eutectic high-entropy alloy as the joining filler. The typical structure of the joint could be described as C_f/SiC/CrSi₂ + HEAF + Al₄C₃ + C-rich phase/HEAF/CrSi₂ + HEAF + Al₄C₃ + C-rich phase/C_f/SiC. Under the pressure of 30 MPa and at 1450 ℃ for 10 min, the shear strength of the joint was 9.85 MPa at room temperature. However, when a 50 µm thick Ti foil was added to obtain Ti foil/AlCoCrFeNi_2.1/Ti foil composite filler, the joint strength was remarkably increased to 21.15 MPa at room temperature. The formation of TiC phase relieved the thermal stress at the joining interface. Due to the high entropy effect of AlCoCrFeNi_2.1 filler, the central zone of the joint still contained the FCC structure of high-entropy alloy. The existence of the pulsed electric field was beneficial to element diffusion and microstructure homogenization, which improved the mechanical properties of the joint while shortening the joining cycle.     

Tailoring thermal and mechanical properties of rare earth niobates by coupling entropy and composite engineering

In this paper, a series of high-entropy rare earth niobates, including fluorite RE₃NbO₇ (HE317), monoclinic RENbO₄ (HE114) and RENbO₄/RE₃NbO₇ composite (HE-composite), are prepared via solid state reaction, following by a study about their thermal and mechanical properties. The high-entropy rare earth niobates exhibit excellent phase stability after thermally exposed to 1300 °C for 100 h, indicating entropy can stabilized high-entropy rare earth niobates. Compared with the single element rare earth niobates, high-entropy rare earth niobates have higher fracture toughness and hardness. The high-entropy RENbO₄/RE₃NbO₇ composite has the best mechanical properties, with a fracture toughness of 2.71 ± 0.17 MPa·m^1/2 and hardness of 9.46 ± 0.24 GPa, respectively. The high-entropy niobates exhibit high coefficients of thermal expansion which is close to 7 wt% Y₂O₃ stabilized ZrO₂. It is also proved that the configurational entropy has little effect on the critical temperature from monoclinic to tetragonal phase transition. The thermal conductivity of HE-composite is lower than HE114, indicating the combination of HE114 and H317 is a more efficient strategy to decrease the thermal conductivity of HE114 than entropy engineering.     

An overview of C-SiC microwave absorption composites serving in harsh environments

Adapting to extremely harsh service environments is an unavoidable challenge for microwave absorption (MA) materials. Among MA materials, C-SiC composites stand out due to their excellent overall performance. This article provides a comprehensive review of the latest and most critical achievements regarding C-SiC MA materials. First, an introduction to the most basic preparation methods for obtaining C-SiC composites is presented. Next, the MA mechanisms of these composites are thoroughly analyzed to clarify the origin and contribution of the dielectric loss mechanism, providing theoretical support and guidance for the design of MA materials. Most importantly, the MA performance of C-SiC composites in harsh environments, including their high-temperature resistance, thermal conduction, thermal insulation, and anti-corrosion behavior, are highlighted. Finally, the achievements and challenges faced by C-SiC composites are summarized and some useful suggestions are proposed to guide the multi-functional application of C-SiC composites in harsh environments.     

Mechanical and heat transfer properties of AlN/Cu joints based on nanosecond laser-induced metallization

In this paper, AlN ceramic was directly joined to copper without active brazing filler metal. By exerting the nanosecond laser irradiation on the AlN surface, the AlN ceramic was thermally decomposed to aluminum and the surface was metalized. The as-metalized AlN ceramic was successfully joined to copper through the eutectic reaction between aluminum and copper. The effect of the groove interface structure fabricated with various laser scanning speeds on the mechanical and heat transfer properties of AlN/Cu joints was investigated. The joints obtained optimal shear strength and thermal diffusivity of 10.64 MPa and 51.75 mm²/s at the scanning speed of 250 mm/s. The micro groove structures of the interface contributed to the enhancement of mechanical and heat transfer properties of joints. The approach of laser-irradiation assisted joining proposed in this paper provided a novel thought for the fabrication of metal/ceramic composite structures.