Zhi Wang

Aiming at the problems of high hardness, high brittleness, and severe damage caused by traditional processing technologies of Diamond/Silicon Carbide (Diamond/SiC) composites, this paper systematically studies the effects of different powers and processing technologies of femtosecond laser on the material properties. The composite material was processed using six laser powers under two processes: cutting (depth-concentrated energy input) and grinding (surface-dispersed energy input). Combined with characterization methods such as XRD, SEM, XPS, and AFM, the influence laws of laser power on the phase composition, graphitization degree, surface morphology, and roughness of the material were systematically analyzed. Additionally, density functional theory (DFT) calculations was used to reveal the influence mechanism of laser power on the structural stability of the material from the perspectives of thermodynamics and phonon properties. The results show that: due to concentrated energy input, the cutting process is prone to thermal accumulation, leading to a high degree of diamond graphitization and severe surface defects. The roughness is the lowest at a power of 2700 W, reaching 80. 6 nm. The grinding process, with dispersed energy input, can weaken thermal accumulation and reduce the degree of diamond graphitization under the same laser power. The roughness is the lowest at a power of 3000 W, which is 71. 3 nm. Density functional theory calculationsconfirms that the thermal damage of Diamond/SiC composites is essentially the synergistic effect of hindered heat conduction caused by interfacial phonon scattering and laser energy-induced temperature exceeding the critical threshold. The intrinsic structure of the material is stable. Under laser irradiation with power higher than 3100 W, the temperature exceeds the critical graphitization temperature of diamond, ultimately leading to severe damage.

Perovskite anodes with in situ exsolved nanocatalysts have been proven to overcome carbon deposition and increase anode catalytic activity as an alternative to conventional Ni/YSZ anodes for direct hydrocarbon solid oxide fuel cells (SOFCs). This study, for the first time, demonstrates the state-of-the-art exsolution over cathode-supported SOFCs, which achieve the highest cell performance compared to conventional electrolyte-supported SOFCs with perovskite anodes using CH₄ as a fuel. The dendritic channel structure of cathode supports retains a high active surface during high-temperature electrolyte sintering. Sr₂Ti_0.8Co_0.2FeO_6-δ perovskite ceramic is employed as anodes, and Co-Fe alloy nanoparticles are exsolved after reduction, which increases the cell power output by about 40%. The peak power densities of the cells are 0.82, 0.59, 0.43, and 0.33 W cm^-2 at 800 °C using hydrogen, methane, methanol, and ethanol, respectively. The SOFCs with the exsolved nanocatalysts demonstrate stable power generation up to 110 h using methane, methanol, and ethanol fuels. Interestingly, the perovskite anodes show high methane fuel utilization by the complete oxidation of methane, which is in contrast to the partial oxidation over Ni catalysts. Robust hydrocarbon SOFCs have been developed by coupling anode catalyst exsolution with dendritically channeled cathode supports.

This is the first report into the temperature-dependent substitution process of Si in Ti3(Si,Al)C2 solid solution.

In this study, Ti₃SiC₂/Al₂O₃ composites were prepared via in-situ hot pressing sintering at 1550 °C. Al used as a sintering aid reduced the production of TiC impurity phase and stabilized the crystal lattice of Ti₃SiC₂ to inhibit its decomposiition at high temperature. This is because Al replaced some of the Si atoms to form Ti₃(Si_1 − xAl_x)C₂, which showed a crystal structure similar to that of Ti₃SiC₂. The addition of Al is a prerequisite for the formation of high density Ti₃SiC₂/Al₂O₃ composites at high temperature. Laminar Ti₃SiC₂ grains and granular Al₂O₃ grains were densely packed and tightly bonded, furthermore, unique mosaic structure of Ti₃SiC₂-Al₂O₃ created at high temperatures improve the mechanical properties such as hardness, bending strength and fracture toughness of Ti₃SiC₂/Al₂O₃ composites, with the highest reaching 16.97 GPa, 553.38 MPa and 9.63 MPa·m^1/2, respectively. The mechanism responsible for improved mechanical properties for Ti₃SiC₂/Al₂O₃ composites were the synergistic action of grain pullout, microcrack deflection, and extend the crack growth from two different kinds of grains.

Ti₃SiC₂/Al₂O₃ and Ti₃SiC₂-TiC/Al₂O₃ composite ceramics with various Al₂O₃ fractions were prepared by Ti, Si, Al, TiC and Al₂O₃ powers via in-situ reaction. Al₂O₃ contents in raw materials could influence the reaction process of Ti₃SiC₂ generated. It would lead to react completely when the Al₂O₃ volume percentage between 50% to 70%, otherwise TiC as an impurity would be found. Finally the Ti₃SiC₂/Al₂O₃ composites with 54.4 wt% Ti₃SiC₂, and Ti₃SiC₂-TiC/Al₂O₃ composites with 54.7 wt% Ti₃SiC₂ and 9.2 wt% TiC were fabricated successfully. There were two types of TiC existed in composites, called intragranular and intergranular particles. The Ti₃SiC₂-TiC/Al₂O₃ composite ceramics with 9.2 wt% TiC showed the higher mechanical properties than Ti₃SiC₂/Al₂O₃ composite. From the analyzing of microcrack propagation paths, the dispersed TiC particles as reinforcement agents would cause significant crack deflection, improving the flexural strength and fracture toughness up to 492 MPa and 7.8 MPa.m^1/2 respectively.