Ti-6Al-4V titanium alloy samples were prepared using an in-situ rolling-assisted laser directed energy deposition process with varying interval rolling, and the effects of interval rolling and subsequent heat treatments on the microstructure and tensile properties were systematically investigated. The results show that plastic deformation induced by rolling promotes recrystallization of the deposited material under complex thermal cycling, resulting in fine equiaxed grains. In contrast, the deposited material without rolling failed to recrystallize due to insufficient deformation energy, leading to coarse equiaxed grains in the unrolled layers, with grain sizes significantly larger than those in the rolled layers. Interlayer rolling generated a microstructure characterized by an alternating distribution of coarse and fine equiaxed grains along the building direction, with the proportion of coarse grain regions increasing as the number of interval rolling passes increased. The accumulation of high-density dislocations and fine grain strengthening from repeated deformation contributed to improved strength in the samples. However, both strength and ductility of the as-built samples along the building direction decreased progressively with an increasing number of interval rolling passes. After stress-relief annealing, the ductility of all samples tended to converge, while solution aging treatment eliminated the microstructural differences introduced by rolling and promoted the formation of acicular phase, which provided high strength but limited ductility. This study offers novel insights into the regulation of microstructure and properties in the additive manufacturing of titanium alloys.
Graphitic carbon nitride (g-C₃N₄) is a nitrogen-rich carbon-based material with promising properties for electrochemical applications. However, the influence of pyrolysis temperature on its intrinsic physicochemical and electrochemical properties requires further understanding. This study systematically investigates pristine g-C₃N₄ synthesized from urea at 450℃, 500℃, 550℃, and 600℃ for 3hours to establish the relationship between pyrolysis temperature and its structural, surface, optical, and electrochemical properties. The X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) were combined with electrochemical measurements in three-electrode configurations. The results demonstrate a strong temperature-dependent evolution of g-C₃N₄ properties, with the sample prepared at 550 ℃ exhibiting the most favorable overall characteristics. It achieved the highest BET surface area of 56.64m²/g, the highest nitrogen content of 57.9 atomic % with the lowest C/N ratio of 0.71, and the lowest photoluminescence intensity. The structural analysis further showed that the g-C₃N₄ prepared at 550 ℃ exhibited the lowest microstrain (0.0554) and the largest crystallite size (2.65nm) among the investigated samples. These characteristics were accompanied by improved charge-transfer behavior, reflected by the lowest charge transfer resistance of 2.203 kΩ, and the highest specific capacitance of 41.25F/g at 1A/g. However, further increasing the pyrolysis temperature to 600 ℃ did not produce additional improvement, indicating an optimum thermal temperature around 550 ℃ under the investigated conditions. Therefore, rather than targeting maximized device-level performance, this work establishes a systematic baseline for understanding and controlling the intrinsic properties of pristine nitrogen-rich GCN (g-C₃N₄) through a pyrolysis temperature, providing a reference for subsequent modification through doping, composite formation, and device development.
The synthesis of homogeneous base-metal multi-principal-element alloy nanoparticles remains a significant challenge hindering technological applications. Using fast moving bed pyrolysis (FMBP) of metal chlorides, we compared FeCoNi and CrMnFeCoNi nanoparticles synthesized under identical conditions (650 °C, 3% H₂/Ar). FMBP produced homogeneous single-crystalline {100}-faceted FCC FeCoNi nanoparticles, whereas CrMnFeCoNi formed rounded particles with a FeCoNi-rich core, unreduced Cr and only partially reduced Mn. Increasing the dwell time (2–6 h) improved Mn reduction but had little effect on Cr. These results identify Cr reduction as the primary barrier for homogeneous CrMnFeCoNi nanoparticles.
