Herein, Clean powders of pre-alloyed GH4099 alloy was firstly prepared via plasma rotating electrode process (PREP), which was subsequently consolidated into powder metallurgy alloy using hot isostatic pressing (HIP). The aquired powders exhibited a normal particle size distribution and good sphericity, whilst, the room and high temperature tensile properties of powder metallurgy alloy reach the level of the corresponding wrought alloy. Electron beam welding (EBW) was employed to join the powder metallurgy alloy, and the microstructure of the welded joints, both as-welded and heat-treated state, was characterized using optical microscopy (OM), scanning electron microscopy (SEM), and electron probe micro-analyzer (EPMA). Mechanical properties and residual stress distribution of the joints were also evaluated. The results indicated that heat treatment significantly enhanced the uniformity of the microstructure of the welded joints, promoted the precipitation of strengthening phases, and facilitated a more uniform distribution of elements, effectively reducing post-weld residual stress concentration at the same time. Both of two heat treatment procedures improved the hardness and room temperature tensile strength of the joints, bringing them close to the level of base metal, and also significantly improved the high-temperature ductility. Furthermore, a finite element model was established to predict the residual stress evolution for EMB joints of GH4099 powder metallurgy alloy. The simulation results were consistent with the measured stress distribution.
The hot deformation behavior of Al-7.2Zn-3.8Mg alloy was studied via gleeble thermal simulation tester by deformation rate of 0.01-0.1 s-1 in temperature range 400-460 oC (lnZ range is 31.1 to 36.6) and then the constitutive equation was constructed. Meanwhile, the microstructure of the alloy was examined by electron backscatter diffraction technique and the dynamic softening mechanism was discussed. The results show that the activation energy of hot deformation of the alloy is 217.702 kJ/mol in the setting range of compression parameters and dynamic recovery is dominant softening mechanism. Dynamic recrystallization occurs at lnZ 34.3, and the recrystallization fraction decreases with the increase of lnZ; within this range, the mechanism includes continuous dynamic recrystallization and discontinuous dynamic recrystallization, and with the decrease of lnZ, the continuous dynamic recrystallization characteristics are more obvious; the geometric dynamic recrystallization appears for 31.1 lnZ 32.1.
In order to improve the overall performance of bimetallic pipelines and optimize their industrial production processes, herein, the effect of different heat treatment procedures on the intergranular corrosion resistance of Inconel 625, as the lining material for bimetallic pipes was studied by taking the pre-requirements for ensuring the performance of the substrate steel X65 into account. Results show that the relationship of heat treatment parameters with microstructure, and corrosion resistance is revealed for the Inconel 625 alloy. The alloy exhibits the best corrosion resistance when subjected to a special heat treatment procedure, which involves holding at 1000 oC for 40 min followed by rapid water quenching through the sensitization zone, and then air cooling. In this state, the alloy shows the lowest annual corrosion rate with only slight intergranular corrosion observed on the surface. As the heat treatment temperature increases from 850 oC to 1000 oC, the intergranular corrosion resistance of the alloy improves progressively. The three key factors influencing the intergranular corrosion behavior of the alloy include grain size, the proportion of low ΣCSL grain boundaries, and intergranular sensitization. The larger the average grain size and the lower the boundary density, the lower the annual corrosion rate. A higher proportion of low ΣCSL grain boundaries can effectively inhibit the propagation of corrosion cracks in the substrate, thereby significantly enhancing the intergranular corrosion resistance. The precipitation of M23C6 at grain boundaries leads to Cr depletion there, which reduces the corrosion resistance. This study clarifies the main mechanisms affecting the intergranular corrosion performance of bimetallic pipeline corrosion-resistant alloy liner and reveals their variations with heat treatment procedures. The findings provide important theoretical guidance for the industrial production of high-performance bimetallic pipelines.
The calyx husk of Physalis Peruviana L. was firstly pre-carburized at 400 oC to acquire carbon, and then porous carbon materials PLCPC-x (the ratio x represents the mass ratio of KOH to the pre-carbonized material) were prepared with the pre-carburized calyx husk as raw material and KOH solution as activating agent. The results showed that PLCPC-3 possessed a well-developed hierarchical 3D porous structure and a high specific surface area of up to 2703.75 m²·g-¹. By means of testing in a three-electrode set with electrolyte of 6 mol·L-1 KOH solution, it exhibited a high specific capacitance of 349.7 F·g-1 at 0.5 A·g-1 and a high capacitance retention rate of 78.9% at 20 A·g-¹. In a two-electrode system, the constructed symmetric supercapacitor achieved an energy density of approximately 9.0 Wh·kg-1 at a power density of 250 W·kg-1, retaining 96.7% of its initial capacitance after 12000 cycles.
Hot rolled plates of a low-carbon medium-manganese test steel 4Mn (Fe-4Mn-3.5Ni-2Cu-0.05C-0.018Nb-0.018Ti, in mass fraction) were heated at 860 oC for 1 h and then water quenching, followed by tempering treated at 600, 640, and 670 °C for 2 h respectively. Next, the effect of tempering process on the microstructure and mechanical property of the steel plates was assessed via SEM+EBSD, XRD, TEM, pendulum impact testing machine and hydraulic tensile testing machine. The results indicate that the microstructure of the steels tempered at different temperatures is composed of tempered martensite/ferrite + reversed austenite + fresh martensite. With the increasing tempering temperature, the ultimate tensile strength and work hardening index increase sequentially, while the yield strength and low-temperature impact toughness decreases sequentially. For tempering at 600 and 640 oC, the increase in ultimate tensile strength is primarily due to the transformation-induced plasticity effect formed by a fresh martensite, with the improving work hardening capability of the steel gradually as the temperature rises. For tempering at 670 oC, the content of fresh martensite significantly increases, enhancing the work hardening capacity and further boosting the ultimate tensile strength. However, the steel becomes excessively hard and brittle, leading to premature necking and a reduction in elongation. The decrease in low-temperature impact toughness is due to two factors, on one hand the mechanical stability of reversed austenite decreases, weakening its ability to mitigate stress concentrations through transformation, resulting in a reduction in the energy required for crack initiation; on the other hand, the increase of twins and blocky reversed austenite leads to a shift in the fracture austenite grain boundaries, thereby reducing the crack propagation energy. The precipitation of Nb/TiC in steel can help refine the grain size. In addition, the Cu-rich phase coarsens with the increase of tempering temperature, significantly reducing the yield strength.
The NH2-UiO-66/BiOBr heterojunction photocatalyst was synthesized via a solvothermal method, and its physicochemical properties were systematically characterized using XRD, SEM, TEM, FT-IR, XPS, and UV-Vis spectroscopy. The results confirmed the formation of a stable Z-scheme heterojunction structure between NH2-UiO-66 and BiOBr, which significantly improved the separation and migration efficiency of photogenerated electron-hole pairs. Under the irradiation of an artificial sunlight, the NUB-1 composite (mass ratio 1∶1) achieved a remarkable 92.48% degradation rate for ofloxacin (OFX), significantly outperforming the performance of either of the two components. NUB-1 also exhibited broad pH adaptability and showed minimal sensitivity to inorganic anions. Photoelectrochemical analyses indicated that NUB-1 exhibited superior charge separation and transport capabilities. Results of reactive species trapping tests and ESR analysis confirmed that holes (h+) and superoxide radicals (•O2-) were the main active species. Furthermore, NUB-1 showed high degradation efficiency for various organic pollutants. After five cycles, the degradation rate remained at 82.11%, demonstrating exceptional stability and reusability.
The block Ti-6Al-4V alloy was fabricated by selective laser melting (SLM) and then subjected to hot isostatic pressing (HIP) treatment. Next, the influence of HIP on the high cycle fatigue performance of the alloy with notch (stress concentration factor Kt = 3) was assessed, while elucidating the mechanisms related with the high notch sensitivity of the SLM+HIP Ti-6Al-4V alloy. The results indicate that although the SLM+HIP Ti-6Al-4V alloy exhibits superior static tensile strength and hardness compared to wrought counterparts, its fatigue performance under notched conditions is significantly compromised, with the fatigue limit decreasing from 250 MPa (wrought) to 150 MPa. Further analysis reveals that the high notch sensitivity of the SLM+HIP Ti-6Al-4V alloy may mainly be attributed to two factors: (1) differences in crack initiation mechanisms, i.e., as the crack initiation region of SLM+HIP alloy exhibits cleavage-like brittle fracture morphology, distinctly different from the ductile fracture morphology of the forged alloy, leading to a higher propensity for brittle crack initiation; and (2) the influence of grain size characteristics, namely the SLM+HIP alloy exhibits a unique lath-like grain structure, with an overall larger grain size compared to the forged alloy. Specifically, the average grain size in the X and Z directions is 2.34 and 2.58 μm, respectively, which is significantly larger than 1.63 μm in the forged alloy. This increased grain size exacerbates its notch sensitivity, making cracks more prone to initiation and propagation during the fatigue process.
