Search

The addition of trace (TiB + TiC) reinforcements could minimize the deformation steps and decreases its costs according to recent study. In present work, the hot deformation behavior and microstructure evolution were studied via the isothermal hot compression at different temperature and strain rate. Based on the DMM model, the activation energy Q and processing map were obtained. Subsequently, two billets were hot-rolled and heat-treated, to study the microstructure and tensile properties of the alloy. Results revealed that the flow behavior of the (TiB + TiC)/Ti–3.5Al–5Mo–6V–3Cr–2Sn–0.5Fe alloy was similar with other near β titanium alloy. When deformation in β region, the deformation mechanism was associated with cDRX by lattice rotation and dynamic recovery; when deformation in (α + β) region, the deformation mechanism was associated with substructure evolution, such as DRX and dynamic recovery. The lower strain rate guarantees abundant time for microstructure transformation, while the higher strain rate leads local flow instability and cracks. The activation energies Q is 264.1 kJ/mol in (α + β) region and 181.8 kJ/mol in the β region. According to the processing map, the optimum deformation windows are 770–800°C and 850–880°C, 0.001 s−1. In addition, the microstructure of 770R + SAT is characteristic of duplex microstructure with a certain amount of αp, considerable precipitation of fine acicular αs and continuous αGB, which is achieved a UTS of 1414 MPa with a poor ductility. Therefore, the (TiB + TiC)/Ti–3.5Al–5Mo–6V–3Cr–2Sn–0.5Fe alloy shows excellent deformability and higher strength, which is possible to achieve both high economy (less deformation step) and advancement (high mechanical properties due (TiB + TiC) reinforcements).

In present study, the microstructure evolution and spheroidization behavior of (TiB+TiC+Y2O3)/α-Ti composite annealed at various temperatures and times were investigated. Results show that the volume fraction of αp is characteristic of S-type curve with the largest change rate in the range of 960–980 ℃. The mean length of αp lamellar is characteristic of Doseresp function, that is, the change rate decreases gradually as temperature increases. In the early stage of annealing, the spheroidization mechanism is associated with boundary splitting, which is controlled by the density of defects. When the heat treatment is prolonged, the spheroidization is completed by termination migration and Ostwald ripening. Owing to the heterogeneous geometrical orientation, crystallographic orientation, and (TiB+TiC+Y2O3), the spheroidization behavior is heterogeneous that is demonstrated by different spheroidization response of kinked and elongated α colonies. A positive spheroidization behavior is observed in particle-rich region, while a relatively negative spheroidization behavior is observed in particle lean region. The reinforcements hindered the dislocations movement and promoted spheroidization, thus, leading to the heterogeneous deformation and spheroidization. Furthermore, it could promote non-uniform nucleation to form remarkable random αs and αp texture, which gave a new inspiration to avoid “Macrozone”.

Biofilm based systems and the hybrid between activated sludge and biofilms have been popularly applied for wastewater treatment. Unlike the suspended biomass, the biofilm concentration and kinetics on the media cannot be easily measured. In this study, a novel and easy-to-use approach has been developed based on pulse-flow respirometer to characterize the biofilm stoichiometry and kinetics in situ. With the new designed breathing reactor, the mutual interference between the magnetic stirring and biofilm media that happened in the conventional breathing reactor was solved. Moreover, Microsoft Excel based programs had been developed to fit the oxygen uptake rate curves with dynamic nonlinear regression. With this new approach, the yield coefficient, maximum oxidation capacity, and half-saturation constant of substrate for the heterotrophic biofilms in a fix bed reactor were determined to be 0.46 g-VSS/g-COD, 67.0 mg-COD/(h·L-media), and 4.4 mg-COD/L, respectively. Those parameters for biofilm ammonia oxidizers from a moving bed biofilm reactor were determined to be 0.17 g-VSS/g-N, 18.6 mg-N/(h·L-media), and 1.2 mg-N/L, respectively, and they were 0.11 g-VSS/g-N, 20.9 mg-N/(h·L-media), and 0.98 mg-N/L for nitrite oxidizers in the same biofilms. This study also found that the maximum specific substrate utilization rate for detached biofilms increased by 3.2 times, indicating that maintaining biofilm integrity was very important in the kinetic tests. Using this approach, the biofilm kinetics on the media can be regularly measured for treatment optimization.

To improve the ductility of Al3Ti alloy, the continuous shape memory alloy NiTi fiber (CSMAR) was introduced into intermetallic Al3Ti matrix for fabricating the novel CSMAR-Al3Ti composite in this work. Microstructure characterizations demonstrated that the CSMAR-Al3Ti composite mainly consists of Al3Ti layer, NiTi fiber, eutectic area and interfacial reaction layer. EBSD results indicated that the eutectic area is made up of Al3Ti and Al3Ni phases, the Al3Ti phase shows a strong [001] crystallographic oriented structure, while the Al3Ni phase has a non-textured structure. TEM results showed that the interfacial reaction layer between NiTi fiber and eutectic area is a multiple phase mixture, including various Ti-Al and Ni-Al intermetallics. Furthermore, TEM and HRTEM analyses revealed a newly formed Ti2Ni layer between NiTi fiber and interfacial reaction layer. Tensile test results confirmed that the CSMAR-Al3Ti composite could effectively improve the ductility of the Al3Ti alloy. Based on the systematic investigations of interfacial microstructure characterization, mechanical behavior and fracture morphology observation, it is found that the toughening mechanism of CSMAR-Al3Ti composite is related to the interfacial fine grain strengthening effect with the gradual distribution characteristic. In addition, the excellent metallurgical bonding between fiber reinforcement and matrix is also beneficial to the mechanical properties. Keywords: Al3Ti alloy, NiTi fiber, Interfacial characterization, Mechanical behavior

In this work, to improve the ductility of Al3Ti alloy, a multi-phase intermetallic mixture structure was achieved by the post annealing treatments (AT) on the as-fabricated continuous shape memory alloy NiTi fiber reinforced Al3Ti composite (CSMAR-Al3Ti). Experimental results revealed that the multi-phase intermetallic mixture structure displays a multi-layer characteristic, including the newly formed intermetallic layer and the eutectic area. Microstructure characterization and formation mechanism confirmed that the newly formed intermetallic layer consists of NiAl, Al3Ni2 and Al3Ti phases, and the eutectic area still consists of Al3Ni and Al3Ti phases. The results of compression and tensile tests indicated that the multi-phase intermetallic mixture structure can simultaneously improve the maximum strength and the failure strain of the monolith Al3Ti alloy. Based on the systematic investigations, it is found that the toughening mechanism is related to the multi-layer characteristic of the multi-phase intermetallic mixture structure, which is beneficial to the crack blunting, crack deflecting and load transformation during the deformation process. Furthermore, the multi-phase intermetallic mixture structure achieved by the 48 h post annealing treatment is the most effective method to improve the ductility of Al3Ti alloy.

Previously an enhanced nitrogen removal process, i.e., intermittent Modified Ludzack-Ettinger (iMLE), was developed by incorporating intermittent aeration into the MLE process. In this research, a field demonstration of iMLE process on enhancing nitrogen removal was conducted in Shenzhen Guangming Wastewater Treatment Plant (WWTP) at a daily treatment capacity of 25,000 m3/d. Results indicated that, when operating the iMLE process with dissolved oxygen (DO) based control mode, its effluent chemical oxygen demand (COD) and ammonia concentrations were consistently less than 30 mg/L and 1.5 mg/L, respectively, similar to the original two-stage Anoxic/Oxic (A/O) process with continuous aeration. Even though the influent had insufficient organic matter (BOD5/TN = 2.5), the effluent TN concentration in the iMLE was still consistently below the new limit of 10 mg-N/L, with an average and removal rate of 6.1 ± 1.0 mg-N/L and 78%, respectively. This performance was similar to that in the two-stage A/O process equipped with step feed and external carbon addition. Without the addition of external carbon in the iMLE process, it saved approximately 0.16 Chinese yuan for one cubic meter of wastewater treated. In addition to eliminating external carbon addition, the iMLE process decreased the air consumption by 20–30%, which would also reduce operation cost. Therefore, the iMLE process operated with appropriate DO control could reduce chemical cost and aeration energy use synergistically, which provides a cost-effective approach for WWTP upgrade.

In order to investigate the influence of service temperature on the mechanical properties of Ti–5Al-2.5Sn ELI titanium alloy, the tensile tests were performed on the polycrystalline Ti–5Al-2.5Sn ELI titanium alloy samples under a wide temperature range from 20 K to 300 K. The scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) tests were conducted to analyze the fracture behavior evolution, crystallographic orientation, grain boundary characterization and dislocation configuration of the samples. Besides, the deformation mechanism of Ti–5Al-2.5Sn ELI titanium alloy was also thoroughly investigated. Experimental results indicate that the Ti–5Al-2.5Sn ELI titanium alloy displays the single dislocation slipping deformation behavior at room temperature, whereas the coupling of dislocation slipping and twinning deformation behaviors dominate at the cryogenic temperature. The twinning deformation improves the plastic deformation capacity of Ti–5Al-2.5Sn ELI titanium alloy by coordinating the crystallographic orientation, promoting the boundary rotating and the dislocation slipping abilities, which induces the acceptable low-temperature elongation and occurs frequently with the decreasing test temperature. On the other hand, the dislocation strengthening effect resulting from a large number of dislocation structures also contributes to promoting the ultimate tensile strength of the Ti–5Al-2.5Sn ELI titanium alloy under cryogenic temperature.

Effects of electropulsing treatment (EPT) on the microstructure evolution, mechanical properties and crack healing of intermetallic Al3Ti alloys were studied in this work. In order to investigate the athermal effect caused by EPT, conventional heat treatment (CHT) was conducted for comparison. The compressive stress-strain curves demonstrated that the failure strains of Al3Ti alloy increase under both the EPT and CHT conditions, while the increment of failure strain of Al3Ti alloy treated by EPT is higher than that treated by CHT. Fracture surface analysis confirmed that the intrinsic brittle fracture of Al3Ti alloy evolves into the quasi-cleavage fracture with increasing frequency of EPT. Based on the systematic investigation into the microstructure evolution, mechanical properties and fracture surface observation, the influence mechanism of EPT on Al3Ti alloy was found to be related to the improvements of atomic diffusion and dislocation movement, which results from the coupling of thermal effect and athermal effect by EPT. Furthermore, the thermal compressive stress and athermal effect could heal the local micro-crack and decrease the crack width of Al3Ti alloy by EPT. Therefore, EPT can work as a novel method for improving the plastic deformation capacity of Al3Ti alloy.

Intermetallic Al3Ti alloys with different volume fractions of residual aluminum were synthesized via reactive foil sintering in vacuum condition using commercial purity aluminum foils and Ti-6Al-4V alloy foils. Microstructure evolution, elemental analysis, fracture mechanism and phase identification were performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) technique, respectively. Mechanical properties were measured by quasi-static compression and Vickers hardness tests. Experimental results indicated that the ductile phase Al distributes in the grain boundaries of the brittle matrix Al3Ti, which increases the compression failure strain of the Al3Ti alloy dramatically compared with the monolithic intermetallic Al3Ti alloy. The compressive stress-strain curve showed a typical elastic-plastic deformation behavior. Moreover, it also demonstrated that the post-heat treatment plays an important role in the mechanical properties due to the formation of α-Al2O3 and Al3Ti grain coarsening. Keywords: Intermetallic, Residual aluminum, Mechanical property, Post heat-treatment

A dense monolithic intermetallic Al3Ti alloy was successfully synthesized via reactive sintering in vacuum using TC4 alloy and pure aluminum foils with appropriate initial thickness. Energy dispersive spectroscopy (EDS), x-ray diffractometry (XRD), and scanning electron microscopy (SEM) were used to characterize the phase and microstructure of Al3Ti alloy. Ultrasonic measurement was performed to evaluate the physical property of Al3Ti alloy. Different thermal analysis, thermogravimetry (TG) and differential scanning calorimetry (DSC) were used to assess the thermal property of Al3Ti alloy. The compressive tests were carried out on a universal load frame to determine the mechanical properties, including the compressive strength and failure strain of the fabricated intermetallic Al3Ti alloy. The current results indicated that the density of Al3Ti alloy is slightly higher than the theoretical density, the average Young’s modulus is lower than the theoretical value. A trace of aluminum in Al3Ti alloy was detected, which is distinctly affected on the density, Young’s modulus and mechanical properties of this titanium aluminide alloy. The stress–strain curves of Al3Ti alloy shows a linear elastic behavior without any plastic deformation, and the fracture features are the mixed fracture of transgranular and intergranular. Some other fundamental physical and mechanical properties of the Al3Ti alloy were also obtained in the present study.

Biofilms developed on support materials with large apertures can be used as live and in-situ formed membranes for solids separation in biofilm-based dynamic membrane bioreactors (bDMBRs). Unlike polymer membranes, biofilms are live, and their composition and structure vary, which further impacts the biofilm resistance. This study repeatedly observed that while starting up a bDMBR to treat biodegradable wastewater, the filtration resistance increased rapidly at the beginning and decreased to a low level corresponding with biofilm succession that was impelled by a variation in the food/microorganism (F/M) ratio. During the rapid rising stage, the F/M ratio was high. Moreover, Meganema, Rhodobacter, Bdellovibrio, Rhizobium, Micobacterium, and Bacillus were the dominant bacterial genera in the biofilms. This promoted biofilm attachment and growth by an excessive secretion of extracellular polymeric substances (EPSs). Consequently, the early biofilms were less permeable and exhibited a resistance of 15.6 × 1011 m−1 on the ninth day. As the start-up time increased and the F/M ratio decreased, the biofilm microbial community was altered significantly, with Legionella, Reyranella, Meganema, Hyphomicrobium, and a few uncultured_bacterium being dominant. Accordingly, the biofilm became more permeable and exhibited a resistance of 0.09 × 1011 m−1 on the 46th day. Then, a flux of 42 L/m2·h was achieved at a pressure of 0.1 kPa. This study indicated that the accumulated resistance in a bDMBR could decrease spontaneously without cleaning by the regulation of the biofilm succession on the support material.

This study revealed that, Thiothrix eikelboomii, a well-known filamentous bacterium that causes sludge bulking, could also interfere oxygen transfer during wastewater treatment. The volumetric oxygen transfer coefficient (KLa) in filamentous-bulking sludge (FBS) was found to be 43% lower than that in floc-forming sludge (FFS) at similar biomass concentrations, partially because the filamentous bacteria had increased the sludge apparent viscosity. The KLa value for FBS, however, was still significantly lower than that for FFS even if both sludges had similar apparent viscosity. Numerous tiny and free-swimming filaments were observed to attach on the air bubble surface, presumably reducing the liquid film renewal and increasing the liquid film thickness. Moreover, the filaments were co-coated with extracellular polymeric substances of protein and polysaccharide, which could make them performing like “amphiphilic molecules” of surfactants to hinder oxygen transfer. Therefore, the particular surface property of filaments and their interaction with air bubbles could also impact oxygen transfer. Thiothrix eikelboomii was identified to be the responsible filamentous bacterium that lowered the KLa value, while other filamentous bacteria with short filaments did not interfere oxygen transfer. This study implies that controlling sludge bulking benefits not only sludge settling but also oxygen transfer.