Introduction of a New Method for Regulating Laves Phases in Inconel 718 Superalloy during a Laser-Repairing Process

The morphology,size,and distribution of Laves phases have important influences on the mechanical properties of laser-repaired Inconel 718(IN718)superalloy.Due to the deterioration of the substrate zone,the Laves phase in the laser cladding zone of IN718 superalloy cannot be optimized by a hightemperature solution treatment.In this study,an in situ laser heat-treatment method was proposed to regulate the morphology and size of the Laves phase in the laser cladding zone of IN718 superalloy without impacting the substrate zone.In the in situ laser heat-treatment process,a laser was used to heat previously deposited layers with optimized manufacturing parameters.A thermocouple and an infrared camera were used to analyze thermal cycles and real-time temperature fields,respectively.Microstructures and micro-segregations were observed by optical microscopy,scanning electron microscopy,and electron probe microanalysis.It was found that the in situ laser heat treatment effectively changed the morphology and size of the Laves phase,which was transformed from a continuous striplike shape to a discrete granular shape.The effective temperature range and duration were the two main factors influencing the Laves phase during the in situ laser heat-treatment process.The effective temperature range was determined by the laser linear energy density,and the peak temperature increased with the increase of the linear energy density.In addition,the temperature amplitude could be reduced by simultaneously increasing the laser power and the scanning velocity.Finally,a flow diagram was developed based on the in situ laser heat-treatment process,and the deposition of a single-walled sample with fine and granular Laves phases was detected.

In situ coagulation-electrochemical oxidation of leachate concentrate:A key role of cathodes

To efficiently remove organic and inorganic pollutants from leachate concentrate,an in situ coagulation-electrochemical oxidation(CO-EO)system was proposed using Ti/Ti_(4)O_(7)anode and Al cathode,coupling the“super-Faradaic”dissolution of Al.The system was evaluated in terms of the removal efficiencies of organics,nutrients,and metals,and the underlying cathodic mechanisms were investigated compared with the Ti/RuO_(2)-IrO_(2)and graphite cathode systems.After a 3-h treatment,the Al-cathode system removed 89.0%of COD and 36.3%of total nitrogen(TN).The TN removal was primarily ascribed to the oxidation of both ammonia and organic-N to N_(2).In comparison,the Al-cathode system achieved 3-10-fold total phosphorus(TP)(62.6%)and metal removals(>80%)than Ti/RuO_(2)-IrO_(2)and graphite systems.The increased removals of TP and metals were ascribed to the in situ coagulation of Al(OH)_(3),hydroxide precipitation,and electrodeposition.With the reduced scaling on the Al cathode surface,the formation of Al^(3+)and electrified Al(OH)_(3)lessened the requirement for cathode cleaning and increased the bulk conductivity,resulting in increased instantaneous current production(38.9%)and operating cost efficiencies(48.3 kWh kg_(COD)^(−1)).The present study indicated that the in situ CO-EO process could be potentially used for treating persistent wastewater containing high levels of organic and inorganic ions.

In situ thickness control of black phosphorus field-effect transistors via ozone treatment

A simple and reproducible method to control the thickness of black phosphorus flakes in real time using a UV/ozone treatment is demonstrated. Back-gated black phosphorus field-effect transistors （FETs） were fabricated using thick black phosphorus flakes obtained by thinning of black phosphorus, as oxygen radicals generated by UV irradiation formed phosphorus oxides on the surface. In order to monitor the thickness effect on the electrical properties, the fabricated FETs were loaded in the UV/ozone chamber, where both the optical （micro-Raman spectroscopy and optical microscopy） and electrical properties （current-voltage characteristics） were monitored in situ. We observed an intensity decrease of the Raman modes of black phosphorus while the field-effect mobility and on/off ratio increased by 48% and 6,800%, respectively. The instability in ambient air limits the investigation and implementation of ultra-thin black phosphorus. However, the method reported in this study allowed us to start with thick black phosphorous flakes, providing a reliable approach for optimizing the electrical performance of black phosphorus-based electronic devices. We believe that these results can motivate further studies using mono- and few-layer black phosphorus.

Effects of in situ biological treatments on heavy metal release of urban river sediment

A typical fiver in Yangzhou City was used to study the effects of artificial aeration, eco-brick cover, biological packing cover, and low-sited plant floating beds on the release of heavy metals from urban river sediments. This work showed that 1） the Cr release rate was decreased by 50.3%-89.6%, with an average of 59.3%, thereby reducing the Cr pollution load to the overlying water by 36.6%-82.7%, with an average of 53.3%; 2） the Zn release rate was reduced by 21.0%-88.9%, with an average of 42.3%, and the Zn pollution load of the overlying water was reduced by 38.0%-67.1%, with an average of 55.0%; 3） the Cu release rate was reduced by 27.5%-91.0%, with an average of 55.3%, and the Cu load of the overlying water was reduced by 57.1%-83.7%, with an average of 71.7%; 4） the Pb release rate was reduced by 11.8%- 79.3%, with an average of 41.2%, and the Pb pollution load of the overlying water was reduced by -1.3%-70.7%, with an average of 29.8%. We also found that the effects of in situ biological treatments on the release of heavy metals were affected by the extent of sediment disturbance. For integrated applications, high-disturbance treatments should be combined with low-disturbance treatments to reduce the explosive release of pollutants caused by sediment disturbance during the treatment operation to achieve better overall treatment effects.

Microstructure Evolution and Mechanical Properties of a SMATed Mg Alloy under In Situ SEM Tensile Testing

Surface mechanical attrition treatment（SMAT） has been recently applied to bulk polycrystalline magnesium（Mg） alloys with gradient grain size distribution from the impact surface to inside matrix, hence effectively improving the alloys＇ mechanical performances. However, in-depth understanding of their mechanical property enhancement and grain size-dependent fracture mechanism remains unclear. Here,we demonstrated the use of in situ micro-tensile testing inside a high resolution scanning electron microscope（SEM） to characterize the microstructure evolution, in real time, of SMATed Mg alloy AZ31 samples with different grain sizes of ~10 μm（＇coarse-grain sample＇） and ~5 μm（＇fine-grain sample＇）, respectively, and compared the results with those of a raw Mg alloy AZ31. The quantitative tensile tests with in situ SEM imaging clearly showed that fracture of ‘fine-grain sample＇ was dominated by intergranular cracks,while both trans-granular and intergranular cracks led to the final failure of the ‘coarse-grain samples＇.It is expected that this in situ SEM characterization technique, coupled with quantitative tensile testing method, could be applicable for studying other grain-refined metals/alloys, allowing to optimize their mechanical performances by controlling the grain sizes and their gradient distribution.

Facile synthesis of porous nitrogen-doped holey graphene as an efficient metal-free catalyst for the oxygen reduction reaction

Nitrogen-doped graphene is a promising candidate for the replacement of noble metal-based electrocatalysts for oxygen reduction reactions （ORRs）. The addition of pores and holes into nitrogen-doped graphene enhances the ORR activity by introducing abundant exposed edges, accelerating mass transfer, and impeding aggregation of the graphene sheets. Herein, we present a straightforward but effective strategy for generating porous holey nitrogen-doped graphene （PHNG） via the pyrolysis of urea and magnesium acetate tetrahydrate. Due to the combined effects of the in situ generated gases and MgO nanoparticles, the synthesized PHNGs featured not only numerous out-of-plane pores among the crumpled graphene sheets, but also interpenetrated nanoscale （5-15 nm） holes in the assembled graphene. Moreover, the nitrogen doping configurations of PHNG were optimized by post-thermal treatments at different temperatures. It was found that the overall content of pyridinic and quaternary nitrogen positively correlates with the ORR activity; in particular, pyridinic nitrogen generates the most desirable characteristics for the ORR. This work reveals new routes for the synthesis of PHNG-based materials and elucidates the contributions of various nitrogen species to ORRs.