Electrostatic Self-Assembling Formation of Pd Superlattice Nanowires from Surfactant-Free Ultrathin Pd Nanosheets

A facile method has been developed for face-to-face assembly of two-dimensional surfactant-free Pd nanosheets into one-dimensional Pd superlattice nanowires. The length of the Pd nanowires can be well controlled by introducing cations of different concentration and charge density. Our studies reveal that cations with higher charge density have stronger charge-screening ability, and their introduction leads to more positive zeta-potential and decreased electrostatic repulsion between negatively charged Pd nanosheets. Moreover, their surfactant-free feature is of great importance in assembling the Pd nanosheets into superlattice nanowires. While the cations are important for the assembly of Pd nanosheets, the use of poly(vinylpyrrolidone) is necessary to enhance the stability of the assembled superlattice nanowires. The as-assembled segmented Pd nanowires display tunable surface plasmon resonance features and excellent hydrogen-sensing properties.MOST of China 2011CB932403 2014CB932004 NSFC 21131005 21333008 21420102001 NFFTBS J131002

Inconel 713C Coating by Cold Spray for Surface Enhancement of Inconel 718

Inconel 713C is a nickel-based superalloy usually considered as a material of poor weldability due to its susceptibility to hot cracking in the heat-affected zones. Cold spray, a solid-state deposition technology that does not involve melting, can be proposed as a methodology to deposit Inconel 713C for surface enhancement of other target components. In this study, Inconel 713C coating was deposited on Inconel 718 substrate with a high-pressure cold spray system. The coating was characterized in terms of microstructure, hardness, and wear properties. The cold-sprayed Inconel 713C coating has a low porosity level and refined grain structures. Microhardness of the Inconel 713C coating was much higher than the Inconel 718 substrate. The sliding wear tests showed that the wear resistance of the cold-sprayed Inconel 713C coating is three times higher than the Inconel 718 substrate, making the coating a suitable protective layer. The main wear mechanisms of the coating include oxidation, tribo-film formation, and adhesive wear

Wearable pressure sensor for athletes’ full-range motion signal monitoring

In order to real-time grasp of various physiological signals of athletes during sports, a high-performance flexible pressure sensor that can monitor various physiological signals and human motion was designed. Porous polydimethylsiloxane (PDMS) foam prepared by the sacrificial template method and graphene as raw materials were used to prepare a flexible pressure sensor with wide working range (0–100 kPa), ultra-high sensitivity (the average sensitivity in the range of 0–30 kPa is 17.9 kPa ^−1 , the sensitivity in the range of 30–100 kPa reaches 79 kPa ^−1 ), fast response ability (response time is 20 ms) and long-term work stability (more than 10 000 cycles). The excellent performance of this pressure sensor depends on the use of PDMS foam with a high elastic modulus and the graphene loading level is controlled to an appropriate ratio. Finally, we used the conductive porous PDMS foam based flexible pressure sensor to demonstrate accurate and real-time monitoring of athletes’ tiny physiological signals (including pulse and electrocardiograph signals), vocalization and facial emotions, as well as violent joint and limb movements (including joint bending, walking, squats, jogging, and jumping), showing the potential in coaching athletes

Rapid post processing of cold sprayed Inconel 625 by induction heating

Cold spray is a solid-state metal deposition technology. One of the major advantages of cold spray over other additive manufacturing technologies is the high deposition rate. Heat treatments are usually conducted for cold sprayed deposit to improve its ductility; however, the long duration of conventional furnace heating would compromise the advantage of fast deposition. The current work explored the use of induction heating to accelerate the heat treatment process. A post-process heat treatment of cold sprayed Inconel 625 by induction heating was carried out at 900 °C for 10 min. Microstructure, hardness, ductility, and adhesion strength of the cold sprayed Inconel 625 deposits were systematically studied before and after the induction heating. For comparison, the conventional furnace heat treatment was also conducted with the same heating temperature and duration. Compared with furnace heating, induction heat treatment yielded larger grain size and larger δ precipitates due to enhanced atomic diffusion promoted by the eddy current. There was a significant improvement of ductility of the Inconel 625 deposit after induction heat treatment, and this can be attributed to enhanced inter-splat bonding. In contrast, the improvement of ductility by furnace heating was limited. The adhesion strength was found to increase more significantly by induction heating when the thickness was within the penetration depth of the eddy current. The results show that rapid post processing of cold sprayed Inconel 625 can be achieved by induction heating.Submitted/Accepted versio

Effect of spray distance and powder feed rate on particle velocity in cold spray processes

Cold spray technology using micron-sized particles to produce coatings is increasingly used for reparative tasks in various industries. In a cold spray setup, the gun is usually connected to a robotic arm to deposit coatings on components with complex geometries. For these components, the standoff distance used in the cold spray process has to be large enough for easy maneuverability of the gun around a small radial feature. However, a small standoff distance is commonly found in most studies, which is thought to prevent a velocity drop of the particles over a larger distance. Here, a study was carried out by measuring the Inconel 625 particle velocity at different spray distances, ranging from 3 to 40 cm. The highest average velocity of 781 m/s was found at a spray distance of 8 cm. Furthermore, a study with varying powder feed rates was also conducted. An increase in the powder feed rate was found to have a minimal effect on the particle velocity. Inconel 625 coatings deposited at the optimum standoff distance (8 cm) were found to have low porosity and high hardness. The results in this study demonstrate that a larger standoff distance can be applied without a significant drop in velocity for cold spray applications requiring high maneuverability.Nanyang Technological UniversityNational Research Foundation (NRF)Published versionThis research was funded by the National Research Foundation of Singapore, Rolls-Royce Singapore Pte Ltd. and Nanyang Technological University through grants #002123-00002 and #002124-00002

Post-Processing of Cold Sprayed CoNiCrAlY Coatings on Inconel 718 by Rapid Induction Heating

Cold spray is a solid-state additive manufacturing process that has been increasingly used for restoration of damaged parts. Due to the nature of powder solid-state bonding, cold spray coatings usually possess pores in the microstructures. Heat treatment has been widely used as a post-processing method to reduce the porosity of cold sprayed coatings. However, it usually requires the whole component to be treated in the furnace and typically takes a few hours to finish the treatment. This study aims to develop a localized and rapid post-processing method for cold sprayed coatings. Multi-layer cold sprayed coatings of CoNiCrAlY on an Inconel 718 substrate were produced. Then the coatings were heat treated at 800 °C, 900 °C, 1000 °C and 1100 °C by rapid induction heating. The porosity level of the coatings reduced significantly after induction heating for a short period of merely 10 min. This is attributed to the preferential Joule heating at pore regions, which results in pore closures within the coatings. The potential application of induction heating as a rapid post-processing method for cold spray coatings has been demonstrated in this work

Post-processing of cold sprayed CoNiCrAlY coatings on Inconel 718 by rapid induction heating

Cold spray is a solid-state additive manufacturing process that has been increasingly used for restoration of damaged parts. Due to the nature of powder solid-state bonding, cold spray coatings usually possess pores in the microstructures. Heat treatment has been widely used as a post-processing method to reduce the porosity of cold sprayed coatings. However, it usually requires the whole component to be treated in the furnace and typically takes a few hours to finish the treatment. This study aims to develop a localized and rapid post-processing method for cold sprayed coatings. Multi-layer cold sprayed coatings of CoNiCrAlY on an Inconel 718 substrate were produced. Then the coatings were heat treated at 800◦ C, 900◦ C, 1000◦ C and 1100◦ C by rapid induction heating. The porosity level of the coatings reduced significantly after induction heating for a short period of merely 10 min. This is attributed to the preferential Joule heating at pore regions, which results in pore closures within the coatings. The potential application of induction heating as a rapid post-processing method for cold spray coatings has been demonstrated in this work.Nanyang Technological UniversityNational Research Foundation (NRF)Published versionThis research was funded by the National Research Foundation of Singapore, Rolls-Royce Singapore Pte. Ltd., and Nanyang Technological University through grants #002123-00002 and #002124-00002

An investigation into microstructure, tribological and mechanical properties of cold sprayed Inconel 625 coatings

In this study, Inconel 625 coatings were successfully deposited on 6061 aluminum alloy using a high-pressure cold spray process. The microstructure, mechanical and tribological properties of the coatings were systematically studied. The cold sprayed Inconel 625 coatings had a low porosity level due to the severe plastic deformation of the splats. EBSD analyses revealed that grain refinement occurred within the coatings and substrates (near the substrate-coating interface), which could be attributed to strain accumulation and fragmentation process. Good adhesion strength of above 57.0 MPa was achieved between the coatings and substrates. Nano-hardness and micro-hardness values were higher than those of bulk Inconel 625 and were uniform along the thickness of the coatings. The effects of normal load and sliding velocity on the tribological properties of cold sprayed Inconel 625 coatings were investigated by sliding wear tests. The wear results demonstrated that both increased sliding velocity and normal load led to higher specific wear rates, which could result from the combined effects of tribo-film delamination, adhesive wear, abrasive wear, and thermal softening. Lower coefficients of friction of the coatings measured under 5 N compared to those measured under 2 N with the same sliding velocity could be explained by transition of wear mechanisms as well as larger coverage of tribo-film on the wear tracks

A narrative review on the role of temperature and humidity in COVID-19: Transmission, persistence, and epidemiological evidence

Since December 2019, the 2019 coronavirus disease (COVID-19) outbreak has become a global pandemic. Understanding the role of environmental conditions is important in impeding the spread of COVID-19. Given that airborne spread and contact transmission are considered the main pathways for the spread of COVID-19, this narrative review first summarized the role of temperature and humidity in the airborne trajectory of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Meanwhile, we reviewed the persistence of the virus in aerosols and on inert surfaces and summarized how the persistence of SARS-CoV-2 is affected by temperature and humidity. We also examined the existing epidemiological evidence and addressed the limitations of these epidemiological studies. Although uncertainty remains, more evidence may support the idea that high temperature is slightly and negatively associated with COVID-19 growth, while the conclusion for humidity is still conflicting. Nonetheless, the spread of COVID-19 appears to have been controlled primarily by government interventions rather than environmental factors