Friction stir welding/processing (FSW/P) involving temperature, mechanics, metallurgy and interaction, is a complex solid state joining and processing technology. FSW has been widely applied to join ...aluminum alloy, titanium alloy and other materials which are difficult to weld by fusion welding. The last scientific study states that FSW has potential to join thermoplastic polymers and polymer matrix composites. In this review, current understanding and development about FSW of thermoplastic polymers and polymer matrix composites, multifunctional composites fabrication as well as dissimilar FSW of metal and polymer are reviewed. Future scientific research and engineering development related to FSW/P of thermoplastic polymers and polymer matrix composites are identified.
Designing and constructing bifunctional electrocatalysts is vital for water splitting. Particularly, the rational interface engineering can effectively modify the active sites and promote the ...electronic transfer, leading to the improved splitting efficiency. Herein, free‐standing and defect‐rich heterogeneous MoS2/NiS2 nanosheets for overall water splitting are designed. The abundant heterogeneous interfaces in MoS2/NiS2 can not only provide rich electroactive sites but also facilitate the electron transfer, which further cooperate synergistically toward electrocatalytic reactions. Consequently, the optimal MoS2/NiS2 nanosheets show the enhanced electrocatalytic performances as bifunctional electrocatalysts for overall water splitting. This study may open up a new route for rationally constructing heterogeneous interfaces to maximize their electrochemical performances, which may help to accelerate the development of nonprecious electrocatalysts for overall water splitting.
A synthetic strategy is provided to rationally construct defect‐rich heterogeneous MoS2/NiS2 nanosheets directly on carbon cloth and the influence of interface configuration on the electrocatalytic performances is investigated. The abundant heterogeneous interfaces in MoS2/NiS2 can not only provide rich electroactive sites but also facilitate the electron transfer, which further cooperate synergistically toward electrocatalytic reactions.
•316/Inconel625 FGM without forming defects was fabricated by LDMD.•The columnar dendritic growth prevailed in the 316L/Inconel625 FGM structure.•Along the graded direction, micro-hardness value ...dropped first and then rose.•The presence of Laves phase induced the materials fracture.
Functionally graded material (FGM) is a composite with innovative structure and function, which has the good overall performance and meets working requirements in harsh environments. FGM has been widely used in aerospace, biological, nuclear, and photoelectric engineering fields. Laser direct metal deposition (LDMD) is an advanced manufacturing method that is excellent at fabricating objects with optimized geometries and minimizing weight using far less material and energy. In this paper, FGM with the constitution varying from 100% 316L stainless steel to 100% Inconel625 alloy was successfully fabricated using LDMD technology. Grain morphology, composition, mechanical properties and abrasive resistance were obtained to investigate the microstructure and mechanical performance of FGM. With the Inconel625 content increasing, primary dendrite arm spacing gradually increased, and white second phases began to precipitate along dendrites boundary when the content of Inconel625 exceeded 80%. Micro-hardness gradually increased from 216.47 HV at the bottom of FGM to 355.7 HV at the top. With micro-hardness and the hard phase volume increasing, the wear rate of FGM declined and the wear resistance was improved. The fracture element analysis showed that a large number of small and uneven distributed second phases led to the graded material fracture and the tensile fracture mechanism was of typical micro-porous aggregation toughness fracture.
To realize high-performance and long life span supercapacitors, highly electrochemically active materials and rational design of structure are highly desirable. Herein, a hierarchical ...NiCo-LDH/NiCoP@NiMn-LDH hybrid electrode (NCLP@NiMn-LDH) was synthesized on carbon cloth via a hydrothermal reaction and phosphorization treatment. Owing to the introduction of NiCoP and design of the core–shell structure, the hybrid electrode showed significantly improved electrochemical performance. The as-fabricated hybrid electrode exhibited a high specific capacitance of 2318 F g −1 at 1 A g −1 , with a superior cyclic stability. Additionally, an asymmetric supercapacitor (NCLP@NiMn-LDH//AC) was assembled with a voltage window of 1.5 V. The ASC device delivered a maximum energy density of 42.2 W h kg −1 at a power density of 750 W kg −1 .
Abstract
Understanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and understand ...failure mechanism. Here, using low-dose imaging technique by direct-detection electron-counting camera in a transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH
3
NH
3
PbI
3
(MAPbI
3
) at the atomic scale. We successfully image the atomic structure of perovskite in real space under ultra-low electron dose condition, and observe a two-step decomposition process, i.e., initial loss of MA
+
followed by the collapse of perovskite structure into 6H-PbI
2
with their critical threshold doses also determined. Interestingly, an intermediate phase (MA
0.5
PbI
3
) with locally ordered vacancies can robustly exist before perovskite collapses, enlightening strategies for prevention and recovery of perovskite structure during the degradation. Associated with the structure evolution, the bandgap gradually increases from ~1.6 eV to ~2.1 eV. In addition, it is found that C-N bonds can be readily destroyed under irradiation, releasing NH
3
and HI and leaving hydrocarbons. These findings enhance our understanding of the photoelectric properties and failure mechanism of MAPbI
3
, providing potential strategies into material optimization.
The electrochemical performance of nanostructured nickel-cobalt sulfides is greatly limited by the sluggish reaction kinetics and limited electroactive sites. Herein, we design and synthesize ...free-standing Se doped nickel-cobalt sulfides with controllable-component directly on carbon cloth, which involves the hydrothermal process and sulfuration/selenylation reaction. Serving as free-standing electrode, as-synthesized Se doped nickel-cobalt sulfides not only favor the fast ion diffusion path and low contact resistance, but also provide rich electroactive sites with electrolyte. More importantly, proper Se doping in nickel-cobalt sulfides greatly increases the electrochemically active surface area and reduces the charge transfer resistance. Based on the X-ray photoelectron spectroscopy and transmission electron microscopy results, the reaction mechanism is convincingly revealed that Se dopants have been changed into SeOx. And electrochemical activated oxyhydroxides are mainly involved in electrochemical reactions. As a result, as-fabricated Se doped nickel-cobalt sulfides show a good electrochemical performance for supercapattery. Further, the supercapattery device is also assembled by using nickel-cobalt sulfide/selenide as positive electrode and activated carbon as negative electrode, which shows a high energy density of 39.6 Wh kg−1 at the power density of 1501 W kg−1.
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•Se doping can provide large the active sites and fast electron transport path.•The Se doped nickel-cobalt sulfides show good electrochemical performances.•The NiCo2S2.2Se1.8//AC device shows a high energy density of 39.6 Wh kg−1.
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The plunging depth of 0.05mm was optimum for joint formation of 0.5mm thick Al-6061 sheet by micro friction stir welding. Increasing rotational velocity from 1500rpm to 2000rpm was ...beneficial to sound surface formation, while the taper pin with three flats owned wider process window than the single taper pin. The minimum ratio of thickness reduction of 2% was attained, which enhanced the area of load bearing. The taper pin with three flats owing to the severe stirring actions resulted in the finer grain size, improving tensile property. The maximum tensile strength by the taper pin with three flats reached 217MPa, equivalent to 90% of base material.
Underwater wire-feed laser deposition (UWLD) of the Ti–6Al–4V alloy was firstly carried out utilizing a laser deposition nozzle, and the deposition appearance, geometry characteristics, ...microstructure and microhardness of deposited tracks were studied. At a lower gas flow rate, the absorption of residual water and scattering of aerosol particles on laser beam caused UWLD instability and decreased molten metal wettability. Upon increasing the gas flow rate, the aerosol particle density decreased, increasing the laser density and decreasing the cooling rate of molten metal; thus, the height and deposition angle of UWLD track decreased as the corresponding width and fusion depth increased. The microstructures of the deposited metal at a gas flow rate of 10 L/min were composed of the coarse lath α phase in upper region and the acicular martensite α′ with different size scales in middle and bottom regions. With increasing the gas flow rate to 20 L/min, the microstructure was primarily acicular martensite along with a small amount of α phase, and the martensite exhibited a larger grain size and stronger texture. At a gas flow rate of 20 L/min, the deposited process was stable and uniform deposition track without oxidation layer was obtained for UWLD Ti–6Al–4V alloy.
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•Underwater wire-feed laser deposition of the Ti–6Al–4V alloy was firstly carried out.•The interaction mechanism between laser beam, water and substrate were investigated.•Deposition appearance and geometry characteristics of single tracks were investigated.•Microstructure, elemental distribution and microhardness of the underwater laser deposition tracks were analyzed.
Organic-inorganic hybrid perovskites are promising candidates for the next-generation solar cells. Many efforts have been made to study their structures in the search for a better mechanistic ...understanding to guide the materials optimization. Here, we investigate the structure instability of the single-crystalline CH
NH
PbI
(MAPbI
) film by using transmission electron microscopy. We find that MAPbI
is very sensitive to the electron beam illumination and rapidly decomposes into the hexagonal PbI
. We propose a decomposition pathway, initiated with the loss of iodine ions, resulting in eventual collapse of perovskite structure and its decomposition into PbI
. These findings impose important question on the interpretation of experimental data based on electron diffraction and highlight the need to circumvent material decomposition in future electron microscopy studies. The structural evolution during decomposition process also sheds light on the structure instability of organic-inorganic hybrid perovskites in solar cell applications.
•The liquid droplet of Aluminum spreads on Silicon Carbide rapidly when with ultrasonic energy.•The removal of shell structure alumina by ultrasonic treatment improves the wettability.•The ...ultrasonically spreading input energy and efficient energy are both decreasing exponentially.
The sonoprocessing of droplet spreading during the wetting process of molten aluminum droplets on SiC ceramic substrates at 700 °C is investigated in this paper. When wetting is assisted by a 20 kHz frequency ultrasonic field, the wettability of liquid metal gets enhanced, which has been determined by the variations in thermodynamic energy and wetting kinetics. Wetting kinetic characteristics are divided into two stages according to pinning and depinning states of substrate/droplet contact lines. The droplet is static when the contact line is pinning, while it is forced to move when the contact line is depinning. When analyzing the pinning stage, high-speed photography reveals the evidence of oxide films being rapidly crushed outside the aluminum droplet. In this work, atomic models of spherical Al core being wrapped by alumina shell are tentatively built, whose dioxide microstructures are being transformed from face-centered cubic into liquid at the atomic scale. At the same time, the wetting experiment reveals that the oxide films show changes in the period of sonoprocessing from 3rd to 5th second.
During the ultrasonic spreading behavior in the late stage, there is a trend of evident expansion of the base contact area. The entire ultrasonic process lasts for no longer than 10 s. With the aid of ultrasonic sinusoidal waves, the wettability of metal Al gets a rapid improvement. Both molecular dynamic (MD) investigations and the experiments results reveal that the precursor film phenomenon is never found unless wetting is assisted by ultrasonic treatments. However, the precursor film appears near the triple line after using ultrasonics in the droplet wetting process, whose formation is driven by ultrasonic oscillations. Due to the precursor film, the ultrasonic wetting contact angle is lower than the non-ultrasonic contact angle. In addition, the time-variant effective ultrasonic energy has been quantitatively evaluated. The numerical expressions of thermodynamic variables are well verified by former ultrasonic spreading test results, which altogether provide an intrinsic explanation of the fast-decreasing contact angle of Al/SiC.
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