Effect of electropulsing-assisted ultrasonic surface rolling process (EP-USRP) on surface mechanical properties and microstructure of Ti-6Al-4V alloy was investigated. Compared with the original ...ultrasonic surface rolling process (USRP), the introduction of electropulsing with optimal parameters can effectively facilitate surface cracks healing, improve surface microhardness and wear resistance. In addition, the residual compressive stress is further enhanced under EP-USRP. Rapid improvement of the surface mechanical properties should be attributed to the ultra-refined grains and enhanced plastic deformation caused by the coupling effect of USRP and electropulsing. High strain rate given by USRP, the accelerated dislocation mobility and atom diffusion induced by electropulsing are likely the primary intrinsic reasons for the observed phenomena.
The present work integrates 3D digital optical microscopy (OM), nano-indentation, X-ray diffraction (XRD), scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) and ...transmission electron microscopy (TEM) to systematically investigate the effect of electropulsing on the surface mechanical properties and microstructure of AISI 304 stainless steel during the ultrasonic surface rolling process (USRP). Compared with the original USRP, the introduction of electropulsing with optimal parameters can effectively facilitate surface crack healing and improve surface hardness and wear resistance dramatically, and the residual compressive stress is further enhanced. Meanwhile, more martensite phase and fewer deformation twins can be found in the strengthened layer. Rapid improvement of the surface mechanical properties should be attributed to the ultra-refined grains, accelerated martensitic phase transformation and suppressed deformation twining induced by the coupling effect of USRP and electropulsing. The high strain rate given by USRP, increased stacking fault energy and accelerated dislocation mobility caused by electropulsing are likely the primary intrinsic reasons for the observed phenomena.
The present work reports the experimental observations of surface property enhancement for austenitic stainless steel treated by electropulsing-assisted ultrasonic surface rolling process (EP-USRP). ...Compared with the original ultrasonic surface rolling process (USRP), the introduction of electropulsing can facilitate the surface cracks healing, and alter the cross-sectional micro-hardness gradient distribution within the surface strengthened layer, i.e. significantly gaining higher surface hardness or greater impact depth under the different experimental parameters. Refined grain and enhanced plastic deformation caused by electropulsing are likely the primary reason for the observed phenomena.
•Introduced electropulsing into the ultrasonic surface rolling process firstly.•Electropulsing can facilitate the surface cracks healing effectively.•Electropulsing can bring higher surface hardness or greater impact depth under different experimental parameters.•A new potential explanation based on electroplastic effect was given.
Microencapsulated paraffin with polyurea/acrylic resin hybrid shells as phase change energy storage materials was obtained in situ by combining interfacial polymerization and suspension-like ...polymerization. Glycerin (GC) acts as a cross-linking agent to modify the shells. The morphologies, particle size distributions, thermal storage properties, thermal stabilities and thermal reliabilities of microencapsulated phase change materials (MicroPCMs) were determined by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TG). The temperature regulation performance of the foam with MicroPCMs was investigated by an infrared thermal imager. DSC results showed that MicroPCMs with polyurea/butyl methacrylate (PU/BMA) possess an improved heat ability and thermal reliability compared to MicroPCMs with polyurea/methyl methacrylate (PU/MMA). The incorporation of GC to shell-forming composition led to an enhancement in thermal storage capacity of the MicroPCMs. The MicroPCMs with GC-modified PU/BMA hybrid shell has the highest PCMs content by as much as 82.6 mass%. The change in latent heat of MicroPCMs with GC-modified PU/BMA hybrid shell was very small of less than 4 mass% after 500 thermal cycles. The infrared thermography indicated that the PU foam incorporating the MicroPCMs with GC-modified PU/BMA hybrid shell has better temperature-regulated property. In conclusion, the MicroPCMs with PU/BMA hybrid shells, especially with GC-modified PU/BMA hybrid shell, possess a promising prospect applying in energy-conserving building materials and thermal control system of shipping packages.
Microencapsulations of n-octadecane with different crosslinked methylmethacrylate-based polymer as shells were carried out by suspension-like polymerizations. 1,4-butylene glycol diacrylate (BDDA), ...divinylbenzene (DVB), trimethylolpropanetriacrylate (TMPTA) and pentaerythritol tetraacrylate (PETRA) were employed as crosslinking agents. The influences of the type and amount of crosslinking agent, the type of initiator and polymerization temperature on the properties of as-prepared microencapsulated phase change materials (MicroPCMs) have been studied. The MicroPCMs were characterized using Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Thermal properties and thermal stability of MicroPCMs were investigated by differential scanning calorimetry (DSC) and thermalgravimetric analysis (TGA). Shell mechanical strength was measured by micro/nano-hardness tester. Thermal properties, thermal resistant temperatures as well as shell mechanical strength of MicroPCMs enhanced as the number of crosslinkable functional moieties of the crosslinking agents increased. The MicroPCMs containing 75.3wt% n-octadecane obtained using PETRA as crosslinking agent has the highest latent heats of melting (156.4J/g) and crystallization (182.8J/g) and displays the highest thermal stability and shell mechanical strength. The MicroPCMs prepared with DVB shows a relatively higher shell mechanical strength and heat capacity compared with those prepared with BDDA. Both heat capacity and thermal stability of MicroPCMs prepared by combining 2,2′-azobisisobutyronitrile (AIBN) and redox initiators at 45°C were lower than that of MicroPCMs prepared with AIBN or benzoyl peroxide (BPO) at 85°C. Hence, MicroPCMs with crosslinked methylmethacrylate-based polymer as shells, especially crosslinked polymer shells of higher crosslinking density, show a good potential as a solar-energy storage material.
▶ n-Octadecane was encapsulated with crosslinked methylmethacrylate-based polymer. ▶ Three types of initiator were used at different polymerization temperatures. ▶ Increasing crosslinkable functional moiety of crosslinking agent increased quality. ▶ Microcapsule with pentaerythritol tetraacrylate has the highest latent heats. ▶ Lower polymerization temperatures led to a lower heat capacity.
Microcapsules containing n-octadecane with different n-butyl methacrylate (BMA)-based copolymer shells were fabricated by a suspension-like polymerization method. n-butyl acrylate (BA), methacrylic ...acid (MAA) and acrylic acid (AA) were employed as monomers to copolymerize with BMA. The surface morphologies of the microencapsulated phase change materials (MicroPCMs) were studied by scanning electron microscopy (SEM). The thermal properties, thermal reliabilities and thermal stabilities of the MicroPCMs were investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The temperature-regulated properties of the MicroPCMs were determined by an infrared thermography. The incorporation of MAA or AA to the acrylic composition of the polymer shells led to an increase in both the heat storage capacities and thermal stabilities of the MicroPCMs. The MicroPCMs with P(BMA-co-MAA) exhibit a greater heat capacity and thermal stability compared with the MicroPCMs with P(BMA-co-AA). The MicroPCMs with P(BMA-co-MAA) have the highest latent heats of melting (144.3J/g) and crystallization (152.9J/g) as well as the highest thermal resistant temperature (249°C). The phase change temperatures and enthalpies of the MicroPCMs varied little after 1000 thermal cycles. Thermal images showed that the gypsum board containing the MicroPCMs with BMA-based copolymers as shells, especially with P(BMA-co-MAA) and P(BMA-co-AA) as shells, possessed temperature-regulated properties. As a result, the MicroPCMs with BMA-based copolymers as shells have good thermal energy storage and thermal regulation potentials, such as solar energy-saving building materials.
•n-octadecane was encapsulated with n-butyl methacrylate (BMA)-based copolymer shells.•Microcapsule with P(BMA-co-methacrylic acid) has the highest latent heat.•Microcapsule with P(BMA-co- methacrylic acid) has the greatest thermal stability.•Phase change enthalpies of the microcapsules varied little after thermal cycles.•Gypsum board with microcapsules possesses temperature-regulated property.
A series of microencapsulated phase change materials (MicroPCMs) with
n-octadecane as core were successfully fabricated by suspension-like polymerization. The influence of initiator type and ...polymerization temperature on MicroPCMs were investigated systemically. The morphology of these microcapsules with different copolymer shells and various phase changing material (PCM) contents were observed by scanning electron microscopy (SEM). In addition, the core-shell structure and the shell thickness of microcapsules were also characterized by SEM. Thermal gravimetric analysis (TGA) curves indicate that the effects of different copolymer shell and various PCM contents on thermal stability of MicroPCMs were insignificant. Besides, SEM micrographs show that all of the MicroPCMs with various PCM contents remained intact after heat treatment at 200 °C for 30 min, however, all of the heat-treated MicroPCMs had no enthalpy as demonstrated by differential scanning calorimetry (DSC) curves. From above results, the weight loss of MicroPCMs may be caused by the penetration of decomposed gas of
n-octadecane through the intact shells.
► A series of MicroPCMs with styrene-based copolymer shells were fabricated. ► Influence of initiator and polymerization temperature on MicroPCMs was investigated. ► Effects of different shells and PCM contents on thermal stability were insignificant. ► The weight loss mechanism of styrene-based copolymer MicroPCMs was investigated.
Microencapsulated phase change material (MEPCM), paraffin, with polymethylmethacrylate shell was prepared by introducing UV irradiation to an O/W emulsion polymerization for approximately 30
min ...under constant stirring. The results of differential scanning calorimetry analyses indicate that the latent heat and the content of paraffin of microcapsules are 101
J
g
−1 and 61.2
wt%, respectively. The phase transition temperature of MEPCM ranges from 24 to 33
°C. The MEPCM was characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. Thermal gravimetric analysis results show that the MEPCM is degraded into two distinguishable steps. Accelerated thermal cycling tests also indicate that the MEPCM displays a good thermal reliability. Gypsum boards composed of as-prepared MEPCM show a good temperature-regulated property. Based on all these results, it can be concluded that the microencapsulated paraffin as MEPCMs have good potential for thermal energy storage purposes such as phase change material slurries, solar space heating applications, textiles and building materials.
Epoxidized soybean oil (ESO) was incorporated into poly(lactic acid) (PLA) to formulate fully biobased and highly tough ESO/PLA blends by using tannic acid (TA) as a green vulcanizing agent. The ...crosslinking degree of ESO molecules and the interfacial compatibility between the ESO phase and PLA matrix were thus improved. The properties of the TA-ESO phase and its interfacial adhesion with PLA matrix were tailored by changing the molar ratio of TA to ESO, which significantly influenced the crystallization behavior, mechanical properties, thermal stabilities, and morphologies of the TA-ESO/PLA blends. After the incorporation of 10 wt% TA-ESO (based on the final blend) with a ‒OH groups to epoxy rings molar ratio of 0.8 into PLA system, the elongation at break (242%) and tensile toughness (57.4 MJ/m3) of the resulting PLA blend were 7 and 4 times higher than those of the blend with 10 wt% ESO, respectively. Compared to the 10 wt% ESO/PLA blend, the glass transition temperatures and thermal stabilities of the TA-ESO/PLA blends were slightly enhanced due to the increased crosslinking density of the TA-ESO phase; however, a slightly decreased crystallinity was observed for PLA after the addition of TA into ESO phase.
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•Fully biobased and highly tough PLA blend was formulated via dynamic vulcanization.•Tannic acid was used as a green crosslinker for ESO to form rubbery phase within PLA.•Added TA increased crosslinking density of ESO phase and its compatibility with PLA.•The properties of blends were tailored by changing ‒OH/epoxy molar ratio in TA-ESO.
The effect of electropulsing-assisted ultrasonic nanocrystalline surface modification (EP-UNSM) on surface mechanical properties and microstructure of Ti-6Al-4V alloy is investigated. Compared to ...conventional ultrasonic nanocrystalline surface modification (UNSM), EP-UNSM can effectively facilitate surface roughness and morphology, leading to excellent surface roughness (reduced from Ra 0.918 to Ra 0.028 μm by UNSM and Ra 0.019 μm by EP-UNSM) and smoother morphology with less cracks and defects. Surface friction coefficients are enhanced, resulting in lower and smoother friction coefficients. In addition, the surface-strengthened layer and ultra-refined grains are significantly enhanced with more severe plastic deformation and a greater surface hardness (a maximum hardness value of 407 HV and an effective depth of 550 μm, in comparison with the maximum hardness value of 364 HV and effective depth of 300 μm obtained by conventional UNSM). Remarkable enhancement of surface mechanical properties can be attributed to the refined gradient microstructure and the enhanced severe plastic deformation layer induced by coupling the effects of UNSM and electropulsing. The accelerated dislocation mobility and atom diffusion caused by the thermal and athermal effects of electropulsing treatment may be the primary intrinsic reasons for these improvements.
