查看更多>>摘要：2 mm low carbon steel plates were successfully welded by the fiat friction stir spot welding (FSSW) using double side adjustable tools,by which the keyhole formed in the conventional FSSW was eliminated and a flat surface on both the top and bottom sides of the welded joints was obtained.In addition,the hook shape usually generated in the conventional FSSW was eliminated by this technique,and the unbonded interface was parallel to the surface of the sheets.Owing to the enlarged bonded interface width by eliminating the keyhole and the intermixed interface by the adjustable probe,the plug fracture occurred under all the welding conditions in the present study.Due to the suppression of the thickness thinning and elimination of the hook shape,the joint performance was improved in the plug fracture mode.The shear tensile performance was considered to strongly depend on the microstructure in the tip area of the unbonded interface and the maximum shear fracture load of 23.0 kN was achieved in this study.
查看更多>>摘要：The mechanical properties of refractory high entropy alloys (RHEAs) strongly depend on their phase structures.In this work,the phase stability ofa BCC TiNbTa0.5ZrAl0.5 refractory high entropy alloy subjected to thermomechanical processing was evaluated,and the effects of phase decomposition on room/high temperature mechanical properties were quantitatively studied.It was found that,the thermomechanical processing at 800 ℃ and 1200 ℃ leads to phase decomposition in the TiNbTa0.5ZrAl0.5 alloy.The phase decomposition is caused by the rapid rising of free energy of the primary BCC phase.The effect of the precipitates on room temperature strength is determined by the competition between the increasing in precipitation strengthening and the decreasing in solid solution strengthening.But at high temperatures (800-1200 ℃),the phase decomposition causes significant reduction in strength,mainly due to the grain boundary sliding and the decreasing in solid solution strengthening.
查看更多>>摘要：Distribution control and formation mechanism of gas inclusions formed in directionally solidified Al2O3-Er3AlsO12-ZrO2 eutectic ceramic rods are explored during laser floating zone melting.In atmospheric environment,highly-dense bubble-free eutectic rods are well fabricated at low solidification rate (＜25 μm/s).Gas inclusions form intermittently when the solidification rate is in the range of 25-50 μm/s,but produce continuously at higher solidification rates (100-200 μm/s).The gas inclusions exhibit an elongated finger-like pattern along the growth direction,which of the maximum value of diameter first increases and then decreases with increasing the solidification rate.Meanwhile,the volume fraction of gas inclusions increased gradually with the solidification rate.Based on the effect of surface tension gradient,heterogeneous nucleation of gas bubbles is evaluated to be the primary formation mechanism of gas inclusions.
查看更多>>摘要：Reactions between basal <a60> dislocations and { 10(1)2 } coherent twin boundaries (CTBs) in a Mg alloy were studied with atomic resolution.Individual dislocation-CTB reactions produced steps with residual dislocations and multiple twinning dislocations (TDs) gliding away,consequently resulting in TB migration.Reactions between {10(1)2} CTBs and low-angle grain boundaries composed of basal<a60> dislocations created either basal-prismatic/prismatic-basal interfaces or asymmetric tilt grain boundaries,depending on whether TDs gliding away or not.Not only the emission of TDs by dislocation-TB reactions may drive TB migration,but also the resultant steps or facets along TBs can act as TD sources to facilitate TB migration.Our results indicate that roughness or severe loss of local coherency induced by dislocation-TB reactions does not intrinsically impede TB migration in Mg alloys.Dislocation-TB reactions may provide another feasible strategy to improve the ductility of Mg alloys,in addition to other techniques like grain refinement and texture modification.
查看更多>>摘要：This study investigated the effect of multi-step heat treatment on the microstructure,mechanical properties and fracture behavior of thick 15Co-12Ni secondary hardening steel.As-quenched sample was found to have elongated prior austenite grain (PAG) and coarse lenticular martensitic structure.On the other hand,heat-treated sample was observed to have fine lenticular martensitic structure due to fine PAG size and a lot of nano-sized carbides.Also,after heat treatment,nano-scale reverted austenite film was formed at the martensite interfaces.The heat-treated sample showed 2.47 GPa superior tensile strength and superior elongation of about 12 ％.The high strength was mainly due to fine block size and high number density of nano-sized carbides.The average value of plane strain fracture toughness (KIC) was 29.3 MPa √m,which indicated a good fracture toughness even with the high tensile strength.The tensile fracture surface was observed to have ductile fracture mode (cup-and-cone) and the formation of about ～1 μm ultra-fine dimples.In addition to this,nano-sized carbides were observed within the dimples.The findings suggested that the nano-sized carbide had a positive effect not only on the strength but also on the ductility of the alloy.The fractured surface after toughness test,also showed ductile fracture mode with a lot of dimples.Based on the above results,correlation among microstructural evolution,deformation and fracture mechanisms along the heat-treatment was also discussed.
查看更多>>摘要：The effects of bentonite content on the corrosion behavior of low carbon steel in 5 mM NaHCO3 + 1 mM NaCl + 1 mM Na2SO4 solution were investigated by electrochemical measurements combined with X-ray diffraction (XRD) and scanning electron microscopy (SEM).In the initial immersion stage,the cathodic process of low carbon steel corrosion was dominated by the reduction of dissolved oxygen,while it transformed to the reduction of ferric corrosion products with the immersion time.The presence of bentonite colloids could suppress the cathodic reduction of oxygen due to their barrier effect on the diffusion of oxygen.However,the barrier performance of bentonite layer was gradually deteriorated due to the coagulation and separation of bentonite colloids caused by the charge neutralization of iron corrosion products dissolved from the steel substrate.More bentonite colloids could maintain the barrier effect for a long time before it was deteriorated by the accumulation of corrosion products.Conversely,it could lose the performance completely,and the corrosion behavior of low carbon steel reverted to the same as that in the blank solution.
查看更多>>摘要：Graphene oxide (GO) has received considerable attention for glucose detection because of high surface area,abundant functional groups,and good biocompatibility.Defects and functional groups of the GO are beneficial to immobilization of glucose oxidase (GOD),but sacrificing electron-transfer capability for highly-sensitive detection.In order to obtain high GOD loading and highly-sensitive detection of biosensors,we first designed and fabricated a graphene-laminated electrode by combining GO and edgefunctionalized graphene (FG) layers together onto glassy-carbon electrode.The graphene-laminated electrodes exhibited faster electron transfer rate,higher GOD loading of 3.80 × 10-9 mol.cm-2,and higher detection sensitivity of 46.71 μA·mM-1·cm-2 than other graphene-based biosensors reported in literature.Such high performance is mainly attributed to the abundant functional groups of GO,high electrical conductivity of FG,and strong interactions between components in the graphene-laminated electrodes.By virtue of their high enzyme loading and highly-sensitive detection,the graphene-laminated electrodes show great potential to be widely used as high-performance biosensors in the field of medical diagnosis.
查看更多>>摘要：Grain boundary precipitation and segregation play an important role in determining mechanical properties of Mg alloys.In the present work,we studied work focuses on the strengthening and deformation mechanism of coarse-grained (CG) and fine-grained (FG) Mg-Gd-Y-Ag-Zr-Ce alloy.The CG alloy is strengthened by means of age-strengthening with the formation of both basal plate γ" and prismatic plate β'precipitates in the grain interior.While the strengthening of FC alloy is completed by intergranular alloying segregation and intragranular precipitates γ" and β'.The segregation of alloying elements at the grain boundary and formation of sub-micron particles can stabilize the grain boundary and suppress the intergranular deformation.Consequently,dislocations could be trapped near γ" and β'precipitates in the grain interior.Unlike CG alloys,the FG alloys exhibit a heterogeneous transition from elastic to plastic deformation via the Lüders plateau.The rapid gliding dislocation multiplications and fine-grained size are necessary and sufficient conditions for the Lüders strains.Our work provides the insights on the evolution of fine-grained microstructure and helps for the design of Mg alloys with good mechanical properties.
查看更多>>摘要：Hot water droplet and oils induced air cushion failure,intensively used fluorine-containing chemicals,tedious preparation process,etc.are the main bottlenecks of the current artificially fabricated superhydrophobic materials,restricting their large-scale production and real-world applications.Herein,a facile,scalable,fluorine-free spray-coating strategy was employed to achieve superhydrophobic and superoleophobic polymerized organosilanes/Al2O3 nanoparticles (POS/Al2O3 NPs) coatings.The POS/Al2O3 NPs coating was achieved through hydrolytic condensation of tetraethyl orthoilicate (TEOS) and hexadecyltrimethoxysilane (HDTMS) in the presence of Al2O3 NPs.A variety of analytical techniques including scanning electron microscopy (SEM),X-ray photoelectron spectroscopy (XPS),energy dispersive X-ray photoelectron spectroscopy (EDS) were used to investigate the fabricated coatings.The POS/Al2O3 NPs coating features high contact angle (＞158°) and low sliding angle (＜5°) for water,glycerol,and ethylene glycol droplets with different surface tensions,verifying both superhydrophobic and superoleophobic properties.Moreover,the coatings present extremely low surface adhesion force,excellent liquid-driven self-cleaning ability,and hot water repellency.The superamphiphobic POS/Al2O3 NPs coating exhibits promising applications in various fields including self-cleaning,corrosion resistance,and preventing scald as this strategy is applicable on various substrates.
查看更多>>摘要：Metal corrosion often results in incalculable economic loss and significant safety hazards.Although numerous traditional methods have been used to mitigate the issue,such as coating and corrosion inhibitors,they are environmentally unfriendly and difficult to maintain.Therefore,in this study,an environmental approach was taken to protect steels from corrosion in a multi-species bacterial environment via synergistic biomineralization.The marine bacterium Pseudoalteromonas lipolytica mixed with Bacillus subtilis or Pseudomonas aeruginosa strains offered extraordinary corrosion protection for steel.The surface characterization and electrochemical tests showed that the biomineralized film generated by the mixed bacteria was more compact and protective than that induced by a single bacterium.Herein,we found that the synergistic mechanisms were rather different for the different bacterial groups.For Pseudoalteromonas lipolytica and Bacillus subtilis group,the related mechanisms were due to the increase of pH in the medium,secretion of carbonic anhydrase.As for Pseudoalteromonas lipolytica and Pseudomonas aeruginosa group,the synergistic mechanism was attributed to the inhibiting corrosive bacteria in biofilm by the growth advantage ofPseudoalteromonas lipolytica.Therefore,this study may introduce a new perspective for future use of biomineralization in a real marine environment.
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