The room temperature creep behavior of Ti-6Al-4V alloy and its effect on subsequent mechanical properties were investigated. The results show that all these factors, such as macro-texture, creep stress level and pre-plastic-strain, have a significant impact on the room temperature creep behavior of Ti-6Al-4V. With the increase of the <0001> peak pole density along the loading direction, the work hardening exponent increases, and the creep exponent becomes smaller, resulting in the better room temperature creep property of Ti-6Al-4V. Enough high stress is the prerequisite for room temperature creep. The obvious room temperature creep behavior can be observed only when the creep stress is not lower than 0.85σy, and the room temperature strain increases with the creep stress level. Pre-plastic-strain can suppress the subsequent room temperature creep of Ti-6Al-4V, no matter the pre-plastic-strain comes from the monotonic loading or from the creep behavior. The pre-plastic-strain can deteriorate the fatigue property of the alloy, although it can reduce subsequent creep strain.
The conventional fatigue damage factor was redefined by analyzing the relevant fatigue damage mechanisms in detail. Then, a model of residual-stiffness and -strength was individually proposed in consideration of the influence of reinforced fiber volume fraction and temperature on the properties of unidirectional fiber reinforced composites. Furthermore, by introducing temperature correction parameters into the above models of room temperature, a correlation model of residual strength with residual stiffness was further acquired, therewith the establish of residual strength model may be facilitated by reducing the dependance on the number of residual strength tests, and relieving the effect of data dispersion as well. Finally, the fatigue test data and residual strength test data of composite collected from the existing literatures were fitted and verified, it follows that the residual stiffness model and residual strength model can accurately describe the degradation behavior of residual stiffness and residual strength. The residual stiffness model can be also used to predict the degradation behavior of the residual stiffness of the composite with different fiber volume fraction at different temperature.
The tunable stiffness step-growth hydrogels were prepared by thiol-ene click chemistry between 4 arm-polyethylene glycol-norbornene (4-PEG-NB) and dithiothreitol and supplemented with REDV biopeptide modification for 2D and 3D extracellular matrix (ECM) simulations, in which the 4-PEG-NB macromonomer was produced by the reaction of 4-PEG-OH with norbornene. The results show that the prepared thiol-ene hydrogels present a porous structure, and the thiol-ene cross-linking reaction with high cross-linking efficiency was also confirmed. The tunable Young's modulus of hydrogels could be precisely regulated to 0.79, 2.40, and 4.52 kPa by changing the thiol-ene ratio. As the crosslink ratio of the hydrogels increased, the porosity gradually increased and the swelling rate gradually decreased. The drug release of the hydrogels was faster in the early stage and then gradually slowed down. The cell culture results of 2D and 3D ECM simulations show that the hydrogel had excellent biocompatibility.
Composites of g-C3N4/Bi12O17Cl2 were prepared by a simple liquid phase precipitation method with bismuth nitrate, sodium chloride, sodium hydroxide and graphitic carbon nitride as raw material. The composition and morphology of the prepared composites were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The effect of g-C3N4 on the photocatalytic activity of g-C3N4/Bi12O17Cl2 composites were evaluated with Rhodamine B as the simulated pollutant under visible light. The results show that the photocatalytic performance of 2 % g-C3N4/Bi12O17Cl2 composite is the best, after 90 min of light exposure the photocatalytic degradation rate of RhB reached 98.64%.
Carbon nanosphere based nitrogen-phosphorus-sulfur composite flame retardant (CNSs-H-D) was synthesized with the desired carbon nanospheres (CNSs) as core, hexachlorocyclotriphosphazene (HCCP) as bridge and amino diphenyl sulfone (DDS) as grafting agent. The morphology and thermal stability of CNSs-H-D were characterized. Afterwards, the composite of CNSs-H-D reinforced epoxy resin (EP) (CNSs-H-D/EP) was made and its flame retardancy and the relevant mechanism were investigated. Results show that the synthesized CNSs-H-D displayed a spherical morphology with a mean diameter of 80 nm and excellent thermal stability. Specifically, the LOI of CNSs-H-D/EP increased from 20.0% (of pure EP) to 27.5% (with addition of 5%(mass fraction) CNSs-H-D/EP), thus its flame retardance reached grade V-2 and its peak value of heat-release rate and fire-risk index reduced by 16.8% and 42.2%, respectively. Moreover, CNSs-H-D could significantly improve the thermal stability and char formation of EP. The initial decomposition temperature and high-temperature char residue of CNSs-H-D/EP increased by 40℃ and 144.7% respectively, in comparison with the pure EP. Furthermore, the initial weight loss temperature of CNSs-H-D/EP was 190℃ higher than that of EP. With good compactness and continuity of char layer, the CNSs-H-D/EP exhibited a typical condensed phase flame-retardant mechanism, where the char residue was as high as 94.5% at 800℃.
The composite absorbing material of MoS2/CoFe/C was prepared via a two-step process, namely, the MoS2/CoFe2O4 was hydro-thermally synthesized with anhydrous glucose as carbon source and reducing agent in a reasonable material ratio, which then was reduced to MoS2/CoFe/C of ternary-nanometer flower structure in nitrogen atmosphere. The morphology, phase structure and electromagnetic parameters of the ternary nanomaterial were characterized, while the relation of the optimum matching thickness and absorbing property of the composite was assessed with computer simulation. The effect of glucose concentrations on the composition and properties of the composites were investigated. The absorption mechanism was discussed based on the Relaxation Polarization theory. When the thickness is 3 mm the lowest reflectivity of MoS2/CoFe/C composite material at 12.4 GHz can reach -42.9 dB. When the thickness is 4 mm the reflectivity frequency of MoS2/CoFe/C composite material is lower than -10 dB with bandwidth up to 7.1 GHz.
The Cu-bearing martensitic stainless steel 5Cr15MoV was heat treated at different temperatures for 30 min and then oil quenched. The effect of quenching temperature on the microstructure, hardness and corrosion resistance of the steel were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), hardness tester and electrochemical test. The results show that the addition of Cu increases the volume fraction of residual austenite and decreases the hardness of the steel, the undissolved carbides in the quenched steel are Cr rich M23C6 type carbides with FCC structure, and the addition of Cu has no obvious effect on the size and morphology of the carbides in the 5Cr15MoV martensitic stainless steel, but its corrosion resistance is slightly reduced. With increase of the quenching temperature from 1000oC to 1100oC the undissolved carbides decrease, while the corrosion resistance of the steel increases. Meanwhile, the content of residual austenite also increases with the increase of quenching temperature. The combined action of carbide and residual austenite makes the hardness versus temperature curve of the quenched steel a parabolic shape with a maximum value at 1050°C.
The suspension of sepiolite powder in the mixture of anhydrous ethanol, ammonia and ethyl orthosilicate was first prepared and then coupling modified with surfactant in varying process conditions. Further, the modified sepiolite powder was acquired from the prepared suspension by means of ultrasonic assisted stirring, centrifugal dehydration, washing, drying and grinding successively. The modified sepiolite powder was dispersed in anhydrous ethanol and applied on the surface of glass slide to prepare a thin superhydrophobic coating. The contact angle (CA) and rolling angle (SA) of the coating with water were measured by using OCA 20 contact angle tester, the structure of functional groups on the surface of powders before and after modification was analyzed by Bruker-80V Fourier transform infrared spectrometer, the changes of elements on the surface of powders before and after modification were analyzed by Escalab 250XI X-ray photoelectron spectroscopy, the micromorphology of the powders before and after modification was observed by Nova Nano SEM450 and JEM-1230 transmission electron microscopy, and the properties of sepiolite superhydrophobic composite coating were investigatied. The results show that: when the modification is carried out at 0℃ for 3 h, with 1 g of sepiolite powder as raw material and 0.8 mL of cetyltrimethoxy silane as modifier. A coating made of the modified sepiolite powder presents a contact angle of 157.2° with a rolling angle of 10.5°. During modification process SiO2 particles were adsorbed on the surface of sepiolite to create a rough surface, which was grafted with long chain alkyl groups of cetyltrimethoxy silane. The adhesion of water droplets to the coating surface decreases rapidly first and then slowly with the increase of the volume of water droplets. Due to the weak adhesion of water droplets to the coating, the water droplets can easy roll on the coating surface, so that resulted in good self-cleaning performance of the coating.
