- Ei，ESCI收录期刊
- 中国科学引文数据库(CSCD)核心期刊
- 中文核心期刊
- 文摘与引文数据库(Scopus)
- 剑桥科学文摘(CSA)
Nb-Si ultra-high temperature material was prepared by sparking plasma sintering (SPS) technology using the mixed powders of niobium and silicon. The effect of process parameters, such as sintering temperature, holding time, heating and cooling rates in the sintering process, on the phase composition, microstructure and room temperature mechanical properties of the material was investigated. The results show that the material mainly consists of two phases of Nbss (Nb based solid solution) and α-Nb5Si3 as sintered above 1300℃. The relative density and mechanical properties of the material are enhanced continuously with increasing sintering temperature. The material prepared at 1600℃ has the optimum mechanical performance. The phase composition and the microstructure remain unchanged with increasing the holding time at 1600℃, while the mechanical properties of the material are improved slightly. The slow heating rate and the rapid cooling rate after sintering are favorable for improving the room temperature mechanical properties. With the application of an optimized SPS process, Nb-Si ultra-high temperature material with superior comprehensive room temperature mechanical properties can be prepared.
SiO2-ZrO2 based ceramic core plates with calcium stabled zirconia were fabricated by ceramic injection moulding. The hollow interfacial reaction plates of DZ125,DD5 and DD6 superalloys were fabricated by directional solidification at 1510℃and 1530℃ using SiO2-ZrO2 based ceramic cores, and the interfacial samples were obtained by horizontally cutting these hollow plates. The microstructure analysis of the interfacial samples shows that the high temperature chemical stability of SiO2-ZrO2 based ceramic core above 1500℃ is poor, due to different chemical reactions with DZ125, DD5 and DD6, and the reaction products are closely related to the compositions of superalloys. For DZ125 superalloy with higher Hf content,the reaction product is HfO2,which is rich on the interface and protects Al in DZ125 superalloy from oxidation. For DD5 and DD6 superalloys with lower Hf,Al2O3 is the reaction product between superalloys and ceramic cores and comes from the reaction between Al in superalloys and SiO2 in ceramic cores,which is accelerated by calcium stabled zirconia.
A duplex process was designed to modify the alloy surface using surface mechanical attrition treatment (SMAT) prior to microarc oxidation (MAO). A surface nanocrystalline (SNC) layer was formed on the surface of Al alloy by SMAT,on which a ceramic coating grew by MAO,finally the SNC-MAO composite coating are fabricated. The tensile properties of the SMATed alloy,MAO coating and SNC-MAO composite coating were comparatively evaluated. Experimental results show that the yield strength and tensile strength of the substrate Al alloy are reduced after MAO treatment,while those of SNC-MAO treated samples are improved due to the introduction of SMAT pre-treatment. When the elongation is 8%,SNC-MAO coating shows better tensile and adhesion properties compared with MAO coating with the same thickness.
Carbon fiber fabric reinforced polyphenylene sulfide (CFF/PPS) composite is one of most important thermoplastic composites for aviation. The main difficulties of preparing tough and strong CFF/PPS are to improve the infiltration and interfacial strength between carbon fibers (CF) and PPS matrix. The effects of surface modifications for CF on the interfacial strength between CF and PPS were investigated. Particularly, the influences of various processing conditions of annealing and coating with three modifiers on mechanical properties of CF and CFF/PPS were discussed. The effectiveness of surface modifications for CF was evaluated with several methods of characterization, including X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), single fiber strength test, interlaminar shear strength (ILSS) test, and dynamic mechanical analysis (DMA). Based on CF surface modification, the method to prepare high performance CFF/PPS thermoplastic composites for aviation was established. Optimized composite exhibits an ILSS of 91.4 MPa, a flexural strength of 953.7MPa, a tensile strength of 797.4MPa, a tensile modulus of 68.4 GPa, and an impact strength of 58.3kJ/m2. SEM observations on the fractural surface show that each CF is covered with substantial PPS matrix, indicating favorable adhesion between CF and PPS.
The heat treatment of laser engineered net shaping two kinds of nickel-based superalloy was carried out,and the influence of heat treatment parameters to the alloy's property was analyzed. The analysis of results indicates that: the room temperature tensile strength of Inconel 625 superalloy is not improved obviously under the stress relieving heat treatment, nevertheless after the solution treatment is done over 1000℃,the room temperature tensile strength is improved. The tensile strength after 1100℃ heat treatment is improved obviously compared with the deposited condition. The room temperature strength of Hastelloy C-276 is not improved obviously under the stress relieving heat treatment. Whereas, when the heat treatment is done above 1000℃, the room temperature tensile strength of laser near net shaping Hastelloy C-276 superalloy gradually increases with the increase of heat treatment temperature. After 1150℃ heat treatment, the tensile strength of Hastelloy C-276 increases obviously, compared with the deposited condition. The fracture mode of the two kinds of laser engineered net shaping nickel-based superalloy is ductile fracture.
Using boric acid and organic silicon prepolymer to modify phenolic resin, meanwhile introducing active monomer resorcinol, a kind of high temperature resistant phenolic resin which can be cured at medium temperature was prepared. The structure of the resin was characterized by fourier transform infrared spectroscopy(FTIR). The curing behaviour and thermal stability were investigated by thermal analysis (DSC and TGA). Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) were used to study the microstructures and the distribution of elements. Modified resin and inorganic filler were mixed together and paraformaldehyde was used as curing agent, then the adhesive was obtained. After cured at 100℃, its thermal and bonding properties were tested. The result shows that the adhesive can be cured at medium temperature has outstanding high temperature resistant and bonding properties. The shear strength at 1000℃ can reach 1.7MPa.
Metallographic observation and SEM graphic analysis were applied to the research of the microstructure and mechanical properties of FV520B affected by austenitizing elements Mn and Ni. The results show that the microstructure of FV520B stainless steel is mainly tempered martensite. With the increase of the alloy elements,the microstructure becomes finer. Mn and Ni can effectively improve the content of austenite in the weld. The effect of alloying elements on the weld strength is small,but the tensile strength and yield strength of the welded joint can be improved when the Mn and Ni elements are added. Mn and Ni elements can improve the impact toughness of the weld by increasing the volume of the austenite. Relative to the Mn element,the Ni element improves the weld toughness better.
K418 Ni-base superalloy was melted in high vacuum arc-melting furnace. The microstructure was observed by using SEM, the phase composition was detected by EDS. The effect of with rare earth elements on pore defects, γ' phase and eutectic phase of the alloy was studied and the effect mechanism was analyzed. The results show that the pore defects of the alloy decrease with the addition of rare earth elements, the density increases, the dendritic structure is refined. The morphology of carbides in alloy turns from bulk into chain and small pieces, the γ' phase in alloy with the addition of rare earth elements becomes smaller in size and much more in numbers. The eutectic phase(γ+γ') volume remarkably increases with the addition of Y, however the eutectic phase volume increases more obviously if two rare earth elements Y, Ce are added simultaneously.
To interpret the effect of multiple factors on pressure, velocity and shear rate distribution of polymer melt extrusion at entrance and exit of the die, a conical die structure and the finite element mesh model were established based on the basic equation of entrance convergent flow, and material parameters, process parameters and die shapes were considered via the numerical simulation and finite element method(FEM). In the FEM, Cross constitute equation, wall no-slip model were employed, and some FEM computing methods, e.g., quadratic interpolation of velocity, linear interpolation of pressure and viscosity Newton iteration algorithm were used for the generalized isothermal flow melt. The results show that the pressure distribution is directly related with the melt viscosity, flow index, relaxation time, entrance flow rate, and channel compression ratio etc, and the normal velocity and shear rate is mainly affected by the entrance flow rate. The quantitative analysis of multiple factors shows that the pressure increases with the increasing of melt viscosity, entrance flow rate and channel compression ratio, but decreases with the increasing of the flow index and relaxation time, and the normal velocity and shear rate increase with the increasing of the flow rate. These factors make the die exit pressure, normal velocity and shear rate not to be zero, thus lead to problems including die swell and etc.
Nanoporous TiO2 photoanodes were coated with thin layers of SrTiO3 by the hydrothermal method. The as-prepared TiO2/SrTiO3 core-shell photoanodes were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, transmission electron microscope and ultraviolet-visible absorption spectra. The effect of reacting time on photoelectrochemical properties of DSSCs based on TiO2/SrTiO3 photoanodes was studied. The results show that the surface of nanoporous TiO2 photoanodes is coated with perovskite SrTiO3 layer to form the photoanodes with TiO2 as the core, and SrTiO3 as the shell. The red-shifts of absorption edge were observed for the SrTiO3-coated samples. Compared to those of uncoated TiO2 photoanodes, DSSCs short circuit current density of TiO2/SrTiO3 electrodes prepared by hydrothermal method increases significantly. Solar cells based on TiO2/SrTiO3 electrodes modified with hydrothermal time of 5h show the optimal performance with short-circuit current density (Jsc) of 13.98mA/cm2, open-circuit voltage (Voc) of 0.74V, fill factor(FF) of 0.45 and photoelectric conversion efficiency (η) of 4.68% with the enhancement of 35.65%.
Laser was used as heating source and laser brazing assisted with ultrasound was performed,aiming to wet Al-based brazing filler metal with low melting points on TiNi SMA substrates. The result shows that with the increase of ultrasonic time,the spreading areas increase firstly and then decrease. Black Al2Si,Al3Si,AlSi phases are observed at wetting frontier. The grain size of AlSi and AlSiTi phases in the center of the droplet near interfacial region, as well as the Si content contain in these grains increases with ultrasonic time. In addition,with the decrease of laser heating power,the spreading areas also decrease,whereas the wetting angle increases. Intermetallic compound AlSi(Ti,Ni) with a width less than 10μm grows in the center of the droplet near interfacial region. Under the following optimal processing parameters,ultrasonic vibration time 1.0s,laser heating power 470W and the substrate surface roughness 0.03μm,the maximum spreading areas obtained is 106.45mm2 and the optimum wetting angle is 16°.
Using raw diatomite and calcined diatomite as carrier, the diatomite based antibacterial inorganic material was obtained by adsorption method to load the cpf antibacterial agent of 20×16-6 on diatomite. The properties of different diatomite carriers were investigated by SEM and BET. Moreover, the antibacterial performance of the ciprofloxacin/diatomite inorganic material was studied. Results show that the adsorption property of the diatomite on ciprofloxacin is very well. The loading rate of raw diatomite can amount to 60.79% and the calcined diatomite can amount to 24.78%.The adsorption capacity of the raw diatomite on ciprofloxacin is better than that of the calcined diatomite. The SEM indicates that the pore size and pore quantity of the raw diatomite are both better than that of the calcined diatomite, which leads to the excellent adsorption capacity of the raw diatomite. The inhibition zone test exhibits that the diatomite based antibacterial inorganic material has good antibacterial activity and release properties. The inhibition zone diameters of the ciprofloxacin/diatomite inorganic materials are all above 20mm.
In order to study the multi-stage cold forging behavior of high strength metallic,the metal flow,microstructure and mechanical properties variation were discussed which the high strength bolts deformation division areas were formed by multi-stage cold forging technology,and used both Deform-3D numerical simulation and actual product deformation methods. The results show that multi-stage cold forging deformation belongs to low dynamic deformation; microstructure and flow lines of big /small deformation areas have obvious "carryover effect"; due to high strength materials "Bauschinger effect",the ferrite grains is changed into equiaxed grains from elongated grains in difficult deformation area while the pearlite band is disappeared,so that the"carryover effect"of microstructure is worst in this deformation area; Both pearlite and ferrite in the microstructure of 20MnTiB high strength steel occur working hardening by low dynamics multi-stage cold forging deformation,and the magnitude of increasing hardness number of the pearlite is fairly near ferrite.
Corrosion behavior of the domestic super 13Cr martensitic stainless steel (00Cr13Ni5Mo2) was investigated by elemental sulfur suspension experimental method in the simulated high temperature and high pressure environment. Corrosion rate was calculated utilizing mass loss method. The micro-morphologies and chemical compositions of corrosion scales were characterized using scanning electron microscope (SEM),energy dispersive spectrometer (EDS) and X-ray diffraction (XRD),and effects of elemental sulfur on the acidification degree of NaCl solution were measured using pH meter. The results show that corrosion resistance of super 13Cr martensitic stainless steel decreases due to the presence of elemental sulfur. Average corrosion rate increases with the increase of sulfur content,and the maximum corrosion rate is present at 90℃,while all of them are less than 0.0125mm/a; the compositions of corrosion scales change from oxides to sulfides,and the percentage of sulfides increases with the increase of elemental sulfur content; pH value on sulfur/metal interface decreases due to the disproportionation reaction between elemental sulfur and water,which decreases corrosion resistance of super 13Cr martensitic stainless steel. The synergistic effect between Cl- and elemental sulfur leads to more serious corrosion.
The recycled polytetrafluoroethylene(r-TPFE) was used as nucleating agent to modify Poly(butylene terephthalate) (PBT), and the non-isothermal crystallization behavior of Poly(ethylene terephthalate) and PBT/r-PTFE composite at different cooling rates was investigated by differential scanning calorimetry (DSC), respectively. The Jeziorny and Liu-Mo methods were used to analyze the non-isothermal crystallization process of pure PBT and its composite, and the activation energies of the PBT and PBT/r-PTFE composite were calculated by Kissiinger method. The results show that r-PTFE can act as efficient nucleating agent for the crystallization of PBT and obviously increase the crystallinity and crystallization rate of PBT. Compared with the Jeziorny method, the Liu-Mo method appropriately describes the non-isothermal crystallization of PBT and PBT/r-PTFE composite. Further analysis of results shows that the incorporation of r-PTFE does not obviously change the nucleation mechanism and crystal growth of PBT, but decreases the crystallization activation energy of PBT, which facilitates the crystallization of PBT.
The lattice parameters and creep behaviors of tandem hot tolled GH4169 alloy were investigated by means of heat treatment, microstructure observation, lattice parameter determination and creep property measurement. The results show that the microstructure of tandem hot tolled GH4169 alloy mainly consists of γ, γ' and γ" phases. After standard heat treatment, some of granular γ' phase remelts, and separates out flat-like γ" phase in the alloy. Comparing with THR-GH4169 alloy, by X-ray analysis, the γ, γ' and γ" phases of THR-ST-GH4169 alloy possess smaller lattice parameters and larger lattice misfits among the phases, which may effectively restrain the dislocation movement, and is one of main important factors for the alloy possessing better creep resistance and longer creep life. During creep, the main deformation mechanism of THR-GH4169 alloy is that the dislocations with double orientations slip in the alloy. While the deformed twins and slipping dislocations may be activated in the THR-ST-GH4169 alloy.
Advanced TiO2-based photocatalysts with novel stability,low cost,and nontoxicity properties are benchmark materials that have been pursued for their high solar-energy conversion efficiency. However,the photocatalytic efficiency is affected by the degree of light absorption,quantum efficiency. In this review,recent researches and developments on TiO2 photocatalysts were summarized and introduced by three methods,namely modulation on morphology and crystal habit,surface plasmon enhanced light absorption,and graphene/TiO2 composite structures. Finally,some challenges are proposed with regards to structure design,modification of synthetic methods and material selection.
The recent progress of researches on the tribological properties of the epoxy resin composites filled by the particles was reviewed. The influences of species,sizes,content,surface modification of the particles on the tribological properties of filled epoxy composites were analyzed. The effects of the external factors such as load,sliding speed and temperature on the tribology were summarized. The mechanism of friction and wear were discussed. It is pointed out that the computer simulation technology will be the developing tendency of friction and wear mechanism of the particles/epoxy resin composites in the future research.
Boron nitride two-dimensional nanomaterials with a similar structure of graphene have a unique application value at insulated,oxygenated and high temperature environmental conditions due to its wide band gap,excellent chemical and thermal stabilities. Research on preparation and properties is one of the hot areas in material science. The exfoliating technology,especially chemical exfoliation,plays an important role in the preparation of the boron nitride two-dimensional nanomaterials because of low cost,high quality and controllability. This review described in detail progress and research status,and pointed out that exfoliation mechanism,development of new effective exfoliating methods,preparation of stable monolayer boron nitride would be the key areas in the future.
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