- 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)
The combination of low absorption and extreme mechanical and thermal properties make diamond a compelling choice for some more extreme far infrared (8-12 μm) window applications. The optical properties of CVD diamond at elevated temperatures are critical to many of these extreme applications. The infrared transmission of free-standing diamond films prepared by DC arc plasma jet were studied at temperature varied conditions. The surface morphology, structure feature and infrared optical properties of diamond films were tested by optical microscope, X-ray diffraction, laser Raman and Fourier-transform infrared spectroscopy. The results show that the average transmittance for 8-12μm is decreased from 65.95% at 27℃ to 52.5% at 500℃,and the transmittance drop is in three stages. Corresponding to the drop of transmittance with the temperature, diamond film absorption coefficient increases with the rise of temperature. The influence of the change of surface state of diamond films on the optical properties of diamond films is significantly greater than the influence on the internal structure.
The silica-titania aerogel beads were synthesized through sol-gel reaction followed by supercritical drying, in which TEOS and TBT as co-precursors, EtOH as solvents, HAC and NH3·H2O as catalysts. The as-prepared aerogel beads were characterized by SEM,TEM,XRD,FT-IR,TG-DTA and nitrogen adsorption-desorption. The results indicate that the diameter distribution of beads are between 1-8mm, the average diameter of beads is 3.5mm. The aerogel beads have nanoporous network structure with high specific surface area of 914.5m2/g, and the TiO2 particles are distributed in the aerogel uniformly, which keep the anatase crystal under high temperature.
Pore spaced pure ZnO and Al2O3-doped ZnO(Al2O3-ZnO) micro-flowers were successfully synthesized by hydrothermal method. The microstructure, morphology and components were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS), respectively. Gas sensors were made to investigate the gas sensing properties. The results reveal that the sensor based on Al2O3-ZnO shows a high sensitivity to acetone. The sensitivity is 82.8 to 100×10-6 acetone gas at 260℃, which is about 4.6 times larger than that of pure ZnO (18.0) at similar conditions. The response time and recovery time are about 3s and 8s, respectively. Al2O3-ZnO also shows an excellent selectivity. Its sensitivity to acetone is 3.16 times higher than that to ethanol, which has the highest sensitivity among interfering gases under the same conditions. Thus, Al2O3-ZnO sensors can successfully distinguish acetone and ethanol with similar properties. In addition, the lowest detection to acetone is about 0.25×10-6 with theresponse is about 3.1.
Using the Gleeble-1500D simulator, the high temperature plastic deformation behavior of SiCp/Al-Cu composite were investigated at 350-500℃ with the strain rate of 0.01-10s-1. The true stress-strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the softening mechanism of dynamic recrystallization is a feature of high-temperature flow stress-strain curves of SiCp/A1-Cu composite, and the peak stress increases with the decrease of deformation temperature or the increase of strain rate.The flow stress behavior of the composite during hot compression deformation can be represented by a Zener-Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 320.79kJ/mol. The stable regions and the instability regions in the processing map were identified and the microstructures in different regions of processing map were studied.There are particle breakage and void in the instability regions.
Ti-Al alloyed coatings with different Nb doping contents were fabricated on TC4 titanium alloy by laser surface alloying to improve high temperature oxidation resistance of the alloy. Structures and high temperature oxidation behaviors of the alloyed coatings were analyzed and tested by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and box-type resistance furnace. The results show that the alloyed coatings consist of TiAl and Ti3Al, and no niobium compound are formed in Ti-Al-Nb alloyed coatings. The alloyed coatings are uniform and exhibit excellent metallurgical bonding with the substrates. A large amount of surface cracks and a few penetrating cracks are formed in Ti-Al alloyed coating without Nb doping, while no obvious cracks are formed in Ti-Al alloyed coating with Nb doping. The oxidation mass gains of all the alloyed coatings were significantly lower than those of the substrate. The alloyed coatings with Nb doping exhibit more excellent high temperature oxidation resistance due to the beneficial machanism of Nb doping. The mechanism of Nb doping on improving high temperature oxidation resistance of Ti-Al alloyed coatings includes reducing the defect concentration of TiO2, refining oxide grains and promoting the formation of Al2O3.
For multi-layer plate, it is a difficult problem to increase product yield rate and improve bonding interface quality. A high yield hot-rolled method of multilayered plate was proposed. The raw strips and plate were fixed by argon arc welding. The combined billet was put into a metal box and vacuum pumped, and then heated and rolled by multi passes at the temperature of 1000-1200℃. The 67 layered plate with the thickness of 2.5mm was successfully produced. The interfacial microstructures and diffusion behavior were investigated and analyzed by optical microscopy and scan electronic microscopy. The tensile and shear strength were tested,and the shear fractures were analyzed. The results show that the multilayered plate yield rate is more than 90% by two steps billet combination method and rolling process optimization. The good bonding interface quality is obtained, the shear strength of multilayered plate reaches 241 MPa. Nickel interlayer between 9Cr18 and 1Cr17 can not only prevent the diffusion of carbon, but also improve the microstructure characteristics.
Al-5Ti-1B refiner was successfully prepared by melt reaction method. Through the thermodynamics calculation, the initial reaction temperature was determined. The influence of reaction temperature on microstructure and absorption rate of the alloy was investigated. The phase and microstructure of the alloy were observed by X-ray diffraction, scanning electron microscope and energy dispersive spectrometer. The Al-5Ti-1B refiner was extruded at high temperature to wire with the diameter of 9.5mm, and then the refinement experiment was carried out on pure aluminium. The results indicate that the refiner consists of TiB2, TiAl3 and α-Al, and the microstructure prepared at 850℃ is the optimum and the absorption rate of Ti and B matches the best. The TiAl3 and TiB2 phases distribute homogeneously in the matrix after extrusion. When adding 0.2%(mass fraction) of Al-5Ti-1B refiner, the grain size of pure aluminium reduces from 3.99mm to 0.45mm.
As ultra-high-temperature structural materials, the mechanical properties of eutectic oxide ceramics are closely related with microstructure characteristics. Melt-grown Al2O3/ZrO2/YAG eutectic ceramic was prepared by high temperature fused method. Effect of melt temperature and crystal seed on solidification microstructure evolution was investigated, the structure evolution mechanism was discussed using the classical nucleation mechanism and Jack-hunt mode. Experiment results show the phase composition of solidified samples changes from α-Al2O3/c-ZrO2/YAG to α-Al2O3/c-ZrO2/YAP as the melt temperature increases from 1750℃ to 2000℃. And the solidification microstructure evolves as follows:non-eutectic ceramic Al2O3/ZrO2/YAG, irregular eutectic ceramic Al2O3/ZrO2/YAG, nano-scale regular fibrous pattern eutectic Al2O3/ZrO2/YAG, and complex coarse metastable composite ceramic Al2O3/ZrO2/YAP. Analysis shows that microstructure evolution is resulted from heterogeneous passivation with elevating temperature followed by variations of nucleation undercooling and solidification path. Therefore, choosing reasonable melt temperature and crystal seed are the key rules to control the microstructure of Al2O3/ZrO2/YAG eutectic ceramic.
There is a significant impact of ablation angle on the anti-ablation performance of C/C composites. A self-designed oxygen-kerosene ablation system was employed to study the ablation behavior and mechanism of C/C composites. Typical ablation angle of the experiment was 90°, 60°, 45° respectively, and particle concentration of the gas-solid two-phase ablation flow was 1.37%. The microstructure of post-test samples was observed with the scanning electron microscope(SEM), and the ablation rate of samples was also calculated. The result shows that when the ablation angle is 90°, 60°, 45°,the corresponding mass ablation rate for ablation experiment is 0.146,0.123,0.100g/s respectively. With the decrease of ablation angle, the mass ablation rate of samples is decreased gradually; while for the samples affected by particle erosion, the corresponding mass ablation rate is 0.452,0.455,0.432g/s and the line ablation rate is 1.863,1.323,0.843mm/s. The mass ablation rate is approximately unchanged and the line ablation rate is decreased. The smaller the ablation angle is, the more serious the thermalchemical ablation of gas, and thus increase the erosion area of axial fiber bundle under ablation condition and ablation gradient of radial fiber under ablation/erosion condition.
The temperature and stress field of aluminum alloy piston mould in gravity casting has been simulated with FEM software ProCAST, and makes a prediction on area prone to failure of the mould and the results are consistent with the actual mold failure area. In addition, the influence of different mould preheating temperature on the stress field was investigated, and the result shows that increasing the mould preheating temperature can effectively reduce the thermal stress on the cavity surface of mould during casting, and therefore helps to improve the mould life.
According to the radial distribution characteristics of PAN pre-oxidized fiber, the optical density method which can quantitatively characterize the radial structure of pre-oxidized PAN fiber is established, taking advantage of the light-absorbing of PAN pre-oxidized structure. The results show that when the sample's width is 400 nm and the light intensity is 800 lx, the optical density method characterize the radial distribution characteristics of PAN pre-oxidized fibers the most effectively and accurately. Compared with the traditional skin-core structure characterization method, this method not only expresses the pre-oxidized degree in the same domain under different pre-oxidation processes, but also obtains the radial distribution of pre-oxidized degree. Applying this method to the process research of pre-oxidized PAN fiber, the results show that this method can reveal a correlation between the process and structure, indicating the optical density method as a new method for characterization of PAN pre-oxidized fiber can play an active role in the study of pre-oxidized PAN radial structure.
The experiment and simulation investigations on out-plane compressive characteristics of FRP sandwich panel were conducted. The results show that two deformation stages are elastic deformation and fracture stages in out-plane compressive deformation. The yielding mode deformation as t1/h which is very big,while the buckling mode deformation as t1/h which is very small. The part 2 in the honeycomb core is main bearing part for sandwich panel,and the part 2 is supported by the part 1 and part 3 in the honeycomb core,while the honeycomb core is supported by the panel. So,the cell wall thickness of part 2 has the most significant influence on the compressive strength,and the influence by the cell wall side length of honeycomb core is the secondary,while the influence by the cell wall thickness of part 1 and part 3 in honeycomb core and the thickness of panel is the weakest. When the honeycomb core height is fixed,the compressive strength of FRP sandwich panel gradually increases along with honeycomb core layers increase.
Polypropylene/rubber powders composites with different kinds of rubber powders were foamed by injection molding machine equipped with volume-adjustable cavity. The effect of dispersity of rubber powders and crystallization behavior of composites on the foaming behavior and mechanical properties was investigated. The results show that the addition of rubber powders can improve the cell structure of foamed PP with fine and uniform cell distribution. And cell density and size of PP/PP-MAH/NBR foams are 7.64×106cell/cm3 and 29.78μm respectively, which are the best among these foams. Combining cell structures with mechanical properties, notch impact strength of PP/PP-MAH/CNBR composites increases approximately by 2.2 times while tensile strength is reduced just by 26% compared with those of the pure PP. This indicates that PP/PP-MAH/CNBR composites are ideal foamed materials.
Four different processes of hot isostatic pressing (HIP) combined with rejuvenation heat treatments (RHT) were adopted to reveal the microstructural evolution of creep damaged DZ125 specimens, finally the mechanical properties were evaluated.The results show that both γ' precipitate degeneration and creep cavities for the creep damaged DZ125 superalloy are found after the pre-endurance damage test.However, the carbided compositions from MC type to M23C6 type or M6C type has not been observed for DZ125.In addition, it is found that the HIP temperature play a dominant role in the cavity healing process for the damaged specimens. The concentrically oriented γ' rafting structure and the incipient melting are observed at 1200℃ and 1250℃ respectively.Meanwhile, it is found that the appropriate HIP schedule adopted can effectively avoid the internal recrystallization for the directionally solidified nickel-based superalloy DZ125. The appropriate HIP schedule combined with RHT process can successfully restore the microstructure induced by creep damage and recover the degraded micro-hardness to the original one, in addition improve the creep rupture life.
The microstructure, retained austenite and mechanical property of low-carbon steels with different precursor microstructures were studied by means of intercritical reheating-quenching and partitioning (IQ&P) processes. The results show that the structure of IQ&P-Ⅰ multiphase steel with precursor ferrite + pearlite (F+P) is blocky ferrite, martensite (M). The blocky retained austenite(RA) of IQ&P-Ⅰ multiphase steel exists in the boundary of ferrite and martensite and film-like retained austenite distributes around the lath martensite as the shape of thin slice. The transformation induced plastic effect of IQ&P-Ⅰ multiphase steel with less content of retained austenite is unapparent. The tensile strength of IQ&P-Ⅰ multiphase steel reaches 957 MPa, but the tensile elongation is only 20%, and the production of strength and elongation is 19905.6 MPa·%. The structure of IQ&P-Ⅱ multiphase steel with precursor martensite is needle or lath grey-black ferrite and martensite. The fine needle like martensite is distributed evenly on the ferrite matrix. The film-like retained austenite is only distributed on the ferrite matrix. The content of retained austenite of IQ&P-Ⅱ multiphase steel reaches 13.2% with more obvious TRIP effect and higher stability. The production of strength and elongation of IQ&P-Ⅱ multiphase steel is 21560 MPa·% with good combination of strength and plasticity.
As a typical material of the third-generation semiconductor with wide band gap, high thermal conductivity and high critical breakdown electric field, silicon carbide(SiC) has a huge potential in the applications of photoelectric devices that can work in some extreme conditions, such as in a high temperature or intense radiation environment. Here, the research status of luminescence properties and applications of SiC was summarized. The preparation methods and characteristic luminescence of monocrystal, nanocrystalline and thin film of SiC were presented. Besides, the progress and prospect of SiC luminescence control was also discussed in this paper. Utilizing the emerging technologies, we will be able to modify SiC's properties like luminescence spectrum and efficiency.
The presence of light elements like C, N, O has wide influence on the properties of solar-grade silicon. Since silicon is the dominating raw material of solar cells, the purity of crystalline silicon has significant influence on electrical properties of solar cells. In this paper, the research progress on carbon, nitrogen and oxygen on the presence, distribution, formation mechanism and process control was summarized. An outlook for light elements research in silicon was also proposed, the combination of different purification methods to control and eliminate impurities in silicon is worth paying attention to investigate, and the further research on the behavior of C, N, O in silicon can also improve silicon quality.
Flow softening behavior during hot compression deformation process of near β titanium alloys was reviewed, including the influencing factors, the flow softening mechanism and its analysis methods, the development of the constitutive model based on softening mechanism. The influence of deformation parameters and initial microstructure on flow softening behavior was primarily analyzed. Besides, the contribution of softening mechanisms such as dynamic recovery, dynamic recrystallization and deformation heating to flow softening was discussed. The problems urgently to be solved during hot deformation process regarding to flow softening were proposed, and it is pointed that quantify and physical modeling will be the important directions of near β titanium alloys during hot deformation process with respect to softening phenomenon in the future.
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