- 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 hydrogenated tests of the before-foaming billets were carried out firstly, and then were used to prepare Ti-6Al-4V foams by gas entrapment through isothermal foaming. The porosity was calculated using Archimedes method, and micro-characteristics were observed by OM and SEM. The influence and action mechanism of hydrogen on billets' isothermal foaming process to produce Ti-6Al-4V foams were studied. The results show that hydrogen of mass fraction 0.15% can reduce the billets' optimum isothermal foaming temperature by 60℃,that is, at 890℃, the Ti-6Al-4V foams can be obtained with porosity of up to 32.88%(volume fraction), pore size of 160μm, and dispersed pore distribution. The main mechanism is:Hydrogen, by decreasing(α+β)/β phase transition temperature,improves ductile β phase ratio and can soften the α phase in some degree and reduce the high temperature flow stress of billets, and further decreases the optimum isothermal foaming temperature.
The pyrolytic carbon produced on flexible graphite foil in chemical vapor deposition was observed by scanning electron microscope. The research shows that pyrolytic carbon is not only distributed on the surface of flexible graphite foils with the shape of cells, but also vapor grown carbon fibers are found. The initial carbon fibers have awl-shaped heads. With the growth of carbon fibers, the diameter of the fiber increases layer upon layer with a concentric circle structure. The vapor grown carbon fiber has a hemispherical head when the diameter exceeds 50μm.
In order to reduce the preparation cost of the superhydrophobic surface on titanium substrate and improve its durability, sandblasting and anodic oxidization were used to construct a micro/nanometer scale rough surface on pure Ti substrate, and then the superhydrophobic surface was obtained via further modification by fluorine carbon varnish. The chemical composition, morphology, wettability and environment durability of the superhydrophobic surface were investigated by FTIR, FE-SEM and contact angle measurement respectively. The results show that the structure at micron level is fabricated by sandblasting while the nano-web structure is prepared by anodizing. After modified by fluorine carbon varnish, this micro/nanometer scale rough surface contained masses of fluoride groups and attains superhydrophobicity. The superhydrophobic surface has a static contact angle of 162°±2.3° with the sliding angle of 2.1°±0.2° and shows excellent air and seawater durability.
A series of Co/Ni multilayers with Ta/Pt underlayer were prepared by magnetron sputtering technique. The effect of Pt, Co, Ni thickness and the periodic number on the performance of anomalous Hall effect of Co/Ni multilayers was investigated. The results show that gradually thickened Pt layer leads to an increase in coercivity and lessening Hall resistance and the thickness of Pt is determined as 2nm. The multilayers have strong perpendicular anisotropy due to the thickness of Co and Ni in a certain range and the thickness of Co and Ni is tested as 0.4nm. Finally, through the optimization of the periodic number the best multilayer structure is acquired as Ta(2nm)Pt(2nm)Co(0.4nm)Ni(0.4nm)Co(0.4nm)Pt(1nm) for the rectangularity of its anomalous Hall loop is very good which shows that it has good perpendicular magnetic anisotropy and the total thickness is with in 7nm.
Temperature-reversion deformation of microalloyed steel was simulated by thermal simulator GLEEBLE 3800. The effect of reverting temperature on microstructure transformation and ferrite dynamic recrystallization behavior was studied. OM,SEM and TEM were used to investigate the morphology of experimental steels, and the orientation relationship of microstructure was analyzed by EBSD. And true stress-true strain curves of experimental steel during deformation were analyzed. The results show that ultrafine grains with equivalent diameter of 2μm are obtained by temperature-reverting deformation. Dynamic recovery induced by deformation during temperature-reversion produces subgrain structure. Ultrafine grains are formed by ferrite dynamic recrystallization during deformation at peak temperature. There are two mechanisms of dynamic recrystallization, i.e. grain boundary migration and subgrain rotation growing. The former dominants when the steels are deformed at 700℃ or 750℃, where recrystallization is inadequate and lots of band like ferrite retains. And the two mechanisms work simultaneously at 800℃, which lead to homogeneous equiaxed ultrafine grain structure. The ferrite dynamic recrystallization activation energy Qd is 250.18kJ/mol calculated by linear regression.
The superplastic deformation behavior of Ti-24Al-15Nb-1.5Mo alloy with two different methods of based on maximum m value and constant strain rate was studied over the range of 940-1000℃, 5.5×10-5-1.7×10-3s-1 and different tensile axis direction. The result shows that the maximum superplastic elongation of maximum m value is higher than that of the constant strain rate method, and 1596% and 932% are obtained, respectively, at 980℃, T direction and 960℃, 3.3×10-4s-1, 45° to rolling direction, respectively. The elongated grain of primary microstructure will be transformed to equiaxed grain during superplastic tension and the equiaxed grain size increases with decreasing of strain rate and increasing of deformation temperature. The maximum m value method can obviously reduce the generation of cavities.
The microstructure of the joint interface in linear friction welding was analyzed. Combined with the flash pattern and characteristic,the formation mechanism of the joint was discussed. The results show that during linear friction welding, the friction interface temperature exceeds the β-transus temperature of the base metal, a small amount of viscoplastic metal with high temperature is retained at the interface, and the recrystallization occurs in it. After welding, the weld zone is complete recrystallized structure. The side weld zone of TC11 is mainly composed of acicular structure with random distribution and is single β for that of TC17. The formation mechanism of the welded joints shows that during linear friction welding, the friction interface always exists. During LFW, the viscoplastic metal with high temperature is not mixed and the weld joint is formed through the atoms interdiffusion. Under the combined effect of diffusion and recrystallization, the weld joint is formed.
NiAl/AlBN seal coatings were prepared by air plasma spraying method on the superalloy substrate. The galvanic corrosion behavior of AlBN top coating and NiAl bond coating was investigated in 5%(mass fraction) NaCl solution. The scanning electron microscopy(SEM), polarization curve, and open circuit potential, were used to characterize the morphology and the corrosion behavior of the as-sprayed coating. The average galvanic current density was calculated to evaluate the galvanic corrosion sensitivity of AlBN and NiAl seal coating. The results show that the corrosion potential of AlBN coating of is about 70mV lower than that of NiAl coating. In the process of galvanic corrosion,AlBN seal coating with the lower corrosion potential is served as an anode, the NiAl coating is protected as a cathode. The galvanic current density of NiAl/AlBN coating is 3.5331μA/cm2. After the galvanic corrosion, the corrosion potentials of the anode and cathode are decreased from -808mV to -883mV(SCE) and -740mV to -800mV(SCE) respectively. The galvanic potential is -814mV(SCE). The protection performance of the coating is decreased gradually with the extension of corrosion time.
Four nano-Ti films with different thickness were deposited by direct current magnetron sputtering(DCMS). The mechanical properties and residual stress of the deposited Ti films were studied using nano indentation and electronic film stress distribution tester, surface roughness and surface morphology were analyzed using fractal dimension and the atomic force microscopy(AFM) respectively. The results show that, with the increase of the film thickness, the Ti crystal grain size increases gradually and both the surface roughness and residual stress increase first and then decrease, while the hardness and elastic modulus exhibit the opposite tendency. When the thickness of the deposited films is 600, 2400nm and 3600nm, the residual compressive stress exists; when the film thickness is 1200nm, the residual tensile stress exists, the distribution of residual stress is most uniform, when the residual tensile stress exists in the thin films, but the hardness and elastic modulus are lower. The analysis shows that residual tensile stress results in the decrease of the hardness and elastic modulus in Ti thin films, the residual compressive stress exhibits an opposite trend.
To study the reliability at low temperature, the SnSb4.5CuNi solder and its welded joints were kept in the constant environments of 25, -10, -20 and -60℃ for 565 days, which offered conditions to observe and study the morphology, phase, density and electrical conductivity changes of SnSb4.5CuNi alloy microstructure at different temperatures. The nanoindentation was applied to measure the hardness and elastic modulus of the intermetallic compound(IMC). The tensile strength, shear strength and the low cycle fatigue properties of the welded joints were tested. The results show that under low temperature condition for 565 days the solder is mainly composed of SbSn and β-Sn, the morphology turns to dendritic structure with definite orientation. The density and conductivity of the solder alloy increases with the temperature decreasing. It shows that no tin pest occurs in SnSb4. 5 CuNi solder after low temperature storage,but the SbSn phase precipitation increasing and the dendrite structure lead to decreasing of the tensile strength of the as cast alloys, and increasing of the rick of the alloy brittle fracture. With the decrease of temperature, hardness and elastic modulus of IMC layer at the interface increase and the tensile failure mode of fractures in SnSb4.5CuNi/Cu interface is moving from the solder to the IMC layer, the fracture tends to be more flat, the tensile strength, shear strength are reduced, and shows trend of low temperature brittle fracture.
In order to study low temperature resistance of the finished fabrics by phase change microcapsules, low-cost microcapsules was prepared. Phase change microcapsules were finished by plain, twill, plain knit fabrics and low temperature resistance of the finished fabric were tested and evaluated. Microcapsules containing n-octadecane(MicroC18) with various compositions of urea and melamine-formaldehyde(MUF) copolymer as shells were fabricated through in-situ polymerization and thermal performance of microcapsules was analyzed. The microcapsules were coated to plain, twill, plain knit fabrics' surface in intumescent coating, and the finished fabrics' multiple sets of performance were tested. The results show that the surface of phase change microcapsules is smooth, round, and particle size is about 20.6μm. Encapsulation efficiency of n-octadecane is 89% and latent heat reaches about 200.5J/g. Thermal resistance performances of three kinds of finished fabrics increase by 31%, 25% and 29%, respectively. The low temperature resistance of the plain weave fabric is the best and resistance time of low temperature is about 6min. However, the air permeability slightly reduces with respect to the microcapsules. Warp and weft breaking strength increase by 17% and 11% respectively.
The indentation morphology of ceramic materials caused by the Vickers indentation process was simulated based on the finite element analysis model. Take two kinds of ceramic materials(Si3N4 and ZrO2) for example, the indentation diagonal half-length and the Vickers hardness from finite element simulation and that from the experimental measurement were compared. The results show that the difference between Si3N4 and ZrO2 in indentation diagonal half-length from finite element simulation and experimental measurement is 0.39% and -0.53% respectively, the difference in Vickers hardness is -2.7% and 4.2%. With the friction coefficient between the indenter and the material changes from 0 to 0.5, the difference in indentation diagonal half-length from finite element simulation and experimental measurement is 0.28% and 0.27%, the difference in Vickers hardness is 0.14% and 0.21%. In addition, apply this method to compare the Vickers indentation finite element simulation values of other typical ceramics materials(Al2O3,ZTA,SiC and Silica) with the experimental measurement values, the difference of indentation diagonal half-length is 1.14%, -0.57%, -0.89% and 0.41% respectively, the difference in Vickers hardness is -2.24%, 1.12%, 1.85% and -0.86% respectively. It can be seen that the Vickers indentation morphology of ceramic materials can be derived by the finite element numerical simulation method, thereby this method can solve the problem of indentation measurement data inaccuracies, which caused by unclear indentation in the process of indentation method to measuring the Vickers hardness of ceramic materials. This method provides the technical foundation for further exploration based on the response of instrumented indentation to identify the Vickers hardness and any other mechanical properties of the ceramic materials.
The microstructure, elemental composition and surface morphology of Al-Mn coatings were analyzed by SEM, EDS and XRD after diffusion annealing. Anti-abrasion performance of alloy coating was studied by using dynamic abrasion tester, and then wear mechanism was discussed. The results show that pure aluminum coating is dominated by Fe4Al13 and FeAl phases. Aluminum-manganese alloy coating surface is dominated by phases including MnAl6, Mn3Al10 and Fe4Al13. The anti-abrasion performance of Al-2%(mass fraction, same as below) Mn sample which manganese content close to the eutectic point is the best. The abrasive wear of pure Al and Al-2%Mn sample is dominated mainly by microscopic fracture mechanism(spalling), the abrasive wear of Al-9%Mn and Al-13%Mn sample is mainly caused by repeated plastic deformation(micro-plow).
Three kinds of weft knitting structure fabrics(weft plain, rib, cardigan) based on ultra-high molecular weight polyethylene(UHMWPE) as raw materials were knitted by computerized flat knitting machine. Each kind of fabric was laminated from six layers into composite material plates respectively, which is laid up in(0°, 90°) 3s by VARTM. The bending performance and the influencing factors of the three kinds of fabrics were studied, which were followed by the comparison and analysis of the stress-deflection curve and the failure mode. The results indicate that the bending stress-deflection curve of three kinds of UHMWPE weft knitting structure composites has nonlinear characteristics and the curves are all similar to a parabola; the bending strength of weft plain knitted fabric laminated plate is the best, rib is the second, cardigan is the last. This shows that the technological parameters of different fabric structures have a great influence on the bending performance of composite materials. The bending failure mainly occurs on the resin matrix, and no fracture, tearing occurs on the reinforcement. This also shows that the reinforcing material made by UHMWPE fiber has strong toughness and high strength.
Al-Fe-V-Si heat resistant alloys prepared by rapid solidification exhibit excellent thermal stability which can be ascribed to the obtained second phase particles of fine dispersoids and with low diffusibility. This paper reviewed the development history of Al-Fe-V-Si alloys. The preparation processes, microstructural control and strengthening measures were especially introduced. The problems met in the development of the alloys were analyzed emphatically and the future development should be focused on the optimization of process and the improvement of thermal stability.
Azole-based energetic salts have become one of the hot topics in the field of new energetic materials in recent years, especially concentrated in imidazole, 1,2,3-triazole, 1,2,4-triazole and tetrazole. In this paper, based on the research results at home and abroad in nearly five years, the research on various energetic ionic salts based on azoles was reviewed. In the future, the research emphasis of azole-based energetic salts will be based on the quantitative calculation, and use simple synthesis route to synthesize the new type of high efficiency and secure energetic ionic salts.
It is particularly important to conduct the non-destructive testing on steel pipes used in many important industries under severe and complicated working conditions. Eddy current testing method with many advantages is a common method for detection of steel pipe after adding saturated magnetic device, but at present, the unique effect of pipe magnetic properties is neglected. It is incomplete to consider that steel pipes will become non ferromagnetic pipeline after magnetic saturation, the lack of understanding the mechanism will cause the distortion in quantitative evaluation on defects. The mechanism and method of eddy current testing on steel pipes were presented. Some magnetic properties parameters, such as magnetic flux leakage field and distortional magnetic permittivity near the defect area which can influence the eddy current testing signal were analyzed. It indicates the inner defect detection of steel pipe will cause a chaos of the existing evaluation methods. The current developing tendency of eddy current testing on steel pipes were summarized, which provides a reference for their future development.
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