- 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 flow tracers of material particles are considered to determine the boundary of the stirring zone in friction stir welding based on a fully coupled thermo mechanical model. The real strain tensors and temperature histories are given from the tracer movements to calculate the Zener-Hollomon parameters. The grain sizes can be then predicted by the empirical formation. The width of SZ on the top surface can increase with the increase of the rotation speed. The average grain size in SZ can be increased with the increase of the welding temperature and can be decreased with the increase of the strain rates. Both the temperature and the strain rates can be obviously increased with the increase of the rotating speed. But the effect of the welding temperature is more obvious, the average grain size is increased with the increase of the rotating speed.
A layer of Al2O3 thin films on Ti-6Al-4V was prepared by ultrasonic surface rolling processing (USRP). The microstructure and properties of Al2O3 films on the surface layer of Ti-6Al-4V USRP specimen were analyzed using scanning electron microscope (SEM), X-ray diffraction (XRD), optical interferometer and micro hardness tester. The results show that the Al2O3 film layer with thickness about 7μm can be formed on the surface of metal substrate after adding Al2O3 powder and followed by USRP and there are residual compressive stress and plastic deformation in the base metal at the jointing zone. Compared with the parent material, the surface roughness of USRP treated specimen is reduced by 50% and the surface hardness is increased by 98%. Meanwhile, residual compressive stress field exists in the surface layer of the treated specimen, the maximum compressive value is -687MPa, located in the top surface, and the depth of residual compressive stress is 420μm. Based on the above results, for specimens with the addition of Al2O3 powder and after USRP treated, both the surface hardness is further improved with the addition of Al2O3 in the surface, and the advantages of USRP are maintained.
Submicron titanium diboride (TiB2) powders were prepared on macroscopic quantity via self-propagating high-temperature synthesis route using TiO2, B2O3 and Mg powders as raw materials and NaCl as diluent. Scanning electron microscope,Energy disperse spectroscopy, X-ray diffraction and particle size analysis were used to investigate the effect of NaCl on the resulting samples. The content of Mg and O impurities in the leached TiB2 powders was determined by atomic absorption spectrum. Results show that NaCl addition has an obvious effect on the morphology, average particle size and phase composition of the product. Average particle size of TiB2 powders decreases from 496nm to 268nm with the increase of NaCl content. All the samples before leaching consist of MgO, NaCl, TiB2 and a small amount of Mg3B2O6 phases. After leaching, the first two phases disappear and the main product is TiB2 and slight Mg3B2O6. When NaCl addition (k value) is 0.5, 1.0, 1.5, 2.0mol, the leached product contains less Mg3B2O6 impurity phase, and product purity is over 98%. The addition of NaCl diluent is conductive to reduce the particle size and improve the product purity. Therefore submicron TiB2 powders can be prepared via this approach on a large scale.
TiBCN powder synthesized by boronizing was successfully sintered into the bulk sample by hot pressing. Then the bulk sample was machined by wire-cut EDM with variable processing parameters. By analyzing machined surface quality and observing SEM micro-morphology, the main factors which influence on quality of machined surface cut by wire-cut EDM and material removal mechanism were studied. The results show that it is possible to obtain suitable quality of TiBCN machined surface through wire-cut EDM processing,the minimum roughness Ra of machined surface obtained is 0.4μm; Discharge Current Ip and Pulse Interval ti are the main factors; longer Discharge Duration te is more favorable to increase removal rate, but surface crack are more easily formed if Pulse Interval is too short. The best range of processing parameters of TiBCN bulk sample cut by EDM are Ip =2-6, te=20-22μs and ti=65-75μs. Three types of material removal mechanism are identified, spalling, melting/resolidification and evaporation.
Using CNFs as the substrate, CNFs/RGOn films were prepared by layer-by-layer assembly method. Further, a new supercapacitor (S-RGP) was fabricated by these CPGP thin film electrodes which were got by in-situ polymerization of PANI on CNFs/GG films. The characteristics of CRGP film electrodes, such as absorbance, crystallization feature and configuration were analyzed by XRD, UV-visible spectrophotometry and SEM. The CV curve, GCD and EIS electrochemical characteristics of supercapacitors S-RGP were further tested. The results indicate that the surface of CRGP films was nonuniform, and some active substance kept in the gap between PANI and substrates paper leading to less internal resistance in S-RGP supercapacitor. Electrochemical characteristics measurement shows that the S-RGP supercapacitor has lower ESR, and its capacitance performance cannot be affected by bending because of relative flexibility. S-RGP supercapacitors have weak electrochromic properties, for the PANI film is thick and thus lower opaque by in-situ polymerization process of PANI on CNFs/RGOn films.
In order to improve the mechanical properties of 8YSZ ceramic, the 8YSZ bimodal particle sizes powders were dry pressed and pressureless sintered. The molding process parameters including the molding pressure, pressure holding time and dosage of binder were optimized. The sintering scheme based on orthogonal test was designed. The influence of the sintering process parameters including sintering temperature, heating rate, holding time, sintering method on the sintering properties and mechanical properties of 8YSZ was discussed and their optimization value were obtained. The results show that the green ceramic with the relative density of 54.9% can be obtained by adopting the optimized molding process parameters with the dosage of PVA of 10%(mass fraction), the forming pressure of 10MPa, the pressure holding time of 30s. The 8YSZ ceramic with the relative density of 98.3% and the bending strength of 100.3MPa can be prepared by adopting the optimized sintering process parameters with the sintering temperature of 1500℃, holding time of 4h, heating rate of 5℃/min, sintering methods of naked burning.
Nano-BaTiO3 and Fe(CO)5/BaTiO3 composites were prepared by sol-gel method and physical blending. The phase, morphology and performance of materials were analyzed and characterized by XRD, TEM and PNA. The results show that the prepared samples are square crystalloid BaTiO3 with grain size of about 60nm and the uniformly dispersed Fe(CO)5/BaTiO3 composites. The microwave absorption ability of the Fe(CO)5/BaTiO3 composites is greatly improved in 0-6GHz, compared with pure iron carbonyl. When the BaTiO3 contents is 4%, it has the best wave-absorbing property, of which the maximum absorption can reach -22.9dB and superior to the -10dB bandwidth of 2.196GHz.
The curing kinetics during vulcanization of polysulfide sealant was investigated using both Differential Scanning Calorimetric method and viscometric method. The heat of curing reaction during vulcanization was measured over the temperature range of 20-40℃ by the non-isothermal and isothermal DSC, the degree of cure and the rate of cure were determined using the data generated by DSC. The activation energy, reaction rate constant and reaction order with on the temperature dependence were obtained by nonlinear fitting method, and the curing kinetics of polysulfide sealant was described subsequently by a modified Kamal kinetic model. Predictions of the rate of cure and the degree of cure by the modified Kamal model agreed with the experimental data. The results indicate the autocatalytic effect in preliminary stage of curing of polysulfide sealant (up to the degree of cure α<0.4), and the diffusion-control effect in later stage. The viscosity was measured as a function of time over the temperature range of 20-30℃, an empirical model correlated the viscosity with temperature and the degree of cure was obtained, predictions of the viscosity change by the empirical model agreed with the experimental data up to the degree of cure α<0.4.
The influencing factors of corrosion processing rate and surface quality of TC1 titanium alloy were investigated. The mechanical properties of TC1 titanium alloy after corrosion processing were tested. Processing rate increases with the increasing hydrofluoric acid concentration; When nitric acid concentration is lower, corrosion dissolution dominates, when it is further increased, passivation plays the main role, when the volume ratio of nitric acid to hydrofluoric acid is two, the processing rate reaches the maximum value; corrosion processing rate exhibits linear relationship with the temperature, during corrosion processing, the temperature is controlled in the range of 28-30℃. Combined surfactants can lower the interface tension; their synergistic effect can improve the filleted corner quality of the transition zone, surface finish and corrosion uniformity. Corrosion processing has little effect on tensile property of TC1 titanium alloy. The fatigue property after corrosion processing is superior to that after mechanical processing, fatigue cracks initiate from the root zone of R filleted corner of the processed surface.
In order to improve the strength of silicon sol shell for investment casting process, short fibers of aluminum silicate were mixed into the slurries. The flexural strength of green shell, fired strength and self-loaded deformation at elevated temperature were investigated and the fracture surface of shell samples were observed by SEM. The results show that as content of aluminum silicate fibers increases from 0.2% to 1.0%(mass fraction, same as below), the green strength of shell specimens is increased and the self-loaded deformation at elevated temperature is decreased. The shell specimen reinforced with 1.0% fibers addition reaches the highest green strength, an increase of 47% than the shell specimen unreinforced with fibers, and the self-loaded deformation at elevated temperature has a decrease of about 50%. The fired strength of shell sample with the content of 0.2%-1.0% aluminum silicate fiber is at least increased 39%. It is found by SEM that the failure of the fiber-reinforced shell specimens at the applied load is resulted by breakdown of silicon sol films and pulling-out, fracturing and debonding of fibers in the shell.
Continuous cooling transformation (CCT) behavior of low carbon steel Q345R was investigated using a Gleeble-3500 thermo-mechanical simulator. A series of thermo-mechanical control process (TMCP) experiments were carried out by a two-roll reversing rolling mill with accelerated cooling system. Stainless steel(316)/low carbon steel(Q345R) clad plate was developed. The reasonable process is: rolling at the austenite recrystallization zone, and finish rolling at 1000-1050℃ with total reduction rate 75% followed by accelerated cooling of 0.2-7℃/s to below 450℃ and then air cooling, as the increasing of cooling speed, the microstructure of Q345R steel transforms from ferrite(F) plus pearlite (P) to ferrite(F) plus bainite(B), yield strength is 330-430MPa, tensile strength is 535-595MPa, average Charpy V Notch (CVN) energy at 0℃ higher than 50J, the interface bonding strength of the composite plate is greater than 350MPa, and the bending performance is qualified.
Dies with different bending fillet were employed to test the bending properties of TNW700 titanium alloy. The hot bending test of TNW700 titanium alloy sheet under conditions of 700-850℃ and 1/4-6t were studied. The results show that the hot bending process window of specimen along the transverse direction is wider than along the rolling direction. The minimum bending radius are 1.5t and 1/4t under deformation temperature of 700℃ and 850℃ respectively along the transverse deformation direction, and the minimum bending radius are 3t and 1t under deformation temperature of 700℃ and 850℃ respectively along the rolling deformation direction. Springback radius and springback angle decrease with the increase of temperature and bending radius. Springback direction depends on the placement sequence of the male die and female die.
Fe-Cr-B-C-Nb cladding layer containing submicron NbC were prepared by PTA on Q235 steel, a series of alloys containing superfine NbC, eutectic boride, NbC + eutectic boride, NbC+primary Fe2B hardphase were designed respectively to study the effect of hardphase of different size on microstructure and properties of Fe-Cr-B-C-Nb cladding layer, and compared with the Fe-Cr-C hardfacing alloy in market. The results show that the fine hardphase can conduce to improve the impact resistance and the wear resistance of the alloy containing submicron NbC and eutectic boride is 4 times more than that of Fe-Cr-C, and the impact resistance is better than that of Fe-Cr-C.
The specimens of the reactor pressure vessel (RPV) model steels were tempered at 660℃ after water quenching from 890℃, aging treatment was then conducted at 400℃ for 13000h. The Cu-rich precipitates were characterized by high resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) in order to study the transition process from metastable to stable structure. The average size of the nano Cu-rich precipitates is about 20nm, besides the metastable 9R,3R and the stable fcc crystal structures, it is observed that three different crystal structures distributed in five different regions existing in the same nano Cu-rich precipitate, including one 9R, two of fcc and two of 3R crystal structures. The boundaries formed by 9R structure with its two adjacent fcc structures have specific crystal orientations, their interfaces are semi-coherent. They are evolved from non-twin 9R structure. The two 3R structures are twins, and evolved from twin 9R structure. The above phenomena reflect the complex processes from metastable to stable structure.
The difference of the creep curves of P92 steel was comparatively analyzed by theta projection method and composite model. The results show that both the creep-time curves of P92 steel with two methods have a higher accuracy. However, when describing the creep rate-time curves, the theta projection method exhibits big error, while, the composite model can show more accurate results; When extrapolating creep rate, the theta projection method has large deflection, while, the composite model can predict more near the actual trend. When extrapolating creep rupture life based on creep curves,the results show that the fracture strain between 5% and 50% has little effect on the life prediction. The values of endurance life extrapolated by the two models are approximately the same.
The microstructure evolution of the coarse grain heat affected zone (CG-HAZ) of 800MPa grade high strength low alloy (HSLA) steel was investigated using thermal simulated method by L78 RITA phase change thermal dilatometer. The experimental steel was heated twice to simulate two welding-pass thermal cycles. The corresponding welding heat input was approximately 20kJ/cm. A time temperature austenization (TTA) curve was established for the experimental steel, and the microstructure, hardness and dilatational curve were analyzed. The results show that, for the CG-HAZ of the first pass thermal cycle, lath martensite and bainite are obtained, and the hardness is 318HV; When Tp2 is 1000℃, complete recrystallization occurs in the structure after the first cycle, fine bainite was obtained, and the hardness is decreased; When Tp2 is 900℃, partial recrystallization occurs, and the hardness is the lowest 239HV; When Tp2 is 800℃, some necklace-like M-A constituents are obtained at the grain boundary and intergranular phase boundary; When Tp2 is lower than Ac1, tempering occurs, the M-A constituents are resolved and carbides are precipitated. The structure heredity is not found in HAZ of this experimental steel, hence, in order to accurately determine the microstructure transformation type , analysis should be carried out on the microstructure transformation process of HAZ using TTA curve.
The composite paraffin was obtained by mixing solid and liquid paraffin. DSC characteristic results show the melting point and the enthalpy of composite paraffin is increasing with the increase of solid paraffin content. The melting point of composite paraffin which prepared with solid/liquid mass ratio 3 : 7 is 28.3℃, the latent heat of phase change is 100kJ/kg. Microencapsulated paraffin/polyurea phase change materials were prepared through an interfacial polymerization method using composite paraffin with solid/liquid mass ratio 3 : 7 as core materials, 2,4 toluene diisocyanate (TDI) and ethylenediamine as monomers, OP-10 as an emulsifier. It was investigated the effect of the particle size of microcapsules on the emulsification stirring speed and polymerization reaction temperature by SEM, FTIR and TGA and DSC methods were used to characterize the microcapsules. The results show that paraffin/polyurea microencapsules prepared with the emulsification stirring speed of 2000r/min and the polymerization reaction temperature of 70℃ are spherical and smooth surface and the average particle size of 3-4 μ m. Its melting point of 28.1℃ is similar with that of composite paraffin 28.3℃, the enthalpy of 58.4kJ/kg is less than that of composite paraffin 100.04kJ/kg, and the encapsulation efficiency is 87.5%.
Cracks, discovered on the edge of 7003 Al-alloy cabinet of the high speed train was analyzed by means of optical microscope, scanning electric microscope (SEM) and electronic differential system (EDS). It is found that cracks with many branches propagated along the grain boundaries, the fracture is sugar candy pattern, and capillary and chicken claw cracks are on the grain plane. The crack is stress corrosion crack (SCC) induced by the hydrogen embrittlement. The SCC sensitivity of 7003 Al-alloy was evaluated by slow strain rate test (SSRT) and constant displacement test. The result of SSRT shows that the sensitivity index of 7003 Al-alloy is 0.2. Its fracture is mixture fracture of transgranular and intergranular in 3.5% NaCl solution. There are many second cracks,cleavage steps and river patterns on the transgranular fracture. The result of constant displacement test indicates that the cracks propagate to 700μm after corrosion for 28 days, and tongue protrusions and grooves occur in the stress corrosion zone. The 7003 Al-alloy is obviously sensitive to the SCC.
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