- 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 non-isothermal oxidation characteristic and the microstructure of the oxidation products were systematically studied by TGA/DSC test methods associated with XRD,SEM and EDS analysis methods. Further, the influence mechanism of vanadium and chromium elements on the non-isothermal oxidation resistance of Ti-V-Cr type fireproof titanium alloys was discussed. The results show that, from room temperature to 1723K, the non-isothermal oxidation resistance obviously decreases with increasing of vanadium content. Simultaneously, the oxidation film thickness increases from 168μm to 370μm, and the oxidation film thickness of Ti-35V alloys is about 1.45 times that of Ti-25V alloys; whereas the non-isothermal oxidation resistance of Ti-V-Cr type fireproof titanium alloys gradually increases with increasing of vanadium content and the differences among these alloys are quite small. The oxidation film thickness changes from 110μm to 85μm, and the thickness of Ti-35V-15Cr decreases about 15.5% than that of Ti-25V-15Cr alloy. The non-isothermal oxidation resistance of Ti-V-Cr alloys is much higher than that of Ti-V alloys, and the main reasons are that the liquid V2O5 formed during non-isothermal oxidation greatly releases the inner stress of oxidation film, which improves the combination ability between oxidation film and alloy matrix and also prevent together with Cr2O3 and TiO2 the massive diffusion of oxygen to the alloy matrix. The non-isothermal oxidation resistance characteristic of Ti-V-Cr fireproof titanium alloys is described quantitatively by non-isothermal oxide mass gain curve and oxidation film thickness, which are consistent with the results of friction ignition test. Therefore, the fireproof property of titanium alloy can be predicted.
The effect of deformation temperature on the mechanical properties and deformation mechanism of Fe-20Mn-3Cu-1.3C twinning induced plasticity (TWIP) steel when deformed at -100-200℃ was analysed by temperature controlled tensile tests.The microstructure of tensile samples was observed and analysed, and then the effect between stacking fault energy of TWIP steels and deformation temperature was calculated by thermodynamic model. The results show that with the deformation temperature increasing from -100℃ to 200℃, the stacking fault energy of this steel gradually increases, but the volume fraction of twins gradually decreases. The tensile strength and yield strength will gradually decline, while the elongation of this steel firstly increases, then decreases. Furthermore, in this process, the plastic strain mechanism is transformed from twinning to slipping. The stacking fault energy γSFE is calculated by the equation γSFE=26.73+9.38×10-2T+4.22×10-4T2-4.47×10-7T3. As compared with slipping, the twinning can obtain higher strain hardening rate, which leads to high strength and plasticity of the TWIP steel.
4343/3003/4343 aluminum alloy clad ingots were prepared by liquid-solid casting. The microstructure, elements distribution and interface bonding strength of the clad ingots were investigated. The interface bonding mechanism of the clad ingots was analyzed. The results show that when the pouring temperature of 4343 aluminum alloy is 725-750℃, the metallurgical bonding of clad ingots is good, and with clear and flat interface. The metallurgical bonding interface of clad ingots consists of Al-Si solid solution layer and diffusion layer of Si and Mn. The thickness of Al-Si solid solution layer is uniform. The diffusion distances of Mn and Si are 10μm and 32μm, respectively.The bonding strength of clad ingots is higher than the ultimate tensile strength of 3003 aluminum alloy. The interface bonding mechanism of liquid-solid 4343/3003/4343 aluminum alloy clad ingot is as follows:firstly, the 4343 aluminum alloy melt is rapidly solidified on the surface of 3003 aluminum alloy ingot to form the Al-Si solid solution layer, then the Si in the Al-Si solid solution layer and the Mn in the 3003 aluminum alloy interdiffused to form the clad ingot with good metallurgical bonding interface.
Cu doped anatase TiO2 films were prepared through direct oxidation of Cu-Ti alloys with hydrogen peroxide solutions. The morphologies, composition and phase structure of the films were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Results show that the films are formed by dissolution-precipitation mechanism. Cu doped amorphous TiO2 films firstly deposit on the surface of Cu-Ti alloys, then Cu doped anatase TiO2 films are obtained by the followed heat treatment at 450℃ for 1h in air. Addition of polycarbonate or polyvinyl acetate in hydrogen peroxide solution is needed to promote the deposition of amorphous TiO2 and the formation of Cu doped TiO2 films. Degradation tests on rhodamine B reveal an excellent photocatalytic property of the films. 31.7% rhodamine B (20mg/L) can be degraded after 4h of illumination under a 12W UV lamp with the prepared film on the surface of Cu30Ti70 alloy.
The flow stress behavior and the microstructure evolution of as-cast 7A85 aluminum alloy were studied by the hot compression test, which was performed on Gleeble-3500 thermal simulation machine at 300-450℃ and strain rate 0.01-10s-1. The results show that the true stress is rising to peak stress rapidly in the initial deformation period, then the flow stress decreases due to dynamic recovery and dynamic recrystallization, finally the flow stress tends to be stable. The peak flow stress increases with decreasing deformation temperature and increasing strain rate. It can be described by Zener-Hollomon parameter. The constitutive equation of 7A85 aluminum alloy is obtained by linear regression, and the hot deformation activation energy Q is 253.68kJ/mol. With the decreasing of lnZ, the grains are elongated radially, the sub-grains grow up, the dislocation density and the quantity of second phase particles decrease. The softening mechanism is mainly dynamic recrystallization.
Compact ceramic coatings were fabricated on the SiCp/A356 composite surface by micro-arc oxidation(MAO). The growing curve and microhardness of coatings were determined. The morphology and phase composition of ceramic coatings were analyzed by scanning electron microscopy and X-ray diffraction respectively. The tribological properties and corrosion resistance of the coatings were investigated. The results show that the SiCp hinders the coating growth, but the integrity of coating is not disrupted. At initial stage of MAO, outward-growth dominates the growth behavior of the coatings in the total thickness. Starting from 30min, the total thickness of the coatings increases gently and the total growth rate declines sharply; at this stage, the outward growth gradually slows down, and the inward growth maintains persistent enhancement. The oxide coating is mainly composed of γ-Al2O3 at the initial reaction stage and composed of γ-Al2O3,α-Al2O3 and mullite after 20min. The ceramic coating shows good wear and excellent corrosion resistance.
To study the effect of temperature and strain rate on the dynamic mechanical properties and microstructure evolution of 2519A aluminum alloy, the dynamic mechanical properties of 2519A aluminum alloy were measured by dynamic impact compression tests using the split Hopkinson pressure bar at different temperatures (-90-350℃) and different strain rates. The dynamic mechanical properties were analyzed, and the microstructure after impact was also investigated by metallographic microscope and transmission electron microscopy (TEM). The results show that the impact flow stress decreases rapidly at 250-350℃. The deformation band is the main deformation character, and obvious dynamic recovery and dynamic recrystallization are generated, so the dislocation density is low. Adiabatic shear band (ASB) occurs when the alloy deforms after dynamic impact at 20-150℃. The strain rate strengthening effect changes at room temperature with strain rate 8200s-1. When temperature drops to -90℃, some short and discontinuous microcracks appear within the ASBs, and some long strip particles are broken by brittle fracture.
In order to explore the effect of short-term aging on crumb rubber (CR) powder modified asphalt, the rheological parameter of before and after aging CR modified asphalt by rolling thin film oven test(RTFOT) was obtained through dynamic shear rheological(DSR) and repeated creep recovery test(RCRT). The change in the internal structure of asphalt was observed from microscopic perspective by SEM and the effect of asphalt rheological properties was analysed. Results show that the component of asphalt changes after aging and asphalt shows hardening phenomenon.The effect of aging on the deformation recovery capability and deformation of CR modified asphalt decreases as the temperature increases. The influence of aging and temperature on the CR modified asphalt is greater than that of the stress;with the temperature increasing, the effect of aging on the rheological property of CR modified asphalt is weakened.
SiCp/A356 composites were brazed with seven kinds of Al-20Cu-9.6Si-xEr filler metals in vacuum.Microstructure of the brazed joints was observed and analyzed by SEM and EDS. Shear strength was evaluated by shear test, and microstructure of the fracture was observed.The results show that the shear strength of the brazed joints is significantly improved when Er is added.When the content of Er is 0%(mass fraction) the aggregation of SiC is very serious, and the shear strength is 43.5MPa. There is no aggregation of SiC in brazing seam boundary, and shear strength reaches the maximum 68.6MPa when the content of Er is 0.05%. The aggregation of SiC is weakened and the shear strength is between 45.3-50.5MPa when the content of Er is between 0.1%-0.4%. The SiC particles are distributed inside the brazing seam, and the joint strength significantly increases to 62.2MPa when the addition amount of Er is 0.5%.
A superhydrophobic magnesium alloy surface with a contact angle of 154° and a sliding angle of 6° was successfully prepared by hydrochloric acid etching, ammonia immersing, and long hydrophobic chains grafting. The surface wettability, microstructure and chemical composition, anti-adhesion behavior, and corrosion resistance were investigated by means of contact angle measurement, SEM observation, FT-IR analysis, anti-adhesion and electrochemical experiments respectively. Results show that the micro-and nano-scale multiple structure presents at the magnesium alloy surface after hydrochloric acid etching and ammonia immersing, while the long hydrophobic alkyl chains are grafted onto the micro-and nano-scale surface with chemical bonds upon stearic acid modification. Just based on the peculiar surface microstructure and chemical composition, the resulting superhydrophobic magnesium alloy surface possesses the excellent anti-adhesion behavior and corrosion resistance.
The short nylon fibers were dispersed in the matrix of silica sol by using ultrasonic vibration and adding the hydroxypropyl methyl cellulose (HPMC); the effect of different ultrasonic power and different addition amount of HPMC dispersants on dispersion of fibers in silica sol was investigated. The digital photos of fibers in silica sol were observed, the movement viscosity of slurry was tested, the variation coefficient and discrepancy ratio of the mass of fibers were applied to evaluate the dispersion of fibers, and uniformity of the distribution of fibers was observed by using SEM. The results indicate that the synergy of the ultrasonic vibration and mechanical stirring is helpful for improving the dispersion of fibers, when ultrasonic power is 900W, the dispersion of the fibers is more even. Adding the HPMC dispersant is efficient to improve the dispersion of the fibers, in the range of 0.2% (mass fraction)-0.3% adding of HPMC, the dispersion of the fibers is the best. However, when adding 0.4% HPMC, the dispersion of fibers is hindered.
By using the method of preplaced powder, laser cladding of Ni-based SiC ceramics coating on Q235 steel substrate was studied. The dry friction and wear experiments of different material coatings were carried out by reciprocating friction wear tester. The microstructure and wear morphology of cladding layers were observed and analyzed using metalloscope (OM), scanning electron microscope (SEM) respectively. The results show that in the condition of dry sliding friction under heavy load, wear resistance of Ni-based SiC composite coatings is significantly improved. When the composite powder with 25% (mass fraction) SiC,wear resistance of cladding coatings is the best. Wear mechanism of the cladding layer is abrasive wear, accompanied by adhesive wear characteristics, and with the increase of SiC content, adhesive wear characteristics become more apparent.
Tungsten carbide particles reinforced iron matrix composites were successfully prepared by the normal pressure sintering technology. The effects of tungsten carbide particles size on the microstructure, interface and mechanical properties of composites were investigated. The results show that the melting degree of the tungsten carbide particles increases with the decrease of particles size. W2C is melted more than WC in the tungsten carbide particles. The main product of the interface reaction is Fe3W3C. The volume fraction of Fe3W3C increases with the decrease of particles size, while the interface is changed from continuous to discontinuous and even disappeared with the decrease of particles size. The hardness and compressive strength of composites increase with the increasing of particles size. When the particles size is 380-550μm, the composites consist of Fe3W3C and tungsten carbide particles in volume proportion of 1:1, the interface is continuous and the composites have good mechanical properties.
A free-standing TiAl based alloy thin sheet with thickness of 0.3mm was prepared by single source evaporation technology with high-power electron beam-physical vapour deposition (EB-PVD) system, and then the as-deposited samples were annealed in vacuum at 650-950℃. The effect of annealing on the microstructure and phase constitution of TiAl based alloy was studied with X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that alternation of Ti-rich area and Al-rich area is presented along the cross section of the sheet due to deviation of saturated vapour pressure between Ti and Al element, and the as-deposited sample is composed of α2-Ti3Al,γ-TiAl and τ-TiAl2 phases. After annealed at 650-950℃ for 24h, obvious interfacial reduction and grain coarsening appear with the diffusion of Al into Ti, leading to ordered phases reduce. The breakdown of layered structure is induced by pore formation, grain growth and grain boundary grooving.
The stress controlled fretting fatigue behavior of 35CrMoA steel under the diamond loading condition was investigated at the contact stress of 150MPa by MTS809 axial/torsional test system and SEM. The results indicate that, with the increase of equivalent stress amplitude, the extent of softening and hardening becomes pronounced; the area of shear stress-strain hysteresis loop increases; the area of crack initiation decreases, the proportion of final fracture in fracture surface region increases, the degree of tearing becomes more serious. The plasticity is exhausted and easy to form crack initiation as a result of fretting wear.
Monodisperse ZnFe2O4 nanoparticles were synthesized by polyol process using triethylene glycol as solvent and iron acetylacetonate and zinc acetylacetonate as precursors. The structure, morphology and magnetic properties of resultant particles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometry(VSM). The results show that as-synthesized nanoparticles have uniform size and good dispersibility. The average size of the nanoparticles is 5.6nm. The monodisperse ZnFe2O4 nanoparticles show a typical magnetic hysteresis loop at room temperature (300K), which indicates that the sample has ferrimagnetic behavior with less residual magnetism, coercive force of 9355A/m at room temperature. The saturation magnetization of the nanoparticles at 300K is determined to be 18.10A·m2/kg. The temperature rise of the suspension of 50mg and 100mg samples in 1mL water can reach up to 22℃ and 30℃under magnetic field respectively, revealing sufficient magnet-heating ability.
Electrochemical potentiodynamic reactivation (EPR), potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS) methods were applied to investigate the intergranular corrosion and the pitting corrosion behaviors of 2507 duplex stainless steel (SAF2507), and the composition of the passive film formed on the corrosive surface of SAF2507 was studied by using the X-ray photoelectron spectrometer (XPS) analysis. The results show that the reactivation rate (Ra) of SAF2507 is 0.68%, which exhibits good intergranular corrosion resistance. The results of potentiodynamic polarization curve, and EIS show that the surface of SAF2507 can engender passivation phenomenon after polarization, the passivation range is -0.5-0.6V, and the charge transfer resistance is 1.389×104Ω·cm2, which shows better pitting corrosion resistance. XPS demonstrates that the composition of the passive film in 5g/L NaClO solution is mainly composed of oxides and hydrogen oxygen compounds of Cr and Fe. Meanwhile, the corrosion mechanism of SAF2507 was further explored.
Polyurethane (PU)/bronze-Sm2O3 composite coatings were prepared through a simple and convenient process by using bronze-Sm2O3 as the pigments and PU as the adhesives, respectively. The infrared emissivity, near-infrared absorption property, and mechanical properties of as-prepared coatings were systematically investigated. The results indicate that the existence of Sm2O3 can obviously decrease the near-infrared light reflectivities at 1.06μm and 1.54μm, the existence of bronze powders can effectively reduce the infrared emissivity at the wavelength of 8-14μm. By adjusting the mass ratio of bronze to Sm2O3, the infrared emissivity at the wavelength of 8-14μm can be tuned from 0.422 to 0.782, and the reflectivities at 1.06μm and 1.54μm can be tuned from 46.8% to 65.0% and 49.3% to 70.7%, respectively. In addition, the coatings have good mechanical properties, the adhesion and impact strength of the coatings with different mass ratios of bronze to Sm2O3 can reach grade 1 and 50kg·cm, respectively.
The electronic and structural properties of Cu2O photocatalyst were outlined. Progress of metal/nonmetal ions modification and semiconductor coupled modification (including MxOy/Cu2O and MxSy/Cu2O) was mainly discussed. Moreover, research status of the stability of Cu2O photocatalyst was analyzed. Future research of Cu2O modification was outlooked. The aspects of preparation technique, characterization and second pollution are considered to be started with, and study on modification mechanism and performance evaluation to be focused on.
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