- 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 temperature field of FeCrNiCu alloy forming layers of continuous wave(CW) and pulsed laser remanufacture was analyzed using the non-contact infrared thermometer.The general rule of temperature field distribution of molten pool and heat-affected zone of the two modes was obtained. The pulsed laser process superiority in heat input, forming deformation control and reducing the temperature in molten pool and heat-affected zone was vilidated. The results show that during pulsed laser forming the peak temperature in the heat-affected zone is 730.4-810.5℃, the peak temperature in the molten pool is 998.7-1383.4℃, which are all obviously lower than the same process of the CW mode; the temperature-rise rate and cooling rate of pulsed laser are higher, which is helpful to the forming of fine grain structures and good mechanical performance; the forming experiment also further verifies more narrow heat-affected zone in pulsed laser process.
The SiO2/PSN core-shell microspheres were prepared via an emulsion reaction combined with the polymer-derived ceramics (PDCs) method using polysilazane (PSN) in situ polymerization on the surface of SiO2 modified by silane coupling agents MPS, followed by pyrolysis process to obtain SiO2/SiCN core-shell ceramic microspheres. The effects of raw mass ratio, curing time and pyrolysis temperature on the formation and the morphology of core-shell microspheres were studied. The morphology, chemical composition and phase transformation were characterized by SEM, EDS, TEM, FT-IR and XRD. The results show that after reaction for 4h at 200℃, SiO2 completely coated PSN forms a core-shell microsphere with rough surface when the mass ratio of SiO2 and PSN is 1:4; when pyrolysis temperature is at 800-1200℃, amorphous SiO2/SiCN core-shell ceramic microspheres are prepared; at 1400℃, the amorphous phase partially crystallizes to produce SiO2, SiC and Si3N4 phase.
The Ce-V conversion coating on magnesium alloy was modified by stearic acid (SA). Scanning electronic microscope (SEM), contact angle measurement, energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectrometer (FTIR) were adopted to study the microstructure, surface wettability, and chemical composition of the modified coating. Self-cleaning behavior and corrosion resistance of the coating were investigated by anti-adhesion and electrochemical experiments, respectively. The results show that the SA modification treatment not only repairs the cracks of the conversion coating, but also renders a superhydrophobic surface by grafting the long alkyl chains onto the rough Ce-V conversion coating. After 8h of treatment at room temperature, the modified coating surface with a contact angle of 154.6° exhibits good self-cleaning property. The modified coating increases the corrosion resistance (Rcoat) by 25 times and decreases the corrosion current density (icorr) by 2 orders of magnitude compared to the Ce-V conversion coating. The modified coating significantly improves corrosion resistance.
The stress corrosion cracking (SCC) susceptibility of 7A04 high strength aluminum alloy in 3.5% (mass fraction) NaCl solution and the Ce3+ inhibition of SCC were investigated by slow stress rate test(SSRT), using constant current polarization, electrochemical noise (ECN) and electrochemical impedance spectroscopy (EIS) techniques. The inhibition mechanism of Ce3+ ions on the initiation and propagation of cracking was also analyzed. The results indicate that both anodic and cathodic galvanostatic polarizations can accelerate the SCC of 7A04, the former increases anodic dissolution but the latter accelerates hydrogen embrittlement of crack tip. SCC susceptibility of 7A04 can be reduced effectively by the addition of cerium ions, the fracture time is delayed and slowed down, but only during the initiation other than the propagation stage of cracking. Ce3+ ions can restrain the initiation of metastable pitting on the surface of 7A04 specimen, which therefore increase the induction time of the cracking since that the micro pits are usually the source of cracking.However, once the crack begins to propagate or the specimen is notched, the addition of cerium ions can rarely inhibit the cracking process. This is possibly attributed to that the radius of Ce3+ ion is too large to diffuse into the crack tip or it is hard to form protective CeO2 layer, Ce3+ ion therefore fails to rehabilitate the active alloy at the crack tip and further reduce the SCC developing rate of 7A04. SEM also indicates that the crack initiation of smooth 7A04 specimens is mainly induced by metastable or stable pits.
B10 Cu-Ni alloy has good corrosion resistance against seawater. Natural seawater from Xiamen, was used to study the seawater corrosion behaviour of B10 Cu-Ni alloy, H2O2 was added as corrosion accelerator. The whole seawater immersion corrosion simulation experiments were conducted in laboratory. Geometric measurement and electrochemical impedance spectroscopy (EIS) technique were used to obtain the tendency of corrosion rate versus corrosion time. The growth and damage of the oxidation film on the surface of the alloy of 1cm2 working area were characterized by the impedance spectra features with different corrosion time.Scanning electron microscope(SEM), energy spectrum analysis(EDX), X-ray photoelectron spectroscopy(XPS) and raman spectrum were used to analyse the constitution of corrosion product and the corrosion types. The results show that the instantaneous corrosion rate exhibits decreasing first then increasing due to the state of oxidation film. The corrosion products consist of Cu2(OH)3Cl and Cu2O. And the corrosion of B10 Cu-Ni alloy starts with pitting corrosion, then gradually goes through the evolution process of intergranular corrosion to exfoliation.
The electrochemical behavior of carbon steel pipeline in simulated solutions containing different concentrations of inhibitor saturated with O2/CO2 was studied by rotating disk electrode (RDE). After comparison with the results tested in CO2 environment, the effect of O2 on the inhibition performance of inhibitor A on the carbon steel was obtained.Potentiodynamic polarization was used to test the inhibition efficiency of inhibitor A. The EIS was used to study the adsorption behavior of the inhibitor and the corrosion process. The data calculated from the EIS fitting were used to study the adsorption behavior of the inhibitor. The morphology and the compositions of the corrosion product were observed by using SEM and XRD respectively. The results indicate that oxygen weakens the adsorption capacity of the inhibitor, which results in less adsorption film coverage ratio of the inhibitor on the steel surface and decreases corrosion inhibition efficiency. The corrosion products are loose and porous Fe2O3 and FeO(OH) in the environment of O2 and CO2 coexisting. The effective acting time of the inhibitor is shortened owing to the increasing corrosion rate and fast growth of the corrosion products in O2/CO2 environment, which results in more weakened adsorption capacity of the inhibitor.
Based on the basic principle of biomineralization, hydroxyapatite fiber (HAF) with high crystallinity was fabricated via a hydrothermal route with Ca(NO3)2·4H2O and (NH4)2HPO4 as the resources, respectively. Effects of the addition of acidic amino acid L-glutamic acid (Glu), neutral amino acid L-phenylalanine (Phe) and basic amino acid L-lysine (Lys) on the phase composition and morphology of the obtained products were laid special emphasis on. The results show that the products obtained by using the three amino acids are all hydroxyapatite (HA) phase with minor CaCO3 in some samples. Meanwhile, all of the amino acids inhibit the growth of the fibers. Spherical morphology exists when Glu is added, the homogeneity of the fibers deteriorates with the addition of Lys. However, rod-like fibers with good uniformity can be obtained with the addition of Phe.
The dynamic viscoelastic behavior and phase morphology of high impact polystyrene (HIPS)/high density polyethylene (HDPE) blends were investigated by dynamic rheological test and scanning electron microscopy (SEM). The compatibilizing effect of 1%(mass fraction, same as below) micron-CaCO3 and nano-CaCO3 on HIPS/HDPE(30/70) immiscible blend was compared. The results indicate that the complex viscosity and storage modulus of HIPS/HDPE blends at low frequencies show positive deviation from the mixing rule when HDPE is less than 30%, while negative deviation is observed when HDPE is more than 30%. The former is related to the interaction between HDPE and PB particles and the latter is attributed to the poor interfacial interaction between HDPE matrix and PS particles. When HIPS is the matrix phase, HDPE particles display broad size distribution. When HDPE acts as a matrix phase, PS dispersed phase exhibits bimodal size distribution corresponding to the presence of two different types of PS dispersed particles. 1% nano-CaCO3 has a certain compatibilizing effect on HIPS/HDPE(30/70) immiscible blend, which is mainly located at HIPS/HDPE interface and in the HDPE matrix, while micron-CaCO3 acts as viscosifier rather than compatibilizer, which is confined in the HDPE matrix.
In the temperature range of 300-800℃, 40%-50% of the mass lost during the processing of polyacrylonitrile based carbon fiber (PANCF). Understanding the degradation behavior will be valuable in understanding the formation mechanism of pseudo-graphite structure, and providing theoretic basis for producing high performance carbon fiber and increasing the carbonization yield. The simulation of the degradation progress was carried out on the thermogravimetric analyzer (TGA), the results show that there are two degradation steps for PAN fiber stabilized in air, and controlled by cyclization coefficient and oxygen content. The cyclization coefficient and oxygen content are effective to the density of carbon fiber by influencing the degradation behavior, which cause defects in the fiber. The higher cyclization coefficient leads to form less structural defects and higher density of the fiber; on the contrary, the higher oxygen content leads to form more structural defects and lower density of the fiber.
Several nitration reagents including fuming nitric acid, HNO3-H2SO4, KNO3-H2SO4, HNO3-KNO3, CH3COOH-KNO3, (CH3CO)2O-HNO3 were used to nitrate cyclic ladder polyphenylsilsesquioxane (CL-PPSQ) in different conditions in order to enhance the compatibility of the CL-PPSQ in polymers, the NO2-PPSQ was obtained. FTIR, element analysis, GPC, TGA and 1H NMR were used to characterize the structures of the nitrated products. The results show that the nitrating abilities of the fuming nitric acid, HNO3-H2SO4 and KNO3-H2SO4 are very strong. Many nitro groups can be linked with phenyl groups in CL-PPSQ, but with low molecular mass, fracture occurs in siloxane segment. However, the Mn of the product NO2-PPSQ sharply drops by 50% compared with that of CL-PPSQ, so the nitration reagents can break the cyclic structure of CL-PPSQ. The nitrating reagents of HNO3-KNO3 and CH3COOH-KNO3 have no nitration effects on CL-PPSQ. At last, NO2-CL-PPSQ was prepared using (CH3CO)2O-HNO3 because of the moderate nitration process and ability. The cyclic structure of PPSQ is remained, although the number of —NO2 group is not too much. At the same time, the nitration mechanism using different nitration reagents was analyzed. A certain amount of NO2+, which is a kind of activator owning strong nitration ability, can be found in the fuming nitric acid and H2SO4-HNO3(KNO3) systems. As to the (CH3CO)2O-HNO3 system, the main activator is CH3COONO2.
The effect of different Mn contents on the σ phase and toughness of 22%Cr (mass fraction, the same below) low-nickel DSS by means of OM, XRD, SEM, TEM, precipitation kinetics and Charpy impact tests was studied. The results show that the morphology of precipitated phases changes from tiny granulated σ phase in δ/γ phase boundary to σ/γ2 eutectoid structure within δ phase with the addition of Mn from 4.3% to 9.7% and 76 hours aging. The increase of Mn content can decrease Avrami exponent n and increase reaction constant B, and the accelerating of σ-phase precipitation with higher Mn addition is due to the participation of Mn. Increasing Mn content can make initial time and ending time of σ-phase precipitation earlier and expand the interval between the initial time and ending time of σ-phase precipitation, that is, the more Mn addition, the earlier precipitation beginning time of σ-phase and the lower precipitation rate of it. The impact toughness is not sensitive to 1% transformation fraction of δ-ferrite, but it drops rapidly while the transformation fraction of δ-ferrite increases from 1% to 5%. More addition of Mn is good to impact toughness at the early stage of aging treatment, but the impact toughness decreases rapidly by accelerating the transformation fraction of δ-ferrite more than 1% earlier at the middle stage of aging time.
Superplastic tensile behavior and deformation mechanism of TC18 titanium alloy were investigated by high temperature tensile test at 720-950℃ with initial strain rates of 6.7×10-5s-1-3.3×10-1s-1.The results show that under the optimal superplastic deformation condition (890℃ and 3.3×10-4s-1), the maximum elongation is 470%, the peak stress is 17.93MPa and with uniform grain size.Below the phase transus Tβ, the elongation firstly increases and then decreases.A maximum elongation of 373% is obtained at 830℃ and with initial strain rate of 3.3×10-4s-1 and the peak stress is 31.45MPa.The superplastic deformation mechanism of the TC18 titanium alloy in two-phase region is mainly grain rotation and boundary sliding, and the deformation coordination mechanism is dislocation slipping and climbing; the superplastic deformation mechanism in single phase region is intragranular dislocation motion and the deformation coordination mechanism is dynamic recovery and dynamic recrystallization.
The joint clearance with 0.5mm was brazed with pre-filled high-melting powder method, by using K465 nickel-base superalloy as base metal, FGH95 nickel-base superalloy powder as pre-filled powder. The effects of different holding time on microstructure and mechanical properties were investigated. The results show that the brazing seam microstructure of the joints brazed at 1220℃ for 0.5h composes of alloy powder particles and phases among the particles. The microstructure is a two-phase structure of γ and γ' inside the powder particles, and among the particles are γ and γ' two-phase based borides, silicides and γ+γ' eutectics. With the increase of holding time, the powder particles grow bigger, the compounds and γ+γ' eutectics merge together, leads to the decrease of the amount of compounds and γ+γ'eutectics. The holding time is prolonged from 0.5h to 16h, the average rupture life increases from 31.59h to 54.58h, but it is not easy to achieve the isothermally solidified joints with good mechanical properties.
The cryogenic treatment (CT) process of carbide-free bainite steel after carburizing was optimized by the method combining thermal magnetic analysis, microhardness analysis and direct reading spectrometric analysis. The results show that cryogenic treatment temperature of the hardened layer should be lower than 134K by measuring thermal magnetic curve of the sample after carburizing at 1193K and air cooling (AC). After cryogenic treatment at 123K and tempering (T) at 463K, retained austenite content of the hardened layer is about 12.2% (mass fraction). The near surface layer of carburized steel is hardened dramatically through the cryogenic treatment, and the hardness of near surface layer reaches about 810HV1.0 after low temperature tempering. The distribution of hardness gradient of carburized steel tends to be reasonable.
T8 steel was carried out surface modification treatment by pulse detonation-plasma(PDP) technology with the capacity of 600, 800, 1000μF respectively. The microstructure and phase structure of T8 steel before and after PDP treatment were analyzed by using XRD and SEM. The microhardness and wear resistance before and after treatment were investigated by microhardness tester and wear tester. The results show that the surface smoothing occur first, and then the craters are formed. The craters are caused by the inhomogeneity of PDT energy and the material itself. PDP treatment makes the surface layer of T8 steel changed from martensite α'-Fe to austenite γ-Fe, and the Fe3N is formed due to nitriding phenomenon. The thickness of modified layer is increased with the increasing of the capacity. When the capacity is 1000μF, the average thickness of modified layer is 68.27μm and it composes of columnar and fine grain structure. The thickness of columnar structure is decreased with the decreasing of the capacity. The microhardness is improved by a factor of about 2, and the wear resistance is also obviously increased. The maximum wear resistance is 2.6 times of the matrix.
The stress relaxation data up to 8760h at 550℃ and 600℃of 12Cr-1Mo-1W-0.25V heat-resistant steel were used as the object to study the method of how to accurately and effectively predict long-term relaxation stress by using short-time relaxation data. When relaxation model is used to extrapolate the long-term relaxation stress directly, it is found that the parameters of the relaxation model depend on the length of the fitted data. The time-dependent parameter model, naming as timing parameter method, is proposed to predict the long-term relaxation stress with high accuracy. By comparison of the results of timing parameter method and direct extrapolation method, timing parameter method has obvious advantages in predicting long time relaxation stress with short time relaxation data, as the timing parameter method has a more accurate prediction than that of direct extrapolation method.
Creep-fatigue interaction tests of P92 steel at 630℃ under stress-controlled were carried out, and the crack propagation behaviour of P92 steel was studied. The fracture mechanism of crack growth under creep-fatigue interaction and the transition points in a-N curves were analyzed based on the fracture morphology. The results show that the fracture of P92 steel under creep-fatigue interaction is creep ductile fracture and the (Ct)avg parameter is employed to demonstrate the crack growth behaviour; in addition, the fracture morphology shows that the crack growth for P92 steel under creep-fatigue interaction is mainly caused by the nucleation and growth of the creep voids and micro-cracks. Furthermore, the transition point of a-lg(Ni/Nf) curve corresponds to the turning point of initial crack growth changed into steady crack growth while the transition point of (da/dN)-N curve exhibits the turning point of steady creep crack growth changed into the accelerated crack growth.
The effect of power ultrasound in molten metal shaping was summarized. The application and mechanism of ultrasonic treatment in the grain refinement, degassing and impurity removal in casting process, as well as strengthening of weld seam by reducing residual stress and promoting interfacial wetting in welding process were reviewed in details. The progress in high-speed photography of ultrasonic cavitation bubbles and synchrotron radiation X-ray imaging of crystal growth in molten metal was reviewed and discussed. It was proposed to adopt in-situ investigation of mechanism of ultrasound in liquid metal medium by combining high-speed photography and synchrotron radiation X-ray imaging. It aims to provide theoretical guidance for further applications of ultrasound in the molten metal shaping.
The new requirements of high-frequency magnetic properties are put forward for electronic components with the rapid development of power electronics industry and the use of new electromagnetic materials. The properties of magnetic core, which is the key unit of electronic components, determine the performance of electronic components directly. Therefore, it's necessary to study the high-frequency soft magnetic materials. In this paper, the development history of four types of soft magnetic materials was reviewed. The advantages and disadvantages of each kind of soft magnetic materials and future development trends were pointed out. The emphases were placed on the popular soft magnetic composite materials in recent years. The tendency is to develop high-frequency soft magnetic composite materials with the particle size controllable, uniform coating layer on the core and a mass production method from laboratory to industrialization.
The recent progress in application of carbon-based nanomaterials in flame retardant polymer was reviewed. The research achievements of carbon-based nanomaterials were discussed such as carbon nanotubes, fullerene, graphene and nanosized carbon black, which were used as flame retardant alone, after modification or synergistically with other materials. It was put forward that the research of polymer/carbon-based nanomaterial flame retardation systems should emphasize the flame retardation mechanism. Furthermore, carbon-based nanomaterials should be used with other flame retardants to play their respective advantages.
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