- 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 microstructure and phase composition of Al-5Ti-1B, Al-4Ti-1C and Al-5Ti-0.8B-0.2C master alloys were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS), and the effects of the three kinds of master alloys on the grain size and mechanical properties of 7050 alloy were investigated. The results show that the existence of Zr reduces the grain refining effects of Al-5Ti-1B and Al-4Ti-1C master alloys, but hardly influences the refinement of Al-5Ti-0.8B-0.2C master alloy. The reason is that Al-5Ti-0.8B-0.2C containing B-doped TiC can resist Zr-poisoning, and after adding 0.2% (mass fraction) Al-5Ti-0.8B-0.2C, the average grain size of 7050 alloy is reduced from about 200μm to (60±5) μm, the ultimate tensile strength increases from 405 MPa to 515 MPa, increasing by 27.2%, and the elongation rate increases from 2.1% to 4.1%. However, after adding 0.2% Al-5Ti-1B and Al-4Ti-1C master alloys, the grain size is larger and the distribution is uneven, exhibiting obvious "refinement poisoning" phenomenon.
The effect of quenching rate on microstructure and hardness of Al-Zn-Mg-Cu-Cr alloy extruded bar was studied by hardness test, scanning electron microscopy and transmission electron microscopy. The results show that at quenching rate below 100 ℃/s, during the cooling process, the hardness begins to fall significantly; and it decreases by 43% at the quenching rate of 2 ℃/s. At quenching rate below 100 ℃/s, the number and size of equilibrium η phase heterogeneously nucleated at (sub) grain boundaries and on dispersoids inside grains increase obviously with the decrease of quenching rate, leading to greatly reduced age-hardening response. At the same quenching rate, the equilibrium η phase inside grains is larger than that at grain boundaries. In the range of the studied quenching rates, a quantitative relationship between hardness and equilibrium η phase area fraction has been established.
The effect of forging pass on the deformation structure of high purity aluminum at room temperature during multi-direction forging process was investigated by experiment. The multi-direction forging process was analyzed by using software of DEFORM-3D. The results show that an X-shape fine grain zone (in the center of the sample) and four coarse grain zones (near the end surface of the sample) are initially formed on the cross section of the sample as forging passes increase to 3. With a further increasing the passes to 9, this X-shape zone tends to spread the whole sample. However, the grain difference between the coarse grain zone and fine grain zone still exists on the sample forged by 9 passes. Limitation in the structural refinement is observed in the center of the sample with the increment of equivalent strain. The grains size in the center is refined to a certain size (about 70μm) as equivalent strain reaches 2.5, and no further grain refinement in the center with increasing the equivalent strain to 6.0. However, the grains size in the area near the surface is continuously refined with the increasing the equivalent strain to 4.0. This indicates that the local deformation state and the equivalent strain are two important factors that affect the grain size.
The wetting behavior and interfacial microstructures of molten magnesium AZ61 alloy on the surface of two different Q235 and galvanized steel plates under the condition of cold metal transfer were investigated by using dynamic sessile drop method. The results show that the wetting behavior is closely related to the wire feed speed. Al-Fe intermetallic layer was observed whether the substrate is Q235 steel or galvanized steel, and the formation of Al-Fe intermetallic layer should satisfy the thermodynamic condition of such Mg-Al/Fe system. The wettability of molten AZ61 magnesium alloy is improved with the increase of wire feed speed whether on Q235 steel surface or on galvanized steel surface, good wettability on Q235 steel surface is due to severe interface reaction when wire feed speed increases, good wettability on galvanized steel surface is attributed to the aggravating zinc volatilization. When the wire feed speed is ≤10.5 m·min-1, the wettability of Mg alloy on Q235 steel plate is better than on galvanized steel plate. However, Zn vapor will result in instability for metal transfer process.
The superplastic tensile tests were carried out for 7B04 Al alloy under a temperature range of 470-530 ℃ at a strain rate range of 0.0003-0.01 s-1. Then, the superplastic deformation behavior and deformation mechanism of the material were investigated. The results show that with the increase of temperature and decrease of strain rate, the flow stress of 7B04 Al alloy is decreased and the elongation is increased. When the deformation temperature is at 530 ℃ and the strain rate is 0.0003 s-1, the elongation reaches the maximum value of 1105%, which indicates that at this process parameter the optimal superplasticity is obtained; the strain rate sensitivity index m value is above 0.3 and increases as the temperature going up; when the deformation temperature is at the range of 500-530 ℃, the m value is above 0.5, the superplastic deformation mechanism of 7B04 Al alloy predominated by grain boundary sliding; the superplastic deformation activation energy Q value is 190 kJ/mol which indicates that the superplastic deformation is significantly controlled by the intercrystalline diffusion; the liquid phase will be produced along the grain boundaries of 7B04 Al alloy during superplastic deformation, which can enhance the superplasticity with a moderate amount.
Fe-17Cr-4C-2V-Mn-Si-Ti complex system hardfacing alloys were deposited by using flux-cored wire self-shielded open arc welding. The effects of silicon on their M7C3 (M=Fe, Cr, V, Mn) phases and abrasion resistance were investigated by OM, XRD and SEM. The results show that, with silicon content increasing from 0.6% (mass fraction) to 2.4%, the size of primary M7C3 carbides gradually reduces and transites from rod-like shape to block-like shape in dispersion distributing state. γ-Fe phases, which adjacent to those primary M7C3 grains, progressively reduce until disappear. It dues to that silicon can change the precursor of primary M7C3 nucleates in nature, e.g. liquid high carbon atom clusters and it results in the change of their morphology, distribution and size. The wear test results indicate that the abrasion resistance of open arc hardfacing alloys improves firstly and then reduces when silicon content increases from 0.6% to 2.4%. The optimum abrasion resistance is acquired at 1.5%Si. The analysis on the surface worn morphologies show that the micro-cutting and micro-spalling wearing mechanisms coexist.
The effect of mischmetal of lanthanum and cerium on the composition and structure of the corrosion products on the surface of AZ91 Mg alloy in deicing salt solution under dry-wet cycles was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The results show that the corrosion products of AZ91 Mg alloy without mischmetal addition (La, Ce) are mainly composed of Mg (OH)2, MgO, CaCO3 and Mg6Al2CO3 (OH)16·4H2O; and (La, Ce) AlO3 can be found in the products of AZ91 with mischmetal addition, meanwhile dense layer occurs in the corrosion products. Electrochemical impedance spectroscopy (EIS) measurements show that the charge transfer resistance of AZ91 alloy with mischmetal addition tested in the same dry-wet cycles is much higher than that of AZ91 alloy, the addition of mischmetal helps to reduce the dispersing effect of impedance spectroscopy, indicating that the corrosion resistance of AZ91 Mg alloy and the stability of corrosion product films can be improved by mischmetal of La and Ce.
The corrosion behaviour of Q235 steel in Qingdao and Wanning of China, the two kinds of polluted marine environment were simulated by cyclic immersion test, and the correlation of indoor cyclic immersion test and outdoor marine atmospheric corrosion test of Q235 steel were studied. The corrosion morphologies, corrosion products, corrosion kinetics of Q235 steel were investigated with methods of scanning electron microscopy (SEM), X-ray diffraction (XRD) and mass loss. The results reveal that the corrosion morphologies and compositions of corrosion products after cyclic immersion test agree with those after the real atmospheric test. Corrosion prediction model of Q235 steel in two kinds of marine atmospheric environment was built combined with Grey correlation method:TQD=137.002t1.093, TWN=102.398t0.952.
Plasma electrolytic borocarbonitriding (PEB/C/N) was successfully used to achieve ternary borocarbonitriding layer on industrial pure iron at the bath voltages of 340, 360 V and 380 V respectively. The morphology, composition, phase constituents and microhardness profiles of PEB/C/N layers were investigated. The influence of bath voltages on wear behaviors of PEB/C/N layers was evaluated by ball-disc friction and wear tester under dry sliding against ZrO2 ball, and their wear mechanism were analyzed. The results show that the thickness and maximum hardness of PEB/C/N layer on pure iron increase with the increase of bath voltage. After 1 h discharge treatment at 380 V, the boride layer and transition layer of the PEB/C/N sample reach 26 μm and 34 μm respectively, and the maximum microhardness of PEB/C/N layer can reach 2318 HV. The wear rate of PEB/C/N layer is only 1/10 of that of the pure iron substrate. The friction coefficient and wear rate of pure iron are greatly reduced after the PEB/C/N surface treatment, but the friction coefficient and wear rate of PEB/C/N layer vary little under different bath voltages.
NiCoCrAl coatings containing Y and Y oxide were made using vacuum plasma deposition and high-velocity oxygen fuel respectively, high temperature oxidation dynamics and cross-section microstructures of NiCoCrAl+Y and NiCoCrAl+Y (O) coatings in Ar-16.7% O2, Ar-3.3% H2O and Ar-0.2% H2-0.9% H2O at 1100 ℃ were investigated by differential thermal analysis (DTA) and optical and electron microscope. The influencing mechanism of Y oxide on the oxidation of coatings at different atmosphere was compared by computation using First-Principles. The results show that Al2O3 layer on NiCoCrAl+Y coatings has more holes for internal oxidation on account of the element Y diffusion and enrichment on the interface. In addition, steam can promote the internal oxidation. While a thinner and uniform alumina form on NiCoCrAl+Y (O) coatings because element Y is pinned by oxygen atoms during the preparation of coatings. Water vapor has less influence on protective alumina formation on the NiCoCrAl+Y (O) coating. Therefore, oxidation behavior of NiCoCrAl coatings vary in composition and structure in different oxidizing atmosphere. Besides, Y and Y-enrichment oxides have key influences on the microstructure and the growth rate.
VAlSiN coatings with different Si contents were deposited at 300 ℃ by reactive magnetron sputtering. The effect of Si content on the microstructure, growth morphology, chemical state, mechanical properties, friction and wear properties was investigated. The results show that the VAlN coating exhibits a single-phase NaCl structure with (111) preferred orientation. The VAlSiN coatings gradually lose their structure of (111) preferred orientation and transfer into amorphous structure with the increase of Si content. The VAlSiN coatings which Si content is more than 1.8% (atom fraction, same as below) are multi-phase composite coatings consisting of nc-VAlN and a-Si3N4. Compared to VAlN coating, the density of VAlSiN coatings with small amount of Si (0.8%) is increased significantly as well as the hardness that reaches 30.1 GPa, while the grain size is decreased. Further increasing Si content, the growth of columnar grains is interrupted, concomitant of the hardness gradually declines and tends to be stable at 22 GPa. The friction coefficient of the VAlSiN coatings decreases first and then increases with the increase of Si content. The wear rate reaches the lowest value of 1.2×10-16 m3·N-1·m-1 is obtained when Si content is 0.8%.
Using W, Zr and ZrH2 as raw materials, W/Zr reactive materials with different proportions were prepared by hot-pressing method. The dynamic behavior of W/Zr materials was investigated by a split Hopkinson pressure bar apparatus (SHPB) and the impact-initiated reaction process was recorded. The characteristics of the samples, such as the phase transformation, component and microstructure before and after reaction, were analyzed by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electronic microscopy (SEM). The results show that the W/Zr material sintered by hot-pressing is more compact and the relative density exceeds 87.5%. W/Zr material is a typical brittle material with high strength, the quasi-static compressive strength is higher than 1022 MPa and the failure strain is less than 1%. The effect of strain rate on the dynamic compressive strength for all three group samples is obvious, strength increases with strain rate. When the impact load is strong enough, W/Zr material crushes, combusts with air violently, and generates ZrO2.
The modeling air-cooled turbine blades specimens of DD6 single crystal superalloy with different distributions of cooling film holes were used to study the high cycle fatigue properties at room temperature. The SEM fracture observation was carried out. The results indicate that the cooling holes have significant effects on the high fatigue life of DD6 single crystal superalloy. The average life of non-hole specimens is four times of that of the three-row holes specimens under the same testing conditions. However, the distribution of cooling film holes has relatively less influence on fatigue life. The fracture of the specimens with non-hole is linear source by SEM analysis, but the cracks are found around the cooling film holes and the fracture of the specimens with single row to three rows is a typical multi-source rupture, and cracks all initiate from near film holes. According to fracture and crystallography theoretical conjecture, the cracks propagate along the {001} slip plane for non-hole, single-row holes and the middle location of the multi-row holes specimens. However, the cracks around the holes grow along the {111} slip plane for upper and lower holes of the specimens with multi-row holes. In addition, the distribution of stress field along cooling holes of four different specimens was analysed by FEM method. The results show that the fracture location and morphology of specimens are consistent well with numerical simulation analysis.
The corrosion behavior of primid-curing solidified polyester powder coating defects in marine environment was investigated by CASS test, immersion test, electrochemical impedance spectroscopy (EIS) and scanning Kelvin probe (SKP). The results show that the primid-curing polyester powder coating has a small amount of blisters along the scratch edge, the maximum single side corrosion width is less than 0.5 mm, and the surface adhesion is 0 after 240 hours′ CASS test. The EIS map in 0.6 mol/L NaCl solution exhibits that the corrosion rate of aluminum alloy is decreased with increasing immersion time and gradually stable. The scanning Kelvin spectrum reveals that the corrosion of the metal under the coating of the polyester powder is extended from scratch to the coating, the anode and the cathode are alternately changed, which leads to the expansion of the corrosion area.
A novel bio-based epoxy resin system with rosin-sourced acid anhydrides was established by formula design and selection according to the resin film's forming performance and state with different storage time. The formula involves epoxy resin/curing agent/accelerator with mass proportion of 100/60/3-4. The curing property and the relationship between viscosity-temperature-time of resin were characterized by dynamic or steady state DSC analysis and cone plate viscometer, respectively. The results show the resin system can be cured at the range of 120-140 ℃, and the range of hot melt prepreg temperature is 60-85 ℃ with the viscosity from 1500 mPa·s to 5000 mPa·s. The processing time of hot melt prepreg is about 180min at 70 ℃. The curing mechanism of bio-based resin was also investigated through the samples with different curing time by IF and DSC.
A mathematical abstraction and three-dimensional modeling method of three-dimensional woven fabric structure was developed for the fine weave pierced fabric, taking parametric continuity splines as the track function of tow. Based on the significant parameters of fine weave pierced fabric measured by MicroCT, eight kinds of the three-dimensional digital models of the fabric structure were established with two kinds of tow sections and four kinds of tow trajectory characteristic functions. There is a good agreement between the three-dimensional digital models and real fabric by comparing their structures and porosities. This mathematical abstraction and three-dimensional modeling method can be applied in micro models for sub unit cell and macro models for macroscopic scale fabrics, with high adaptability.
A three-dimensional finite element model of the repaired structure was established, by which the impact of patch parameters on effect of one-side boned repaired structure under uniaxial tensile loading was analyzed based on the stress concentration factor (SCF) and deflection. The results show that the repair effect is better when the crack length is 3.5 times of the hole diameter, the thickness is 60% to 80% of the hole depth and the lay-up is 0°/90°. Then the finite element results were subjected to the uniaxial tension tests. The failure strength of the repaired plate increases by 10.1% compared with that of the unrepaired plate.
Nanorod Ag doped hydroxyapatites (Ag-HA) were synthesized by precipitation and hydrothermal method. Crystal structure, morphology and antibacterial property of prepared samples with silver contents prepared by different synthesis methods were investigated. The results show that Ag doped hydroxyapatites synthesized by hydrothermal method possess a higher length to diameter ratio, higher degree of crystallinity, better dispersion, larger grain size and smaller unit cell parameters. The average crystal size of prepared samples by precipitation method at 70 ℃ and hydrothermal method at 180 ℃ are (22.7±0.7) nm and (50.7±0.9) nm, respectively. In addition, adding silver into hydroxyapatite may increase grain size and unit cell parameters. When silver content is 1.30%, average grain size and unit cell parameters are (53.7±0.9) nm and a=0.9465 nm, c=0.6970 nm, respectively. Antibacterial test results indicate that Ag-HA exhibits good bactericidal property against Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus). The antibacterial rate is 100% when silver content varies after different hours (1, 3, 6, 12, 24 h).
The CNTs/rGO/NG composite lithiumion battery anode material was synthesized by thermal reducing, using graphene oxide (GO) and carbon nanotubes (CNTs) as precursors for a 5：3 proportion. The morphology, structure, and electrochemical performance of the composite were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared spectra (FTIR) and electrochemical measurements. The results show that reduced graphene oxide and carbon nanotubes form a perfect three-dimensional network structure on the surface of natural graphite. CNTs/rGO/NG composite has good rate performance and cycle life, compared with pure natural graphite. The initial discharge capacity of designed anode is 479 mAh/g at 0.1 C, the reversible capacity up to 473 mAh/g after 100 cycles, the capacity is still 439.5 mAh/g, the capacity retention rate is 92%, and the capacity is 457, 433, 394 mAh/g at 0.5, 1, 5 C, respectively.
The critical issues of CNTs/Cu composites were reviewed. The preparation techniques of the composites were classified, and the research progress on powder metallurgic methods, electrochemical methods and other methods was summarized, with an emphasis on the relationship between preparation methods and properties. The interfacial characteristic of the CNTs/Cu composites was analyzed, and the research progress and existing problems of mechanical properties, electrical properties, thermal properties and wear and friction properties of the composites were also summarized. It was pointed out that the key to increase the comprehensive properties of the composites is to obtain the homogeneous distribution of CNTs and good interfacial bonding between CNTs and the Cu matrix by improving the preparation methods.
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