- 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)
Effects of intercritical tempering temperature on formation of metastable austenite and mechanical properties of a kind of Mn-Mo series microalloyed steel were investigated by X-ray diffraction (XRD), dilatometer and electron back scattering diffraction (EBSD). The results show that when intercritical tempering temperature is below 650℃,metastable austenite with good stability in test steel can be achieved, whose volume fraction at room temperature rises with the increase of intercritical tempering temperature. When intercritical tempering temperature exceeds 650℃, the stability of metastable austenite declines significantly, some of austenite transform to "fresh" martensite during tempering cooling. As a result, the volume fraction of metastable austenite at room temperature decreases with the increase of intercritical tempering temperature. The best match in the volume fraction and the stability of metastable austenite is obtained when intercritical tempering temperature is at 650℃. Mechanical test results show that when intercritical tempering temperature is at 650℃, mechanical properties of test steel reach the best with yield and tensile strength 748MPa and 813MPa respectively. The elongation is 27.5%, and impact energy is 217J at -20℃ and 117J at -100℃.
The friction stir additive manufacturing (FSAM) process experiment was conducted by using the zero tilt angle forming tool with 4mm thickness plates of Al alloy 5A03-H. The influence of the process parameters on the formation of FSAM zone was investigated. The results show that as the traveling speed increases, the width of single pass as well as the migration height and width of interface all decrease. When the traveling speed is 60mm/min, migration of interface is small and the width of single pass is bigger. When the FSAM space is big, there are uncombined interface and migration interface defects between two adjacent passes. As the space decreases, uncombined interface gradually transforms into migration interface. When the FSAM space reaches a definite value, migration interface disappears. In order to achieve excellent FSAM zone, the FSAM space must be optimized. Compared with the same direction FSAM, the reverse direction FSAM can effectively restrain and eliminate the interface migrating to the center of FSAM zone, thus, the more effective width of FSAM zone can be obtained.
The microstructure and mechanical properties of 4343/3003/4343 hot-rolled aluminium composite sheet after annealing at 100-500℃ and 15min-10h were investigated by optical microscope, scanning electron microscope, transmission electron microscope, X-ray diffractometer, tensile testing machine and hardness tester. The results show that recrystallization of the core alloy occurs at 300℃ for 1h, which is accomplished above 370℃ with amounts of dispersoids precipitation. The dispersoids retard the recrystallized grain growth by pinning grain boundary. With increasing of annealing temperature for 1h, the grain size of the core alloy firstly increases and then decreases, and the tensile strength and hardness of the sheet vary conversely. Meanwhile, with annealing time at 370℃, the volume fraction of recrystallization for the core alloy increases and grain size grows gradually, and the tensile strength and hardness of the sheet decrease. The optimum annealing treatment for the sheet is 370℃/1h.
CuMnNiCo filler metal was developed to braze MGH956 oxide dispersion strengthened (ODS) superalloy. The microstructural evolution was analyzed during brazing. The effects of different brazing temperatures on microstructures and properties of the joints were investigated. The results show that sound joints can be obtained at 1000-1050℃ for 20min. The brazing joints consist of Cu-Mn based solid solution in the central zone of brazed seam and Fe-Mn based solid solution at the diffusion reaction zone of both sides of brazed seam, with formation of three different compounds. When brazed at 1030℃/1050℃, the room temperature (RT) tensile fracture of the joints occurs at the center of seam, exhibits mainly the intergranular brittle fracture feature. By increasing the brazing temperature to reduce (Mn,Ni)-Si brittle phase distributed along the grain boundary, the strength of brazed joints can be improved. The RT tensile strength of joint reaches up to about 75% of the base material.
A kind of composite buffering material was made by filling the voids of honeycomb paperboard with polyurethane. Drop tests were performed to evaluate the dynamic mechanical properties of the material. Based on the experimental results, the mechanical behavior of the material was analyzed through influencing factors including honeycomb core diameter, thickness, cross-section area and impact velocity. It is shown that the dynamic yield strength and elastic limit increase with the increase of impact velocity, and decrease with the increase of honeycomb core diameter, thickness and cross-section area. Then the dynamic constitutive model is established. It is proved that the curves of constitutive model fit well with those of experimental data.
The nitrogen-alloying hardfacing alloy of martensite stainless steel was made through the addition of nitrogen alloy and the nitrogen-fixing elements of niobium, vanadium and titanium. The corrosion resistance of hardfacing alloy was investigated through electrochemical corrosion and chemical erosion tests. The results show that nitrogen-alloying of hardfacing alloy inhibits the precipitation of chromium carbides and the chemical stability of passivating film is effectively strengthened, the corrosion potential increases from -345mV to -264mV, and thus the electrochemical corrosion resistance of hardfacing alloy is strengthened.Owing to the uniform and fine microstructure of nitrogen-alloying hardfacing alloy, pits are fine and dispersed when pitting corrosion occurs on the hardfacing alloy in the FeCl3 solution, therefore the corrosion resistance of hardfacing alloy is improved by nitrogen alloying.
Thermodynamic calculations for studying the influence of elements W, Mo, Nb and Fe on precipitation of topologically close-packed phases(TCP) and carbide phases,high temperature mechanical properties of a new Ni-Fe base superalloy were carried out using material phase diagrams and by JMatPro thermodynamic software. The results show that the main strengthening phases are γ' and M23C6 at inner grain and grain boundaries, respectively. The additions of Mo,W and Nb into the superalloy are beneficial to improve the high temperature creep rupture life and yield strength. Meanwhile, the increments of Mo, Nb and Fe could promote the precipitation tendency of Laves and σ phase. Therefore, in order to avoid the appearance of TCP phases in this superalloy, the addition of Nb mass fraction should be less than 0.6%, and the additions of Mo and W should be no more than 1.0%.
The Fe3O4 and graphite composites are prepared by in-situ chemical precipitation. The effect of mass ratio of Fe3O4 to graphite on electromagnetic wave absorbing property of the composites was investigated. The results show that the intensity of Fe3O4 XRD increases with the increase of the adding amount of Fe3O4 in composites. The Fe3O4 nanoparticles mainly deposit on the surface of graphite particles. The Fe3O4 nanoparticles coat the graphite surface completely with the increase of the adding amount of Fe3O4 in composite and some Fe3O4 nanoparticles disperse between graphite particles. The dielectric constant of composites decreases with the increase of Fe3O4 amount in composites. The magnetic permeability is less affected by the amount of Fe3O4 in composite. The Fe3O4-graphite composites with mass ratio of 5:1 and 4:1 show better absorbing property than that of other samples. The sample of 5:1 shows maximum absorption value of -31.9dB and the frequency bandwidth of reflection loss over -10dB about 5.0GHz at the thickness of 1.5mm.
The flame retarding and mechanical properties of new flame retardant composites(FR/APP/MH/EP) were studied using limited oxygen index (LOI) measurement,UL-94 and cone test. The new flame retardant composites were prepared by adding nano-magnesium hydroxide(MH) into six-(4-of DOPO hydroxymethyl phenoxy) cyclotriphosphazene (FR),polyphosphate (APP) and epoxy resin(EP). The results show that when fix the FR/APP 1:1, adding 1% mass fraction MH, the limited oxygen index(LOI) value of EP2 (10%FR/10%APP/1%MH/EP) can reach 36.4%, the peak heat release rate (pk-HRR),average effective heat of combustion (av-EHC),average specific extinction area (av-SEA),average CO release rate (av-CO) of EP2 are reduced by 79.8%,6.73%,47.2%,33.3%, respectively, compared with those of pure EP (EP0) and decrease 20.0%,69.6%,83.6%,58.6%, respectively, compared with those of EP1 (10%FR/10%APP/EP),meanwhile, the tensile,bending and impact strengths of EP2 increase 47.6%, 75.2% and 196%, separately, compared with those of EP1.SEM observation reveals that EP2 forms a uniform, compact and continuous charred layers after burning, which has good flame retarding,smoke suppression and the toxic effects.
The compounding minerals form of Nd-doped zirconolite(CaZrTi2O7) and sphene(CaTiSiO5) was prepared by vacuum hot-press sintering using natural zirconite(ZrSiO4), calcium carbonate(CaCO3), titanium dioxide(TiO2), neodymium oxide(Nd2O3),aluminum oxide(Al2O3) and silicon dioxide(SiO2)as raw materials. The hot-press sintering temperature, phase composition, and leaching performance of synroc form were investigated by means of X-ray diffraction(XRD), scanning electron microscopy(SEM),backscattering scanning electron microscopy(BSE), inductively coupled plasma mass spectrometry(ICP-MS). The results indicate that the range of optimized hot-press sintering temperature of the compounding minerals form is 1130-1170℃ with the relative density over or equal 97.2%, while the main phase is the compounding minerals of zirconolite and sphene. The normalized leaching rates of Nd3+(42d) are 1.9×10-6g·m-2·d-1 (pH=5),1.5×10-6g·m-2·d-1(pH=7), and 1.2×10-6g·m-2·d-1(pH=9) at 90℃, respectively. Thereby the compounding minerals form has excellent chemical stability. pH values have no obvious effect on the leaching rates of Ca2+ and Zr4+. The normalized leaching rates of Ti4+ and Nd3+ are lower, and those of Si4+ and Al3+ are higher in weak base aqueous solution (pH=9).
The Al/Fe diffusion couples were prepared by using the inset technology and diffusion heat treated at the temperature above the melting point of aluminum and below the melting point of iron. The growth kinetics of the diffusion reaction layer (DRL) of Al/Fe liquid-solid interface was analyzed and the growth kinetics equation was established. The results show that Fe2Al5 is the only new phase formed during the heat treatment temperature holding process. The growth of the Fe2Al5 is controlled by the chemical reaction of the Al atoms and Fe atoms before the Fe2Al5 continuous single-phase layer is formed. Once the continuous Fe2Al5 single-phase layer is formed, its growth is primarily dependent on the diffusion of Al atoms along Fe2Al5 grain boundaries, accompanied with Fe2Al5 grain size increasing. When heat treatment below 800℃, the effect of the grain growth on the diffusion of atoms can be ignored, and the growth kinetics equation is y=2020.96exp(-78490/RT)t0.25. But, when the heat treatment temperature is 0.7 times exceeding the melting point of iron, the effect of grain growth can not be ignored, and the value of the growth index in the growth kinetics equation should be reduced appropriately.
Tri-(triethylene glycol-monobutyrate)citrate (TTBC) as a new ether-ester plasticizer was synthesized by two-step esterification. The chemical structure of TTBC was characterized by 1H-nuclear magnetic resonance and infrared spectroscopy. TTBC was used for plasticizing poly(lactic acid)(PLA) via a melt-compounding process. The effect of TTBC content on the properties of PLA/TTBC blends was studied by differential scanning calorimetry, polarizing optical microscopy, electronic testing machine and parallel plate rheometer. The results show that with the increase of TTBC content, the glass transition temperature (Tg), melting point (Tm), and cold crystallization temperature (Tcc) of PLA gradually shift to a lower temperature and their Shore D hardness decreases. The breaking elongation of PLA/TTBC blends is above 300%, while the corresponding tensile strength of PLA/TTBC blends maintains at above 10MPa. The rheology of PLA/TTBC shows that the complex viscosity (η*) and viscous flow activation energy (ΔEη) reduce significantly. Compared with PLA/TBC-25, TTBC has a higher plasticizing efficiency and migration resistance than TBC.
Two kinds of austempered ductile iron (ADI) with different microstructure and hardness were obtained by using different heat treatment and spheroidizing process. The rolling wear and damage properties of two kinds of ADI, wheel material and U71Mn rail were investigated using MMS-2A testing apparatus. The results show that the friction coefficient of ADI and U71Mn materials is obviously lower than that of wheel material. The wear rate of ADI material is obviously smaller than that of wheel material due to a function of self-lubricating. Furthermore, the self-lubricating of ADI material decreases the wear rate of U71Mn rail material. The wear rates of ADI2 with large spherical graphite nodule dimension and less residual austenite and U71Mn rail are the smallest. The wear mechanism of ADI material is slight fatigue wear and the wear mechanism of corresponding U71Mn rail material is adhesion and slight fatigue wear. However, there is obvious plastic flow when the wheel/rail materials are applied. The surface fatigue crack and delamination damage are the main wear mechanism.
Aero composite stiffened panel achieved absorbing moisture saturation in hygrothermal environment (70℃ distilled water). The compressive experiments were conducted on the untreated composite stiffened panels(type A) and the saturated ones(type B).Failure modes of the both types stiffened panels are similar with three major ways, including fracture and debonding of stiffeners together with the splitting and ripping of the panels. The fracture locations of type A are around the middle of panels while those of type B are towards either end of the panels, indicating the uncertainty of fracture locations for type B. The buckling patterns for both types are buckling of panels between stiffeners and buckling of the two middle stiffeners. The bending direction of type B is opposite to that of type A in the panel of same position, showing hygrothermal environment imposes much effect on the bending direction of panels. There still exists a post-buckling process for type B under compression, showing hygrothermal environment has less effect on the buckling load and more effect on the failure load of panels, whose buckling load and failure load decrease by 3.1% and 22.2%, respectively, compared with those of type A.
Research progress on the low velocity impact response of continuous fibre reinforced polymer matrix composites was reviewed. The effect of testing methods and the related affecting parameters, such as impactor shape and impact velocity on the impact to composite, was discussed. Major impact-induced damage modes were introduced. Furthermore, the influences of laminate structural parameters, like laminate thickness, layup and stitching, together with the properties of component,such as fibre, resin and fibre/resin interface, preload and environment on impact properties of composite were described. The development direction of future research was put forward on the impact response of fibre reinforced polymer matrix composite.
The preparation methods, luminescence mechanism and application research progress of carbon dots (CDs) were summarized. Approaches for synthesizing CDs were emphasized, and can be generally classified into two main ways: bottom-up and top-down methods. Top-down methods include arc discharge, laser ablation and electrochemical oxidation methods and others, and bottom-up approaches consist of combustion routes, template synthesis methods, hydrothermal methods, thermal methods and others. The advantages and disadvantages of these methods and fluorescent quantum yield were evaluated, and the research trend of these methods was prospected. It is pointed out that the synthetic/modified methods of CDs and the luminescence mechanism need to be further studied to improve the quantum yield in the future research, and it is crucial to synthetic CDs with the fluorescent which can be precisely, sensitively, rapidly and easily detected in the application of CDs as a new technique and a new method in all kinds of chemical detections and analysis.
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