- 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)
SiC ceramic was brazed in vacuum with Ti-35Zr-35Ni-15Cu (mass fraction/%) filler metal. The formation of interfacial structure and effects of technological parameters on joint shear strength were studied. The results show that a series of interface products form owing to the complex interface reactions between the SiC ceramic and filler metal. When the brazing temperature is 960℃ for 10min, TiC and Ti5Si3+Zr2Si layers form on the SiC ceramic side. Ti5Si3+Zr2Si grows towards to the middle of the joint and shows a long strip shape. Microstructure from SiC ceramic to the middle of the joint can be indicated as SiC/TiC/Ti5Si3+Zr2Si /Zr(s,s)/Ti(s,s)+Ti2(Cu,Ni)/(Ti,Zr)(Ni,Cu). When the brazing temperature is 960℃ for 30min, long strip shape Ti5Si3+Zr2Si runs through the entire joint. Shear strength of the brazed joint firstly increases then decreases with the rising of the brazing temperature and holding time. The maximum shear strength of the joint with 110MPa is obtained at brazing temperature 960℃ for 10min.
Aimed at the engineering actual demand of laser remanufacture forming for compressor blade, based on the hypothesis of surface smoothness for laser remanufacture forming, the mathematics model of cladding layer overlapping rate was obtained and verified by experiment. Through analysis on the shape of single laser cladding layer and screening the dilution, the optimized matched process parameters for the FeCrNiCu series alloy powder on the FV520(B) substrate were determined. Thro-ugh quantitative analysis on the laser remanufacture forming process, the scanning path and technical process were planned. Also the laser remanufacture forming of the blade simulator with volume damage was realized. The results of the penetration testing and metallographic microscope measurement show that there is not blowhole and crack on the surface of the forming places, the shape dimension error of the forming places is controlled less than 2mm, and the angle error is controlled less than 3°.
Magnesium and aluminum alloys were welded by diffusion bonding using Ni foil as interlayer. Scanning acoustic microscopy (SAM), electronic probe microanalysis (EPMA), scanning electron microscopy (SEM) and universal testing machine were used to characterize the interfacial structure and mechanical properties of the joints. The results show that Mg and Al are bonded successfully by diffusion bonding using Ni interlayer and the Mg-Al inter-diffusion is inhibited. There is no Mg-Al intermetallic compound formed. The maximum shear strength of 20.5MPa is obtained at 440℃ for 90min. Mg/Ni/Al joints are formed by the inter-diffusion of Al, Ni and Mg, Ni. Al-Ni and Mg-Ni diffusion zone formed at the joint interface. Al3Ni2 and Al3Ni are formed at the Al-Ni diffusion zone, and Mg2Ni is formed at the Mg-Ni diffusion zone. The thickness of diffusion zone increases with the increase of welding temperature.
Al2O3-TiC particles reinforced ferro-matrix composite were successfully prepared by in -situ synthesis from ilmenite. The effects of in -situ synthesis and adding synthesis on microstructures and properties were analyzed by using XRD, SEM and mechanical testing methods. The results show that the reinforcing phases of the synthesis ferro-matrix composite comprise of Al2O3, MgAl2O4, TiC and Fe. Some of the TiC phases are oxidized during the synthesis process. The iron matrix of in -situ synthetic composite is distributed as thick block strip and the iron matrix of adding synthetic composite is in a uniform distribution. The properties of synthetic material are excellent. The optimal flexural strength and Vickers hardness are 937MPa and 532, respectively.
Effects of cerous nitrate sealing on corrosion resistance of adipic-sulfuric acid anodic oxide films on 2A12 aluminum alloy were investigated. The corrosion resistance of anode oxide films was studied by using salt spray tests, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The surface microtopography of anodic oxide films was observed by using the field emission scanning electron microscope (FE-SEM) and was compared with diluted chromic acid sealing and boiling water sealing. The results show that after sealing in the cerous nitrate solution, corrosion current of the anodic oxide films decreases, the impedance increases and the corrosion resistance is enhanced significantly. The surface morphologies of anodic oxide films are petaloid like with some cerium oxide or cerium hydroxide adhering to surface of the anodic oxide films and porous layer. The corrosion resistance of films with cerous nitrate sealing is better than that of films with boiling water sealing and are corresponded with diluted chromic acid sealing.
NiCuFeBSi alloy coatings were fabricated with CO2 laser on gray cast iron substrate HT250 at different preheating temperatures. The effect of preheating temperature on microstructure, elements distribution and tensile strength was investigated. Results show that the chill structures in the semi-molten zone are controlled and distributed discontinuously with increasing of preheating temperatures. Coating dilution rates increase as preheating temperatures increase, which induces the diffusion of more Si, P elements into molten pool and the formation of harmful impurities in the coatings. The tensile tests suggest the strength of NiCuFeBSi coating is superior to HT250, while the butt sample strength is the lowest of all. And the failure types consist of cleavage and quasi-cleavage fractures. Mass of dislocations are observed in the grains after solidification of NiCuFeBSi coating. The tangle-ment between dislocations forms the substructure. Therefore, the grain is further refined, which is beneficial for enhancing the coatings strength. Eventually, the best preheating temperature for laser NiCuFeBSi alloy coating on the substrate of HT250 is considered as 30℃.
Ti3Al and Ti2AlNb alloys were joined by direct diffusion welding. The influence of bonding pressure, bonding temperature and holding time on the interface morphology and property of the joint was studied. The interface structure was analyzed by SEM, EDS and XRD, and the mechanical properties of joints were tested. The results show that typical interface structure of direct diffusion bonding joints is Ti3Al/O-phase and α2-phase/B2-rich phase/Ti2AlNb. When bonding temperature is 1000℃, holding time is 60min, bonding pressure is 5MPa, the shear strength could reach 635MPa and the tensile strength could reach 795MPa. Both joints fracture at the Ti3Al-base alloy. After thermal cycling (1000℃/60min), the tensile strength of Ti3Al decreases to 76% of the original strength. Welding defects occur when bonding temperature is below 950℃ or holding time is less than 60min. The bonding temperature higher than 1050℃ or holding time more than 120min will lead to phase transition of Ti3Al.
ZnO/Cu/ZnO transparent conductive thin film was prepared by magnetic sputtering deposition at room temperature. The relationships between post-annealing and the structure, morphology, electrical and optical properties of the multilayer film were investigated by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), Hall effect measurement system and UV-Vis spectrophotometer. The results indicate that ZnO films have (002) preferential orientation before and after annealing.With the increase of annealing temperature, the crystallization, grain size and surface roughness increase. The resistivity decreases at first and then increases, while the optical transmittance and band gap energy increase at first and then decrease. ZnO/Cu/ZnO film annealed at 150℃ has the best performance with the highest transmittance of 90.5% in the visible range, a resistivity of 1.28×10-4Ω·cm and a carrier concentration of 4.10×1021cm-3.
Nano-SiO2 powder was coated on the polished and laser etched surface by the sol-gel and dip-coating method to prepare hydrophobic/superhydrophobic warship aluminium alloy surface. The durability of the hydrophobic/superhydrophobic surface was tested by using the method of the sample load and friction slide on sand paper. The results show that the contact angle of polished surface increases with increasing SiO2 concentration up to 150.8°, but the surface has high adhesive force for the droplet. When the length of sliding reaches 10m, the contact angle is 72.3° less than the original. The surface fabricated by laser etched grid or dot microstructures exhibits both superhydrophobic and low adhesive force. The grid surface has greater contact angle as high as 155.4°, and smaller roll angle, the minimum is only 0.34°. When the length of sliding reaches 10m, the surface is still hydrophobic, and the grid microstructure has greater durability.
The corrosion behavior of Super304H coated alkali metal sulfate at 750℃ was investigated by means of XRD, SEM and EMPA. The results show that high-temperature oxidation mainly occurs at the earlier corrosion stage and the kinetics curves follow a parabolic law. Moreover, the compact and protective Fe/Cr oxide films form on the surface of the sample. Corrosion time is prolonged, and volatile corrosion product Na4(CrO4)(SO4) is produced. The oxide films are thickened and become loose as well as porous. Meanwhile, fine porosity initiates near base material surface, gathers and grows into micro-cracks, micro-pores, and thus internal sulfidation and micro-defects occur inside the base material. It is concluded that the formation of low melting point eutectic Na2O·Na2SO4 and the basic fluxing of Cr2O3 in molten Na2SO4 accelerate the development of corrosion process.
In order to improve the microstructure and properties of MGH956 alloy TIG weld, the alloy was welded with TIG in -situ alloying. The effects of V on the microstructure and properties of MGH956 alloy weld were studied, and the mechanism of V was discussed. The OM and SEM results show that the microstructure of the welds are refined and homogenized with different content of V added in the consumables, and as wV=1.5%, the grain size is the smallest and the most uniform. At the same time the weld porosity is the lowest. The EDS results show that there are (Ti, V) C particles generated in addition to YAlO3, TiC, TiN particles in the weld. It can be observed by TEM that the interface between carbide particles and the matrix is clean and joins well. The strength of the weld is the highest when wV=1.5%, and the fracture mode of the joints changes from complete brittle fracture to ductile fracture.
The nominal composition of Ti-45Al-8Nb-xY(x=0,0.1,0.3,atom fraction/%) alloys was prepared by the non-pole-consuming vacuum arc furnace. The effect of Y addition and different homogenization treatments on the microstructure of the TiAl-based alloys with high Nb content was investigated by using the optical microscope (OM), scanning electronic microscope (SEM), X-ray diffraction (XRD), energy dispersive spectroscope (EDS). The results show that (α2+γ) lamellar colonies are refined by the element Y and the refining effect is improved with the increase of Y addition. The Y distributes along the grain boundaries and internal of lamellar colonies in the form of Y2O3 and YAl2 particles. The increase of phase transformation temperature Tα caused by the Y addition results in different microstructures formed in the TiAl-based alloys with high Nb content on the same homogenization process.
The macro piezoceramic fiber composite actuators were fabricated by cutting-filling method. The structure of this actuator was made up of three parts, including interdigitated electrode plates, epoxy resin bonding layer and macro piezoceramic fiber composite layer. The piezoelectric properties of the macro piezoceramic fiber composite were calculated by theoretical model. The P-E loop and strain properties of the actuator were tested by TF Analyzer 2000 ferroelectric analyzer and dynamic strain acquisition system based on LabVIEW. The results show that the theory piezoelectric constants d33 and remanent polarization Pr of the macro piezoceramic fiber composite are 634pC·N-1and 31.4μC·cm-2, respectively. Moreover, the actuator can also generate longitudinal strain of 30με and transverse strain of 20με at ±1,000V sinusoidal alternating voltage. That means, the stretching of longitudinal and transverse directions of the actuator is 0.63μm and 0.34μm, respectively.
Rotating bending fatigue tests were conducted on the super duplex stainless steel of SAF 2507 to investigate fatigue properties in both air and 3.5%NaCl aqueous environment. The results show that on the macro scale, compared to the air fatigue, there is no significant reduction in the fatigue strength of SAF2507 under corrosive environment, which is 90% of the air fatigue strength. But on the micro scale, the fatigue failure exhibits ductile fracture with fatigue striations observed in both ferrite and austenite in air. While in 3.5%NaCl, austenites have ductile fracture and ferrites exhibit cleavage fracture mode. The width and space between fatigues striations vary with grain orientations and second cracks, indicating that ferrite and austenite phase on fracture surface could not be identified simply by fatigue striations space.
The mechanical properties of original and hanging over hydrogenation reactor 2.25Cr1Mo steel were investigated in order to analyze the material degradation. The microstructure and fracture morphology of original and in-service alloy were observed by metallographic microscope and scanning electron microscope. The results show that the 120000h hanging time leads to obvious performance degradation. The ductile to brittle transition temperature of 2.25Cr1Mo steel increases. A number of cracks appear at the grain boundary and carbides. Carbides tend to chain distribution and coarsening which results in grain boundary weakness. The decrease of matrix alloying elements content causes grain boundary segregation of phosphorus and lower tempering resistance.
Stress corrosion cracking (SCC) behavior and sensitivity of X80 pipeline steel and weld joint in NS4 solutions were investigated using slow strain rate tension (SSRT) test. The results show that X80 pipeline steel and weld joint appear mainly plastic damage. The plastic damage of weld joint is higher than that of base metal. The fracture mode of X80 pipeline steel and weld joint exhibits typical ductile fracture in the air, and the transgranular SCC in NS4 solution. Both base metal and weld joint fracture's middle areas of X80 pipeline steel exhibit more obvious brittle fracture feature than that of the edge area in NS4 solutions. The corrosion mechanism of X80 steel is anodic dissolution(AD) above -749.86mV, and the mixed mechanism of AD and hydrogen embrittlement(HE) between -749.86-839.19mV, and HE mechanism below -839.19mV.
The variation of six mechanical properties of high-density polyethylene (HDPE), used as rotational packaging case, with five meteorological factors within one year were investigated by principal component analysis(PCA). The susceptibility and relationships between meteorological factors and mechanical properties at four particular climatic conditions were analyzed. The results show that the impact strength and bending modulus are highly susceptible to the meteorological factors. The tensile strength is with secondary susceptibility dependent on climate, while the bending strength, hardness and tensile modulus are insusceptible. The synergetic correlation analysis shows that the impact strength with the monthly total radiation and total amount of precipitation is presented, while being anti-correlated with the mean monthly atmospheric pressure and weak-correlated with the mean monthly relative humidity. The correlations of the bending modulus with different meteorological factors are equivalent and are weaker than that of the impact strength.
The physical structure, performance and recent advances of carbon nanotubes microwave absorbers were reviewed and summarized. The approaches for further researches were also suggested. Recent researches on carbon nanotubes microwave absorbers are mainly focused on carbon nanotubes microwave absorbers with different structures, magnetic metal/carbon nanotubes microwave absorbers, rare earth/carbon nanotubes microwave absorbers, ferrite/carbon nanotubes microwave absorbers, polymer/carbon nanotubes microwave absorbers and ceramic/carbon nanotubes microwave absorbers. For the broad application of carbon nanotubes as electromagnetic wave absorbers, further investigations should focus on aspect control, structure optimization, surface decoration, composite doping modification, interface bonding and oxidation protection of carbon nanotubes.
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