- 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)
Texture evolution in surface layer and subsurface layer during high temperature annealing process of 0.20mm CGO silicon steel was analyzed by X-ray diffraction (XRD) texture analysis technique and electron back-scattered diffraction (EBSD) micro-texture analysis technique. The results indicate that 0.20mm CGO silicon steel experiences low-temperature recovery, primary recrystallization, recrystallized grain growth, and secondary recrystallization process, finally forms sharp Goss texture. Goss oriented grains originate from the Goss grain sub-structure residues in {111}<112> deformation bands of recovery matrix initially, after 2h thermal insulation at 600℃, Goss grain nucleation occurs in the deformation matrix in the first place, then recrystallizes gradually in the following heating process, Goss oriented grains do not have the size advantage in this process, primary recrystallization finishes at 700℃, γ fiber texture and {112}<110> are the major texture components in the matrix. With the increase of annealing temperature, the content and average grain size of Goss oriented grains are improved gradually. At 900-1000℃, Goss grains grow up rapidly and sharp Goss texture is formed by swallowing other oriented grains, secondary recrystallization has taken place at 1000℃.
The hot deformation behavior of 0Cr16Ni5Mo low carbon martensitic stainless steel was studied by the isothermal compression of cylindrical specimens at 900-1150℃ with the strain rate of 0.01-10s-1 on a Gleeble-3800 simulated machine. The relations of the thermomechanical parameters with strain were obtained using the hyperbolic-sine mathematics model and the hot deformation constitutive relationship was established. Processing map was also established based on the dynamic materials model. The microstructure evolution at different conditions was analyzed. The results show that the flow stress decreases with the increase of deformation temperature and increases with the increase of strain rate, the deformation condition has a great influence on the material microstructure. The relationship between deformation parameters and strain have a good relativity, which can be expressed using four polynomial fitting. An optimum processing parameters of hot deformation for this steel can also be obtained by the maps, in which the hot temperature is 980-1150℃ and the strain rate is 0.01-0.2s-1.
The hot deformation behavior of the advanced ultra-high strength hot stamping steel 22MnB5Nb was studied through the isothermal uniaxial tensile tests at 650-950℃ and strain rates of 0.1, 1.0s-1 and 10s-1 by Gleeble 1500D system. The conventional Arrhenius-type hyperbolic sine equation, the Arrhenius-type model considering the material constant strain compensation and the new Arrhenius-type model based on Quasi-Newton BFGS algorithm were established to describe the high-temperature deformation behavior of 22MnB5Nb. The results indicate that 22MnB5Nb steel shows typical work hardening and dynamic recovery softening behavior during hot tensile. And the strain rate and deformation temperature have significant effects on the flow stress. The peak flow stress values predicted by these models are highly consistent with the experimental values, and the Quasi-Newton BFGS algorithm can solve all the material parameters in one time and it is simpler in calculation process and has the highest accurate(R=0.99578, Re=11.03MPa, E=2.48%), while, the Arrhenius-type model considering material constant strain compensation with lower accuracy, but can directly predicts not only the flow stress curve under different deformation conditions, but also the work hardening behavior, the dynamic recovery behavior and the strain rate strengthening effect of the experimental steel during the deformation process.
In order to enhance comprehensive properties of ferritic stainless steel used for automobile exhault manifolds working at high temperature, (Ti, Nb, W)-modified ferritic stainless steel (without Ni) with ultra-low C and N contents was fabricated by means of vacuum melting. Hardness and tension tests, field-emission scanning electron microscope and transmission electron microscope were employed to characterize tensile properties and precipitation behavior of the materials isothermally aged at 550,600℃和700℃. The results indicate that the materials reach the optimized mechanical properties when they are aged at 600℃ for 40h. Two types of precipitates in nanometer size are observed inside the grain and grain boundaries, which are (Ti,Nb)C carbides with irregular shape and Laves phase Fe2(Nb,W) with strip-like shape. Both precipitated phases have consistent orientation relationships with ferritic matrix, i.e.,[011]Fe//[011](Ti,Nb)C and (0${\rm{\bar 1}}$1)Fe//(200)(Ti,Nb)C (orientation deviation ca. 3°), and [011]Fe//[0001]Fe2(Nb,W) and (200)Fe//(01${\rm{\bar 1}}$0)Fe2(Nb,W)(orientation deviation 4°-5°). With the increase of the aging temperature, the sizes of the precipitated phases increase. Meanwhile, the dominant precipitated phases change from (Ti,Nb)C to Fe2(Nb,W).
The significant deterioration effect of σ phase precipitation on the room temperature impact toughness of Z3CN20.09M cast austenite stainless steel used for primary coolant pipe of nuclear power plant was investigated. On the base of above results, the heat treatment process and mechanism of eliminating of σ phase in stainless steel by means of isothermal annealing technology, optical microscope (OM) and scanning electron microscope (SEM) were studied.The results show that the precipitated σ phase can be completely eliminated by the transformation σ→α when the aged specimens are isothermally annealed at 850-1000℃ for a period of time, but the lower annealing temperature is, the longer time required, and vice versa.The diffusion rate of alloying elements is slow when temperature is low,so the transformation of σ phases is also slow.With the increase of temperature, the diffusion rate of alloying elements accelerates and the driving force of σ phases transformation into α phases increases, so the transformation of σ phases becomes higher,thus the transformation time is short.After comprehensive consideration,isothermal annealing at 950℃ for 0.5h is an optimum heat treatment process parameter. The mechanical property of aged Z3CN20.09M specimens after annealed at 950℃ for 0.5h can be completely recovered. The annealing process eliminates embrittlement effect of σ phase on toughness of aged Z3CN20.09M specimens.
A method of high temperature thermo-mechanical treatment (TMT) and subsequent cold (heat) treatment was applied to a novel ultra-high-strength steel (G33 steel). The effect of different process parameters on microstructure and mechanical properties of quasi-static (10-3s-1) tensile samples of G33 steel was investigated. The results show that the optimum treatment process of G33 steel is high temperature (1078℃) TMT with 50% deformation + cooled at -73℃ for 1h + tempered at 200℃ for 2h, and after the process, the yield strength of G33 steel is 1685MPa, the ultimate tensile strength is 2130MPa, and the total elongation is 14.0%.
Bismaleimide foam using azodicarbonamide (AC) as the foaming agent was prepared through prepolymerization and foaming. The influence of AC on bubble structure, density, high-temperature dimensional stability temperature(HDT) as well as compressive properties of the bismaleimide(BMI) foam was investigated. The results show that foam density could be adjusted from 60kg/m3 to 280kg/m3 by content of AC, meanwhile, AC dosage has little influence on cell size and its distribution. As the content of AC decreases, the HDT and compressive strength increase. When the foam density is 280kg/m3, the HDT is 220℃, compressive strength and modulus are 4.8MPa and 200MPa respectively, meeting the requirements of the high-temperature and mechanical properties of structural foams.
The WC-reinforced Fe-based coating was fabricated successfully on Q235 plate by plasma in-situ metallurgy process with Fe-Ni-W-C powder blends. Microstructure and growth characteristic of WC were analyzed by SEM, XRD and EDS. Dry sliding wear tests were made by M-2000 tester with load of 300N, sliding speed 0.836m/s and distance 500m. Results show that the morphology of in-situ synthesized WC is regular trigonal prism (RTP) which is growing along the crystal direction <0001> on the surface (0001) with multi-layered structure. The maximum length of RPT is nearly 60μm, being a type of coarse crystalline WC. Under the same dry sliding wear condition, the wear resistance of WC-reinforced Fe-based coating is about eleven times bigger than that of the non-WC-reinforced Fe-based coating. The friction stability of WC-reinforced coating decreases as the hard phase WC gradually protruding from the coating. The main wear mechanism of WC/Fe is abrasive wear and oxidation wear.
Mg-3%Al alloy containing trace 0.1%Fe was inoculated by carbon. The carbon-inoculated Mg-3%Al-0.1%Fe melt was held for different time after inoculation to study the effect of holding time on grain size and characteristic of carbonaceous nuclei. The results show that when the holding time is within 20min, there mainly exist Al4C3 particles and the particles with duplex phase structure of Al4C3 coated on Al-(C)-Fe in the samples. The number of particles of Al4C3 and Al4C3 coated on Al-(C)-Fe decreases with the increase of holding time due to aggregation, settlement and structure change of the potent nuclei. Consequently, the grains become coarse and inoculation fading occurs.
UMT-Ⅱ multi-functional friction and wear tester was used to investigate the sliding friction behavior of polyvinyl alcohol/hydroxyapatite(PVA/HA)composite hydrogel under different contacting scales, and the sliding friction mechanism of PVA/HA composite hydrogel was studied by finite element method (FEM). The results show that in the process of the sliding friction, the average friction, the average friction coefficient and the deformation depth of PVA/HA composite hydrogel decrease gradually with the contacting diameter increasing, and exhibit an increase trend with the contacting load; as the contact diameter increases, the fluid load support increases, then the average friction and deformation depth decrease; as the contact load increases, the loss of the liquid phase increases, then the fluid load support decreases, which causes that the average friction and deformation depth increase.
To overcome the difficulty in microstructure distinction of fine weave pierced C/C composites for their low contrast in micro-CT, a two-step filtration was suggested to obtain the eligible grey value threshold indicating fiber bundles/matrix boundary. Binary images of fiber bundles and matrix void were converted from original images, and abatement of noise effect and boundary smoothened by using techniques of mid-filter and inflation/corrosion. Based upon the refined images, matrix porosity and the local curvatures of X fiber bundles are found satisfying normal distribution, while Y fiber bundle curvature satisfying Laplace distribution, statistically. A mechanical model which represents these local features is established and the predicted tensile and shear modulus agree with Laplace distribution while the predicted Poisson's ratio agrees with normal distribution. The distribution regularity of predicted tensile modulus is validated by experiment.
The Ce68Al10Cu20Nb2 bulk amorphous alloy was prepared by injection casting into copper mold. The corrosion behaviors of the alloy in 1mol/L NaOH solution were investigated by potentiodynamic polarization curve method and electrochemical impedance spectroscopic (EIS) technique. The surface morphology of passive film was investigated by scanning electron microscopy (SEM). The composition of passive film was characterized using X-ray photoelectron spectroscopy (XPS). The results show that the Ce68Al10Cu20Nb2 bulk amorphous alloy exhibits a self-passivation phenomenon in 1mol/L NaOH solution with the passive region from -0.25V to 0.50V and the passive current density between 10-5-10-6A/cm2. The passive film obtained through electrochemical passivation consists of a porous outer layer and a dense inner layer. The outer layer is mainly composed of the oxides/hydroxides of Ce and the oxides of Nb,the inner layer is composed of the oxides/hydroxides of Ce, Cu,Al and the oxides of Nb. The content of hydroxides gradually decreases and the content of oxides gradually increases from the surface to the inside of the passive film.
The method of low current loading on single carbon fiber composite system was designed for carbon fiber/epoxy resin. By means of single fiber fragmentation test, the effects of low current on interfacial bonding properties of two kinds of carbon fiber/epoxy resin systems were investigated. The results show that the interfacial bonding strength and interfacial load transfer efficiency of T300B and T700SC carbon fiber systems decrease after loading with 0.60-0.67mA direct current. The decreasing degrees do not change obviously with current-loading time. The interfacial bonding property of the T300B carbon fiber system shows higher sensitivity to low current. This may be attributed to different surface characteristics of the two carbon fibers. By changing the curing degree of the matrix, the interfacial bonding strength of samples after low current loading was analyzed, and the mechanism of carbon fiber/epoxy resin interfacial property affected by low current is related to change of stress state at interfacial region and the joule heating effect generated by current.
The change tendency of passive film-induced stress and susceptibility to stress corrosion cracking (SCC) with various pH values of 7050 aluminum alloy in 3.5% (mass fraction) NaCl solution was investigated by slow strain rate testing (SSRT) and flowing stress differential method. The results show that when pH≤7, with the increase of pH value, the passive film-induced stress and the susceptibility to SCC decrease, correspondingly; when pH>7, they increase with the increase of pH value. However, when pH=1,14, the corrosion type is exfoliation corrosion, the alloy matrix exfoliated, there is no film formed on the specimens surface. Moreover, the variation of passive film-induced stress is changed slowly when the pH value is between 6 and 9, nevertheless, it is much more severe when the pH value is between 2 and 5 as well as between 10 and 13. The whole variation plot is presented as valley shape and the passive film-induced stress and susceptibility to SCC is of a close relationship. The film-induced stress is related to the compositions of the passive film by X-ray photoelectron spectrum (XPS).
The influence of different cooling holes distribution on stress rupture property and fracture behavior of air-cooled turbine blades modeling specimens of single crystal superalloy DD6 at 980℃/300MPa was analyzed. The results show that cooling holes distribution is the main factor affecting the stress rupture life at the same temperature and stress conditions. The stress rupture life of modeling specimens declines regularly as rows of cooling holes increase, however, the stress rupture life of modeling specimens with one row cooling holes or two rows cooling holes is slightly longer than that without cooling holes. Based on fracture surface and metallurgical observations, the specimens without cooling holes fracture in the mode of microvoid coalescence. The fracture surface is made up of small square-shaped facets and there are heart checks near the fracture surfaces of the specimens,but for the specimens with cooling holes, the fracture cracks initiate from the cooling holes and stress rupture deformation concentrates on the region near cooling holes. The whole fracture surface oxidizes seriously and the small square-shaped facets reduce, dimples increase. In addition, there are cracks and oxidization characteristics near the fracture surfaces of the specimens. Based on the crystal plasticity theory, the distribution of stress along cooling holes is obtained. The simulated results show that stress concentration and redistribution occur around the cooling holes, and the form of the fracture surface is consistent with numerical analysis.
Graphene-based composite materials have extensive potential applications in many fields due to excellent properties,especially in supercapacitor.The structures of graphene-based composite supercapacitor materials were classified, the progress in research of different graphene-based composite supercapacitor materials was reviewed from the point of graphene-carbon based composites, graphene-conductive polymers composites and graphene-transition metal compound composites,and the relationship of optimizing the electrode structure and improving the performance of electrode were focused.Meanwhile, the applications of graphene-based composite materials in the fields of lithium ion battery, solar cell, catalysis were outlined. The development tendency of graphene-based composite electrode materials is to assemble excellent supercapacitors with high energy density, power density and long cycle life.
The research status, progress and development tendency of mechanical properties of graphene/metal composites were reviewed. Effects of micromechanical models of linear elastic heterogeneous materials in predicting of the strengthening mechanism involved in graphene/metal composites were introduced. The effects of the structural integrity of graphene and dispersion technique on the strengthening efficiency were focused and discussed. The problems of reinforcing metal matrix composites with graphene were summarized. The research direction of mechanical properties of graphene/metal composites was proposed from the aspects such as graphene development, theoretical exploration, dispersion technique development and synergetic enhancement and etc.
The research progress of iron-rich phase morphology, formation conditions, and its influencing factors of iron-rich phase in Al-Si alloy was reviewed, and the latest research status of iron-rich phase morphology and distribution affected by alloy elements, melting & casting process was also dicussed. The research status shows that the needle iron-rich phase does great harm to the properties of Al-Si alloys, more severe than the Chinese-script iron-rich phase. Besides, the morphology of the iron-rich phase is significantly affected by alloy component and casting process. Therefore, the important research trend is to study the interaction and effect principle of elements and melting & casting process on iron-rich phase morphology, in order to obtain the useful form of iron-rich phase or to mitigate the hazard of Al-Si alloy iron-rich phase.
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