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2006年  第13卷  第5期

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Mineral
Effect of the textural properties of rocks on their crushing and grinding features
B. Kekec, M. Unal, C. Sensogut
2006, 13(5): 385-392. doi: 10.1016/S1005-8850(06)60079-0
摘要:
To study the effect of the textural properties of rocks on their crushing feature, the distribution of particle size, the texture, grinding and crushing characteristics of the rocks were investigated, and the relations among them were then analyzed using statistical methods. The relations between the textural properties and the physical and mechanical features of rocks were determined.
Metallurgy
Numerical and physical simulation of a twin-roll strip caster
Bo Wang, Jieyu Zhang, Yin Zhang, Youduo He, Junfei Fan, Yuan Fang, Shengli An
2006, 13(5): 393-400. doi: 10.1016/S1005-8850(06)60080-7
摘要:
The 1:1 water model of a twin-roll strip caster was set up based on the Froude number and the Reynolds number similarity criteria. A new type metal delivery system was designed for the twin-roll strip caster. The level fluctuation and the fluid flow in the pool of the water model were measured using the level detector and the 3D-LDV (laser Doppler velocimetry) technology. It is shown that a wedged delivery system can produce the desirable level fluctuation and even fluid flow distribution in the pool. Numerical simulations for the water model were performed. Comparisons between the numerical and physical simulation results show good agreement near the side dams.
Metallurgy
An efficient analytical decomposition and numerical procedure for boundary layer flow on a continuous stretching surface
Xuehui Chen, Liancun Zheng, Xinxin Zhang
2006, 13(5): 401-405. doi: 10.1016/S1005-8850(06)60081-9
摘要:
An efficient Adomian analytical decomposition technique for studying the momentum and heat boundary layer equations with exponentially stretching surface conditions was presented and an approximate analytical solution was obtained, which can be represented in terms of a rapid convergent power series with elegantly computable terms. The reliability and efficiency of the approxi- mate solution were verified using numerical solutions in the literature. The approximate solution can be successfully applied to provide the values of skin friction and the temperature gradient coefficient.
Materials
Comparison and analysis of dislocation density,morphology and evolution in mi-crostructure of low-carbon steel produced using different technologies
Hao Yu, Yonglin Kang, Hongbo Dong
2006, 13(5): 406-410. doi: 10.1016/S1005-8850(06)60082-0
摘要:
Three kinds of specimens were produced from hot strips of similar composition and same thickness (nominal gauge 4.0 mm) but produced using different technologies, and the dislocation density of these strips was quantitatively measured by positron annihila- tion technique test. The dislocation morphology and evolution in microstructure of each pass for producing the 1.9 mm hot strip using CSP (compact strip production) technology were observed under an H-800 transmission electron microscope; its density was also quantitatively measured using the positron annihilation technique test, and the factors influencing the dislocation density during the production process were analyzed. The experimental results show that the dislocation density in the microstructure produced using CSP technology is higher than that in the microstructure produced using conventional technology. This result was discussed and confirmed on the basis of the finite element simulation and the theory relevant to dislocations.
Materials
Effect of Nb on the transformation kinetics of low carbon(manganese) steel during deformation of undercooled austenite
Guoan Chen, Wangyue Yang, Shouzhen Guo, Zuqing Sun
2006, 13(5): 411-415. doi: 10.1016/S1005-8850(06)60083-2
摘要:
The hot compression tests using Gleeble 1500 were performed by varying the true strain up to 1.6 (80% reduction) in Nb-free and Nb-microalloyed steels. The effect of Nb addition on the transformation kinetics during deformation of undercooled austenite was investigated. It was found that as compared with Nb-free steel,the transformation incubation period of Nb-bearing steel was pro-longed and the transformation kinetics curves parallelly moved to higher strain because of the solute Nb drag effect. Studies on kinetics also showed that the deformation-enhanced ferrite transformation (DEFT) of the two steels were composed of three stages,which can be expressed by the J-M-A equations individually. However,the parameter n related to the mode of nucleation and growth is somewhat different in the first and second stages of the two steels,and the same in the third stage for both the steels corresponding to the nuclea-tion of retained austenite.
Materials
Mechanical properties and microstructure of TRIP steels produced using TSCR process
Yinghui Zhang, Yanli Ma, Yonglin Kang, Hao Yu
2006, 13(5): 416-419. doi: 10.1016/S1005-8850(06)60084-4
摘要:
C-Si-Mn TRIP steels were produced using the thin slab casting and rolling (TSCR) process under simulation in laboratory. The results of tensile tests show that the yield strength,tensile strength,and the total elongation of the experimental TRIP steels are 430 MPa,610 MPa,and 28.4%,respectively. Optical microscopy,scanning electron microscopy (SEM),and transmission electron micros-copy (TEM) were employed to identify the microstructures of the TRIP steels. The final microstructures consist of ferrite,bainite,and retained austenite. The results of quantitative color metallography show that the fraction of the retained austenite is about 5.8%.
Materials
Morphology and orientation relationship of VC precipitates in HSLA steel
Shijian Yan, Xiaoping Liu, Wenhuai Tian
2006, 13(5): 420-423. doi: 10.1016/S1005-8850(06)60085-6
摘要:
The morphology and distribution of VC precipitates in HSLA steel as well as the orientation relationship between VC pre-cipitate and α-Fe were studied by transmission electron microscopy (TEM). The chemical composition of the VC precipitate was analyzed qualitatively by using analytical electron microscopy (AEM) equipped with an energy dispersive spectrum (EDS) system. The VC precipitate is needle-like in shape with a size of about 10 nm in length and is homogeneously dispersed in the α-Fe matrix. The smaller lattice misfit along the <100> lattice direction of α-Fe matrix leads to VC precipitate forming with its long axes nearly parallel to the <100> lattice direction of α-Fe matrix. It is confirmed that the orientation relationship between VC precipitate and α-Fe is the “N-W” orientation relation by selected area electron diffraction (SAED) patterns.
Materials
Distribution,evolution and the effects of rare earths Ce and Y on the mechanical properties of ZK60 alloys
Anru Wu, Changqing Xia, Jiewen Wang
2006, 13(5): 424-428. doi: 10.1016/S1005-8850(06)60086-8
摘要:
Eight kinds of Mg-RE alloys were prepared. The distribution,evolution,and effects of RE Ce and Y in the investigated alloys were studied by examining the mechanical properties of Mg alloys using X-ray diffraction and scan electron analysis,and by TEM observation. The results show that among the investigated alloys,ZK60-1.5%Ce and ZK60-1.0%Y possessed the optimal mechanical properties. Ce and Y were distributed on the grain boundary during casting. After extrusion and T5 (150°C/0-24 h) heat-treatment,Ce and Y were distributed along the extrusion direction and they existed in compound form for both as-casting and as-extrusion specimens. The mechanical properties of the investigated alloys were better than those of ZK60 because of the solid solution strengthening of RE and the dispersion strengthening of Mg-RE or Mg-Zn-RE compounds.
Materials
Microscopic phase-field simulation of L12 and D022 phases during the early precipitation process of Ni-Cr-Al alloys
Zhong Chu, Zheng Chen, Yongxin Wang, Yanli Lu, Yongsheng Li
2006, 13(5): 429-434. doi: 10.1016/S1005-8850(06)60087-X
摘要:
The influence of temperature on the precipitation mechanism and sequence of L12 and D022 phases during the early pre-cipitation process of a Ni-15.5at%Cr-14at%Al alloy was simulated based on the microscopic phase-field model. In the range from 873 to 1373 K,the precipitation mechanism transformed from spinodal decomposition to non-classic nucleation and growth; the in-cubation period prolonged gradually with increasing temperature. The volume fraction of L12 phases increased and that of D022 phases decreased. D022 phases disappeared at 1373 K,and finally single-phase L12 phases were formed.
Materials
A set of microstructure-based constitutive equations in hot forming of a titanium alloy
Xiaoli Li, Miaoquan Li
2006, 13(5): 435-441. doi: 10.1016/S1005-8850(06)60088-1
摘要:
A physical model of microstructure evolution including dislocation density rate and grain growth rate was established based on the deformation mechanism for the hot forming of a class of two-phase titanium alloys. Further,a set of mechanism-based constitu-tive equations were proposed,in which the microstructure variables such as grain size and dislocation density were taken as internal state variables for characterizing the current material state. In the set of constitutive equations,the contributions of different mecha-nisms and individual phase to the deformation behavior were analyzed. The present equations have been applied to describe a correla-tion of the flow stress with the microstructure evolution of the TC6 alloy in hot forming.
Materials
Morphology and microstructure characterization of 95W-3.5Ni-1.5Fe powder prepared by mechanical alloying
Islam S. Humail, Xuanhui Qu, Chengchang Jia, Mingli Qin, Xinbo He
2006, 13(5): 442-445. doi: 10.1016/S1005-8850(06)60089-3
摘要:
The mechanism of mechanical solid-state reactions for formation of tungsten heavy alloy powder was discussed. A high-energy ball mill operating at room temperature was used for preparing tungsten heavy alloy powders,starting from elemental tungsten (W),nickel (Ni),and iron (Fe) powders. X-ray diffraction (XRD),particle size analyzer,scanning electron microscopy (SEM),and transmission electron microscopy (TEM) were used to follow the progress of the mechanical solid-state reaction of W,Ni,and Fe pow-ders. These morphological studies revealed three stages in the milling process. In the first stage,the particle deformation changes the irregular structure of the as-received powder particles to flattened morphology,and the average particle size increases. In the second stage,the powder is sufficiently deformed and the tendency to fracture predominates over welding,and the particle size decreases. With continuous milling,the system reaches steady state,and relatively small and uniform particle size distribution is obtained after 20 h of milling.
Materials
Analysis of switching conditions of chalcogenide alloys during crystallization
Wanhua Yu, C. D. Wright
2006, 13(5): 446-449. doi: 10.1016/S1005-8850(06)60090-X
摘要:
To understand the principle and limitation of chalcogenide alloy Ge2Sb2Te5 (GST) in solid-state memory devices during crystallization,it was necessary to develop a physically realistic model that could reflect the electrical and thermal properties of these media. A novel comprehensive numerical model has been developed for simulating these memory devices,which describes the electrical and thermal behavior using the solution of the nonlinear,time-dependent electrical and heat conduction equation. The fi-nite-difference-time-domain technique was adopted to compute the electrical field and heat distribution in the device. Several con-tributing factors that affect the crystallization switching process such as the geometry of the GST layer,temperature and electric field dependency of the electrical conductivity have been discussed. The results of the simulations were then used to provide critical guidelines for fabrication and optimization of the device performance.
Materials
Growth characterization of anodic film on AZ91D magnesium alloy in an electrolyte of Na2SiO3 and KF
Weiping Li, Liqun Zhu, Yihong Li, Bo Zhao
2006, 13(5): 450-455. doi: 10.1016/S1005-8850(06)60091-1
摘要:
Anodization of AZ91D magnesium alloy in the electrolyte solution of 0.5 mol/L of sodium silicate and 1.0 mol/L of potassium fluoride was investigated. The anodic films were characterized using optical microscopy (OM),scanning electron micros-copy (SEM),and X-ray diffraction (XRD). The corrosion resistance of the various anodized alloys was evaluated by a fast corrosion test using the solution of hydrochloric acid and potassium dichromate. The results showed that the addition of KF resulted in the presence of NaF in the anodic film. The thickness of the anodic film formed under a constant current density of 20 mA/cm2 for 16 min at 60°C exceeded 100 μm. The growth of the anodic film could be divided into three stages based on the anodizing time; the growth rate was much faster during stage II than in stages I and III. The anodic film exhibited the highest corrosion resistance for the AZ91 alloy,which is attributed to the fact that the anodization was maintained until the end of stage II.
Materials
Investigation on the thermal decomposition of aged La2O3
Qifeng Shu, Jianhua Liu, Jiayun Zhang, Mei Zhang
2006, 13(5): 456-460. doi: 10.1016/S1005-8850(06)60092-3
摘要:
The thermal decomposition process of air-aged La2O3 in argon atmosphere was studied using nonisothermal TG-DSC. X-ray diffraction and TG-DSC analysis showed that the aged powder was composed of La(OH)3 with small amounts of oxycarbonate. The decomposition process of air-aged La2O3 involves the two-step decomposition of La(OH)3 and the decomposition of oxycarbonate. The kinetic analysis of the two-step decomposition of La(OH)3 was carried out using Coats-Redfern and isoconversion (Ozawa) methods. The kinetics of the two-step decomposition can be described in terms of the nucleation and growth model A (m=1.5,m is the model parameter) and A (m=2.5),respectively. The apparent activation energy for the first step is 136-144 (Coats-Redfern) and 137-164 kJ/mol (isoconversion). The apparent activation energy for the second step is 191-194 (Coats-Redfern) and 186-213 kJ/mol (isoconversion).
Materials
Study on ceramic photonic bandgap structure with three-dimensional diamond lattice
Haiqing Yin, Wenbin Cao, Y. Miyamoto
2006, 13(5): 461-464. doi: 10.1016/S1005-8850(06)60093-5
摘要:
A novel process,which was based on powder injection molding,was investigated for the fabrication of ceramic photonic bandgap structure with three-dimensional diamond lattice. The SiO2-TiO2 ceramic powder was mixed with a water-soluble agent to produce slurry. The slurry was then injected into an epoxy mold with inverse diamond lattice,fabricated by the stereolitographic rapid prototyping process. To increase the density of the green compact,cold isostatic pressing was applied on the unit. Using thermal de-binding,the water-soluble agent and the epoxy were extracted at 360 and 650 K,respectively. Sintering was immediately done at 950 K for 5 h and the desired three-dimensional ceramic structure was obtained. The calculated band diagram for this structure indicated the existence of an absolute photonic bandgap for all wave vectors. At 14.7-18.5 GHz,a complete band gap was located with a maximum attenuation of 30 dB at 17 GHz,when transmission was measured in the <100> direction between 10 and 20 GHz.
Materials
Microstructure and properties of Si3N4 ceramics obtained from addition of β-phase seeds and celsian
Jun Yang, Jiqiang Gao, Jianfeng Yang, Guanjun Qiao, Yonghong Luo
2006, 13(5): 465-468. doi: 10.1016/S1005-8850(06)60094-7
摘要:
The silicon nitride based ceramics obtained by the addition of β-Si3N4 seeds was fabricated using celsian as the additive and by pressureless sintering. The microstructure of the material was observed and analyzed using XRD,SEM,and TEM and the mechanical response of this array microstructure was characterized for flexural strength and fracture behavior. The result shows that the growth of the larger aspect ratio grains initiate mainly from the seeds through the heterogeneous nucleation mechanism during the process of phase transformation,and the intergranular phase BaAl2Si2O8 services as good refractory materials. In contrast to conven-tional processing,a stable bimodal microstructure and complicated component with a lower cost can be achieved using the above-mentioned process theoretically and practically.
Materials
Sol-gel derived bioactive hydroxyapatite/titania composite films on Ti6Al4V
Bing Su, Guoqing Zhang, Xudong Yu, Chengtao Wang
2006, 13(5): 469-475. doi: 10.1016/S1005-8850(06)60095-9
摘要:
The composite films consisting of the titania gel impregnated with hydroxyapatite (HAP) submicron particles were prepared on commercial Ti6Al4V plates processed by a sol-gel route. HAP powders were synthesized based on wet chemical precipitation method with Ca(NO3)2·4H2O and (NH4)2HPO4 as starting reagents. After being calcined at 900°C,HAP powders were ultrasonically scattered in ethanol to produce HAP sol. The titania sol was prepared using titanium (IV) isopropoxide {Ti[OCH(CH3)2]4} as precursor. Both the titania sol and the HAP/titania mixture were sequentially spin-coated on the substrates and calcined at various temperatures. The characteristics and mechanical adhesion of the composite films were investigated. The results show that the as-prepared films are dense,homogeneous,well-crystallized,and there is a good interfacial adhesion between the film and the substrate. The in vitro bioac-tivities of these films were discussed based on the analysis of the variations of Ca and P concentrations in the simulated body fluid and their surface morphologies against immersion time.
Materials
Fixation for the helical structure of a glassy cholesteric liquid crystal reflective film
Jiumei Xiao, Wanli He, Jin Gao, Huai Yang
2006, 13(5): 476-479. doi: 10.1016/S1005-8850(06)60096-0
摘要:
The planar texture of glassy cholesteric siloxane cyclic side-chain liquid crystals was fixed by quenching initially. Then the polymer network formed by the optically active polymerizable monomers imposed additional constraints on the motion of chain seg-ments of the glassy liquid crystal and then further stabilized the molecule arrangement. A cholesteric liquid crystal film with stable optical properties was developed by this method.