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2009年  第16卷  第6期

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Minerals
Evaluation of boring machine performance with special reference to geomechanical characteristics
K. Goshtasbi, M. Monjezi, P. Tourgoli
2009, 16(6): 615-619. doi: 10.1016/S1674-4799(10)60001-5
中文摘要(303) PDF(19) SpringerLink
摘要:
The duration of tunneling projects mostly depends on the performance of boring machines. The performance of boring machines is a function of advance rate, which depends on the machine characterizations and geomechanical properties of rock mass. There were various theoretical and empirical models for estimating the advance rate. In this paper, after determining the geomechanical properties of rock mass encountered in the Isfahan metro tunnel, the performance of the roadheader and tunnel boring machine (TBM) were then evaluated using various models. The calculation results show that the average instantaneous cutting rate of the roadheader in sandstone and shale are 42.8 and 74.5 m3/h respectively. However the actual values in practice are 34.2 and 51.3 mm3/h. The operational cutting rate of the roadheader in sandstone and shale are 8.2 and 9.7 mm3/h respectively, but the actual values are 6.5 and 6.7 mm3/h. The penetration rate of the TBM in shale is predicted to be 50-60 mm/round.
Metallurgy
Reduction of 1-3 mm iron ore by H2 in a fluidized bed
Jian-ming Pang, Pei-min Guo, Pei Zhao, Chao-zhen Cao, Ding-guo Zhao, Duo-gang Wang
2009, 16(6): 620-625. doi: 10.1016/S1674-4799(10)60002-7
中文摘要(335) PDF(27) SpringerLink
摘要:
The reduction of 1-3 mm fine powder of iron ore by H2 was conducted in a lab-fabricated kg class high temperature fluidized bed. The results show that the differential pressure in the fluidized bed, which has small fluctuation with time, increases with the increase of gas flowing velocity. The utilization ratio of gas decreases when the reaction lasts longer time indicating that the reaction is faster at the beginning of reduction and becomes slower in the latter process. The higher the reaction temperature is, the higher the utilization ratio of gas is, but the difference of utilization ratio among the different temperatures becomes smaller with time. The utilization ratio of gas and the metallization ratio can reach 9% and 84% respectively at 750℃ for 20 min, which shows the reduction reaction by H2 is very fast. The increase of metallization ratio with gas velocity performs quite good linearity, which shows that a higher velocity of reducing gas can be used to improve the productivity of the reactor when H2 is used as reducing gas. With the increase of charge height, the metallization ratio decreases, but the utilization ratio of gas increases. The reaction temperature can be reduced to 700-750℃ from 800-850℃ when H2 is used as reducing gas.
Metallurgy
Temperature distribution and dynamic control of secondary cooling in slab continuous casting
Liang-liang Guo, Yong Tian, Man Yao, Hou-fa Shen
2009, 16(6): 626-631. doi: 10.1016/S1674-4799(10)60003-9
中文摘要(259) PDF(15) SpringerLink
摘要:
To predict and optimize the temperature distribution of slab continuous casting in steady operational state, a three-dimensional model (named "offline model") based on the heat transfer and solidification theories was developed. Both heat transfer and flux distribution characteristics of the nozzle sprays on the slab were considered, and the complicated boundary conditions, such as spray cooling, natural convection, thermal radiation as well as contact cooling of individual rolls were involved in the model. By using the calibrated caster dependent model factors, the calculated temperature and shell thickness accorded well with the measured. Furthermore, a dynamic secondary water cooling control system was also developed on the basis of a two-dimensional transient heat transfer model (named "online model") and incremental PID control algorithm to reduce slab surface temperature fluctuation in unsteady state. Compared with the traditional spray table control method, the present online model and dynamic PID control demonstrate a higher capability and flexibility to adjust cooling water flowrate and reduce slab surface temperature fluctuation when the casting speed is changed.
Metallurgy
Micro-analysis of high-temperature oxidation-resistance of a new kind of heat-resistant grid plate in grate-kiln
Jun-you Liu, Feng Li, Jie Liu, Yi Zhang, Yu-lei Wang
2009, 16(6): 632-639. doi: 10.1016/S1674-4799(10)60004-0
中文摘要(289) PDF(7) SpringerLink
摘要:
To further improve the oxidation-resistance of materials and reduce the cost of grid plates in grate-kiln, a new kind of heat-resistant grid plate was developed. The microstructure of this grid plate with a life more than 18 months was studied by XRD, SEM and EDS techniques. The results show that high hardness, high intensity and good impact property make the new kind of heat-resistant grid plate and its oxide film have a higher resistance to deformation and abrasion at 900-1000℃ Besides, small grain size is beneficial to form a complete protective oxide film. The oxide film composed of SiO2 layer, Cr2O3 layer and Fe2O3 layer is rather thin and bonds closely with the backing. The forming of the chemical stable nickel-rich layer increases the density of Cr2O3 layer.
Materials
Numerical simulation of 3D-microstructures in solidification processes based on the CAFE method
Jin-long Wang, Fu-ming Wang, Yan-yu Zhao, Jiong-ming Zhang, Wei Ren
2009, 16(6): 640-645. doi: 10.1016/S1674-4799(10)60005-2
中文摘要(308) PDF(19) SpringerLink
摘要:
It was analyzed that the finite element-cellular automaton (CAFE) method was used to simulate 3D-microstructures in solidification processes. Based on this method, the 3D-microstructure of 9SMn28 free-cutting steel was simulated in solidification processes and the simulation results are consistent with the experimental ones. In addition, the effects of Gaussian distribution parameters were also studied. The simulation results show that the higher the mean undercooling, the larger the columnar dendrite zones, and the larger the maximum nucleation density, the smaller the size of grains. The larger the standard deviation, the less the number of minimum grains is. However, the uniformity degree decreases first, and then increases gradually.
Materials
In-situ observation on the deformation behaviors of Fe-Mn-C TWIP steel
Zhen-li Mi, Di Tang, Yong-juan Dai, Hai-tao Jiang, Jian-chong Lü
2009, 16(6): 646-649. doi: 10.1016/S1674-4799(10)60006-4
中文摘要(267) PDF(13) SpringerLink
摘要:
The microstructure and crack behaviour of twinning induced plasticity (TWIP) steel during tensile deformation was investigated with in-situ scanning electron microscopy (SEM). The results show that there are two modes of plastic deformation during tensile test in the Fe-Mn-C TWIP steel: dislocation gliding and deformation twins. During the process of tensile deformation, secondary deformed twins are found. Inclusions have played a role in the course of ductile fracture, and microcracks initiate from inclusions and twin-twin intersections.
Materials
Effects of sulfur addition methods and Ca-Si treatment on the microstructure and properties of 30MnVS
Guo-zhong Li, Fu-ming Wang, Rong Hui, Wen-kui Cao
2009, 16(6): 650-653. doi: 10.1016/S1674-4799(10)60007-6
中文摘要(197) PDF(18) SpringerLink
摘要:
The effects of sulfur addition methods and Ca-Si treatment on the microstructure and properties of free-cutting non-quenched and tempered steel 30MnVS were investigated by using optical microscopy, SEM and tensile test methods. The results show that sulfur addition methods influence the morphology of sulfides and the properties of 30MnVS slightly. Ca-Si treatment is beneficial for the formation of complex sulfides which normally have oxide cores, therefore, improving the distribution of sulfides in the tested steel and enhancing its toughness. The two methods, pyrite addition during LF process and S wire feeding during VD process, slightly influence the morphology and distribution of sulfides and the properties of 30MnVS; Ca addition not only promotes the nucleation of sulfides on the cores of calcium aluminate inclusions, but also creates modification effect on MnS, reducing the relative plasticity and hot deformability of sulfides during hot rolling process, thereby reducing the length/width value of sulfides and improving their distribution, and significantly enhancing its mechanical properties, in particular, the impact toughness increased by 30%.
Materials
Intergranular corrosion behavior of high nitrogen austenitic stainless steel
Hua-bing Li, Zhou-hua Jiang, Zu-rui Zhang, Yang Cao, Yan Yang
2009, 16(6): 654-660. doi: 10.1016/S1674-4799(10)60008-8
中文摘要(239) PDF(10) SpringerLink
摘要:
The intergranular corrosion (IGC) behavior of high nitrogen austenitic stainless steel (HNSS) sensitization treated at 650-950℃ was investigated by the double loop electrochemical potentiodynamic reactivation (DL-EPR) method. The effects of the electrolytes, scan rate, sensitizing temperature on the susceptibility to IGC of HNSS were examined. The results show that the addi-tion of NaCl is an effective way to improve the formation of the cracking of a passive film in chromium-depleted zones during the reactivation scan. Decreasing the scan rate exhibits an obvious effect on the breakdown of the passive film. A solution with 2 mol/L H2SO4+1 mol/L NaCl+0.01 mol/L KSCN is suitable to check the susceptibility to IGC of HNSS at a sensitizing temperature of 650-950℃ at a suitable scan rate of 1.667 mV/s. Chromium depletion of HNSS is attributed to the precipitation of Cr2N which results in the susceptibility to IGC. The synergistic effect of Mo and N is suggested to play an important role in stabilizing the passive film to prevent the attack of IGC.
Materials
Effect of Ca2+ on CO2 corrosion properties of X65 pipeline steel
Chen Ding, Ke-wei Gao, Chang-feng Chen
2009, 16(6): 661-666. doi: 10.1016/S1674-4799(10)60009-X
中文摘要(442) PDF(14) SpringerLink
摘要:
The effect of Ca2+ on CO2 corrosion to X65 pipeline steel was investigated in the simulated stratum water of an oil field containing different concentrations of Ca2+. It is found that Ca2+ can enhance the corrosion rate, especially in the Ca2+ concentration from 256 to 512 mg/L, which can be attributed to the growing grain size and loosing structure of corrosion scales with increasing Ca2+ concentration. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) investigations reveal that a complex carbonate (Fe, Ca)CO3 forms at high Ca2+ concentration due to the gradual replacement of Fe2+ in FeCO3 by Ca2+.
Materials
Textures of high-strength and low-expansion Fe-Ni alloy wires during cold-drawing processes
Leng Chen, Jian-fu Zhang, Li Zhang, Li Meng
2009, 16(6): 667-671. doi: 10.1016/S1674-4799(10)60010-6
中文摘要(217) PDF(10) SpringerLink
摘要:
Textures of high-strength and low-expansion Fe-Ni alloy wires during cold-drawing processes were investigated using X-ray diffraction (XRD) and electron back scatter diffraction (EBSD) techniques. The experimental results show that the 〈111〉 and 〈100〉 fibre textures are the main texture components, and crystalline grains in the surface are more fine and uniform than those in the center of Fe-Ni alloy wires during cold-drawing processes. It is found that the volume fraction of the 〈111〉 fibre texture component determined by quantitative regression calculation of the Gaussian distribution function reaches more than 60% and the strong 〈111〉 fibre texture component favors the torsional property of Fe-Ni alloy wires.
Materials
Effect of heat treatment on microstructures and mechanical properties of a bulk nanostructured Al-Zn-Mg-Cu alloy
Han-bin Chen, Bin Yang
2009, 16(6): 672-676. doi: 10.1016/S1674-4799(10)60011-8
中文摘要(213) PDF(7) SpringerLink
摘要:
A bulk nanostructured Al-10.0Zn-2.8Mg-1.8Cu alloy was synthesized by cryomilling first and then by spark plasma sintering (SPS), and the effect of heat treatment on the microstructures and mechanical properties of this alloy were studied. Most MgZn2 particles with a coarse size lie on the grain boundaries of the SPS-processed sample. After solid solution and artificial aging, fine spherical-like MgZn2 particles precipitate uniformly in the grain interiors. No obvious grain growth is found after the heat treatment. A nanoindentation study indicates that no clear change is found in the Yong's modulus of the nanostructured alloy after the heat treatment. However, the hardness of the nanostructured alloy increases by about 33% after the heat treatment, which is attributed to the effect of precipitation-hardening.
Materials
Effects of nano-sized Ag reinforcing particulates on the microstructure of Sn-0.7Cu solder joints
Feng Tai, Fu Guo, Zhi-dong Xia, Yong-ping Lei, Yao-wu Shi
2009, 16(6): 677-684. doi: 10.1016/S1674-4799(10)60012-X
中文摘要(151) PDF(7) SpringerLink
摘要:
Composite solders were prepared by mechanically dispersing different volumes of nano-sized Ag particles into the Sn-0.7Cu eutectic solder. The effects of Ag particle addition on the microstructure of Sn-0.7Cu solder joints were investigated. Besides, the effects of isothermal aging on the microstructural evolution in the interfacial intermetallic compound (IMC) layer of the Sn-0.7Cu solder and the composite solder reinforced with 1vol% Ag particles were analyzed, respectively. Experimental results indicate that the growth rate of the interfacial IMC layer in the Ag particles reinforced composite solder joint is much lower than that in the Sn-0.7Cu solder joint during isothermal aging. The Ag particles reinforced composite solder joint exhibits much lower layer-growth coefficient for the growth of the IMC layer than the corresponding solder joint.
Materials
Electromigration in eutectic SnAg solder reaction couples with various ambient temperatures and current densities
Guang-chen Xu, Fu Guo, Wan-rong Zhu
2009, 16(6): 685-690. doi: 10.1016/S1674-4799(10)60013-1
中文摘要(207) PDF(8) SpringerLink
摘要:
The electromigration behavior of eutectic SnAg solder reaction couples was studied at various temperature (25 and 120℃ when the current density was held constant at 104 A/cm2 or 5×103 A/cm2. Under the current density of 104 A/cm2, scallop type Cu6Sn5 spalls and migrates towards the direction of electron flow at room ambient temperature (25℃), but transforms to layer type Cu3Sn and leaves Kirkendall voids in it at high ambient temperature (120℃). Under the current density of 5×103 A/cm2 plus room ambient temperature, no obvious directional migration of metal atoms/ions is found. Instead, the thermal stress induced by mismatch of dissimilar materials causes the formation of superficial valley at both interfaces. However, when the ambient temperature increases to 120℃, the mobility of metal atoms/ions is enhanced, and then the grains rotate due to the anisotropic property of β-Sn.
Materials
Effect of Ag and Ni on the melting point and solderability of SnSbCu solder alloys
Yan-fu Yan, Yan-sheng Wang, Li-fang Feng, Ke-xing Song, Jiu-ba Wen
2009, 16(6): 691-695. doi: 10.1016/S1674-4799(10)60014-3
中文摘要(289) PDF(13) SpringerLink
摘要:
To improve the properties of Sn10Sb8Cu solder alloy, two new solders (SnSbCuAg and SnSbCuNi) were formed by adding small amounts of Ag or Ni into the solder alloy. The results show that the melting point of the SnSbCuAg solder alloy decreases by 14.1℃ and the spreading area increases by 16.5% compared to the matrix solder. The melting point of the SnSbCuNi solder alloy decreases by 5.4℃ and the spreading area is slightly less than that of the matrix solder. Microstructure analysis shows that adding trace Ag makes the melting point decline due to the dispersed distribution of SnAg phase with low melting point. Adding trace Ni, Cu6Sn5 and (Cu, Ni)6Sn5 with polyhedron shape on the copper substrate can be easily seen in the SnSbCuNi solder alloy, which makes the viscosity of the melting solder increase and the spreading property of the solder decline.
Materials
Enhancement of magnetic properties and thermal stability of nanocrystalline (NdDyTb)12.3(FeZrNbCu)81.7B6.0 alloy with Co substitution
Xiao-qian Bao, Wei Li, Jie Zhu, Xue-xu Gao, Shou-zeng Zhou
2009, 16(6): 696-700. doi: 10.1016/S1674-4799(10)60015-5
中文摘要(262) PDF(7) SpringerLink
摘要:
The major drawbacks of Nd-Fe-B magnets are relatively low Curie temperature and poor thermal stability. Ribbons with the near stoichiometric 2:14:1 composition of Nd10.8Dy0.75Tb0.75Fe79.7-xCoxZr0.8Nb0.8Cu0.4B6.0 (x=0, 3, 6, 9, 12, 15) were prepared by rapid quenching and subsequent heat treatment. The effect of Co element on the magnetic properties, thermal stability, and microstructure of the ribbons was systematically studied by vibrating sample magnetometer (VSM), thermal magnetic analysis, atomic force microscopy (AFM), and transmission electron microscopy (TEM). It was found that Co substitution was significantly effective in improving the magnetic properties and the thermal stability of nanocrystalline ribbons. Although the intrinsic coercivity decreased from 1308.7 kA/m for x=0 to 817.4 kA/m for x=15, the remanence polarization and maximum energy product increased from 0.839 T and 116.5 kJ/m3 for the Co-free samples to 1.041 T and 155.1 kJ/m3 for the 12at% Co-substituted samples, respectively. About 10 K increase in Curie temperature was observed for the 2:14:1 phase with 1at% Co substitution. The absolute values of temperature coefficients of induction and coercivity were significantly decreased with Co substitution, which may be attractive for high operational temperature applications. The microstructure of nanocrystalline ribbons was slightly refined with Co substitution.
Materials
Preparation, characterization and photocatalytic activity of N-doped TiO2 nanocrystals
Hong-tao Gao, Jing Zhou, Dong-mei Dai, Guang-jun Liu
2009, 16(6): 701-706. doi: 10.1016/S1674-4799(10)60016-7
中文摘要(316) PDF(9) SpringerLink
摘要:
N-doped TiO2 nanocrystals were prepared using titanium alkoxide as precipitant with different proportional materials. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectra. It is confirmed experimentally that the photocatalytic activity of N-doped TiO2 is much higher than that of Degussa P25, when used for the degradation of crystal violet. The degradation kinetics follows an apparent first-order reaction, which is consistent with a generally observed Langmuir-Hinshelwood mechanism. The doping of TiO2 with nitrogen significantly increases the absorption in the region of visible light. The energy of the band gap of N-doped TiO2 is 2.92 eV. The better performance of N-doped TiO2 can be explained by the fact that it is also excited with longer-wavelength light.
Materials
Characterization and wear behavior of WC-0.8Co coating on cast steel rolls by electro-spark deposition
Jian-sheng Wang, Hui-min Meng, Hong-ying Yu, Zi-shuan Fan, Dong-bai Sun
2009, 16(6): 707-713. doi: 10.1016/S1674-4799(10)60017-9
中文摘要(225) PDF(10) SpringerLink
摘要:
To prepare high wear resistance and high hardness coatings, electro-spark deposition was adopted for depositing an electrode of a mixture of 92wt%WC+8wt%Co on a cast steel roll substrate. The coating was characterized by classical X-ray diffractometer (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). The results indicate that the coating shows nanosized particulate structure and dendritic structure including columnar structure and equiaxed structure. The primary phases of the coating contain Fe3W3C, Co3W3C, Fe2C and Si2W. The coating has a low friction coefficient of 0.13, its average wear-resistance is 3.3 times that of the cast steel roll substrate and the main mechanism is abrasive wear. The maximum microhardness value of the coating is about 1573.9 Hv0.3. The study reveals that the electro-spark deposition process has the characteristic of better coating quality and the coating has higher wear resistance and hardness.
Materials
Effects of binder strength and aggregate size on the compressive strength and void ratio of porous concrete
P. Chindaprasirt, S. Hatanaka, N. Mishima, Y. Yuasa, T. Chareerat
2009, 16(6): 714-719. doi: 10.1016/S1674-4799(10)60018-0
中文摘要(278) PDF(31) SpringerLink
摘要:
To test the influence of binder strength, porous concretes with 4 binder strengths between 30.0-135.0 MPa and 5 void ratios between 15%-35% were tested. The results indicated that for the same aggregate, the rates of strength reduction due to the increases in void ratio were the same for binders with different strengths. To study the influence of aggregate size, 3 single size aggregates with nominal sizes of 5.0, 13.0 and 20.0 mm (Nos. 7, 6 and 5 according to JIS A 5001) were used to make porous concrete. The strengths of porous concrete are found to be dependent on aggregate size. The rate of strength reduction of porous concrete with small aggregate size is found to be higher than that with larger aggregate size. At the same void ratio, the strength of porous concrete with large aggregate is larger than that with small aggregate. The general equations for porous concrete are related to compressive strength and void ratio for different binder strengths and aggregate sizes.
Materials
Preparation of fly ash and rice husk ash geopolymer
S. Detphan, P. Chindaprasirt
2009, 16(6): 720-726. doi: 10.1016/S1674-4799(10)60019-2
中文摘要(525) PDF(41) SpringerLink
摘要:
The geopolymer of fly ash (FA) and rice husk ash (RHA) was prepared. The burning temperature of rice husk, the RHA fineness and the ratio of FA to RHA were studied. The density and strength of the geopolymer mortars with RHA/FA mass ratios of 0/100, 20/80, 40/60, and 60/40 were tested. The geopolymers were activated with sodium hydroxide (NaOH), sodium silicate, and heat. It is revealed that the optimum burning temperature of RHA for making FA-RHA geopolymer is 690oC. The as-received FA and the ground RHA with 1%-5% retained on No.325 sieve are suitable source materials for making geopolymer, and the obtained compressive strengths are between 12.5-56.0 MPa and are dependent on the ratio of FA/RHA, the RHA fineness, and the ratio of sodium silicate to NaOH. Relatively high strength FA-RHA geopolymer mortars are obtained using a sodium silicate/NaOH mass ratio of 4.0, delay time before subjecting the samples to heat for 1 h, and heat curing at 60oC for 48 h.

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