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Based on a simple macro/micro mathematical model developed in this paper and its predicted results, the forming mechanism of equiaxed crystal zone for 1Cr18Ni9Ti stainless steel twin-roll thin strip is investigated and analyzed. In the developed model, the latent heat is treated with the enthalpy method, the grid and nodes are divided by the assumed streamlines. Moreover, the heterogeneous nucleation and columnar-to-equiaxed transition (CET) models are also introduced, together with the revising of dendrite growth dynamic model of Kurz–Giovanola–Trivedi (KGT). Finally, with the help of solid fraction, the coupling of macro/micro models is realized by using different grid-sizes and time-steps, macro and micro, together with the columnar dendrite front tracing. The predicted results of mathematical models indicate that, regardless of the solidification types (semi-solid, rolling or ideal type) of 1Cr18Ni9Ti stainless steel thin strip, the thin strips include the equiaxed crystal zone. The forming of equiaxed crystal zone is possibly related to the following mechanisms: (1) the sedimentation and accumulation of free crystals floating in molten pool onto the dendrites solidification fronts and the accumulated crystals growth and (2) the suppression of the growth of dendritic solidification front and preferential growth of fine free crystals in unsolidified layer near the strip center by the abrupt decrease in the heat transfer coefficient on the strip surface after leaving the minimum gap between the rolls. 相似文献
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Surface Tension of Molten Ni and Ni-Co Alloys 总被引:3,自引:0,他引:3
Kiyoshi NOGI 《材料科学技术学报》2005,21(2):201-206
Surface tension of molten Ni and Ni-Co (5 and 10 mass fraction) alloys was measured at the temperature range of 1773-1873 K using an improved sessile drop method with an alumina substrate in an Ar+3%H2 atmosphere. The error of the data obtained was analyzed. The surface tension of molten Ni and Ni-Co (5 and 10 mass fraction) alloys decreases with increasing temperature. The influence of Co on the surface tension of Ni-Co alloys is little in the studied Co concentration range. 相似文献
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《Wear》2002,252(3-4):306-310
There has been a growing concern for the use of water-based fluids because of the worldwide interest in environmental issues. This has promoted the research and use of water-soluble additives as environmental friendly lubricants. A kind of potential water-soluble additive, S-(carboxylpropyl)-N-dialkyl dithiocarbamic acid was prepared in this work. The friction and wear behaviors of the synthesized compounds as an additive in water-based liquid were evaluated with a four-ball tester and a ring-on-block rig. The wear scar morphology of the ball and the chemical nature of the antiwear films generated on the steel counter face were investigated with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It was found that the synthesized additives had excellent antiwear, load-carrying and extreme pressure performance. The additive reacted with the counter-face metal and generated a surface protective film consisting of FeS, FeS2, FeSO4 and an absorbed compound containing N and acid. 相似文献
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《Materials Letters》2007,61(11-12):2333-2337
Microstructures and mechanical properties of an AZ91D magnesium alloy prepared with semi-solid die-casting (SSDC) were characterized in as-cast conditions. The SSDC alloy exhibits a unique microstructure featuring primary α-Mg globules uniformly distributed in the matrix of fine secondary α-Mg grains and β-Mg17Al12 intermetallic. High ultimate tensile strength and elongation have been achieved before fracture. Observations on the vertical-section microstructure of the fractured sample by scanning electron microscopy (SEM) show that the crack mainly originated from the brittle fracture of the eutectic phase causes the interface decohesion of the ductile Mg phase, making fracture a rather critical event. Before that, the deformation of ductile α-Mg phase in the matrix as well as the “pulling out” of primary α-Mg phase combines to provide the SSDC alloy a certain strain. 相似文献
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YE Hong YAN Zhonglin SUN Zhifu 《武汉理工大学学报(材料科学英文版)》2005,20(3):81-83
After diffusion processing of thermal spraying , aluminum on 20^# steel is discussed in this article. Variations of microstructure, composition as well as mierohardness and corrosion resistatwe of diffusion layer of spray aluminum were explored by means of X-ray diffraction, scanning electron microscopy (SEM) and electron probe microanlysis ( EPMA ) . The result shows that the diffusion layer of spray aluminum consists of η phase ( Fe2Al5 ), ξ phuse ( FeAl2 ), β2 phase ( FeA1 ),β1 plmse ( Fe3Al ) and α pluse from surface to substrate. There are balanced transitions between phases. The layer has extra high hardness and corrosion resistance. 相似文献
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《International Journal of Hydrogen Energy》2020,45(19):11108-11115
In this work, initial activation mechanism of CO2 over MgO supported Ni catalysts has been systematically studied through the periodic DFT calculations. In addition, the role of metal cluster, interface and support for CO2 activation is investigated and the active site is identified. CO2 is most favored to be activated on the interface instead of neither Ni cluster nor MgO support. The effective energy for this process is around 0.67 eV, and the dissociation of CO2 (0.62 eV) is the rate-determining step, since it requires much higher energy than that of the CO2 adsorption process (0.05 eV). Thus, the interface between metal cluster and support plays a key role for C=O bond activation. Moreover, CO1 is preferred to be adsorbed on the Ni cluster, while the O1 is likely to bind on Mg atom of support. To illustrate the adsorption behavior of CO2 at different sites, the Mulliken atomic charge and electron density difference have been calculated. It was found that the total amount of electron gain for CO2 binding at different sites follows the order of Interface (−0.03 e) < MgO support (−0.05 e) < Ni cluster (−0.07 e), and effective energy barrier rises linearly with the increase of electron gain of CO2 binding at different sites. In addition, electron gain of oxygen atom O1 and oxygen atom O2 of CO2 is the same for Ni cluster and MgO support, however, the electron gain of O1 and O2 is different for Interface. The difference of electron gain for two oxygen atoms shows the electron unbalance of CO2 molecule, which is in favor of C=O activation. This study could shed some light on understanding the active sites of CO2 thermal-catalytic activation over MgO supported Ni catalysts, and is helpful to elucidate the reaction on an atomic level. 相似文献
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《International Journal of Hydrogen Energy》2020,45(31):15465-15475
First-principle density functional theory (DFT) calculations are performed to study the active sites in FeN4G electrocatalysts, as well as ORR activity and mechanism. The possible intermediates and transition states existing in the possible reaction paths from Langmuir-Hinschelwood (LH) mechanism are investigated. The results show that the associative pathways of OOH1 formation is prior to that of O21 dissociation. The condition of proton adsorbed on top N sites (T2) is more beneficial to the reduction of O-contained species adsorbed on top Fe site (T1) compared to the conditions of proton adsorbed on top C sites (T3). However, the dissociation of O21, OOH1 and H2O21 is more likely to occur on the paired T1-T3 sites, since their lower energy barriers compared to other paired sites. The most favorable four-electron reduction pathway follows the mechanisms: O21→ OOH1→ O1+H2O→ OH1+H2O→ 2H2O. The rate determining step for ORR on FeN4G is the reduction of O1 into OH1 (barrier, 0.47 eV). The most feasible pathway for ORR is downhill at a high electrode potential (0.76 V vs. SHE at pH = 0) according to the free energy diagram. Compared to the ideal catalyst, the adsorption energy of OOH1 on FeN4G is much lower in free energy, while those of OH1 and O1 are slightly higher. Additionally, the elementary reaction rate for OOH1→O1+H2O is much larger than that of OOH1→H2O2 based on the parameter of activation barrier. Therefore, the formation of H2O2 (l) is unfavorable on FeN4G catalysts. 相似文献
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