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21.
《Calphad》2019
The growth kinetics, diffusion kinetics and mechanical properties of intermetallics in Mg-Zn binary systems have been investigated in this work. Four intermetallic compounds (IMCs) Mg2Zn11, MgZn2, Mg21Zn25, and Mg4Zn7 have been observed in the Mg-Zn diffusion zone at the temperature range of 523–593 K. The square of thickness for IMCs diffusion layer increases linearly with time, which is consistent with the parabolic growth law, and also indicates that the growth of IMCs is controlled by diffusion. Growth constants and growth activation energies of Mg-Zn IMCs have been evaluated. Average effective interdiffusion coefficient of each phase has been calculated by the Wagner's method based on the concentration distribution obtained by EPMA. The diffusion activation energy has been estimated and compared with the available results. Finally, displacement-unloading curve measured by nanoindentation was used to estimate the hardness and Young's modulus to characterize the mechanical and creep properties of Mg2Zn11, MgZn2, Mg21Zn25 and Mg4Zn7. The present results should be beneficial to the design and performance of Mg-based alloys. 相似文献
22.
Jiahong Dai Hong Xiao Bin Jiang Hongmei Xie Cheng Peng Zhongtao Jiang Qin Zou Qingshan Yang Fusheng Pan 《材料科学技术学报》2018,34(2):291-298
The diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couple method were investigated. Results demonstrate that Al_2Ca is the only phase existing in the diffusion reaction layers.The volume fraction of Al_2Ca in diffusion reaction layers increases linearly with temperature. The standard enthalpy of formation for intermetallic compounds was rationalized on the basis of the Miedema model. Al-Ca intermetallic compounds were preferable to form in the Mg-Al-Ca ternary system under the same conditions. Over the range of 350–400?C, the structure of Al_2Ca is more stable than that of Al_4Ca, Al_(14)Ca_(13) and Al_3Ca_8. The growth constants of the layer Ⅰ, layer Ⅱ and entire diffusion reaction layers were determined. The activation energies for the growth of the layer Ⅰ, layer Ⅱ and entire diffusion reaction layers were(80.74 ± 3.01) k J/mol,(93.45 ± 2.12) k J/mol and(83.52 ± 1.50) k J/mol, respectively.In layer Ⅰ and Ⅱ, Al has higher integrated interdiffusion coefficients D~(Int, layer)ithan Ca. The average effective interdiffusion coefficients D_(Al)~(eff) values are higher than D_(Ca)~(eff) in the layer Ⅰ and Ⅱ. 相似文献
23.
High temperature Bi10Ag solders with different amounts of Cu were used to investigate the impacts of Cu on the microstructures, melting characteristics, wettability and shear strength of the Bi-10Ag-xCu (x = 0, 0.5, 1, and 2 wt%) solders. A metastable Cu-rich phase was formed due to the addition of Cu. The Cu has negligible effect on the solidus but it can decrease about 6 °C on the liquidus. Doped with 0.5 wt% of Cu, the solders showed the largest melting range in the DSC curves and improved wettability on Cu substrates. When the Cu addition excesses to 0.5 wt%, it will induce negative effects on wettability of the solders on the substrate. Moreover, the addition of Cu has no significant influence on the strength of the Bi10Ag lap solder joints. The Bi-10Ag-0.5Cu solder joint has higher shear strength than that of Pb5Sn. 相似文献
24.
《Journal of the European Ceramic Society》2017,37(4):1305-1310
Based on a kind of equivalence between heat energy and fracture energy, assuming that there is a constant maximum storage of energy that includes both heat energy and fracture energy, a new temperature dependent fracture surface energy model is developed. Using the new model and the classical ACK theory, a temperature dependent first matrix cracking stress model is obtained for the fiber reinforced ceramic composites. According to the model, the temperature dependent first matrix cracking stress of materials can be easily predicted using some basic material parameters such as matrix fracture surface energy and Young’s modulus. The model is verified by comparison with experimental data of SiC fiber reinforced reaction-bonded Si3N4 composites at different temperatures. Good agreement is obtained between predicted and experimental data of first matrix cracking stress. The dependency of first matrix cracking stress on fracture surface energy and interfacial shear strength is systematically analyzed. 相似文献
25.
《Journal of the European Ceramic Society》2017,37(15):5071-5077
A novel temperature-dependent fracture strength model for ceramic materials is developed, based on a critical fracture energy density associated with material fracture comprising strain energy, the corresponding equivalent potential energy, and kinetic energy of atoms per unit volume. It relates the fracture strength at high temperatures to that at the reference temperature, the temperature-dependent Young’s modulus, the temperature, and the melting point. The model is verified by comparison with experimental data of ceramic materials. The model predictions and the experimental data are in excellent agreement with each other. As the Young’s modulus can easily be obtained by experiments and the melting point can easily be obtained by materials handbook, the model can easily predict the fracture strength of ceramic materials at arbitrary temperatures. 相似文献
26.
《Current Opinion in Solid State & Materials Science》1999,4(2):163-170
Low-field magnetoresistance is observed both below and above the three-dimensional Curie temperature of the intrinsically layered Ruddlesden–Popper manganates Sr2−xLa1+xMn2O7. Significant differences from the more extensively investigated n=∞ three-dimensional perovskites include a much more rapid suppression of ferromagnetic ordering as the size of the lanthanide cation is reduced and more complex magnetic and structural behaviour in the manganese oxidation state range which produces charge ordering in the n=1 and n=∞ homologues. Control of chemical imperfections, such as intergrowth and phase co-existence, is required to allow understanding of the physical properties of this system. 相似文献
27.
《Acta Metallurgica Materialia》1993,41(5):1577-1585
Secondary recrystallization behavior in the presence of AlN and MnS precipitates in Fe-3% Si alloy, processed by one stage cold rolling method, was investigated with special reference to a role of inhibitor for secondary recrystallization. The sharpness of Goss secondary texture is higher in the early stage of secondary recrystallization. In the case of stronger grain growth inhibition by precipitates during secondary recrystallization, the evolution of secondary recrystallized grains in orientations dispersed from Goss orientation is smaller than that in the case of weaker grain growth inhibition. The mechanism of these experimental results is explained by the specific grain boundary migration characteristics in the presence of inhibitor, namely, the critical frequency of Σ9 coincidence oriented grains in relation to nucleus for the evolution of secondary recrystallization is considered to be higher in the case of stronger grain growth inhibition during secondary recrystallization. 相似文献
28.
High purity tantalum was respectively processed by unidirectional rolling (UR) and clock rolling (CR), and the through-thickness microstructures were investigated by multiple characterization techniques including electron backscatter diffraction (EBSD), Vickers hardness (HV) and X-ray diffraction (XRD). Results show that the through-thickness stored energy distribution in CR specimens is more homogeneous than in UR specimens due to uniform texture distribution. {111} grains possess larger Schmid factors and the corresponding Schmid factor difference ratio than {100} grains, indicating the activation of uniserial slipping in {111} grains, which leads to inhomogeneous deformation and higher stored energy. Besides, X-ray line profile analysis (XLPA) suggests that the stored energy of {111} grains increases successively from the surface to center layer, regardless of strain paths, due to the influence of redundant friction on the surface layers. While the occurrence of multiple slipping in {100} grains leads to homogeneous deformation and lower stored energy. 相似文献
29.
30.
Bo Li Xiaoling Liao Li Zheng Huawei He Hong Wang Hongsong Fan Xingdong Zhang 《Materials science & engineering. C, Materials for biological applications》2012,32(4):929-936
Microwave sintering using the activated carbon as embedding material was applied in preparation of porous A-type carbonated hydroxyapatite ceramics with nano(nCHA) and submicron (mCHA) structure. By examining the linear shrinkages and the compressive strengths of samples at different temperatures, a suitable microwave sintering temperature was achieved. The microwave sintering method was successfully used to prepare A-type CHA with nano or submicron structure, and the mechanism of the formation of A-type carbonate groups was discussed also. Compared with the samples prepared by the conventional sintering method (mHA), the nCHA bioceramics synthesized by the microwave sintering approach had smaller grain size and more uniform microstructure, and showed a compressive strength similar to the conventional samples. In vitro dissolution test proved that nCHA exhibits better degradation property in comparison to pure HA. Rat osteoblasts were cultured with nCHA, mCHA and mHA to evaluate their biocompatibility, and nCHA showed significant enhancement of cells in attachment, proliferation and differentiation. In conclusion, carbonate groups can be easily introduced to HA crystal structure using the activated carbon as embedding material, and microwave sintering is an effective and simple method in preparing A-type CHA with a nanostructure. Results from this in vitro biological study suggest that porous A-type carbonated hydroxyapatite nanoceramics may be a much better candidate for clinical use in terms of bioactivity. 相似文献