共查询到20条相似文献,搜索用时 31 毫秒
1.
Structural, elastic and electronic properties of Mg(Cu1−xZnx)2 alloys calculated by first-principles
Meng-Meng WuYi Jiang Ji-Wei WangJian Wu Bi-Yu Tang Li-Ming PengWen-Jiang Ding 《Journal of Alloys and Compounds》2011,509(6):2885-2890
The structural, elastic and electronic properties of Mg(Cu1−xZnx)2 alloys (x = 0, 0.25, 0.5,and 0.75) were investigated by means of first-principle calculations within the framework of density functional theory (DFT). The calculation results demonstrated that the partial substitution of Cu with Zn in MgCu2 leaded to an increase of lattice constants, and the optimized structural parameters were in very good agreement with the available experimental values. From energetic point of view, it was found that with increase of Zn content the structural stability of Mg(Cu1−xZnx)2 alloys decreased apparently. The single-crystal elastic constants were obtained by computing total energy as a function of strain, and then the bulk modulus B, shear modulus G, Young's modulus Y and Poisson's ratio ν of polycrystalline aggregates were derived. The calculated results showed that among the Mg(Cu1−xZnx)2 alloys, MgCuZn exhibited the largest stiffness, while Mg2Cu3Zn showed the best ductility. Finally, the electronic density of states (DOSs) and charge density distribution were further studied and discussed. 相似文献
2.
D. EgusaE. Abe 《Acta Materialia》2012,60(1):166-178
We propose structural models of the unique long period stacking/order (LPSO) phases formed in Mg-Zn-RE alloys, based on Z-contrast scanning transmission electron microscopy observations and first principles calculations. The LPSO structures are long period stacking derivatives of the hcp Mg structure, and the Zn/RE distributions are restricted at the four close-packed atomic layers forming local fcc stacking (i.e. a local ABCA stacking). Chemical order is well developed for the LPSO phases formed in Mg97Zn1Er2 (14H type) and Mg85Zn6Y9 (18R type) alloys with pronounced superlattice reflections, and the relevant Zn/RE distributions clearly emerge in the Z-contrast atomic images. Initial ternary ordered models were constructed by placing all the atoms at the ideal honeycomb sites, leading to plausible space groups of P63/mcm for the 14H type and C2/m, P3112 or P3212 for the 18R type. The characteristic ordered features are well represented by local Zn6RE8 clusters, which are embedded in the fcc stacking layers in accordance with the L12 type short-range order. Energy favored structural relaxations of the initial model cause significant displacement of the Zn/RE positions, implying that strong Zn-RE interactions may play a critical role in phase stability. The LPSO phases seem to tolerate a considerable degree of disorder at the Zn and RE sites with statistical co-occupations by Mg, extending the non-stoichiometric phase region bounded along the Zn/RE equiatomic line from ∼Mg94.0Zn2.0Y4.0 to ∼Mg83.3Zn8.3Y8.3. 相似文献
3.
Mg–Cu–Y–(Gd) alloy rods are made by arc-melting and injection casting methods in this research. The improvement of glass forming ability and mechanical properties by using Gd to substitute Y in Mg58Cu31Y11 bulk metallic glasses (BMGs) is of interest. The results of thermal analysis present that the Mg–Cu–Y base alloys with the addition of 6 and 8 at% Gd are the best BMG former. The Vickers indentation tests and the compression tests are carried out in order to explore the mechanical properties of alloys. It reveals that there is no obvious change in Young's modulus (45 GPa) of the Gd-containing Mg-based BMG, in contrast with the base alloys. Vickers (micro-) indentation fracture toughness measurements are performed for comparison. Shear bands and the corner cracks around the inverted pyramind mark are showed. An average fracture toughness of Mg–Cu–Y–Gd alloy is calculated as 4 MPa m1/2, which is a little higher than that of base alloys studied in the paper. Meanwhile, the fracture surface of Mg-based BMGs is dominant by featureless mirror-like and river-like pattern. Only nano-scaled shear bands and vein patterns are displayed, indicating that the plasticity of the Mg–Cu–Y–Gd BMGs are shown in nano-scale indeed. 相似文献
4.
Improving the strength and the toughness of Mg–Cu–(Y,Gd) bulk metallic glass by minor addition of Nb
Mg65Cu25Re10 (Re = Y, Gd) and Mg64Cu25Nb1Re10 (Re = Y, Gd) bulk metallic glasses (BMGs) have been fabricated by copper mould casting. It is shown that the minor addition of Nb can not only increase the thermal stability but also improve the fracture strength and the toughness of the Mg-based BMG alloys greatly. The fracture strength of Mg64Cu25Nb1Y10 and Mg64Cu25Nb1Gd10 reaches as high as 1023 MPa and 973 MPa, respectively. The Young's modulus has also been increased by the addition of Nb. From the fracture morphologies of the Nb bearing Mg-based BMG alloys, it is known that the size of plastic deformation zone can be increased to micrometer scale. This work proves that it is possible to improve the strength and toughness of Mg-based BMG by adding an element having positive heat of mixing with the constituent elements. 相似文献
5.
Ab initio calculations are becoming increasingly useful to engineers interested in designing new alloys, because these calculations are able to accurately predict basic material properties only knowing the atomic composition of the material. In this paper, single crystal elastic constants of 11 bcc Mg–Li alloys are calculated using density functional theory (DFT) and compared with available experimental data. Based on DFT determined properties, engineering parameters such as the ratio of bulk modulus over shear modulus (B/G) and the ratio of Young’s modulus over mass density (Y/ρ) are calculated. Analysis of B/G and Y/ρ shows that bcc Mg–Li alloys with 30–50 at.% Li offer the most potential as lightweight structural material. Compared with fcc Al–Li alloys, bcc Mg–Li alloys have a lower B/G ratio, but a comparable Y/ρ ratio. An Ashby map containing Y/ρ vs B/G shows that it is not possible to increase both Y/ρ and B/G by changing only the composition of a binary alloy. 相似文献
6.
Rafał Babilas Katarzyna Cesarz-Andraczke Ryszard Nowosielski Andrzej Burian 《Journal of Materials Engineering and Performance》2014,23(6):2241-2246
The Mg60Cu30Y10 and Mg65Cu20Y10Zn5 bulk metallic glasses in the form of a rod 2 mm in diameter were successfully prepared by the conventional Cu-mold casting method. The addition of Zn caused the decrease in the crystallization and melting temperatures in comparison with the Mg60Cu30Y10 alloy. The crystallization and melting temperatures are crucial factors that influence the casting process. An increase in annealing temperature leads to structural changes by the formation of the crystalline phases and lowers the compressive strength. These results obtained for the Mg-based bulk metallic glasses (Mg-BMGs) are important for some practical reasons, in particular, for developing the fabrication process. It has been shown that minor addition of an alloying element can change glass-forming ability and strength of the Mg-BMGs. 相似文献
7.
本文考察了快速凝固条件下不同含量Li元素添加对长周期有序结构相增强Mg-Gd-Zn合金微观组织和力学性能的影响。结果表明,随着Li元素的添加,铸态合金中Gd、Zn溶质原子在镁基体晶粒中的过饱和度降低、(Mg,Zn)3Gd晶界析出相增加、镁基体晶粒尺寸减小。而固溶处理后,随着Li含量的增加,合金中14H型长周期堆垛有序结构相(LPSO)的形成受到抑制,同时纳米/亚微米(Mg,Zn)3Gd颗粒相大量析出,当Li为7.6at. %时合金中无LPSO形成。经热挤压变形后,合金中块状14H相发生扭着分层开裂、层片状14H相发生不同程度溶解、(Mg,Zn)3Gd相破碎细化、基体发生不同程度再结晶;不加Li的Mg96.5Gd2.5Zn1表现出最佳的力学性能(UTS=325,δ=9.5%),而含Li合金则随Li含量的增加,力学性能逐步下降。合金在不同条件下的组织转变机理及力学行为变化被进行了分析。 相似文献
8.
Microstructural investigation on Ti63.5Fe30.5Sn6 and Mg72Cu5Zn23 alloys reveals that bimodal eutectic structure containing the synchronization of structural and spatial heterogeneities in the spherical lamellar entity homogeneously forms upon solidification. Furthermore, the bimodal eutectic Ti63.5Fe30.5Sn6 and Mg72Cu5Zn23 alloys present the enhancement of both strength and plasticity at room temperature compared to the recently developed high strength Ti- and Mg-based alloys. This implies that the bimodal eutectic structure can be one of the effective ways to improve the plasticity of the high strength alloys. 相似文献
9.
The 18R and 14H long-period stacking ordered structures formed in Mg–Y–Zn alloys are examined systematically using electron diffraction and high-angle annular dark-field scanning transmission electron microscopy. In contrast to that reported in previous studies, the 18R structure is demonstrated to have an ordered base-centred monoclinic lattice, with Y and Zn atoms having an ordered arrangement in the closely packed planes. Furthermore, the composition of 18R is suggested to be Mg10Y1Zn1, instead of the Mg12Y1Zn1 composition that is commonly accepted. The 14H structure is also ordered. It has a hexagonal unit cell; the ordered distribution of Y and Zn atoms in the unit cell is similar to that in the 18R and its composition is Mg12Y1Zn1. The 18R unit cell has three ABCA-type building blocks arranged in the same shear direction, while the 14H unit cell has two ABCA-type building blocks arranged in opposite shear directions. 相似文献
10.
《中国有色金属学会会刊》2022,32(10):3222-3237
This work investigated the effects of different Y additions (0, 1.5, 3.0 and 4.5 wt.%) on the microstructural evolution and mechanical performance of cast Mg-3Nd-0.2Zn-0.5Zr alloy. The results show that as the Y content increases, the key secondary phases in as-cast alloys change from the Mg12Nd type to the Mg24Y5 type. Meanwhile, the number density of Zn-Zr particles in the grains of as-quenched alloys gradually decreases. HAADF-STEM observations of peak-aged samples reveal that element Y is greatly enriched in the globular β′ precipitates, leading to a significantly increased volume fraction and promoted precipitation kinetics of β′ precipitates, resulting in enhanced strength of the alloy. Tensile tests reveal that, with the addition of 4.5 wt.% Y, the yield strength of the base alloy is substantially increased by 88 and 61 MPa after being aged at 200 and 225 °C under peak-aged conditions, respectively. 相似文献
11.
This study presents the first experimental evidence of a hydrogen-induced decomposition reaction in an Mg–6Zn–0.6Zr–0.5Cu alloy from combined transmission electron microscopy and atom-probe tomography characterization. The reaction takes place due to the presence of H in the Mg matrix, causes the decomposition of pre-existing, high-temperature Zr–Zn intermetallic rods into Zr-rich hydride and β′ (Zn3Mg2), and forms novel composite precipitates in the Zr-rich cores of the alloy during ageing at 180 °C. The stoichiometry of the Zr–Zn rods was found to be Zn3(Zr1?x, Mgx)2, rather than Zn2Zr3, although both have a similar tetragonal crystal structure. The intrinsic link between the high-temperature Zr–Zn rods and the subsequent elongated composite precipitates, as depicted by the reaction, highlights the importance of engineering the Zr–Zn rod microstructures to control the final precipitate microstructure and effectively strengthen the Zr-rich cores, and hence the advanced Mg alloys. 相似文献
12.
《Acta Materialia》2007,55(6):2183-2199
The strength of Al–Mg–Si aluminium alloys depends critically on nanometre-size MgxSiyAlz-type precipitates that have a face-centered cubic-based structure. In this work, a large number of early structures are investigated by means of first-principles calculations. Both platelet-type and needle-type precipitates are considered. Calculations show that for alloys with an Mg:Si ratio smaller than one, needle-type precipitates with Si pillars extending in the needle direction are energetically favoured. The formation of Si pillars and the low density cylinder is described. For alloys with an Mg:Si ratio larger than one, platelet-type precipitates consisting of stacked layers of Mg, Si and Al atoms are energetically favoured. Using both the information on the formation enthalpies and the calculated lattice mismatch with the Al matrix, it is discussed which structures are likely to be formed. The earliest, most favourable structures with high Al content are the needle-type initial-β″ Mg2Si3Al6 structure and the platelet-type structures {MgSi}2Al10, {MgAl}1Al10, Mg3Si2Al5 and Mg2Si1Al3. 相似文献
13.
The effects of Y on the microstructure and mechanical properties of Mg–6Zn–1Mn alloy were investigated. The results show that the addition of Y has significant effect on the phase composition, microstructure and mechanical properties of Mg–6Zn–1Mn alloy. Varied phases compositions, including Mg7Zn3, I-phase (Mg3YZn6), W-phase (Mg3Y2Zn3) and X-phase (Mg12YZn), are obtained by adjusting the Zn to Y mass ratio. Mn element exists as the fine Mn particles, which are well distributed in the alloy. Thermal analysis and microstructure observation reveal that the phase stability follows the trend of X>W>I>Mg7Zn3. In addition, Y can improve the mechanical properties of Mg–Zn–Mn alloy significantly, and the alloy with Y content of 6.09% has the best mechanical properties. The high strength is mainly due to the strengthening by the grain size refinement, dispersion strengthening by fine Mn particles, and introduction of the Mg–Zn–Y ternary phases. 相似文献
14.
Large-scale Mg90Cu10 and Mg90Cu3Zn7 nanostructure-dendrite composites were successfully fabricated using a water-cooled squeeze casting. The Mg90Cu3Zn7 nanostructure-dendrite composite consisting of a mixture of hexagonal α-Mg and tetragonal MgCuZn phases has plasticity up
to 8.4 % in excess of that of the Mg90Cu10 nanostructure-dendrite composite consisting of a mixture of hexagonal α-Mg and orthorhombic Mg2Cu phases. This implies that phase selection plays an important role in controlling the strength and plasticity of large-scale
Mg-based nanostructure-dendrite composites. 相似文献
15.
Mg68Zn28Y4 alloys with stable icosahedral quasicrystals (Zn60Mg30Y10) were prepared by cast method. By simulating the environment of ocean, the alloy was eroded in 3.5% (mass fraction) NaCl for 2, 4 and 30 h. The microstructures of the samples and eroded alloys were analyzed by OM and SEM. The compositions and the quasiperiodic structures were identified respectively by EDS and TEM. And the corrosion potential and corrosion current density before and after immersion were measured by potentiodynamic polarization measurements in 3.5% NaCl. The results show that I-phases grow in the mode of conglomeration, piling and transfixion. The Mg7Zn3 matrix and α(Mg) solid solution are eroded badly, while W-phase is eroded partially. At the same time, the I-phases exhibit excellent corrosion resistance property. The resistance to corrosion of Mg68Zn28Y4 alloy is improved by increasing exposed I-phases. With adding element Y to Mg68Zn32 alloy, the corrosion current is decreased by one order of magnitude. And after the immersion of as-cast Mg68Zn28Y4 alloy for 30 h, the corrosion current density is reduced by two orders of magnitude compared with that of uneroded Mg68Zn32 alloy. 相似文献
16.
The relation between corrosion resistance and microstructure of Mg-Zn-Y alloys with a long period stacking ordered (LPSO) phase has been investigated. In order to clarify the influence of microstructure evolution by rapid solidification on the occurrence of localized corrosion such as filiform corrosion, several Mg97.25Zn0.75Y2 (at. %) alloys with different cooling rates were fabricated by the gravity casting, copper mould injection casting and melt-spinning techniques and their corrosion behavior and microstructures were examined by the salt immersion tests, electrochemical measurements, XRD and TEM. When the cooling rate was less than 3 × 104 K s−1, filiform corrosion propagated in the early stage of salt immersion test, due to formation of a massive block-shaped LPSO phase during casting. On the other hand, when the cooling rate was increased up to 3 × 104 K s−1, rapidly solidified (RS) alloys exhibited excellent corrosion resistance because of grain refinement and formation of a supersaturated single-phase solid solution. Large-sized Mg97.25Zn0.75Y2 alloys fabricated by consolidation of the RS ribbons also exhibited excellent corrosion resistance with passivity. Enhancement of microstructural and electrochemical homogeneities in the Mg-Zn-Y alloys by rapid solidification techniques results in the passivity of substrate materials. 相似文献
17.
The metastable β′ phase is a key strengthening precipitate phase in a range of Mg–RE (RE: rare-earth elements) based alloys. The morphology of the β′ precipitates changes from a faceted and nearly equiaxed shape in Mg–Y alloys to a truncated lenticular shape in Mg–Gd alloys. In this work, we study effects of interfacial energy and coherency elastic strain energy on the morphology of β′ precipitates in binary Mg–Y and Mg–Gd alloys using a combination of first-principles calculations and phase-field simulations. Without any free-fitting parameters and using the first-principles calculations, CALPHAD databases and experimental characterizations as model inputs (lattice parameters of the β′ phase, elastic constants and chemical free energy of Mg matrix and interfacial energies of the coherent β′/Mg matrix interfaces), the phase-field simulations predict equilibrium shapes of β′ precipitates of different sizes that agree well with experimental observations. Factors causing the difference in the equilibrium shape of β′-Mg7Y and β′-Mg7Gd precipitates are identified, and possible approaches to increase the aspect ratio of the β′ precipitates and thus to enhance the strength of Mg–RE alloys are discussed. 相似文献
18.
To explore the corrosion properties of magnesium alloys, the chemical behavior of a high strength Mg97Zn1Y2-1 wt.%Si C alloy in different corrosion environments was studied. Three solutions of 0.2 mol·L-1 NaCl, Na2SO4 and NaNO3 were selected as corrosion solutions. The microstructures, corrosion rate, corrosion potential, and mechanism were investigated qualitatively and quantitatively by optical microscopy(OM), scanning electron microscopy(SEM), immersion testing experiment, and electrochemical test. Microstructure observation shows that the Mg97 Zn1Y2-1 wt.%Si C alloy is composed of α-Mg matrix, LPSO(Mg12 ZnY) phase and Si C phase. The hydrogen evolution and electrochemical test results reflect that the Mg97Zn1Y2-1 wt.%SiC in 0.2 mol·L-1 Na Cl solution has the fastest corrosion rate, followed by Na2SO4 and NaNO3 solutions, and that the charge-transfer resistance presents the contrary trend and decreases in turn. 相似文献
19.
S. Valdez B. Mena J. A. Juarez-Islas J. Genesca 《Journal of Materials Engineering and Performance》2001,10(5):596-601
This paper forms part of an overall effort to develop Al-sacrificial In/Hg free anodes; our research has been directed toward
developing Al alloys appropriate for cathodic protection. The Al-Zn-Mg system has been particularly selected due to the presence
of precipitates in the α-Al matrix, which are capable of breaking down passive films while presenting good electrochemical efficiencies. At the same
time, the effect of Li additions on superficial activation of the anode by means of precipitation of AlLi-type compounds was
examined. The microstructure was characterized in the as-cast and as-aged ingots, showing the presence of α-Al dendrites as well as eutectic of Al2Mg3Zn3 and precipitates of Mg7Zn3 in interdendritic regions. Electron microscopic observations performed on specimens with and without heat treatments showed
in the α-Al matrix the presence of a uniform distribution of precipitates of (τ-Al2Zn3Mg3, Mg7Zn3, and δ-AlLi type. The electrochemical behavior of the alloy was investigated in a 3% NaCl solution simulating seawater at room temperature.
After evaluation of the electrochemical efficiency, values up to 67% were obtained. The relationship between microstructure
and electrochemical efficiency is discussed in this work and suggestions of future research are given in order to improve
the electrochemical behavior of Al anodes in the field. 相似文献
20.
H. Zhang S.L. Shang Y. Wang A. Saengdeejing L.Q. Chen Z.K. Liu 《Acta Materialia》2010,58(11):4012-4018
The elastic, phonon and thermodynamic properties of Al12Mg17 have been investigated by first-principles calculations. The obtained structural parameters, phonon dispersion curves and the predicted thermodynamic properties for all the phases studied herein agree well with available experimental data. The temperature-dependent single-crystal elastic constants are also predicted along with the polycrystalline aggregate properties, including bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio. The brittleness of Al12Mg17 that we predict is consistent with experiments, in contrast to the previous calculation showing ductile behavior. Detailed analysis of density of states further explains the present theoretical findings. 相似文献