【作者】 马丽；

【导师】 唐壁玉；

【作者基本信息】 广西大学 ， 化学工艺， 2013， 博士

【摘要】 以金属间化合物为基体的合金是当前正在发展的一种新型金属材料。随着科技的不断发展,对材料性能的要求越来越高,有关金属间化合物的科技研究工作也越来越受到重视。目前常见的金属间化合物材料的开发有两类,一类是发展新型轻质结构材料,制造出质轻、比强度高、抗应力强、耐腐蚀性好的合金材料,如镁基合金；另一类是发展高温结构材料,制造出具有高熔点、抗蠕变能力强、抗腐蚀和抗氧化性能好的合金材料,如Laves相铬基合金。虽然镁基和铬基合金因其自身优异的性质得到了认可与应用,但是它们都存在一个共同的缺点——低温易脆性。这一缺点阻碍了镁基和铬基合金的进一步发展与广泛应用。低温脆性与材料的塑性形变密切相关,而塑性形变主要受到层错、反相畴界和位错等有序微观缺陷结构控制。通过研究金属间化合物的微观缺陷结构,了解其塑性形变特征、形变机理和相关力学性质,进而设计具有优异力学性能的材料,是目前金属间化合物性能优化研究的关键性课题。本文基于密度泛函理论第一性原理计算研究了C14Laves相MgZn2及C15Laves相Cr2X(X=Nb, Zr, Hf)的广义层错能曲线,讨论了它们的形变机制,并从电荷密度分布、原子间相互作用和化学成键等电子原子水平揭示了Laves相中层错的形成特征。此外,本文系统地计算了B2-MgRE (RE=La-Er)中<111>{110}方向和L12-Al3X(X=Sc,Mg)中<110>{111}方向的广义层错能曲线,联合Peierls-Nabarro模型研究得到了它们的位错芯结构和性质。本论文主要内容包括以下四个方面：(1)基于协同剪切机制,建立了C14Laves相结构合金的内禀型层错intrinsic stacking fault(I2)和类孪生层错twin-like stacking fault (T2)的形成模型。通过第一性原理计算了C14Laves相MgZn2的I2和T2的广义层错能曲线。结果表明即使通过协同剪切机制,MgZn2中I2的非稳定层错能仍然很大,在MgZn2中形成I2层错比较困难。基于已有的内禀型层错I2构型,继续协同剪切操作,可以形成类孪生层错T2。非稳定和稳定类孪生层错能比非稳定和稳定内禀型层错能稍大,表明形成T2层错和形成I2层错的过程是类似的。基于获得的广义层错能,我们讨论了C14Laves相MgZn2的形变机制,结果表明MgZn2中主要的形变机制为扩展不全位错滑移。为了进一步揭示C14Laves相MgZn2的I2和T2形成的本质特征,其层错形成过程中的电荷密度分布也被进一步研究。(2)基于协同剪切机制,建立了C15Laves相结构合金的本征层错stacking fault (SF)和孪生层错twinning fault (TF)的形成模型。通过第一性原理计算了C15Laves相Cr2X(X=Nb, Zr, Hf)的广义层错能曲线,并讨论它们相关的形变机制。结果表明即使通过协同剪切机制,C15Laves相Cr2X(X=Nb, Zr, Hf)中SF和TF的非稳定层错能仍然很大,相应的稳定层错能较小。在C15Laves相Cr2X(X=Nb, Zr, Hf)中,可行的形变模式是扩展不全位错和孪生。研究还表明,Cr2Nb的孪生化趋势最强,随后为Cr2Zr和Cr2Hf。为了进一步揭示C15Laves相Cr2X(X=Nb, Zr, Hf)中SF和TF层错形成的本质特征,其层错形成过程中的电荷密度分布也被进一步研究。(3)通过第一性原理计算了B2-MgRE(RE=La-Er)合金中<111>{110)方向的广义层错能曲线。基于获得的层错能曲线联合Peierls-Nabarro模型研究了合金的<111>{110}超位错的结构和性质。结果表明在B2-MgRE合金中,<111>位错分解为两个共线的不全位错。对于同一物质同一体系,螺位错分解宽度比刃位错分解宽度小,螺位错的Peierls力和Peierls能比刃位错大。对比不同B2-MgRE合金可知,MgEu的<111>{110}螺位错和刃位错的Peierls能和Peierls力最大,MgSm的最小,表明在MgEu中移动<111>{110}位错最困难,而在MgSm中相对最容易。此外,研究还表明随着稀土元素原子序数的增加,B2-MgRE(RE=La-Er)合金中<111>{110}的位错分解宽度、Peierls力和Peierls能分段减少(La to Sm)和(Eu to Er)。(4)通过第一性原理计算了Ll2-Al3Sc和Al3Mg合金中<110>{111}方向的广义层错能曲线,获得了它们的反相畴界能。基于获得的广义层错能曲线联合Peierls-Nabarro模型研究了L12-A13Sc和Al3Mg合金中共线分解的<110>{111}超位错的结构和性质。计算估测的Al3Sc的<110>{111}刃位错的分解宽度与已报道的实验值相吻合。Al3Sc的<110>{111}刃位错和螺位错的位错分解宽度、Peierls力和Peierls能比Al3Mg的小。在L12-A13Sc和Al3Mg中,<110>{111}螺位错分解宽度比刃位错分解宽度小,螺位错的Peierls力和Peierls能比刃位错大。更多还原

【Abstract】 Alloys which have intermetallic compounds as matrix, have been developed as a new type of metal materials. With the development of science and technology, the requirements of the material property are higher and higher. More and more attention has been paid to the research on the intermetallic compounds. At present, the development of common intermetallic compound materials can be divided into two categories. One is the development of new lightweight material, which has low density, high specific strength and good corrosion resistance, such as magnesium-based alloys; the other one is the development of high-temperature structural material, which has high melting point, high creep resistance, good corrosion resistance and oxidation resistance, such as Laves phase chromium-based alloys. Although magnesium-based and chromium-based alloys gain the recognition and application owing to their superior properties, they have a common drawback--brittleness at low temperature. This drawback hinders the further development and the application of magnesium-based and chromium-based alloys.Brittleness at low temperature is closely related to plastic deformation characteristics which are been controlled by micro-defects structures, such as the stacking faults, antiphase boundary and dislocations. Through the study of micro-defects structures of the intermetallic compounds, revealing their plastic deformation characteristics and deformation mechanisms as well as the related mechanical properties, thereby designing materials having excellent mechanical properties, which is the key subject of this study.Based on density function theory, the stacking faults and deformation mechanism in C14Laves phase MgZn2and C15Laves phases Cr2X (X=Nb, Zr, Hf) have been studied by first-principles calculations. The charge density distribution, interaction of atoms and chemical bonding have been analyzed in detail to reveal the intrinsic mechanism for the formation of stacking faults in C14Laves phase MgZn2and C15Laves phases Cr2X (X=Nb, Zr, Hf). Furthermore, the structure and properties of<111>{110} superdislocations in B2-MgRE (RE=La-Er) and<110>{111} superdislocations in L12-A13X (X=Sc,Mg) have been investigated using the Peierls-Nabarro model in combination with generalized stacking fault energies. The thesis is mainly divided in to four parts:(1) Based on synchroshear mechanism, the formation of intrinsic stacking fault I2and twin-like stacking fault T2in C14Laves phases has been modeled in details and the generalized stacking fault energy curve of I2and T2for C14Laves phase MgZn2has been calculated from first-principles. The results demonstrate that the unstable stacking fault energy of I2by synchroshear is still very large, implying that the formation of I2SF in MgZn2is difficult. Upon the pre-existing I2configuration, the T2stacking fault can be further formed by following a next synchroshear. The unstable and stable stacking fault energies of T2are only slightly larger than those of I2, implying that the formation of T2may be essentially similar to that of I2. From the obtained generalized stacking fault energy, the relevant deformation mechanism of MgZn2is also discussed. The result suggests that deformation is performed by partial dislocations in C14Laves phase MgZn2. Finally, the electronic structure during synchroshear process is further studied to unveil the intrinsic mechanism for the formation of I2and T2in C14Laves phase MgZn2.(2) Based on the synchroshear model, the formation of stacking fault and twinning fault in C15Laves phases is modeled, then the generalized stacking fault energy curves and deformation mechanism in C15Laves phases Cr2X (X=Nb, Zr, Hf) alloys are investigated by ab initio calculations based on the density functional theory. The results demonstrate that the unstable stacking fault and twinning fault energies of C15Laves phases Cr2X (X=Nb, Zr, Hf) by the synchroshear are still large while the stable stacking fault and twinning fault energies are low, and the deformation modes by extended partial dislocation and twining are feasible in C15Laves phases Cr2X (X=Nb, Zr, Hf). Moreover, the Cr2Nb has the largest deformation twinning tendency, followed by Cr2Zr and Cr2Hf. The evolution of electronic structure during the synchroshear process is further studied to unveil the intrinsic mechanism for the formation of stacking fault and twinning fault in C15Laves phases Cr2X (X=Nb, Zr, Hf). (3) The structure and properties of<111>{110} superdislocations in B2-MgRE (RE=La-Er) intermetallics are investigated using the Peierls-Nabarro model in combination with generalized stacking fault energies. The results demonstrate that the<111>{110} superdislocations in B2-MgRE have dissociated into two collinear partials bound to anti-phase boundary. For the same material system, the dislocation dissociated width of screw is narrower than that of edge, while the Peierls energy and stress are larger. Among the B2-MgRE, MgEu has the highest Peierls energies and stresses for screw and edge superdislocations, while those for MgSm are the lowest, indicate that movement of<111>{110} superdislocation in MgEu is the most difficult, while it is the easiest in MgSm. With increasing of atomic number, the dislocation dissociated width, Peierls energy and stress in B2-MgRE decrease for both early lanthanides from La to Sm and late lanthanides from Eu to Er.(4) The generalized stacking fault energy curves along the<110> direction on{111} slip plane for L12Al3SC and Al3Mg are calculated within framework of density functional theory, and the anti-phase boundary energies are obtained. Then the structures and properties of collinear dissociated<110>{111} dislocations in Al3Sc and Al3Mg are studied using Peierls-Nabarro model combined with generalized stacking fault energies, the obtained dislocation dissociation width of the<110>{111} edge dislocation in Al3Sc is in agreement with the available experimental value. In comparison with Al3Mg, the dislocation dissociation widths of both screw and edge in Al3Sc are narrower and the Peierls energies and stresses are lower. Furthermore, for both Al3Sc and Al3Mg, the dislocation dissociation width of screw dislocation is smaller than that of edge dislocation, while the Peierls energy and stress of screw dislocation is slightly larger.更多还原