合金元素掺杂对AlRu力学性能影响的第一性原理研究

发布时间：2018-02-05 04:44

本文关键词： 高温合金铝钌金属间化合物第一性原理塑性合金化　出处：《昆明理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：AlRu合金拥有优良的高温抗氧化能力和耐腐蚀能力是军用发动机部件的首选材料。但是AlRu呈现脆性,难以塑性变形和加工成型材。因此,本论文研究通过掺杂合金元素对改善AlRu塑性的影响,并根据计算结果挑选元素加以实验验证。依据铝钌二元相图,运用基于密度泛函理论的第一性原理计算方法计算了Al6Ru、Al13Ru4、Al2Ru、AlRu四种在常温下存在的金属间化合物的剪切模量G与体模量B,并依据经验判据发现四种化合物的G/B值都大于0.5属于脆性材料,但是AlRu金属间化合物是四种化合物中最塑性好的一个。对AlRu态密度的分析表明A1原子的3p轨道电子与Ru原子的3p与4d轨道电子发生杂化,从而使电子参与成键的几率增加,体系也更加稳定；进一步的布居数计算结果显示AlRu化合物中存在的Al-Ru键布居数为正,这可能导致形成更多的共价键,降低AlRu的塑性；通过分析AlRu的差分电荷密度图发现：Ru原子的电子云为典型的花瓣状,外层电子分布呈现各向异性,这同样会导致A1Ru塑性降低。为改善AlRu的塑性,本文选择了掺杂Cr、Mn、Co、Mo、V、Ti、Ta、Ni、 W、Re十种置换型原子与间隙型原子B作为合金元素,研究它们对AlRu塑性的影响。对于置换型原子Cr、Mn、Co、Mo、V、Ti、Ta、Ni、W、Re、本文建立了原子百分含量为1.56at%、3.125at%以及6.25at%的三种计算模型,计算结果表明,合金元素均是在含量为6.25at%时G/B值最低,但是只有Re、Ti、W、Co、 Mo五种元素可以提高其塑性,其中尤以Co、Mo元素为最佳；对于间隙型原子B,本文建立了质量百分含量为0.178wt%、0.238wt%、0.475wt%以及0.711wt%的四种八面体间隙模型,其中G/B值随B元素含量的增加呈现出先降低后升高的变化趋势,最低值(0.467)出现在B含量为0.475wt%,这比掺杂置换型合金原子后效果最好的6.25at%的Co元素的G/B值(0.473)还要低。对这些有利于AlRu塑性改善的元素通过态密度的分析都显示p轨道与d轨道的电子杂化减弱,掺杂这些元素后降低了体系的稳定性,布居数与差分电荷密度的分析则表明Al-Ru键能降低,且形成不同强度的Ru-Ru反键,Ru原子外层电子分布的各向异性减弱,这些都有利于AlRu塑性的增强。实验部分本文选取对AlRu塑性改善效果最显著的B元素来进行验证,设计了B含量为0.2wt%、0.5wt%、0.7wt%以及3wt%的五个试样,试样是通过放电等离子烧结与电弧熔炼制备得到的。在扫描电镜下对试样的组织形貌进行观察,并用纳米压痕仪与万能试验机测量了杨氏模量与剪切模量,计算出G/B值。结果发现,试样组织分布较为均匀,存在部分空隙,测出的剪切模量与体模量比计算值要低,但G/B值随B元素含量增加的变化趋势与计算结果基本一致。
[Abstract]:AlRu alloy has excellent high temperature oxidation resistance and corrosion resistance is the first choice for military engine components, but AlRu is brittle, difficult to plastic deformation and processing profile. In this paper, the effect of doping alloy elements on improving the plasticity of AlRu was studied, and the elements were selected for experimental verification according to the calculated results. The first principle calculation method based on density functional theory is used to calculate Al6Ru-Al13Ru4Al2Ru. The shear modulus G and bulk modulus B of four intermetallic compounds existing in AlRu at room temperature are found to be brittleness materials. According to the empirical criterion, it is found that the G / B values of the four compounds are greater than 0. 5. But the AlRu intermetallic compound is the most plastic one of the four compounds. The analysis of AlRu density of states shows that the 3p orbital electron of A1 atom and the 3p and 4d orbital electron of Ru atom are hybridized. . Thus, the probability of electronic participation in bonding is increased, and the system is more stable. The results of further population calculation show that the Al-Ru bond population in AlRu compounds is positive, which may lead to more covalent bonds and reduce the plasticity of AlRu. By analyzing the differential charge density diagram of AlRu, it is found that the electron cloud of the Ru atom is a typical petal, and the electron distribution in the outer layer is anisotropic. In order to improve the ductility of AlRu, we have chosen the doped CrMn-Mn-CoA Mo-Mo-V Ti-Li, Ta-Ni, W to improve the ductility of A1Ru, which also leads to the reduction of the ductility of A1Ru. Ten kinds of replacement atoms and interstitial atoms B are used as alloy elements to study their effect on the plasticity of AlRu. Re. in this paper, three kinds of calculation models with atomic percent content of 3.125 at% and 6.25at% have been established. The calculation results show that the atomic content is 1.56at% and 6.25at% respectively. When the content of alloy elements is 6.25at%, the value of G / B is the lowest, but only Retiao Weng Co. can improve the plasticity of the alloy elements, especially the element Coomo. For interstitial atom B, four octahedral interstitial models with 0.178 wtwt% content 0.238 wt% and 0.711 wt% have been established. The G / B value decreased first and then increased with the increase of B element content, and the lowest value (0.467) appeared in the B content of 0.475wt%. This is better than the G / B value of 0.473 for Co element (6.25at%), which is the best after doping substitution type alloy atoms. The analysis of the density of states of these elements, which are beneficial to the improvement of AlRu plasticity, shows that the electron hybridization between p-orbital and d-orbital is weakened. The stability of the system was reduced by doping these elements. The analysis of population number and differential charge density showed that the Al-Ru bond energy was decreased and Ru-Ru anti-bond with different strength was formed. The anisotropy of the electron distribution in the outer layer of Ru atom is weakened, which is beneficial to the enhancement of AlRu plasticity. In the experiment part, we select B element, which has the most remarkable effect to improve the plastic property of AlRu. Five samples with B content of 0.2wtand 0.5wt% and 3wt% were designed. The samples were prepared by spark plasma sintering and arc melting. The microstructure of the samples was observed by scanning electron microscope. The Young's modulus and shear modulus were measured by nano-indentation instrument and universal testing machine. The G / B value is calculated. The results show that the microstructure of the sample is more uniform and there are some voids, and the measured shear modulus and bulk modulus are lower than the calculated values. However, the change trend of G / B value with the increase of B element content is basically consistent with the calculated results.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG146.2

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