【作者】 胡标；

【导师】 杜勇； 刘树红；

【作者基本信息】 中南大学 ， 材料科学与工程， 2013， 博士

【摘要】 摘要：Al合金由于其优良的综合性能,被广泛应用于航空航天、汽车等领域。Cu、Mg、Mn、Ni、Si、Fe、Cr、Ti等元素是Al合金中主要的合金元素或添加元素。相关体系的相图和热力学信息是研究Al合金性能的理论基础。为了提高Al合金性能、改善生产工艺以及开发新型Al合金材料,建立多元Al合金精确的相图热力学数据库是非常有必要的。本论文以多元商用Al合金中的五个重要体系(Al-Cr-Si、 Mn-Ni-Si、Cr-Ni-Ti、Al-Fe-Mg-Ni-Si和Al-Cu-Fe-Mg-Ni)为研究目标,通过集成关键实验、第一性原理计算和CALPHAD (CALculation of PHAse Diagram)技术的方法获得相应体系精准的热力学数据库。本工作的主要研究成果如下：(1)对Al-Cr-Si体系进行了详细的文献评估,同时,借助于第一性原理计算了τ1(Al13Cr4Si4)和τ2(Al9Cr3Si)两个三元化合物在0K时的形成焓。基于本工作第一性原理的结果以及文献报道的实验数据和边界二元系的热力学描述,对Al-Cr-Si三元系进行了重新优化,最终得到了一套能够准确描述Al-Cr-Si体系整个成分和温度范围内的热力学参数。此外,本工作还构筑了该体系的液相面投影图和希尔反应图。(2)采用XRD、SEM/EDX等实验手段,测定了Mn-Ni-Si体系1000℃等温截面。同时,借助于第一性原理计算了τ4(MnNiSi)在0K时的形成焓。基于本工作实验和第一性原理计算的结果以及可靠的文献数据,优化计算了Mn-Ni-Si三元系。首次成功地应用同一个吉布斯自由能表达式描述了该体系中的Fcc_Al/L12和Bcc_A2/Bcc_B2有序-无序转变,并获得了一套自洽的热力学参数。此外,本工作还构筑了Mn-Ni-Si体系的液相面投影图和希尔反应图。(3)应用CALPHAD方法,修订了Ni-Ti二元系的热力学描述,并对Cr-Ni-Ti体系进行了热力学优化。首次使用四个亚点阵模型描述三元系中的Bcc_A2/Bcc_B2有序-无序转变。基于文献报道的实验数据,获得了一套自洽的热力学参数。通过计算结果与实验结果相比可知,本工作获得的热力学参数能够准确地描述所有可靠的实验数据。(4)本工作重新优化了Al-Fe-Si三元系的富Al角并修正了描述Al-Fe-Ni三元系中Al9FeNi相的参数。结合本工作所获得的Al-Fe-Si和Al-Fe-Ni体系的热力学参数和文献中已报道的其他三元系的热力学参数,优化计算了Al-Fe-Ni-Si、Al-Fe-Mg-Si和Al-Cu-Fe-Ni三个四元系,并外推计算了Al-Fe-Mg-Si. Al-Cu-Fe-Mg和Al-Cu-Mg-Ni三个四元系,最后建立了Al-Fe-Mg-Ni-Si和Al-Cu-Fe-Mg-Ni五元系的热力学数据库。利用该数据库计算的相图数据、平衡凝固和Gulliver-Scheil非平衡凝固行为能很好地描述实验数据。基于显微模型计算了商用6063合金(Al-0.39Si-0.20Fe-0.43Mg,质量百分数)和2618合金(Al-2.24Cu-1.42Mg-0.9Fe-0.9Ni,质量百分数)的凝固过程中的相变序列。模型计算的凝固序列结果与实验数据符合得很好,说明本工作建立的热力学数据库具有较高的精准度。更多还原

【Abstract】 Abstract:Al alloys are widely applied in aeronautics, astronautics and automobiles due to their excellent comprehensive properites. Cu, Fe, Mg, Mn, Ni, Si, Cr and Ti are the important alloying elements or additives in the Al alloys. Knowledge of phase diagrams and thermodynamic properties of related systems is the theoretical basis to understand the performance of Al alloys. In order to promote the properties, improve the production process and develop new Al alloys, it is essential to establish an accurate thermodynamic database of the multicomponent Al alloys.Five key systems (Al-Cr-Si, Mn-Ni-Si, Cr-Ni-Ti, Al-Fe-Mg-Ni-Si and Al-Cu-Fe-Mg-Ni) in the multicomponent commercial Al alloys are selected as research objectives in the present thesis. A hybrid approach of key experiments, first-principles calculations and CALPHAD (CALculation of PHAse Diagram) is employed to establish the accurate thermodynamic databases of these key systems. The major research achievements of the present work are:(1) The available experimental data of the Al-Cr-Si system are first critically evaluated. The enthalpies of formation of the τi (Al13Cr4Si4) and τ2(Al9Cr3Si) phases at0K are computed via the first-principles calculations. The Al-Cr-Si system is re-optimized based on the present first-principles results and the previous descriptions of the Al-Cr, Al-Si and Cr-Si systems as well as the experimental data from the literature. Finally, an optimal set of thermodynamic parameters of the Al-Cr-Si system is obtained. In addition, the liquidus projection and reaction scheme of this system are also constructed in the present work.(2) The isothermal section of the Mn-Ni-Si system at1000℃is determined by means of XRD and SEM/EDX. The enthalpy of formation for the τ4(MnNiSi) phase at0K is computed via the first-principles calculations. Based on the present obtained experimental data and first-principles results as well as the experimental data from the literature, the thermodynamic modeling of the Mn-Ni-Si system is performed. One single function is used to describe the Gibbs energies of both the ordered and disordered phases including L12and Fcc_A1as well as Bcc_B2and Bcc_A2. A set of self-consistent thermodynamic parameters is obtained. In addition, the liquidus projection and reaction scheme of the Mn-Ni-Si system are also constructed.(3) A thermodynamic assessment of the ternary Cr-Ni-Ti system together with a refined binary Ni-Ti sub-system is made using the CALPHAD method. The ordered-disordered transition between Bcc A2and Bcc_B2phases is described using a four-sublattice model for the first time. An optimal set of thermodynamic parameters for the Cr-Ni-Ti system is obtained by considering the experimental data from the literature. Comparisons between the calculated and measured phase diagrams indicate that all of the reliable experimental information is satisfactorily accounted for by the present modeling.(4) The Al-rich corner of the Al-Fe-Si system is re-optimized and the parameters of the Al9FeNi phase in Al-Fe-Ni system are modified in present work. Combining the thermodynamic parameters of these two systems and those of other ternary systems from literature, three quaternary systems (Al-Fe-Mg-Si, Al-Cu-Fe-Mg and Al-Cu-Mg-Ni) are extrapolated and three quaternary systems (Al-Fe-Ni-Si, Al-Fe-Mg-Si and Al-Cu-Fe-Ni) are modeled. Then, a thermodynamic database of two quinary systems (Al-Fe-Mg-Ni-Si and Al-Cu-Fe-Mg-Ni) is constructed. The established database is used to describe the solidification behaviors of6063alloy (Al-0.39Si-0.20Fe-0.43Mg, in wt.%) and2618alloy (Al-2.24Cu-1.42Mg-0.9Fe-0.9Ni, in wt.%) under equilibrium and Gulliver-Scheil non-equilibrium conditions. The reliability of the obtained thermodynamic database is verified by the good agreement between calculation and experiment.更多还原