【作者】 孙伟华；

【导师】 黄伯云； 杜勇；

【作者基本信息】 中南大学 ， 材料科学与工程， 2013， 博士

【摘要】 材料显微组织的描述是进行材料设计的重要前提之一。利用相图计算CALPHAD (CALculation of PHAse Diagram)方法建立的热力学和动力学数据库可以为材料显微组织定量模拟提供精确的相图热力学和扩散动力学信息。近年来,建立在精确热力学和扩散动力学基础上的相场模拟成为一种非常有效的显微组织模拟方法。Cu、Mn、Ni、Si和B是多元铝合金中重要的合金元素或者添加元素,它们之间的相互作用影响多元A1合金的相平衡关系。采用相场方法模拟Al合金的制备过程可以获得该过程中的显微组织演变信息,但是关于多元多相Al合金的定量模拟目前并不多见。本工作集成实验测定、CALPHAD方法和第一性原理计算对多元A1合金的重要子体系Mn-Ni-B、Cu-Mn-Ni和Cu-Ni-Si进行相图热力学研究,所获得的热力学参数完善了多元Al合金热力学数据库。结合A1合金热力学和动力学数据库,采用多相场方法对五元工业铝合金A1356.1(Al-0.46Fe-0.3Mg-0.32Mn-6.97Si, wt.%)的凝固和Al-Ni合金的时效过程进行模拟。本工作主要研究成果如下：(1)XRD分析证实NiB12和NiB2在950℃是非稳定相。测定了Ni-B体系中的零变量反应温度。采用第一性原理计算了所有化合物的生成焓来辅助热力学计算。通过热力学计算获得的Ni-B和Mn-B体系的热力学参数能够描述体系的相图热力学性质。结合Ni-B、Mn-B和Mn-Ni体系的热力学参数,对Mn-Ni-B三元系进行了热力学计算并采用所获得的参数构筑了希尔反应图。(2)测定了Cu-Mn-Ni体系600℃的等温截面。观察到了cbcc_A12、 cub_A13和fcc_Al的三相平衡。三个边际二元系中的fcc_Al相在三元体系中形成连续固溶体。Cu在Ll0-MnNi相中的溶解度达到16at.%。通过对该体系实验数据的热力学计算获得了能描述该体系相图热力学性质的一套参数。(3)测定了Cu-Ni-Si体系700℃的等温截面。首次发现了新的线性化合物Cu45.8Ni25Si29.2,并且证实了三元化合物Cu56.8-63Ni10.4-16.1Si26.6-27.3的存在。首次精确测定了所有化合物在700℃的固溶度。在Ni-Si二元体系中820℃以上稳定存在的Ni2SiH在三元体系中可以在700℃稳定存在,并且溶解12.7-20.6at.%的Cu。对体系热力学计算得到的参数计算的结果与实验结果符合。所得到的参数不仅可以结合相关体系参数准确计算Al-Cu-Ni-Si四元体系,而且还可以用于Cu基Corson合金在低温时效强化过程中析出相种类和相分数的预测。(4)采用多相场方法结合热力学和动力学数据库对多元工业Al合金Al356.1的凝固过程进行了模拟。模拟中涉及到五组元和五个相。定量得到了合金化元素Fe、Mg、Mn和Si的成分分布。模拟结果合理并且优于Scheil非平衡模型模拟。模拟中尝试了2套液相扩散系数数据库,发现液相扩散系数对凝固过程中的显微组织演变模拟结果有显著影响。(5)耦合热力学和动力学数据库,采用多相场方法对Al-Ni合金时效过程中,γ相在金属间化合物γ’基体相中析出、长大和熟化过程进行了模拟。界面能和共格弹性应力的作用不仅使γ相析出物由球形变成方块,最后成片状,而且还促使了两个γ相晶粒的分离行为,使体系能量达到最低。本论文包含84幅图、21个表和246篇参考文献。更多还原

【Abstract】 Description of materials microstructure is important for materials design. The thermodynamic and kinetic databases established by CALPHAD method provide accurate thermodynamic and kinetic data for quantitative simulation of microstructure. The phase field method based on accurate thermodynamic and kinetic inputs has been an effective method for simulation of microstructure evolution in recent years.Cu, Mn, Ni, Si and B are important alloying elements or additives in Al-based alloys, their phase relationships have influence on the phase equilibria of multicomponent Al alloys. The microstructure evolution of Al alloys in the preparation process can be obtained by phase field simulation. However, quantitative phase field simulation of multi-component Al alloys is rare. In the present work, a hybrid approach of experiments, first-principles calculations and CALPHAD is used to investigate the phase diagrams of Mn-Ni-B, Cu-Mn-Ni and Cu-Ni-Si systems, which are important sub-systems of multi-component Al alloys. The thermodynamic parameters obtained in the present work improve the thermodynamic database of Al alloys. Moreover, by coupling to the thermodynamic and kinetic databases of Al alloys, the multi phase field method is used to simulate the microstructure evolution of A1356.1(Al-0.46Fe-0.3Mg-0.32Mn-6.97Si, wt.%) alloy in the solidification process and the Al-Ni alloy in the aging process. The major research achievements of the present work are:(1) The NiB)2and NiB2are demonstrated to be unstable phases at950℃by XRD. The invariant temperatures in the Ni-B system are measured. The enthalpies of formation of all compounds are calculated by first principles calculation to assist the thermodynamic calculation. The thermodynamic parameters of Ni-B and Mn-B system are obtained by thermodynamic calculation and the calculated results agree with the experimental data. By combining the parameters of Ni-B, Mn-B and Mn-Ni systems, the thermodynamic calculation is performed on the Mn-Ni-B system. The liquidus projection and Scheil reaction scheme of Mn-Ni-B system are constructed using the obtained parameters.(2) The isothermal section of Cu-Mn-Ni system at600℃is measured. The three-phase equilibrium of cbcc_A12, cub_A13and fcc_Al is observed. The fcc_Al phases in binary systems form continuous solid solution in the ternary system. The solubility of Cu in Ll0-MnNi phase is up to16at.%。 A set of thermodynamic parameters is obtaind and the calculated results generally agree with the experimental data.(3) The isothermal section of Cu-Ni-Si system at700℃is measured. The line ternary compound Cu45.8Ni2.5Si29.2is observed for the first time. The ternary compound Cu56.8-63Ni10.4-16.1Si26.6-27.3reported in literature is demonstrated. The solubities of all compounds at700℃are accurately measured. The Ni2SiH phase stable above820℃in the binary Ni-Si system can be stable at700℃and dissolve12.7-20.6at.%Cu in the ternary system. A set of thermodynamic parameters for this system is obtained and the calculated results agree with the experimental data. The current set of parameters can successfully extrapolate to high order Al-Cu-Ni-Si system and predict the phase type and molar fraction of precipitates formed in the aging process of Cu based Corson alloy.(4) The solidification process of A1356.1alloy is simulated by multi phase field method. The simulation involves five components and five phases. The concentration distribution of alloying elements Fe, Mg, Mn and Si in the primary (Al) phase is quantitatively obtained. The simulation result is reasonable and better than the result of Scheil model. Two sets of diffusion databases of liquid phase are used, and it is found that the diffusion coefficients of liquid have significant influence on the simulation of microstructure evolution in the solidification.(5) The precipitation, growth and coarsening process of γ precipitate in y1matrix in the Al-Ni system is simulated. Under the effect of interfacial energy and elastic stress, the shape of y precipitate evolves from sphere to cubic and finally plate like shape. In addition, the splitting behavior is observed as to minimize the total energy in the system.There are84figures,21tables and246references in this thesis.更多还原