镍基高温合金中σ及γ′相原子占位及相稳定性研究

The thermodynamic sublattice model is constructed based on the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) method to predict the phase stability of intermetallic compounds. Most model parameters are with physical basis but their assignments are normally empirically estimated. It is thus not possible to accurately predict the phase stability in the multicomponent system. The above problems can be solved in principle by increasing the experimental and theoretical data. However, in order to economically and efficiently establish a thermodynamic model with a physical background, it requires the in-depth atomic-level study of atomic occupancy (i.e. atomic constituent distribution or site occupancy preference on inequivalent sites of a crystal structure) and its interaction between and within sublattice. In the present project, the atomic occupancy and the interaction between and within sublattice of the precipitates, σ and γ′ phases in Ni-based superalloys, are investigated. First, by using first-principles calculations, the CALPHAD method combining with the experimental determination, we investigate the influence of temperature on the atomic occupancy of the σ and γ′ phases to explore the atomic occupancy regularity in a wide temperature range. Based on the above, the correlation between the atomic occupancy, and the interaction between and within sublattice is built up. Further, the thermodynamic sublattice model parameters with physical basis are acquired. In addition, by using the above method, the Ni-based superalloys related Ni-Cr-Fe ternary system is modeled to achieve the phase stability. The innovation of the present proposal is that the correlation between the atomic occupancy and the interaction energy within sublattice is constructed. In addition to the traditional considerations of the experimental thermodynamic and phase equilibrium data as well as theoretical calculations, the thoroughly study of the experimental site occupancy data are also adopted during the thermodynamic modeling.

在基于计算热力学方法建立的金属间化合物的亚点阵模型中，多数模型参数虽有一定物理意义但其赋值大多是经验估算，因而难以准确预测多元体系中的相稳定性。大量实验及理论数据原则上可解决上述问题，但要经济高效地建立有物理背景的模型及其参数，则需要深入到原子层次研究其交互作用。本项目以镍基合金中σ及γ′相为研究对象，研究原子的点阵占位以及亚点阵之间、同一亚点阵内部的交互作用。首先结合第一性原理计算、计算热力学方法及实验测试，考察温度对σ及γ′相原子占位的影响，揭示宽广温度范围原子占位优先顺序规律。在此基础上建立原子占位与亚点阵之间及内部交互作用的关联关系，获取有物理意义的亚点阵模型参数。然后，运用上述方法建立Ni-Cr-Fe三元热力学模型，确定相稳定性。本项目的特色为建立原子占位与亚点阵内部交互作用能的关联，在传统的考虑热力学、相平衡实验和理论计算的基础上，在建模过程中引入对占位分数实验数据的深入分析。

本项目以镍基高温合金中的有害析出相σ和强化相γ′相为主要研究对象，揭示了金属间化合物的原子占位规律、原子键合规律以及同一亚点阵内部原子之间交互作用规律，建立了合理可靠的热力学及摩尔体积模型。其中热力学模型在构建过程中考虑了原子占位分数实验数据，并且模型参数采用了具有物理依据的第一性计算数据，大大增加了模型的可靠程度，对于解决计算热力学方法对镍基高温合金中有害拓扑密堆相稳定性预测不准确的问题具有重要意义。此外，本项目针对金属间化合物提出了一种新的摩尔体积模型，这为镍基高温合金成分设计过程中的重要筛选因子即γ/γ′相点阵错配的建模提供了重要的模型基础。总体来讲，本项目的研究成果为缩短镍基高温合金的设计周期及节约设计成本奠定了模型与理论基础。