A physically consistent method to implement volume properties in Calphad-type thermodynamic descriptions of alloys

合金中体积变化的影响对于优化材料的性能和密度、接头的发展以及研究发生相变的加工过程中的材料行为是至关重要的，例如铸造和热处理。提出了一种新的方法来推广CALPHAD方法，这样就可以利用体积性质的非平凡特性来构造物理上一致的热力学数据库。对体积相关性质的正确的自洽热力学描述，如热膨胀性和压缩性，以及热力学函数的压力相关性，将在该项目成功完成后受益。到目前为止，开发包括体积性质推导在内的热力学数据库的认真尝试仅限于矿物物理和地球物理领域。在这些领域，开发硅酸盐和氧化物系统数据库的热力学模型的重点转移到振动模型和从头计算方法，以防止热力学性质中不切实际的行为，并在实验数据缺失的条件下实现对性质的更好预测。虽然已经证明这些方法在开发热力学数据库方面是相当成功的，但在现阶段的研究阶段，将热力学数据库与基于CALPHAD方法的Gibbs能量公式相耦合是不可行的。这项研究的目标是发展一个吉布斯能量公式，由此可以推导出所有的热力学性质，包括与体积有关的性质。这种形式主义是一种临时解决方案，可以适用于CALPHAD类型的建模。这种形式主义的发展得到了振动形式主义和从头算方法的帮助，以确保防止热力学性质中物理上不现实的行为。此外，它们还用于预测目前尚无实验数据的性质。它们还将被用来更深入地了解组成对振动和静态晶格性质的影响，以获得物理效应到超额性质的划分。为了加强该方法的应用，我们建立了一个包含体积性质的热力学数据集，用于Ag-Au-Cu-Ni-Pd-Pt体系中的二元和三元体系。振动形式化被用来实现对该系统中的相的物理自洽描述。这一描述包括一个包含振动输入参数的数据集，类似于矿物物理和地球物理中开发的那些参数。这些参数可用于未来在固体地幔和地核普遍存在的极端条件下研究物质的这些领域。更好的约束热力学性质作为过渡解中的约束，可以在目前的CALPHAD类型的模拟中被适应。这导致了一个在CALPHAD方法中普遍适用的数据集，以推导出压力-温度-组成空间中的热力学性质。由于所发展的吉布斯能量公式是自洽的，与所选择的体系无关，因此它还适用于在低压区域预测这些性质，这对于工业过程中的应用是很重要的。

The impact of volume changes in alloys is of utmost importance in optimizing performance and density of materials, the development of joints and in the study of materials behavior during processing when phase transformations occur, such as casting and heat treatment. The development of a new method is proposed to generalize the Calphad approach in such a way that physically consistent thermodynamic databases can be constructed with the non-trivial characteristic that volume properties are derived from them. A correct self-consistent thermodynamic description of volume related properties, such as thermal expansivity and compressibility, along with the pressure dependence of thermodynamic functions, benefits after the successful completion of this project.So far serious attempts to develop a thermodynamic database including the derivation of volume properties have been limited to the fields of mineral physics and geophysics. In these fields the accent in the thermodynamic modelling for the development of databases of silicate and oxide systems shifts to vibrational models coupled with ab initio methods to prevent unrealistic behavior in thermodynamic properties and to achieve better predictions of properties at conditions where experimental data are missing. Although it has been shown that these methods are quite successful to develop thermodynamic databases, it is impracticable at this stage of research to remake thermodynamic databases, which are coupled to Gibbs energy formulations based on the Calphad approach. It is the goal of the proposed research to develop a Gibbs energy formalism from which all thermodynamic properties, including the volume related properties, can be derived. This formalism serves as an interim solution that can be accommodated in Calphad-type modelling. The development of this formalism is assisted by vibrational formalisms and ab initio methods to assure that physically unrealistic behavior in thermodynamic properties is prevented. Additionally they are used to predict properties for which presently no experimental data are available. They will also be used to gain more insight in the effect of composition on vibrational and static lattice properties to obtain a partitioning of physical effects into the excess properties. To enhance the application of the proposed method, a thermodynamic dataset including volume properties is developed for selected binary and ternary systems in the system Ag-Au-Cu-Ni-Pd-Pt. Vibrational formalisms are employed to achieve a physically self-consistent description of phases in this system. This description consists of a dataset containing vibrational input parameters, analogous to those developed in mineral physics and geophysics. These parameters could be used in these fields for future studies of materials at the extreme conditions prevailing in the solid mantle and core of the earth. The better constrained thermodynamic properties serve as constraints in the interim solution, which can be accommodated in present day Calphad-type modelling. That results in a dataset generally applicable in the Calphad approach to derive thermodynamic properties in pressure-temperature-composition space. Because the developed Gibbs energy formalism is self-consistent and independent of the chosen system it is additionally applicable in a general way to make predictions of these properties in the low pressure regime, which are important for applications in industrial processes.