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、接头的发展以及在相变发生时（如铸造和热处理）的加工过程中研究材料的行为至关重要。提出了一种新的方法来推广calphhad方法，使物理上一致的热力学数据库可以构建具有非平凡特征的体积性质。一个正确的自一致的体积相关性质的热力学描述，如热膨胀率和可压缩性，以及热力学函数的压力依赖性，在这个项目成功完成后受益。迄今为止，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学和地球物理学领域。在这些领域中，为了开发硅酸盐和氧化物系统的数据库，热力学建模的重点转向了振动模型，结合从头算方法，以防止热力学性质中的不现实行为，并在缺乏实验数据的情况下实现更好的性质预测。虽然这些方法已经被证明是非常成功的建立热力学数据库，但在目前的研究阶段，重建热力学数据库是不切实际的，因为热力学数据库与基于calphhad方法的吉布斯能量公式相耦合。提出的研究目标是建立一个吉布斯能量形式，从中可以推导出所有热力学性质，包括与体积相关的性质。这种形式主义作为一种临时解决方案，可以适应于calphad型建模。这种形式的发展是由振动形式和从头算方法来协助，以确保防止物理上不现实的行为在热力学性质。此外，它们还用于预测目前没有实验数据的性质。它们还将被用于更深入地了解组成对振动和静态晶格性质的影响，以获得物理效应到多余性质的划分。为了增强所提出方法的应用，开发了包括Ag-Au-Cu-Ni-Pd-Pt体系中选定的二元和三元体系的体积性质的热力学数据集。采用振动形式来实现该系统中相的物理自洽描述。该描述由包含振动输入参数的数据集组成，类似于矿物物理学和地球物理学中开发的数据集。这些参数可以用于这些领域，以便将来研究地球固体地幔和地核中普遍存在的极端条件下的物质。较好的约束热力学性质作为临时解决方案的约束，可以容纳在目前的calphad型模型中。这就产生了一个数据集，一般适用于Calphad方法来推导压力-温度-成分空间的热力学性质。由于所开发的吉布斯能量形式是自洽的，与所选择的系统无关，因此它还适用于低压状态下这些性质的一般预测，这对于工业过程中的应用非常重要。

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.