CALPHAD Model Calculation of Thermal Expansion Coefficient in Metal Solid Solution

An important goal of materials genome initiative program is to build the calculation model and to establish the database of physical properties of the materials, aiming to shorten the development period of the materials, reduce the cost of research and development in material and accelerate the production of new material. Although the existing model has been available for the calculation of pure component's thermal expansion coefficient, a proper model to deal with metal solid solution's thermal expansion coefficient is still lacking. Here, based on the calculation of phase diagram method (CALPHAD method), a model of the thermal expansion coefficient of solid solution containing ferromagnetic-paramagnetic transition was constructed by modifying the traditional heat capacity model and adding extra magnetic item. The experimental data of Ni-Fe binary system were used to assess the model parameters by Levenberg-Marquardt method. The interaction parameters in the temperature range of 300~1200 K were obtained after the assessment. Using assessed parameters, the thermal expansion coefficient of Ni-Fe binary alloy were calculated. Results indicate the sharp peak around Curie's temperature precisely. The height of the peak gradually decreased as increasing Fe content and the shape of the thermal expansion curve changed from a peak into a valley, which were in agreement with the experimental data. This model can precisely predict the thermal expansion coefficient of any Ni-Fe binary alloy when the Fe content is less than 50wt%. This work provided a general calculation model for the thermal expansion coefficient in metal solid solution, and obtained the basic CALPHAD database of thermal expansion coefficient for Ni-Fe binary system, which can provide theoretical guidance for the design of low-expansion superalloy and also pave the way to establish the physical properties database of multi-element metal solid solution in the future. © 2019, Science Press. All right reserved.