金属固溶体热膨胀系数的CALPHAD计算模型

CALPHAD Model of Thermal Expansion Coefficient in Metal Solid Solution

摘要:

基于计算相图方法(CALPHAD方法),借鉴经典热容模型,通过增加额外的磁性项参数,构建了包含铁磁-顺磁转变的金属固溶体热膨胀系数的CALPHAD计算模型。结合Ni-Fe二元合金的实验结果,采用Levenberg-Marquardt法对模型参数进行了评估,优化得到了300～1200K范围内Ni-Fe二元金属固溶体热膨胀系数的相互作用参数。采用得到的模型参数,对Ni-Fe二元金属固溶体的热膨胀系数进行了计算,计算结果准确地描述了Ni-Fe二元金属固溶体在居里温度附近的尖锐峰。随着Fe含量的增加,居里温度处的峰值减小,热膨胀曲线由峰状变成谷状,与实验值吻合。该计算模型可以准确计算任意Fe含量<50wt.%的Ni-Fe二元金属固溶体的热膨胀系数。

Abstract:

An important goal of materials genome initiative program is to build the calculation model and 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 is 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 300~1200K were obtained after assessment. Using assessed parameters, the thermal expansion coefficient of Ni-Fe binary alloy were calculated. Results indicated the sharp peak around Curie’s temperature precisely. The height of the peak gradually decreased as increasing Fe’s 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 Fe’s 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.