Establishment Of Thermal Expansion Coefficient Model And Database Of Nickel-base Superalloy Based On CALPHAD Method

The coefficient of thermal expansion(CTE)is a main property for the selection of metal materials and the design of processing technology,as well as the important thermophysical parameters of materials in engineering design and scientific research.Especailly when the material used in extreme high temperature environment,the CTE should be paid more attention.However,due to the limitations of experimental conditions,experimental information on the CTE of metallic materials is quite few.Therefore,it is very important to build a reasonable theoretical model to calculate the CTE and establish a database,which can provide necessary basic information for material design and selection.Based on CALPHAD method,this paper built a CALPHAD model of CTE of metal solid solution containing ferromagnetic-paramagnetic transformation by adding additional magnetic parameters.Combining the experimental information reported in the literature with the first principle,the model parameters were evaluated by the Levenberg-Marquardt method.The main contents are summarized as follows:(1)Based on CALPHAD method,a model for CTE in the binary and ternary alloys was constructed.A simple method to deal with magnetic transition was proposed.Based on CALPHAD method and the classical heat capacity model,this paper built a simple and effective ferromagnetic-paramagnetic treatment model,which can process the magnetic transition in the whole component range.This model is a general model for metal solid solution's thermal expansion behavior.(2)The model parameters were evaluated by the Levenberg-Marquardt method,and the interaction parameters of Ni-Fe binary in the range of 200-1200K were optimized.The model can accurately calculate CTE in Ni-Fe(FCC)binary system.(3)The first-pr,inciples was used to calculate CTE of Fe,Cr,Co,Mo,W,which are common element in the FCC structure of Nickel-based superalloys.And the expression of CTE with temperature was evaluated by Levenberg-Marquardt method.(4)The CTE of Ni-Co,Ni-Mo and Ni-W system,the partial sub-binary system with FCC structure in Nickel-base superalloys,were calculated by first-principles,and the interaction parameters were evaluated by Levenberg-Marquardt method.(5)Based on the parameters of the pure element Ni,Fe,Cr,Co,Mo,W,partial sub-binary Ni-Fe,Ni-Co,Ni-Mo and Ni-W and Ni-Fe-Cr(FCC)ternary system,the calculation model of Nickel-base Superalloys was established.The calculated values were in agreement with experimental results.The CALPHAD database of Ni-Fe-Cr-Co-Mo-W alloys was optimized.In this paper,a CALPHAD calculation model for CTE of Nickel-base Superalloys is established.The interaction parameters of pure components Ni,Fe,Cr,Co,Mo,W,partial sub-binary systems Ni-Fe,Ni-Co,Ni-Mo and Ni-W,Ni-Fe-Cr(FCC)ternary system was fitted.And the CALPHAD database of CTE of Ni-Fe-Cr-Co-Mo-W alloys was established,and the CTE of common grade commercial high temperature alloys was predicted by this CALPHAD database.For comparison,the results show that the calculated values are in good agreement with the experimental datas.The CALPHAD database of Nickel-base Superalloy CTE obtained in this study is an important part of Materials Genome Initiative and can provide important theoretical guidance for alloy design and engineering application.