Interpolation and extrapolation with the CALPHAD method

Qun Luo¹，Cong Zhai¹，Dongke Sun²，Wei Chen³，Qian Li¹

1. State Key Laboratory of Advanced Special Steel & Shanghai Key Laboratory of Advanced Ferrometallurgy & School of Materials Science and Engineering,Shanghai University & Shanghai Institute of Materials Genome & Materials Genome Institute, Shanghai University2. School of Mechanical Engineering, Southeast University3. Key Laboratory of Power Beam Processing, AVIC Manufacturing Technology Institute

摘 要：It is widely reported that CALPHAD is an extrapolation method when the thermodynamic properties of a multicomponent system are approximated by its subsystems. In this work the meaning of the words extrapolation and interpolation is discussed in context of the CALPHAD method. When assessing the properties in binary and ternary systems, extrapolation method is indeed often used. However, after assessment, the Gibbs energies are in fact interpolated from the lower order systems into the higher order systems in the compositional space. The metastable melting temperatures of bcc and hcp in Re–W and the liquid miscibility gap in Mg–Zr system are predicted to illustrate the difference between interpolation and extrapolation.

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