Phase diagram calculation and validation of wrought Ni base superalloys

摘要

Thermodynamic phase calculation and itsexperimental confirmation were made on a series of wrought Nibase superalloys. The Gibbs free energy of the constituent phasessuch as γ, γ', σ, etc can be expressed by applying the Sublatticemodel. Minimum Gibbs free energy condition was selected as thecriteria for determining the equilibrium state. The calculated phasefraction and the transition temperature were experimentallyvalidated by comparing the calculated value with the measured one.Isothermal aging treatment followed by electrochemical extractionand quantitative X-ray diffraction was employed for experimentalvalidation of the calculated phase fraction, and the differentialthermal analysis for the phase transition temperature. Thecalculated values for both phase fraction and transitiontemperature are well matched with the measured values. Thecalculated phase diagrams offer lots of useful information such assolution treatment temperature, TCP(Topologically Close Packed)phase formation, γ' phase fraction and driving force for precipitation, etc.