Design of Re-free nickel-base single crystal superalloys using modelling and experimental validations

Abstract

Lowering the rhenium (Re) content in nickel-base single crystal superalloys has been a hot topic in recent years. To explore the design space of Re-free nickel-base single crystal superalloys, computer-aid modelling procedures were developed based on thermodynamic calculations and regression analysis. Regression coefficients for alloy density were updated based on Caron’s density model and newly-collected data. A new regression model for creep resistance was also proposed to improve the predictive accuracy and capability. To isolate the alloys with a targeted microstructure, property constraints were defined for the γ′ fraction, γ′ solvus, heat treatment window, γ/γ′ lattice misfit and phase stability number. Two Re-free alloys SC11 and SC21 were tested to validate the modelling procedures. The results indicated after ageing treatment, SC11 that violated the constraints of misfit and phase stability number exhibited premature γ′ coalescence; while SC21 that fulfilled all the constraints exhibited the targeted microstructure. The inappropriate misfit and phase stability number in SC11 caused severe microstructural degradation during creep, resulting in inferior creep resistance than prediction; while SC21 exhibited creep resistance as expected although a limited amount of TCP phases were formed during high temperature creep.