A Predicting Method of the Creep Rupture Life of Nickel-Base Precipitation Hardened Superalloys from Chemical Composition

Abstract

The program for estimating the creep rupture life at 900°C from chemical composition has been developed on nickel-base precipitation hardened superalloys.
In this program, the steady state creep rate (ε_S) and the creep rupture life (t_r) have been estimated by Evans-Harrison's and Monkman-Grant's equations, respectively, which have been represented by the following equations.
ε_S=B'{ (σ-σ₀) /σ_0.05}^3.5 … (1)
log tr+m·log ε_S=c… (2)
σ, σ₀ and σ_0.05 are applied stress, friction stress and 0.05% proof stress, respectively. B' is the constant for all alloys. m and c are constants for each alloy. σ₀, σ_0.05, m and c have been represented as a function of structural factors calculated from chemical composition. Relationship between σ₀ and structural factors has been led by the theoretical analysis based on the dislocation theory.
About 80% of the experimental creep rupture lives have fallen within a factor of two of the estimated lives at the various stress levels corresponding to the lives up to 10⁴ h as for twenty eight alloys. Especially, for cast alloys with higher γ' volume fraction, the creep strength has been estimated accurately by this program.