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 (
tr) 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-σ
0) /σ
0.05}
3.5 … (1)
log
tr+
m·log ε
S=
c… (2)
σ, σ
0 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. σ
0, σ
0.05,
m and
c have been represented as a function of structural factors calculated from chemical composition. Relationship between σ
0 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 10
4 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.
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