On the Stress- and Temperature-Dependence of Creep of Nimonic 80A

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Abstract
The dependence of the steady creep rate, ε s , on stress, σ, and temperature, T, for Nimonic 80A at 1023K can be described as ɛ ˙ s = A σ n exp ( Q c / R T ) The values of the stress exponent, n (∼ 8.3) and the activation energy for creep, Qc , (≃460 kJ/mol) are considerably higher than those for the nickel-20% chromium matrix material. These anomalously high values of n and Qc are accounted for in terms of the stress- and temperature-dependence of the friction stress, σ0, which is determined by a technique involving consecutive small stress reductions during creep. The stress- and temperature-dependence of ε s for Nimonic 80A can then be represented as ɛ ˙ s = A ( σ − σ 0 ) 4 exp ( Q c * / R T ) where Qc *, determined from creep rates recorded at different temperatures at the same value of (σ – σ0), is 305 kJ/mol, which is close to that for creep and diffusion in the matrix material. This suggests that creep of two-phase alloys is controlled by processes occurring in the matrix.