On the applicability of boundary condition based tensile creep model in predicting long-term creep strengths and lifetimes of engineering alloys

Determination of Activation Energy and Prediction of Long-Term Strength of Creep Rupture for Alloy Inconel 740/740H: A Method Based on a New Tensile Creep Rupture Model

“…These results differ fundamentally from those of the conventional creep rupture model described previously. Nevertheless, they are consistent with those obtained by the new creep rupture model for other types of creep-resistant alloys such as martensitic [5,8,9,[13][14][15][16] and austenitic [12] creep-resistant steels and Ni-base superalloys. [8,14] The results in Figure 4 also suggest that stress and temperature have equivalent effects on creep lifetime, i.e., varying stress has the same effect as varying temperature on creep lifetime.…”

“…Nevertheless, they are consistent with those obtained by the new creep rupture model for other types of creep-resistant alloys such as martensitic [5,8,9,[13][14][15][16] and austenitic [12] creep-resistant steels and Ni-base superalloys. [8,14] The results in Figure 4 also suggest that stress and temperature have equivalent effects on creep lifetime, i.e., varying stress has the same effect as varying temperature on creep lifetime. This is precisely the basis required for predicting long-term creep rupture strengths from short-term creep rupture test data measured at higher temperatures and stresses.…”

“…This model result-guided approach to microstructural investigation and hence to relating microstructural changes to creep properties is described in more detail in a previous study. [14] Equations [7] and [8] can be used to make creep rupture strength predictions. Such predictions are calculated using Eqs.…”

“…Such predictions are calculated using Eqs. [7] and [8] for different temperatures and are shown together with experimental data in a conventional plot of logr versus logt r in Figure 5, where the points are experimental data and the curves are predictions of Eqs. [7] and [8].…”

“…It shows clearly that the stress exponent n* determined in this way is a strong function of temperature T -its value decreases continuously with increasing temperature from 8.1788 °C at 650 °C to 3.9919 °C at 875 °C. It has been shown previously that this strong dependence of n* on T will mathematically inevitably lead to a strong dependence of creep rupture activation energy Q c * on stress r. [8] These conventional model results are difficult to rationalize, indicating that the conventional model, i.e., Eq. [1], and the analytical method associated with it are flawed.…”