On the prediction of the yield stress of unimodal and multimodal γ ′ Nickel-base superalloys

Abstract

a b s t r a c tA new model for the yield stress in superalloys accounting for unimodal and multimodal c 0 size distributions is presented. A critique of the classic models on c 0 shearing is presented and important features not previously considered are incorporated in our model. This is extended to account for multimodal particle size distribution effects by weighting the individual particle contribution to the total strength. This analysis is focused on powder metallurgy alloys. The yield stress and particle strengthening are predicted for eight superalloys containing wide variations in initial microstructure, composition and at temperatures up to 700°C. We demonstrate through a theoretical approach that the strength of alloys with multimodal c 0 is lower than those with unimodal c 0 radius in the vicinity of 10-30 nm. For the first time, a parameter-free physics-based model is able to predict the yield stress in superalloys with complex microstructures, including unimodal and multimodal c 0 size. This has been possible by removing limitations inherent to the classical models. Such approach also enables critical evaluation of the relevant factors contributing to the yield strength of polycrystalline superalloys.

Formation and Dissolution of γ’ Precipitates in IN792 Superalloy at Elevated Temperatures

“…Since the additional precipitation affects the mechanical properties of the alloy, these properties depend on the thermal history of the material. The observations in this study fit well with the modeling presented in earlier [6] or recent [7] studies highlighting significance of strengthening by tertiary precipitates in polycrystalline superalloys.…”

“…The new modeling approach was tested on several types of polycrystalline superalloys (RR1000, Udimet, IN100, KM4). Nevertheless, the qualitative output of the novel modeling approach [7] is for tertiary precipitates the same as found by Kozar et al: the tertiary, i.e., the small, precipitates provide the main part of strengthening.…”

“…It was found that additional precipitates in the channels between the large primary ones are formed either during slow cooling from high temperature or after reheating above 570˝C [4]. The new precipitates presumably affect mechanical properties as such small (tertiary) precipitates very significantly contribute to strengthening in polycrystalline superalloys [6,7].…”

“…The earlier models of precipitate strengthening like the one of Kozar et al [6] were improved recently to unify the weak pair-coupling and the strong pair-coupling mechanism into one comprehensive model [7]. Moreover, this model can be used for complex multimodal precipitate distributions as well.…”

Gamma Prime Precipitate Evolution During Aging of a Model Nickel-Based Superalloy

“…[3,55,56] Specifically, the high Mo and low Ti concentrations will affect multiple mechanisms of alloy strengthening concurrently, including solid solution, coherency, and order strengthening. Consequently, the contribution from each strengthening mechanism will vary between the secondary and tertiary γ′ populations as a result of their different compositions.…”