On the long-term aging of S-phase in aluminum alloy 2618A

Abstract

The aluminum alloy 2618A is applied for engine components such as radial compressor wheels which operate for long time at elevated temperatures. This results in coarsening of the hardening precipitates and degradation in mechanical properties during the long-term operation, which is not taken into account in the current lifetime prediction models due to the lack of quantitative microstructural and mechanical data. To address this issue, a quantitative investigation on the evolution of precipitates during long-term aging at 190 °C for up to 25,000 h was conducted. Detailed transmission electron microscopy (TEM) was combined with Brinell hardness measurements and thorough differential scanning calorimetry (DSC) experiments. The results show that GPB zones and S-phase Al2CuMg grow up to < 1,000 h during which the GPB zones dissolve and S-phase precipitates form. For longer aging times, only S-phase precipitates coarsen, which can be well described using the Lifshitz–Slyozov–Wagner theory of ripening. A thorough understanding of the underlying microstructural processes is a prerequisite to enable the integration of aging behavior into the established lifetime models for components manufactured from alloy 2618A.

Brinell-Hardness data (HBW 2.5/62.5) of aluminum alloy EN AW-2618A after different aging times and temperatures

“…The hardness loss is due to the microstructural evolution of the nm-sized S-phase Al 2 CuMg, which is the strengthening phase in this Al-alloy. We have shown in [1 , 2] for this aging temperature, that the average radii of the S-phase increase with aging time and the hardening phase coarsens. Initially, the increase is very rapid, followed by a pronounced change in slope after 1,000 hours of aging, which is due to the initial growth kinetics of the precipitates.…”

“… The dataset can be used to calibrate and validate numerical thermodynamic and thermokinetic models. Hardness data can be correlated with microstructural data given in [1] , [2] , [3] . The data can be used for comparative material selection processes.…”

“…The data presented here was the basis of two publications [1 , 2] and also includes data on additional aging temperatures and times. The spreadsheet “Average” of the Excel file “Brinell_hardness_ENAW2618A.xlsx” in the repository [4] summarizes the average values of the 5 individual measurements of Brinell hardness HBW 2.5/62.5 of all investigated aging and creep conditions, respectively.…”

Designed Y3+ Surface Segregation Increases Stability of Nanocrystalline Zinc Aluminate

“…Shifts away from Ostwald ripening are more likely in metals than ceramics although since ceramic vapor pressures are much lower than in metals even at the nanoscale, meaning that ripening likely occurs via different transport mechanisms than in metals. Additionally, these types of transitions typically lead to sharp changes in the rate of crystal growth with time . The coarsening curves in Figure instead show gradual changes in growth rate for both compositions at 850 and 900 °C, implying that the observed zinc aluminate growth behavior is unlikely to be due to a change in the dominant growth mechanism.…”

Quantitative Shape-Classification of Misfitting Precipitates during Cubic to Tetragonal Transformations: Phase-Field Simulations and Experiments

“…The elastic constants of the matrix are obtained by a lever rule as described in [5], where the content of γ″ phase is assumed to be 11%. The phase-field simulations of θ′ precipitation, discussed here, were performed in conjunction with experimental studies of the mechanical properties of Al alloys by Häusler et al [42] and Rockenhäuser et al [43], respectively. As for the simulation of the θ′ phase, first principles data are available for the elastic data of all phases [7,8,44].…”