Strain Induced Abnormal Grain Growth in Nickel Base Superalloys

Bozzolo, Nathalie; Agnoli, Andrea; Souaï, Nadia; Bernacki, Marc; Logé, Roland E.

doi:10.4028/www.scientific.net/msf.753.321

Cited by 35 publications

(9 citation statements)

References 11 publications

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“…As seen here, initial strain bears a definite and significant influence on not only the emergence rate for AGG, but also, by extension, the continued progression rate. These findings are supported by the work of Decker et al [32], He et al [33][34][35], and Cho et al [36], who all showed that among instances of self-similar AGG, initial strain content can serve as a significant driving force for grain boundary migration among low-energy, high-mobility grain boundaries [9,36,37]. In this work, this driving force is incorporated into the predictive estimate for AGG advancement as a superposition of a nominal rate (where ε = 0) combined with a weighted contribution from the additional plastic strain present.…”

Section: Discussionsupporting

confidence: 77%

Emergence and Progression of Abnormal Grain Growth in Minimally Strained Nickel-200

Underwood

Madison

Thompson

2017

Metals

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Grain boundary engineering (GBE) is a thermomechanical processing technique used to control the distribution, arrangement, and identity of grain boundary networks, thereby improving their mechanical properties. In both GBE and non-GBE metals, the phenomena of abnormal grain growth (AGG) and its contributing factors is still a subject of much interest and research. In a previous study, GBE was performed on minimally strained (ε < 10%), commercially pure Nickel-200 via cyclic annealing, wherein unique onset temperature and induced strain pairings were identified for the emergence of AGG. In this study, crystallographic segmentation of grain orientations from said experiments are leveraged in tandem with image processing to quantify growth rates for abnormal grains within the minimally strained regime. Advances in growth rates are shown to vary directly with initial strain content but inversely with initiating AGG onset temperature. A numeric estimator for advancement rates associated with AGG is also derived and presented.

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Section: Discussionsupporting

confidence: 77%

Emergence and Progression of Abnormal Grain Growth in Minimally Strained Nickel-200

Underwood

Madison

Thompson

2017

Metals

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“…Bozzolo et al showed that in low strain torsion tests Alloy 718 produced abnormally large grains that grew unhindered despite the presence of δ phase particles [5]. The large grains seen in this study had roughly twice the amount of twin boundaries than normalsized grains, appearing scattered throughout a low strained part of the microstructure.…”

Section: Introductionsupporting

confidence: 49%

“…Samples of the alloy came from regions of low strain during forging. Simulations and previous studies [5,6] suggest that the critical strain for abnormal grain coarsening during solution heat treatment is less than 0.2. However initial tests on this material have produced negative results.…”

Section: Discussionmentioning

confidence: 62%

Characterization of abnormal grain coarsening in Alloy 718

Watson

Preuss

Fonseca

et al. 2014

MATEC Web of Conferences

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Abstract. Even though the phenomenon of abnormal grain coarsening (AGC) or "exploded grains" has been known to occur in Alloy 718 industrial forgings there is still no satisfactory explanation for it. For this reason, detailed microstructure analysis has been carried out in normal and abnormal regions. Electron Backscatter Diffraction (EBSD) was employed to determine grain size, boundary distribution and measure stored energy, while backscattered imagining in a FEGSEM was used to measure δ precipitate size and morphology. It was found that abnormal regions show almost 3 times as many twin boundaries compared to a normal region. In addition, the δ phase morphologies differ very significantly when comparing these two different regions. Normal regions display δ phase with a plate like nature, whereas in abnormal regions, δ particles appear to be more spherical. Furthermore, there are clear indications of differences in δ volume fractions between the two regions. Whilst in normal regions the δ phase is found predominantly at grain boundaries, in abnormal regions the δ is also found within grains. Both backscatter images and EBSD scans indicate that there are higher levels of stored energy within the normal regions, compared to the abnormal regions. These observations suggest that AGC occurs in regions where dynamic recrystallization does not happen and where recrystallization during solution heat treatment is affected by the local particle distribution.

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“…3. A fully recrystallized microstructure was observed [17]. Table 2 illustrates the evolution of average grain size after compression of samples deformed at 980°C and 1020°C.…”

Section: Resultsmentioning

confidence: 95%