Morphology evolution of γ′ precipitates in a powder metallurgy Ni-base superalloy

Fan, Xianqiang; Guo, Zhipeng; Wang, Xiaofeng; Yang, Jie; Zou, Jixing

doi:10.1016/j.matchar.2018.02.038

Cited by 61 publications

(12 citation statements)

References 41 publications

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“…Other explanations, such as convective forces [54][55][56], precipitation-related phenomena [45], interactions with the mold wall [47][48][49], gravity [49] and asymmetric distributions of the solute around dendrite stems [46] have also been put forward. [15,[28][29][30]) affect performance and how they can be controlled, there is one aspect which has received insufficient attention. With other single crystals, SXs share the phenomenon of mosaicity, which was first described by C.G.…”

Section: Introductionmentioning

confidence: 99%

On Crystal Mosaicity in Single Crystal Ni-Based Superalloys

et al. 2019

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In the present work, we investigate the evolution of mosaicity during seeded Bridgman processing of technical Ni-based single crystal superalloys (SXs). For this purpose, we combine solidification experiments performed at different withdrawal rates between 45 and 720 mm/h with advanced optical microscopy and quantitative image analysis. The results obtained in the present work suggest that crystal mosaicity represents an inherent feature of SXs, which is related to elementary stochastic processes which govern dendritic solidification. In SXs, mosaicity is related to two factors: inherited mosaicity of the seed crystal and dendrite deformation. Individual SXs have unique mosaicity fingerprints. Most crystals differ in this respect, even when they were produced using identical processing conditions. Small differences in the orientation spread of the seed crystals and small stochastic orientation deviations continuously accumulate during dendritic solidification. Direct evidence for dendrite bending in a seeded Bridgman growth process is provided. It was observed that continuous or sudden bending affects the growth directions of dendrites. We provide evidence which shows that some dendrites continuously bend by 1.7° over a solidification distance of 25 mm.

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Section: Introductionmentioning

confidence: 99%

On Crystal Mosaicity in Single Crystal Ni-Based Superalloys

et al. 2019

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“…These specimens were extracted from the billet after HIP for hot deformation. To eliminate the effect of γ’ precipitate on hot deformation, specimen A, B, C, and D were rapidly heated to 1150 °C and holding for 30 min to dissolve all γ’ precipitates [ 33 ] prior to hot deformation using a Gleeble 1500 thermal simulator system. Without any deformation, specimen A was used as a blank control contrast group.…”

Section: Methodsmentioning

confidence: 99%

Grain Refinement of a Powder Nickel-Base Superalloy Using Hot Deformation and Slow-Cooling

et al. 2018

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A pre-hot-deformation process was applied for a polycrystalline nickel-base superalloy to active deformation twins and dislocations, and subsequent slow cooling treatment was used to achieve grain refinement and microstructure homogenization. The microstructural evolution of the alloy was investigated, and the corresponding underlying mechanism was discussed. It was found that twinning mainly occurred in large grains during pre-hot-deformation owing to the stress concentration surrounding the large grains. High density dislocations were found in large grains, and the dislocation density increased approaching the grain boundary. The average grain size was refined from 30 μm to 13 μm after slow cooling with a standard deviation of grain size decreasing from 10.8 to 2.8, indicating a homogeneous microstructure. The grain refinement and microstructure homogenization during cooling process could be achieved via (i) static recrystallization (SRX), (ii) interaction of twin tips and γ’ precipitates, and (iii) grain coarsening hindered by γ’ precipitates in grain boundaries.

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“…Figure 6c also shows the γ 0 phase precipitated in the two-step aged atomized powder of Ni-based superalloy with the similar composition. Except some larger coarsened γ 0 discussed widely in the literature by the Ostwald ripening effect, [24][25][26][27][28] the main precipitates have near-spherical morphology in submicrometer size. As both solution-aged and atomized Ni-based superalloy powders have the same spherical morphology of γ 0 , it clearly suggests that severe plastic deformation during mechanical alloying change γ 0 morphology to irregular-shaped morphology in microscale characterization.…”

Section: Comparison Of Maed and Atomized Conditionsmentioning

confidence: 99%

Evaluation of Processing Conditions on the γ′ Morphology of an Oxide Dispersion Strengthened Ni‐Based Superalloy

et al. 2020

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Herein, the evolution of the microstructure of a newly developed oxide dispersion strengthened (ODS) Ni‐based superalloy with emphasis on γ′ morphology during different processing conditions is investigated. X‐ray analysis of severely deformed mechanically alloyed (MAed) powders shows that the as‐milled nano‐sized crystallite size increases with annealing associated with the sharp drop of dislocation density. At the same time, by annealing MAed powders γ′ precipitates above 300 °C, and depending on the aging treatment regime, Vickers microhardness changes mainly due to γ′ distribution and dislocation release. The thorough evaluation of γ′ morphology in the microscale shows that in contrast to the spherical shape of γ′, after heat treatment of solutionized MAed ODS superalloy, irregular‐shaped γ′ exist in the MAed ODS superalloy due to severe plastic deformation during mechanical alloying. However, a unique nanostructured lamellar morphology forms in the γ′ precipitates with different lamellae directions. This structure is stable in all subsequent processing steps with γ′ lamellae of (011true¯) planes and intervals of 20–30 nm. The scanning transmission electron microscopy (STEM)–high‐angle annular dark‐field (HAADF) composition analysis clarifies that the nanostructured lamellar morphology shows no partitioning of alloying elements, and its origin may be attributed to the formation of antiphase domain boundaries.

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Morphology evolution of γ′ precipitates in a powder metallurgy Ni-base superalloy

Cited by 61 publications

References 41 publications

On Crystal Mosaicity in Single Crystal Ni-Based Superalloys

On Crystal Mosaicity in Single Crystal Ni-Based Superalloys

Grain Refinement of a Powder Nickel-Base Superalloy Using Hot Deformation and Slow-Cooling

Evaluation of Processing Conditions on the γ′ Morphology of an Oxide Dispersion Strengthened Ni‐Based Superalloy

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