Simulation of equiaxed growth ahead of an advancing columnar front in directionally solidified Ni-based superalloys

Dong, Haibo; Yang, Xinliang; Lee, Peter; Wang, W.

doi:10.1023/b:jmsc.0000048733.96958.c3

Cited by 23 publications

(16 citation statements)

References 19 publications

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“…Columnar grains were observed in the middle and bottom regions of the deposit for all five conditions considered. The grains at the bottom that grew epitaxially from the substrate were comparatively smaller compared to those found in the middle region of the deposit [43,44]. Cooling rates (ε) are considered critical in influencing the microstructural scales formed during solidification [38].…”

Section: Ebsd Mappingmentioning

confidence: 99%

Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718

Sreekanth

Ghassemali

Hurtig

et al. 2020

Metals

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The effect of three important process parameters, namely laser power, scanning speed and laser stand-off distance on the deposit geometry, microstructure and segregation characteristics in direct energy deposited alloy 718 specimens has been studied. Laser power and laser stand-off distance were found to notably affect the width and depth of the deposit, while the scanning speed influenced the deposit height. An increase in specific energy conditions (between 0.5 J/mm2 and 1.0 J/mm2) increased the total area of deposit yielding varied grain morphologies and precipitation behaviors which were comprehensively analyzed. A deposit comprising three distinct zones, namely the top, middle and bottom regions, categorized based on the distinct microstructural features formed on account of variation in local solidification conditions. Nb-rich eutectics preferentially segregated in the top region of the deposit (5.4–9.6% area fraction, Af) which predominantly consisted of an equiaxed grain structure, as compared to the middle (1.5–5.7% Af) and the bottom regions (2.6–4.5% Af), where columnar dendritic morphology was observed. High scan speed was more effective in reducing the area fraction of Nb-rich phases in the top and middle regions of the deposit. The <100> crystallographic direction was observed to be the preferred growth direction of columnar grains while equiaxed grains had a random orientation.

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Section: Ebsd Mappingmentioning

confidence: 99%

Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718

Sreekanth

Ghassemali

Hurtig

et al. 2020

Metals

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“…In 1984, Hunt developed the fi rst CET model [2] . Since then, many numeric models have been developed to predict the CET during the solidifi cation of alloys [3][4][5][6][7][8][9][10][11][12][13][14][15] . Hunt's model assumed that the equiaxed grains can nucleate and grow in the undercooled region in front of columnar dendrites.…”

Section: School Of Materials Science and Engineering Shenyang Ligongmentioning

confidence: 99%

“…Gandin and Rappaz [7] first predicted the dendritic grain structures in solidifi cation processes by a fully coupled finite element-cellular automaton model (CAFE). Dong and Lee [8,9] developed a cellular automaton model coupled with fi nite diff erence method (CAFD) to simulate the CET during the solidification of an Al-3wt.%Cu alloy. The simulated results were in agreement with experimental observations.…”

Section: School Of Materials Science and Engineering Shenyang Ligongmentioning

confidence: 99%

Effect of thermal convection on columnar-to-equiaxed transition during solidification of Al-Cu alloy

Zhang

Feng

et al. 2018

China Foundry

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To investigate the effect of three-dimension (3D) thermal convection on columnar-to-equiaxed transition (CET), the CET transition during the solidification of an Al-Cu alloy was simulated by 3D cellular automaton model coupled with the fi nite element method (CAFE). The thermal convection in the liquid phase was considered. The results show that the thermal convection in the liquid phase promotes the CET. When the convection is present, the temperature gradient at the start position of CET increases and the growth velocity of columnar dendrite decreases. The convection infl uences the formation of elongated equiaxed grain through changing the local temperature gradient and dendritic growth velocity.

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“…Although the model was later extended to solve an unsteady temperature field and to track the position of the columnar front explicitly by a parabolic velocity-undercooling relation, etc., [4,5] and still later improved to include a more precise dendrite growth model and to consider the concentration profile ahead of the columnar tip front, [6] it is still far from being able to predict the CET for real casting processes. Recent advancements of numerical CET models available at the process scale can be classified according to the type of modeling approach: [7][8][9][10][11][12] stochastic or deterministic. According to Reference 7, the stochastic approach, i.e., the cellular automaton model coupled with macroscopic thermal or solute fields, has the advantage of modeling the details of the columnar and equiaxed morphologies, while the deterministic approach embodies the physical mechanisms involved in the solidification process, especially in regard to convection and grain transport.…”

Section: Introductionmentioning

confidence: 99%

Using a Three-Phase Deterministic Model for the Columnar-to-Equiaxed Transition

Ludwig

2007

Metall Mater Trans A

111

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In order to overcome the limitations of previous columnar-to-equiaxed (CET) models, which neglect melt convection and the movement of free equiaxed grains, this article presents a three-phase deterministic CET model. With appropriated multiphase volume-averaging approaches, it is possible to account for nucleation and growth of equiaxed grains ahead of a growing columnar front, the influence of melt convection, and grain sedimentation, and the occurrence of a CET in a casting of engineering scale. Special modeling assumptions ensure that both CET mechanisms, namely, ''hard'' and ''soft'' blocking, are tackled. It is highly recommended that both mechanisms should be considered, especially in the situation where grain sedimentation and melt convection are present. Although the current model incorporates almost all the physical variables relevant to a CET event, under special condition of a one-dimensional case, the model still reproduces the results of Hunt's classical CET approach.

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Simulation of equiaxed growth ahead of an advancing columnar front in directionally solidified Ni-based superalloys

Cited by 23 publications

References 19 publications

Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718

Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718

Effect of thermal convection on columnar-to-equiaxed transition during solidification of Al-Cu alloy

Using a Three-Phase Deterministic Model for the Columnar-to-Equiaxed Transition

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