Geometrical effect of freckle formation on directionally solidified superalloy CM247 LC components

Hong, Jun; Ma, Dexin; Wang, Jun; Wang, Fu; Dong, Anping; Sun, Baode; Bührig–Polaczek, Andreas

doi:10.1016/j.jallcom.2015.07.016

Cited by 25 publications

(26 citation statements)

References 28 publications

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“…The cooling temperature curve of the heating and the shadow side of the Ø19 mm casting rod (at a height of 190 mm from the chill plate) during directional solidification process is presented in Figure 6 . As shown in Aune’s research [ 15 ], the solidus and liquidus of alloy CM247 LC are 1282 °C and 1368 °C, respectively. Therefore, the cooling rate of the heating side and the shadow side of the Ø19 mm casting rod are 1.8 K/min and 1.7 K/min, respectively.…”

Section: Methodsmentioning

confidence: 97%

Freckle Defect Formation near the Casting Interfaces of Directionally Solidified Superalloys

Hong

Wang

et al. 2016

Materials

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Freckle defects usually appear on the surface of castings and industrial ingots during the directional solidification process and most of them are located near the interface between the shell mold and superalloys. Ceramic cores create more interfaces in the directionally solidified (DS) and single crystal (SX) hollow turbine blades. In order to investigate the location of freckle occurrence in superalloys, superalloy CM247 LC was directionally solidified in an industrial-sized Bridgman furnace. Instead of ceramic cores, Alumina tubes were used inside of the casting specimens. It was found that freckles occur not only on the casting external surfaces, but also appear near the internal interfaces between the ceramic core and superalloys. Meanwhile, the size, initial position, and area of freckle were investigated in various diameters of the specimens. The initial position of the freckle chain reduces when the diameter of the rods increase. Freckle area follows a linear relationship in various diameters and the average freckle fraction is 1.1% of cross sectional area of casting specimens. The flow of liquid metal near the interfaces was stronger than that in the interdendritic region in the mushy zone, and explained why freckle tends to occur on the outer or inner surfaces of castings. This new phenomenon suggests that freckles are more likely to occur on the outer or inner surfaces of the hollow turbine blades.

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Section: Methodsmentioning

confidence: 97%

Freckle Defect Formation near the Casting Interfaces of Directionally Solidified Superalloys

Hong

Wang

et al. 2016

Materials

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“…In the present work, we focus on the evolution of the cast microstructure. While there is a good understanding on how large-scale (cast microstructure: dendritic and interdendritic regions, cast microporosity [21], segregation [15,[17][18][19], and defects such as freckles [22][23][24], stray grains [25,26] and slivers [27]) and small-scale heterogeneities (γ' volume fractions, γ' sizes, γ channel widths, [15,28-30]) 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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“…Based on our recent work, [37,38] freckles occur not only on the external surfaces, but also inside the castings where a core was inserted. This is also attributed to the above-stated surface effect or wall effect, because both the shell and core wall can provide very high permeability for freckling convection in the mushy zone.…”

Section: DX Ma Zh Dong F Wang and Hb Dongmentioning

confidence: 99%

A Phenomenological Analysis of Freckling in Directional Solidification of Ni-Base Superalloy: The Role of Edge and Curvature in Casting Components

Dong

Wang

et al. 2019

Metall Mater Trans A

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The geometrical factor in freckle formation has rarely been taken into account. In this work, freckle formation in superalloy components is examined. It is found that freckle formation is subject to the effects of the edge and curvature. In polygonal casting sections, freckles are formed preferably on the convex edges. In the components with a curved contour, freckles are exclusively formed on the outward-curving surface having positive curvature.

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Geometrical effect of freckle formation on directionally solidified superalloy CM247 LC components

Cited by 25 publications

References 28 publications

Freckle Defect Formation near the Casting Interfaces of Directionally Solidified Superalloys

Freckle Defect Formation near the Casting Interfaces of Directionally Solidified Superalloys

On Crystal Mosaicity in Single Crystal Ni-Based Superalloys

A Phenomenological Analysis of Freckling in Directional Solidification of Ni-Base Superalloy: The Role of Edge and Curvature in Casting Components

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