Quantitative analysis of withdrawal rate on stray grain formation in the platforms of a Ni-Based single crystal dummy blade

Li, Yafeng; Liu, Lin; Sun, Dejian; Yue, Quanzhao; Huang, Taiwen; Gan, Bin; Zhang, Jun; Fu, Hengzhi

doi:10.1016/j.jallcom.2018.09.217

Cited by 26 publications

(18 citation statements)

References 24 publications

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“…In both the experiments and simulations, typical elongated columnar grains along the casting height were detected, independently of the process carried out. The number of these grains decreased while their transverse size increased with increasing distance from the chill plate, due to the mechanism of competitive dendrite growth, similar to the other presented investigations [3,4,5,12,16,22,33,34]. However, in the outer area of casting, the grain boundaries were inclined mainly towards the plate axis in both the simulation and experiments for the standard process without IRBs (Figure 12a–d and Figure 13a,b).…”

Section: Resultssupporting

confidence: 90%

“…The CMSX-4 Ni-based superalloy consists of two main phases, such as the γ phase and γ′ intermetallic phase (Ni 3 Al), with a face-centered cubic lattice [1,44]. The growth direction of the dendrite trunks (dendritic grains) coincides with <100> crystallographic direction in the new nucleus (grains) nucleated at the surface of the chill plate [5,12,33,34,42]. The mechanical properties of directionally solidified Ni-based superalloys are dependent on the crystallographic orientation of grains.…”

Section: Resultsmentioning

confidence: 99%

“…The mold surface close to the chill ring is cooled the most intensively, and the temperature gradient in the radial direction also occurs apart from the one in the axial direction. Thus, the temperature profile in the casting is uneven, and the mushy zone attains the unfavorable concave shape [12,13,14]. The curvature of the mushy zone increases with an increasing withdrawal rate of the mold when the liquidus isotherm is located in the cooling area of the furnace, especially in the large-size IGT blades.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, a ring-shaped radiation baffle is usually used, whose opening is matched as much as possible to the largest cross-section of the blade, providing undisturbed withdrawal of the mold from the heating to the cooling area of the furnace [8]. However, this solution does not provide the same solidification conditions on the whole cross-section of the blade because non-axial heat extraction occurs from the surface of the mold [8,12,13,28]. Therefore, the directional solidification of Ni-based superalloy using the conventional Bridgman process has been still subjected to modifications of either the baffle, mold or heaters.…”

Section: Introductionmentioning

confidence: 99%

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Application of Inner Radiation Baffles in the Bridgman Process for Flattening the Temperature Profile and Controlling the Columnar Grain Structure of Directionally Solidified Ni-Based Superalloys

et al. 2019

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The technique of flattening the temperature profile and controlling the formation of both the dendritic microstructure and grain structure in the directional solidification of nickel-based superalloy casting, using the novel inner radiation baffles (IRBs) in the Bridgman process, is presented in this paper. These baffles matched to the shape of mold and were placed horizontally along its height at various distances from the casting base. The plate castings of CMSX-4 superalloy were fabricated without and with the use of IRBs, withdrawing the mold at the rate of 6 mm/min from the heating to the cooling area of the industrial Bridgman furnace. Thermal analysis of the directional solidification of castings was carried out using the ProCAST software for a process where the various designs of the radiation baffle were applied. The results of the solidification conditions, the shape of liquidus and solidus isotherms, and grain structure obtained for the IRBs were compared with those reached for the standard ring-shaped (AERB) or perfectly adjusted (PARB) radiation baffles. The use of IRB resulted in flattening of the temperature distribution and decrease of the curvature of liquidus and solidus isotherms, as well as an increase of temperature gradient and cooling rate, compared with the process where AERB was only used. Consequently, primary dendrite arm spacing (PDAS) reached similar values across the width of casting and equaled to approximately 370 μm, reducing its average value by 26%, compared with the standard process. The change in predicted axial temperature gradient in casting was not found when thermophysical properties of molybdenum IRBs were used. The increase in graphite IRBs number in mold from seven to 14 caused the reduction of inhomogeneity of axial temperature gradient along the casting height.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Application of Inner Radiation Baffles in the Bridgman Process for Flattening the Temperature Profile and Controlling the Columnar Grain Structure of Directionally Solidified Ni-Based Superalloys

et al. 2019

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“…The character of the bends of the UF section described by the local maxima B 1 and B 2 ( Figure 7) are similar to the isotherm bends described by the cellular automaton finite element (CAFE) simulations in Ref. [32] for the platform region of the blade, and these are called "wave-shaped". The platform region has one common feature with the SE area-a step increase of the blade cross-section.…”

Section: Resultssupporting

confidence: 56%

Variation of Crystal Orientation and Dendrite Array Generated in the Root of SX Turbine Blades

et al. 2019

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The variation of the crystal orientation and the dendrite array generated in the root of the single-crystalline (SX) turbine blades made of CMSX-4 superalloy were studied. The blades with an axial orientation of the [001] type were solidified by the industrial Bridgman technique using a spiral selector at a withdrawal rate of 3 mm/min. The analysis of the crystal orientation and dendrite arrangement was carried out using scanning electron microscopy, X-ray diffraction topography, and Laue diffraction. It was found that the lateral growth of such secondary dendrite arms, which are defined as “leading” and grow in the root at first, is related to the rotation of their crystal lattice, which is the reason for creation of the low-angle boundary (LAB) type defects. The primary crystal orientation of the selector extension (SE) area determines the areas and directions of the lateral growth of the leading arms. Additionally, it was found that in the SE areas of the root, near the connection with the selector, the spatial distribution of the [001]γ′ crystallographic direction has a complex wave-like character and may be related to the shape of the crystallization front.

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Eliminating Equiaxed Grain Defects in a Ni‐Based Single‐Crystal Blade Platform by Flattening the Liquidus Isotherm

Szeliga

2023

Adv Eng Mater

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The article presents a mechanism for the formation of equiaxed grain defects and a new approach to eliminate them during the directional solidification of single‐crystal CMSX‐4 nickel‐based superalloy blades. The standard Bridgman method produces blade castings with clusters of equiaxed grains in platform areas above the root corners containing long freckle chains. The mechanism proposed considers the curvature of the liquidus isotherm and suggests that isolated dendrite fragments move upward from the freckle channel to the melt of the platform area. The floating surviving grains settle at the columnar dendrite tips, where they continue to grow into large equiaxed grains that block the development of the single‐crystal structure in the platform area located above the root corners. To eliminate these defects from the platform, a new approach is proposed, which involves introducing inner radiation baffles along the mold height to control the liquidus isotherm curvature in the blade. This stops the movement of small dendritic fragments from the root corner to the platform area, resulting in a significant reduction of freckles at the root and obtaining a typical single‐crystal structure free of equiaxed grains in the platform.

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Quantitative analysis of withdrawal rate on stray grain formation in the platforms of a Ni-Based single crystal dummy blade

Cited by 26 publications

References 24 publications

Application of Inner Radiation Baffles in the Bridgman Process for Flattening the Temperature Profile and Controlling the Columnar Grain Structure of Directionally Solidified Ni-Based Superalloys

Application of Inner Radiation Baffles in the Bridgman Process for Flattening the Temperature Profile and Controlling the Columnar Grain Structure of Directionally Solidified Ni-Based Superalloys

Variation of Crystal Orientation and Dendrite Array Generated in the Root of SX Turbine Blades

Eliminating Equiaxed Grain Defects in a Ni‐Based Single‐Crystal Blade Platform by Flattening the Liquidus Isotherm

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