Generation mechanism and motion behavior of sliver defect in single crystal Ni-based superalloy

Xia, Huxiang; Yang, Yanhong; Feng, Qiushui; Xu, Qingyan; DONG, H; Liu, Baicheng

doi:10.1016/j.jmst.2022.07.045

Cited by 10 publications

(3 citation statements)

References 62 publications

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“…Peter et al [22] simulated the deformation behavior of dendrites in three dimensions. However, recent research [23,24] has failed to clarify the cause of dendrite deformation in different castings. In addition, most previous studies have focused on solidification defects at the edge plate of the turbine blade.…”

Section: Introductionmentioning

confidence: 99%

Dendrite Deformation in the Rejoined Platforms of Ni‐Based Single‐Crystal Superalloys

2023

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Dendrite deformation often occurs during the preparation of single‐crystal superalloy blades by directional solidification and can cause solidification defects, such as low‐angle boundaries (LABs), slivers, and orientation deviations. Continuous dendritic deformation is uncommon and its mechanisms and influencing factors are poorly understood. However, this can lead to significant orientation deviation and performance degradation. Herein, a model with rejoined platforms is designed to study the dendrite growth and orientation evolution in a rejoined platform of Ni‐based single‐crystal superalloys. It is indicated in the results that, under certain conditions, the developed secondary dendrites deform continuously near the mold wall of the rejoined platforms and the resulting disorientation has a cumulative effect. Finally, LABs and dendritic fragments appear on the rejoined platforms. Thus, the integrity of the single crystal is destroyed. This can be the result of the local shrinkage stress on the long secondary dendrites within a sufficient growth space.

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Section: Introductionmentioning

confidence: 99%

Dendrite Deformation in the Rejoined Platforms of Ni‐Based Single‐Crystal Superalloys

2023

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“…There are two prevalent techniques for fabricating SX blades: the grain selection technique and the seeding method. However, no matter which method is adopted, misorientation defects [2][3][4] are almost inevitable. Stray grain (SG) defects are common, particularly around the platforms and shroud regions [5][6][7][8][9] of the turbine blade, and can lead to component invalidation.…”

Section: Introductionmentioning

confidence: 99%

The Stray Grains from Fragments in the Rejoined Platforms of Ni-Based Single-Crystal Superalloy

Huo

Chen

Han

et al. 2023

Metals

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Nickel-based single crystal superalloy is the most important material for blade preparation. However, some solidification defects inevitably occur during the process of preparing single-crystal blades through directional solidification. In this study, in order to study the origin of misorientation defects during solidification, a model with rejoined platforms was designed according to the geometry of single-crystal guide vanes. Electron Back-Scattering Diffraction (EBSD) was used to quantify the orientation deviation of the dendrites and identify the solidification defects in the rejoined platforms. The results showed that stray grain defects appeared in the platforms and their misorientation changed gradually, not abruptly. Combined with the simulation results, it was proposed that the stray grains formed as the result of the dendrites fragment, which was induced by solute enrichment in the mushy zone during solidification. Meanwhile, it was accompanied by a obvious dendritic deformation, which was caused by solidification shrinkage stress. This suggested that the fragmentation was induced by multiple factors, among which, the concave interface shape provided favorable conditions for solute enrichment, and the dynamic variability in the local thermal gradient and fluctuations of the solidification rate might play catalytic roles.

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“…However, in recent studies, the sliver defect was found by using the C-shaped grain selectors during investment casting of SX blades. The sliver is a easily neglected defect, which could cause a decrease in the performance of single-crystal blades and the rejection of casting for the mass manufacturing of blades [10,11], when the single-crystal blades were produced via the single-crystal directional solidification process. Therefore, the causes of the sliver defect must be investigated in-depth when the C-shaped grain selectors are applied in investment casting of single-crystal blades.…”

Section: Introductionmentioning

confidence: 99%

A Study of Sliver in C-Shaped Grain Selectors during Investment Casting of Single-Crystal Superalloy

Yang

Zhu

Wang

et al. 2023

Metals

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In this study, the formation mechanism of sliver defects in C-shaped 2D grain selectors during investment casting of single-crystal superalloy was investigated by analyzing the effects of the C-shaped 2D grain selectors on the solidification behavior of superalloy. The physical field properties of the sliver formation and solidification characteristics of CM247LC nickel-based superalloy were determined. The temperature and stress fields were simulated using ProCAST. The results showed that the stress fields of solidification played an essential role in the formation of sliver, indicating that the solidification interval characteristics of the alloy and stress based on the geometry of the C-shaped 2D grain selector are crucial for the formation of sliver. In addition, the origin of sliver depended upon tensile stress during solidification, relying on the constraints of dendrite boundaries. The findings suggested that the joint sections of the starter block—i.e., selector and selector-casting joint of C-shaped selector sections—are stress-sensitive areas where sliver can form readily. Furthermore, sliver is formed in the final stages of solidification and especially originates in the grain selection part where the accumulated thermal stress is high, and there is only a small quantity of liquid phase with a low melting point between the dendrites. Therefore, the solidification and stress conditions generate thermal cracks, which can also cause sliver defects.

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Generation mechanism and motion behavior of sliver defect in single crystal Ni-based superalloy

Cited by 10 publications

References 62 publications

Dendrite Deformation in the Rejoined Platforms of Ni‐Based Single‐Crystal Superalloys

Dendrite Deformation in the Rejoined Platforms of Ni‐Based Single‐Crystal Superalloys

The Stray Grains from Fragments in the Rejoined Platforms of Ni-Based Single-Crystal Superalloy

A Study of Sliver in C-Shaped Grain Selectors during Investment Casting of Single-Crystal Superalloy

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