Ni-base superalloy single crystal (SX) mosaicity characterized by the Rotation Vector Base Line Electron Back Scatter Diffraction (RVB-EBSD) method

Thomé, P.; Medghalchi, Setareh; Frenzel, Jan; Schreuer, J.; Eggeler, Gunther

doi:10.1016/j.ultramic.2019.112817

Cited by 21 publications

(32 citation statements)

References 31 publications

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“…It has been documented in the literature [41,42] by combined in situ solidification and radiography experiments using small volume samples that dendrites are mainly deformed by bending. This is in line with findings observed by post-mortem electron back scatter diffraction (EBSD) [37][38][39]42,52]. Recently, direct evidence for dendrite bending and torsion during conventional Bridgman solidification of larger melt volumes has been provided [30].…”

Section: Introductionsupporting

confidence: 86%

“…The present work differs from other studies where a three-dimensional microstructural characterization was performed, e.g., [54][55][56][57][58][59][60][61]. In fact, most related studies addressed different research objectives, e.g., [51][52][53][54][55][56], or focused on significantly smaller volumes, e.g., [59][60][61].…”

Section: Introductionmentioning

confidence: 80%

“…Recently, direct evidence for dendrite bending and torsion during conventional Bridgman solidification of larger melt volumes has been provided [30]. Several reasons for dendrite deformation have been discussed in the literature, e.g., [29,30,41,43,[46][47][48][49][50][51][52][53]. While some studies invoke thermal and shrinkage stresses as main factors [29,[46][47][48], others propose strong convective forces [49][50][51], thermomechanical interactions with the casting environment [41][42][43], and precipitation-related phenomena [53].…”

Section: Introductionmentioning

confidence: 99%

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A 3D Analysis of Dendritic Solidification and Mosaicity in Ni-Based Single Crystal Superalloys

et al. 2021

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Ni-based single crystal superalloys contain microstructural regions that are separated by low-angle grain boundaries. This gives rise to the phenomenon of mosaicity. In the literature, this type of defect has been associated with the deformation of dendrites during Bridgman solidification. The present study introduces a novel serial sectioning method that allows to rationalize mosaicity on the basis of spatial dendrite growth. Optical wide-field micrographs were taken from a series of cross sections and evaluated using quantitative image analysis. This allowed to explore the growth directions of close to 2500 dendrites in a large specimen volume of approximately 450 mm3. The application of tomography in combination with the rotation vector base-line electron back-scatter diffraction method allowed to analyze how small angular differences evolve in the early stages of solidification. It was found that the microstructure consists of dendrites with individual growth directions that deviate up to ≈4° from the average growth direction of all dendrites. Generally, individual dendrite growth directions coincide with crystallographic <001> directions. The quantitative evaluation of the rich data sets obtained with the present method aims at contributing to a better understanding of elementary processes that govern competitive dendrite growth and crystal mosaicity.

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Section: Introductionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

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A 3D Analysis of Dendritic Solidification and Mosaicity in Ni-Based Single Crystal Superalloys

et al. 2021

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“…The final polishing step was performed using a 1 µm diamond suspension. In addition to optical microscopy, superalloy microstructures were characterized by orientation imaging SEM using a new correlative EBSD method with a high angular resolution (RVB-EBSD method [65]). This technique yields a significantly higher angular resolution as conventional EBSD.…”

Section: Methodsmentioning

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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“…As main reasons for the higher hardness and reduced scratch depth after LMD processing (in comparison to the cast specimen), a higher dislocation density and the cellular substructure were considered. Thome et al found a high density of geometrically necessary dislocations at grain boundaries in a Ni-base superalloy after additive manufacturing using selective electron laser beam melting [30]. The oxide inclusions with sizes in the range of ~ 100 nm were not believed to have a significant impact on the strength of the LMD specimen.…”

Section: Scratching and Indentationmentioning

confidence: 99%

Orientation-Dependent Deformation Behavior of 316L Steel Manufactured by Laser Metal Deposition and Casting under Local Scratch and Indentation Load

et al. 2020

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This study analyzes the local deformation behavior of austenitic stainless steel 316L, manufactured conventionally by casting and additively by laser metal deposition (LMD). We produced directionally solidified 316L specimens with most grains showing (001) orientations parallel to the longitudinal specimen axis. We conducted nanoindentation and scratch experiments for local mechanical characterization and topography measurements (atomic force microscopy and confocal laser scanning microscopy) of indentation imprints and residual scratch grooves for the analysis of the deformation behavior and, in particular, of the pile-up behavior. The local mechanical properties and deformation behavior were correlated to the local microstructure investigated by scanning electron microscopy with energy dispersive X-ray spectroscopy and electron backscatter diffraction analysis. The results show that the local mechanical properties, deformation behavior, and scratch resistance strongly depend on the crystallographic orientation. Nearly (001)-oriented grains parallel to the surface show the lowest hardness, followed by an increasing hardness of nearly (101)- and (111)-oriented grains. Consequently, scratch depth is the greatest for nearly (001)-oriented grains followed by (101) and (111) orientations. This tendency is seen independently of the analyzed manufacturing route, namely Bridgman solidification and laser metal deposition. In general, the laser metal deposition process leads to a higher strength and hardness, which is mainly attributed to a higher dislocation density. Under the investigated loading conditions, the cellular segregation substructure is not found to significantly and directly change the local deformation behavior during indentation and scratch testing.

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Ni-base superalloy single crystal (SX) mosaicity characterized by the Rotation Vector Base Line Electron Back Scatter Diffraction (RVB-EBSD) method

Cited by 21 publications

References 31 publications

A 3D Analysis of Dendritic Solidification and Mosaicity in Ni-Based Single Crystal Superalloys

A 3D Analysis of Dendritic Solidification and Mosaicity in Ni-Based Single Crystal Superalloys

On Crystal Mosaicity in Single Crystal Ni-Based Superalloys

Orientation-Dependent Deformation Behavior of 316L Steel Manufactured by Laser Metal Deposition and Casting under Local Scratch and Indentation Load

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