Additive manufacturing of Ni-based superalloys: The outstanding issues

Attallah, Moataz M.; Jennings, Rachel; Wang, Xiqian; Carter, Luke N.

doi:10.1557/mrs.2016.211

Cited by 239 publications

(100 citation statements)

References 55 publications

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“…This was similar to the results reported in [19,36]. In metallic materials manufactured by LPBF, microsegregations are not uncommon and they can cause undesirable effects like hot cracking [41,42]. In LPBF 316 L steel, segregation of Cr and Mo on cell boundaries has been reported [22,43,44].…”

Section: Influence Of Solidification Conditions On Microstructure Andsupporting

confidence: 87%

Microstructure, Solidification Texture, and Thermal Stability of 316 L Stainless Steel Manufactured by Laser Powder Bed Fusion

Krakhmalev

Fredriksson

Svensson

et al. 2018

Metals

144

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This article overviews the scientific results of the microstructural features observed in 316 L stainless steel manufactured by the laser powder bed fusion (LPBF) method obtained by the authors, and discusses the results with respect to the recently published literature. Microscopic features of the LPBF microstructure, i.e., epitaxial nucleation, cellular structure, microsegregation, porosity, competitive colony growth, and solidification texture, were experimentally studied by scanning and transmission electron microscopy, diffraction methods, and atom probe tomography. The influence of laser power and laser scanning speed on the microstructure was discussed in the perspective of governing the microstructure by controlling the process parameters. It was shown that the three-dimensional (3D) zig-zag solidification texture observed in the LPBF 316 L was related to the laser scanning strategy. The thermal stability of the microstructure was investigated under isothermal annealing conditions. It was shown that the cells formed at solidification started to disappear at about 800 • C, and that this process leads to a substantial decrease in hardness. Colony boundaries, nevertheless, were quite stable, and no significant grain growth was observed after heat treatment at 1050 • C. The observed experimental results are discussed with respect to the fundamental knowledge of the solidification processes, and compared with the existing literature data.

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Section: Influence Of Solidification Conditions On Microstructure Andsupporting

confidence: 87%

Microstructure, Solidification Texture, and Thermal Stability of 316 L Stainless Steel Manufactured by Laser Powder Bed Fusion

Krakhmalev

Fredriksson

Svensson

et al. 2018

Metals

144

View full text Add to dashboard Cite

show abstract

“…The limited number of grain boundaries in columnar samples will tend to have a more highly concentrated and continuous films extending over several grains, which appears to be highly detrimental to the structural integrity of the build. The typical criterion for non-weldability, namely the content of (Ti+Al) [2], does not seem to apply here. In the alloy that we investigated, this criterion is superseded by the content of B, Cr and Mo found at HAGBs.…”

Section: Hot Cracking Caused By Grain Boundary-segregation Induced LImentioning

confidence: 94%

“…Additive manufacturing (AM) has a great potential for the production of novel engineering components for aerospace and power generation applications, where nickel-based superalloys are predominantly used [1]. However, it is very challenging to produce safety-critical components by AM with zero-crack tolerance, yet the digitalisation inherent to AM promises large gains in manufacturing and repair efficiency [2]. The AM community currently invests great efforts to 3D print well-known superalloys compositions considered as non-weldable such as IN738 [3][4][5], CMSX-4 [6], CM247LC [7] among others [8,9].…”

Section: Introductionmentioning

confidence: 99%

Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

et al. 2019

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There are still debates regarding the mechanisms that lead to hot cracking in parts build by additive manufacturing (AM) of non-weldable nickel-based superalloys. This lack of in-depth understanding of the root causes of hot cracking is an impediment to designing engineering parts for safety-critical applications. Here, we deploy a near-atomic-scale approach to investigate the details of the compositional decoration of grain boundaries in the coarse-grained, columnar microstructure in parts built from a non-weldable nickel-based superalloy by selective electron-beam melting. The progressive enrichment in Cr, Mo and B at grain boundaries over the course of the AM-typical successive solidification and remelting events, accompanied by solid-state diffusion, causes grain boundary segregation induced liquation. This observation is consistent with thermodynamic calculations. We demonstrate that by adjusting build parameters to obtain a fine-grained equiaxed or a columnar microstructure with grain width smaller than 100 μm enables to avoid cracking, despite strong grain boundary segregation. We find that the spread of critical solutes to a higher total interfacial area, combined with lower thermal stresses, helps to suppress interfacial liquation.

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“…Ni-based superalloys possess excellent mechanical properties and corrosion resistance up to high temperatures primarily due to the fine precipitation of Nb-rich phases and are therefore used in gas-turbine and jet-engine components [1]. The laser powder bed fusion (LPBF) additive manufacturing (AM) process is used to fabricate or repair these alloys by layer-bylayer application of the alloy powder and subsequent repeated melting, solidification and solid-state phase transformations [2][3][4][5].…”

mentioning

confidence: 99%

“…It is generally accepted that γ cells grow in the direction of thermal gradient. The orientation/texture of these cells however can be different in different locations in a solidifying molten pool [1,6,35]. A slight deviation, for instance, of the scanning path of the laser beam can markedly change the spatial and temporal solute redistribution across the cell-liquid interface.…”

mentioning

confidence: 99%

Formation of Nb-rich droplets in laser deposited Ni-matrix microstructures

et al. 2018

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Ni-rich γ cells and Nb-rich eutectic droplets that form during laser power bed fusion solidification of Ni-Nb alloys are studied using experiments and simulations. Finite element simulations estimate the cooling rates in the melt pool and phase-field simulations predict the resulting cellular microstructures. The cell and droplet spacings are determined as a function of cooling rate and fit to a power law. The formation of Laves phase is predicted for a critical composition of Nb in the liquid droplets. Finally, our simulations demonstrate that anisotropy in the γ orientation influences the Laves fraction significantly.

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Additive manufacturing of Ni-based superalloys: The outstanding issues

Abstract: Abstract

Cited by 239 publications

References 55 publications

Microstructure, Solidification Texture, and Thermal Stability of 316 L Stainless Steel Manufactured by Laser Powder Bed Fusion

Microstructure, Solidification Texture, and Thermal Stability of 316 L Stainless Steel Manufactured by Laser Powder Bed Fusion

Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

Formation of Nb-rich droplets in laser deposited Ni-matrix microstructures

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