Microstructure and Mechanical Properties of CMSX-4 Single Crystals Prepared by Additive Manufacturing

Körner, Carolin; Ramsperger, Markus; Meid, Carla; Bürger, David; Wollgramm, P.; Bartsch, Marion; Eggeler, Gunther

doi:10.1007/s11661-018-4762-5

Cited by 128 publications

(64 citation statements)

References 29 publications

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“…This behavior is often reversed when a high density of cracks is present in the as-printed microstructure, resulting in reduced yield strengths as the print orientation changes and preexisting cracks become oriented perpendicular to the loading direction 66 . The SX Ni-base superalloy CMSX-4 has recently been printed in cylindrical bar form by EBM, producing a SX core with equiaxed grains at the surface 67 . Removing samples from the as-printed SX core yielded a room temperature yield strength of 829 MPa and elongation of 6.1%, with no apparent cracking.…”

Section: Discussionmentioning

confidence: 99%

A defect-resistant Co–Ni superalloy for 3D printing

et al. 2020

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Additive manufacturing promises a major transformation of the production of high economic value metallic materials, enabling innovative, geometrically complex designs with minimal material waste. The overarching challenge is to design alloys that are compatible with the unique additive processing conditions while maintaining material properties sufficient for the challenging environments encountered in energy, space, and nuclear applications. Here we describe a class of high strength, defect-resistant 3D printable superalloys containing approximately equal parts of Co and Ni along with Al, Cr, Ta and W that possess strengths in excess of 1.1 GPa in as-printed and post-processed forms and tensile ductilities of greater than 13% at room temperature. These alloys are amenable to crack-free 3D printing via electron beam melting (EBM) with preheat as well as selective laser melting (SLM) with limited preheat. Alloy design principles are described along with the structure and properties of EBM and SLM CoNi-base materials.

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Section: Discussionmentioning

confidence: 99%

A defect-resistant Co–Ni superalloy for 3D printing

et al. 2020

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“…The opened fracture surface in Figure 1(f) reveals a dendritic morphology typical of hot cracking [20], which implies that a continuous liquid film had covered almost the sample's entire cross section. Cracking only takes place at high-angle grain boundaries [21] and building height greater than 10 mm in the build, where the columnar grains are wider than 100 μm. LAGBs, consisting of dislocation arrays, are systematically found to be crack-free.…”

Section: Microstructural Characterization: Cracked Columnar Samplementioning

confidence: 99%

“…The latter observation suggests that producing samples without HAGBs can be considered as a possible route to achieve crack-free parts. Körner et al [21] and Chauvet et al [22] took advantage of the digital control of the melting strategy to grow single crystals of nonweldable nickel-based superalloys by S-EBM. Interestingly, the single crystals grown by S-EBM are free of cracks, in agreement with the observation that cracks propagate exclusively along HAGBs.…”

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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“…The versatile 3D‐printing technique emerging in recent years appears to be a powerful route toward this goal 3. Via “epitaxial” deposition of the alloy, one layer at a time, additive manufacturing can preserve the crystallographic orientation of the substrate single crystal 4–11. However, as 3D printing involves fast cooling, the γ′ precipitates are either undetectable12 or excessively small with uneven sizes and rounded corners13,14 and hence less stable during high‐temperature service.…”

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confidence: 99%

Rafting‐Enabled Recovery Avoids Recrystallization in 3D‐Printing‐Repaired Single‐Crystal Superalloys

Chen

Huang

et al. 2020

Advanced Materials

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The repair of damaged Ni‐based superalloy single‐crystal turbine blades has been a long‐standing challenge. Additive manufacturing by an electron beam is promising to this end, but there is a formidable obstacle: either the residual stress and γ/γ ′ microstructure in the single‐crystalline fusion zone after e‐beam melting are unacceptable (e.g., prone to cracking), or, after solutionizing heat treatment, recrystallization occurs, bringing forth new grains that degrade the high‐temperature creep properties. Here, a post‐3D printing recovery protocol is designed that eliminates the driving force for recrystallization, namely, the stored energy associated with the high retained dislocation density, prior to standard solution treatment and aging. The post‐electron‐beam‐melting, pre‐solutionizing recovery via sub‐solvus annealing is rendered possible by the rafting (i.e., directional coarsening) of γ ′ particles that facilitates dislocation rearrangement and annihilation. The rafted microstructure is removed in subsequent solution treatment, leaving behind a damage‐free and residual‐stress‐free single crystal with uniform γ ′ precipitates indistinguishable from the rest of the turbine blade. This discovery offers a practical means to keep 3D‐printed single crystals from cracking due to unrelieved residual stress, or stress‐relieved but recrystallizing into a polycrystalline microstructure, paving the way for additive manufacturing to repair, restore, and reshape any superalloy single‐crystal product.

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Microstructure and Mechanical Properties of CMSX-4 Single Crystals Prepared by Additive Manufacturing

Cited by 128 publications

References 29 publications

A defect-resistant Co–Ni superalloy for 3D printing

A defect-resistant Co–Ni superalloy for 3D printing

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

Rafting‐Enabled Recovery Avoids Recrystallization in 3D‐Printing‐Repaired Single‐Crystal Superalloys

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